How can I get more performance out of my 2.5?

TJ4Jim said:
I have been saying this for years, the 2.5 is a good setup based on those driving parameters. I like mine and although I have the tools and ability for an engine swap she is staying put under the hood.
Click to expand...

I agree 100%. If you use it for the right driving parameters, it's great.

If you want to put 35s on it and drive it on long highway trips, life will suck. Though admittedly even my 4.0 sucked with that setup :ROFLMAO:
 
OK then let me ask another question where would be a good place to go to have my engine done on my 1994 yj. My mechanic won't do it he will sub it out to somebody else that's why his opinion is it's far too expensive to do an engine swap. He is trying to convince me I am better off doing the stroker or just rebuilding the stock motor. Keep in mind I can get the brand new stroker motor for $2400 install for about $1300 for total of about $3700 bucks. I would consider just buying a whole new Wrangler but I have already done so much to this one that I would hate to have wasted all that money it's in really tip top shape minus the dead motor
 
Snowkilla73 said:
OK then let me ask another question where would be a good place to go to have my engine done on my 1994 yj. My mechanic won't do it he will sub it out to somebody else that's why his opinion is it's far too expensive to do an engine swap. He is trying to convince me I am better off doing the stroker or just rebuilding the stock motor. Keep in mind I can get the brand new stroker motor for $2400 install for about $1300 for total of about $3700 bucks. I would consider just buying a whole new Wrangler but I have already done so much to this one that I would hate to have wasted all that money it's in really tip top shape minus the dead motor
Click to expand...

I would say Golen, but I'm not sure if they do 2.5s. I know they definitely do 4.0s, and they are probably the best-of-the-best for 4.0 stroker engines and performance builds.

I would say this should really be it's own thread, as you're going to get more attention with your own thread as oppose to piggybacking on this one (y)
 
Ok sorry not trying to hijack your thread. Im just new to the wrangler 2.5 world. This will be my third wrangler but first 2.5. I got this for my wife and I hate to say this and will deny it if asked lol but my wife told me not to buy this jeep. She had a bad feeling about the seller they seemed to eager to sell. Guess I should have listened. Well you live and you learn. I need to replace the motor sooner rather than later. It runs great but you can tell its tired. I noticed your area is Salem where I purchased the Wrangler so you might know of some shops that I dont. Im working with My Dads Automotive just cause they are one of my clients and have worked with them in the past. I guess im just looking for direction from a knowledgeable jeep fan on a route to go. Sounds like I should just go with the stock 2.5 motor for now drive it and then upgrade. From the sounds of it a 4.0 swap will be just as labor intensive as a v8. I have a 74 wrangler with the Amc v8 all new from top to bottom. Done by woodys 4x4 but my dad wants 10k for it. So long story short do you have a recommendation of someone or somewhere I could take my jeep to and do a motor for a good price. My Dads Automotive will just sub it to someone else and woodys is freakn expensive. Charged my dad 8000 just for a new motor. Thanks for your time.
 
I am the new owner of an 03 TJ SE 2.5 with 265/75 R16 Dynapro All Terrain tires. I have a problem when going uphill - at a very minor incline - the jeep can't maintain speed. If I'm traveling at 65mph it will bog down to the high 50's.

My question is are my large tires causing the problem?
Am I better off buying something closer to stock which I think is 205/75 R15?
Do my tires matter as it's just a problem with the 2.5 and I'm getting all that I can?

Thanks
 
What transmission do you have? It's helpful to put your vehicle's details in your profile. If you have a manual, the clutch could be slipping.
 
There's a couple of thing going on here @dmkfw, neither of which is a big deal.

Unless you have corrected the speedometer for the larger than stock tire size, your speedometer is off by about 8-10%. You're going faster than the speespeedometer says by about that amount.

Down shift into the next lower gear if you start to bog down. If the hill is steep enough, down shift two gears. You can run the four bangers up a hill between 3,000 and 4,000 rpm with no ill effects. Torque peak is about 3,100 rpm and peak hp is about 4,200 rpm. Give or take.

Try that and let us know what you think.
 
  • Like
Reactions: billiebob and TJ4Jim
I have put a rotrex c-38 supercharger biggest one they make with intercooler and split second piggy back with 5th injector 1.7 roller rockers header bigger injectors running 15lbs of boost on stock bottom end with out issue and has more power then any 4.0 runs 95 up highway with 37" tires 5.13 gears ford 8.8 rear 9" long arm lift crawls and goes over anything you point it at like a champ dont let anyone tell you it cant be done! They just scared lol
 
Bastard.sc said:
I have put a rotrex c-38 supercharger biggest one they make with intercooler and split second piggy back with 5th injector 1.7 roller rockers header bigger injectors running 15lbs of boost on stock bottom end with out issue and has more power then any 4.0 runs 95 up highway with 37" tires 5.13 gears ford 8.8 rear 9" long arm lift crawls and goes over anything you point it at like a champ dont let anyone tell you it cant be done! They just scared lol
Click to expand...

Pictures?
 
  • Like
Reactions: Wheeler and TJ4Jim
StG58 said:
TJ SE's and the 2.5 liter engine

There's a lot of discussion around the Jeep 2.5 liter engine and how to increase horse power and torque.

The short answer is, you can't. No one likes that answer, but it's the truth. The 2.5 is what it is. There are a lot of reasons to purchase an SE. Lighter weight, lower purchase price, successfully burns anything that looks and smells like regular pump gas, simpler and slightly less expensive to maintain are among of them. Oh, and they last bloody forever!

The common modifications that are attempted to gain performance are:
4.0 Throttle body
Throttle body spacer
Cold air induction
High flow air filters
IAC sensor relocation
Ford yellow top, 4 hole injectors
Headers
Cat back exhaust system
Power chips
Electric fans

Some of the less common modifications are:
Roller rockers
High performance cams
Ported and polished heads
Stroker kits
Turbocharging
Wet shot nitrous injection

Let's start with the common modifications first.

Intake modifications:
The TJ SE intake system is designed, and comes from the factory, to flow more air than the 2.5 liter engine needs to produce maximum HP and torque at wide open throttle and maximum load. True fact. There are no meaningful restrictions to air flow. The engineers did a good job of designing the intake system from the start. The only way to get additional air and fuel into the combustion chambers is to put a cam with higher lift and / or longer duration in, bigger intake valves, some form of forced air induction or a wet shot nitrous system on the engine.

Putting a 4.0 throttle body on will give me an extra 10 HP, right? Nope, sorry. Even with port matching the TB to the intake manifold, all you are gaining is the potential to flow more air. The 2.5 is really only an exotic air pump. The head will only flow so much air, and that amount is the air required to fill the combustion chambers at bottom dead center. That is especially true at lower RPMs, where our TJ SE's normally operate on the trail.

Putting a throttle body spacer in has got to improve performance, right? Nope, with the port injection there are no gains to be had with increasing plenum volume with a throttle body spacer. This is especially true of the magic throttle body spacers that promise miracle gains from swirling the intake air. That trick is a left over from the days of carburetors, and even then it wasn't effective. The length of the intake runners and the plenum volume needs to be matched to the engine's displacement, HP and torque bands. The Jeep engineers did that already. No gain to be had there.

Cold air induction has got to give me something, right? After all, cold air is denser than warm air! This is a true statement, as far as it goes. BUT, the difference in air temperature and air density going into the engine with a cold air induction system compared to the stock system is minimal at best. I have never seen or heard of a temperature difference greater than about 10 to 15 degrees F between a cold air system and the stock system. Most of the time the temperature difference is lower than that. The engine realistically doesn't see a difference and any power gains are unnoticeable.

High flow air filters will get more air into my engine, right? Sorry, the stock paper element and air box flow as much air as the engine needs. It also does a much better job of filtering the intake air than any of the aftermarket air filters. It's cheaper as well, and readily available.

So, how about relocating my IAC sensor to the air box? Again, this is only going to show a difference of a few degrees in temperature between the relocated position and the stock position. Once the engine reaches operating temperature and the ECM goes into closed loop mode, the O2 sensor takes over anyway as the ECM controls the air fuel mixture at 14.something to 1. No gains to be had there.

High flow four hole fuel injectors are the clear ticket, right? More fuel = more power! Not going to happen, sorry. Once the engine warms up and the ECM goes into closed loop operation, the amount of fuel injected is based off of the signal from the O2 sensor. The ECM will maintain that roughly 14/1 ratio no matter how much the injectors will potentially flow.

Now about the exhaust system:
Headers will give me more power! Uh, no. The TJ SE exhaust system is not restrictive. It will easily flow all of the exhaust gasses that the 2.5 will generate. The only thing you will gain is noise. And probably exhaust leaks from gasket miss-matches and failures. Headers will also put more heat into your engine compartment. The chances of the tube diameter and tube length matching the power band are also probably lower than the stock cast header.

Cat back exhaust systems are the cat's meow for performance gains. Not really. The Jeep engineers designed the exhaust system to flow the right amount of exhaust and generate the correct amount of back pressure for the 2.5. You can over scavenge the cylinders and kill performance and gas mileage with an ill designed exhaust system.

What about an electric fan? Let's get rid of all that parasitic drag! All the new cars have them. There are reasons to have an electric fan, but for the most part, no. It takes X amount of energy to move Y amount of air through the radiator to keep the 2.5 engine properly cooled. The stock fan does a good job of that, and doesn't generate a ton of parasitic loss at normal speeds. That's what the fan viscous coupling does. There's just not enough gain there to make it worthwhile.

A power chip will rock my 2.5! Nope, not really. You're already getting optimal air flow and the correct fuel mixture. Any gains from additional spark advance are minimal at best and will restrict the octane requirements for the 2.5.

Now we're getting into the more old school hot rodding tricks for generating more power out of the 2.5. Forced air induction, displacement changes, compression ratio increases, that sort of things. These will increase power, but the cost goes through the roof quickly.

Let's step back a moment and talk about what generates power. Power comes from burning a specific amount of gasoline and air at a specific ratio. We are starting out with 2.5 liters of displacement. That's not a lot of air / fuel being burned in the grand scheme of things, and it will only generate so much power. Let me repeat that. You can only burn a certain amount of the proper air / fuel mixture in the 2.5. That's all the power available out of the engine.

We can increase the amount of power generated by increasing the compression ratio and by extension the efficiency of the engine. Doing so increases the octane rating required to prevent detonation and the destruction of the engine. One of the bonuses of the 2.5 is that it will happily burn anything that looks and smells like gasoline. So we may not want to go there.

Another way to increase efficiency is to eliminate as much parasitic drag in the engine as we can. We can try to make as much power go to the transmission as possible. One of the ways to do that is with roller cams and roller rockers. With a four banger, that is a loosing proposition because there really isn't enough parasitic loss there to justify the expense. A full roller valve train would be expensive and result in an almost unnoticeable gain.

We can balance and blueprint the engine, so that it operates closer to it's theoretical efficiency. Again, that's a lot of expense for not a lot of gain. I estimate that you are only going to gain 15 - 20 HP at the top end with both a roller valve train and a balanced and blueprinted engine. And you'll only see that gain in the higher RPM ranges.

What about camming the engine? There's the possibility of gaining a little here, but we want a nice, flat HP and torque curve for the way we end up using the 2.5. Going with a lot of duration and overlap on the cam generates HP, but the power curve move up in the RPM range. Not what we are looking for. What about higher lift on the cam? We can get some gains there, and it can be done with rocker arms of a higher ratio. The longest rocker arms that will fit under the valve cover are approximately 1.6 to 1. We also have to be careful to not drive a valve into a piston doing this. Especially if you rev it and float a valve.

How about a stroker engine? That increases the amount of fuel / air mixture being burned and generates more power! Yup, it sure does. I've seen 2.5 stoker engines go for $3000 and up. That puts you in the same HP and torque range as a stock 4.0.!That's a lot of money to turn an SE into a stock Sport or X. If you can pick up an SE for $7000 and add in $3000 for a stroker, you're not far off from a decent Sport or X. Plus you still have the AX5 to deal with in the SE. It does solve the riddle of how to burn more fuel / air.

There's always head modifications as well. These work best in conjunction with a high lift and long duration cam. It will get more fuel / air mixture into the combustion chamber, but you'll only see the increase at higher RPM's. You can do things like bigger valves, CC'ing the heads so that all four combustion chambers are as close to the same size as possible, polishing the combustion chambers, raising the intake ports and port matching, contouring the intake valve bowl, lots of tricks to tried there. My take is that there just isn't enough displacement in the 2.5 to really make any of this worthwhile at the lower RPM ranges.

Forced air induction. Now this works. More fuel / air into the engine = more power. My preference would be something like a roots type positive displacement blower. It would generate power from idle to wherever you lifted the throttle. With supercharging and turbocharging the 2.5, you are faced with replacing the ECM with something that would control spark and fuel management. It's out there and available, but man is it expensive and hard to find. Plus you need to program these controllers from scratch to match your engine parameters. It's a good way to end up buying another 2.5. Good thing 2.5's are cheap!

Wet shot nitrous injection. This technology has been around since WWII, but it has nothing to recommend it to an SE owner. Just don't.

Repeat this as many times as it takes to sink in. You CAN NOT get more power out of these 2.5 liter 4 bangers unless you want to spend some serious coin.

All of the bolt on mods are a complete waste of money, most of them offering no performance gain at all, only an empty wallet (i.e. intakes, headers, etc.).

The ONLY real way to improve these 4 bangers in terms of power output would be to dump $3000 plus into a stroker engine, or dump $5000 plus into a supercharger system and custom standalone engine management system.

When you start putting that in perspective, you're better off selling your SE and getting a clean 4.0 model Wrangler. Either that, or if you really don't want to sell it, invest in a V8 swap and call it a day.

I see it asked all the time, "How do I get more power out of my 4 cylinder?", and the way to answer that is with this simple question: "Are you prepared to spend $3000 or more?"

And we know the answer to that question, so it's almost senseless to even ask.

OK, now let's talk about what you can do to increase the performance of your 2.5 powered TJ SE...

Keep the weight down. The 2.5 is perfectly happy pushing a 3,300 – 3,500 pound TJ around, especially on 31” tires. Around town, off road, on the Highway. Keep it Light for true Jeeping bliss!

Tires, Tires, Tires. Keep your tires to 31”, 32” or 33” tires. This effects the lift you require, the weight of the rotating mass involved and keeps you in the range of available gearing for the Dana 35 / 30 that comes with your 2.5.

Gears. You will end up changing gears out for one of two ratios. 4.88 or 5.13. That may sound pretty extreme, but those are the gear ratios that normally work the best with the 2.5 SE. Remember that the 2.5 is happy at 3,000 RPM.

The 2.5 SE is a good little Jeep that can be purchased economically in good condition. Use it within it's performance parameters and you'll be very happy with it!
Click to expand...
How did I miss this.... one of the best write ups ever. Should be a stickie. Well said !!
 
First off, thanks to @StG58 and @Chris and everyone else who has contributed to the thread. I completely understand that the 2.5 is what it is and highway performance is somewhat anemic.....

However, most of the posts involved people running larger than stock tires and sometimes lifts. I was wondering if you ran stock tires (205/75R15 or maybe up to 225/75R15) would that help a little with highway driving? Not that it's going to make you think you've got a 4.0, but maybe the confidence you can merge safely!
 
  • Like
Reactions: Chris
NOVA-Jeep said:
First off, thanks to @StG58 and @Chris and everyone else who has contributed to the thread. I completely understand that the 2.5 is what it is and highway performance is somewhat anemic.....

However, most of the posts involved people running larger than stock tires and sometimes lifts. I was wondering if you ran stock tires (205/75R15 or maybe up to 225/75R15) would that help a little with highway driving? Not that it's going to make you think you've got a 4.0, but maybe the confidence you can merge safely!
Click to expand...

All I can tell you is that even on my stock tires, the 2.5 was still terrible on the highway.

@StG58 is seldom active on the forum anymore, but I know he's had very good experiences with his 2.5, so my experience isn't the same as his.

If you wan 205s or 225s, then yes, that would absolutely help!

Don't get me wrong, even the 4.0 isn't the greatest highway vehicle. A lot of this stems from the piss poor aerodynamics of the TJ in general.
 
all that being said, I have a 2001 tj, the body is super clean. but its got the 2.5l. seems to me it might be worth looking for a late (er) model chassis and put my body on it. How can I find out which year frames/ Chassis my body will fit on?
 
StG58 said:
TJ SE's and the 2.5 liter engine

There's a lot of discussion around the Jeep 2.5 liter engine and how to increase horse power and torque.

The short answer is, you can't. No one likes that answer, but it's the truth. The 2.5 is what it is. There are a lot of reasons to purchase an SE. Lighter weight, lower purchase price, successfully burns anything that looks and smells like regular pump gas, simpler and slightly less expensive to maintain are among of them. Oh, and they last bloody forever!

The common modifications that are attempted to gain performance are:
4.0 Throttle body
Throttle body spacer
Cold air induction
High flow air filters
IAC sensor relocation
Ford yellow top, 4 hole injectors
Headers
Cat back exhaust system
Power chips
Electric fans

Some of the less common modifications are:
Roller rockers
High performance cams
Ported and polished heads
Stroker kits
Turbocharging
Wet shot nitrous injection

Let's start with the common modifications first.

Intake modifications:
The TJ SE intake system is designed, and comes from the factory, to flow more air than the 2.5 liter engine needs to produce maximum HP and torque at wide open throttle and maximum load. True fact. There are no meaningful restrictions to air flow. The engineers did a good job of designing the intake system from the start. The only way to get additional air and fuel into the combustion chambers is to put a cam with higher lift and / or longer duration in, bigger intake valves, some form of forced air induction or a wet shot nitrous system on the engine.

Putting a 4.0 throttle body on will give me an extra 10 HP, right? Nope, sorry. Even with port matching the TB to the intake manifold, all you are gaining is the potential to flow more air. The 2.5 is really only an exotic air pump. The head will only flow so much air, and that amount is the air required to fill the combustion chambers at bottom dead center. That is especially true at lower RPMs, where our TJ SE's normally operate on the trail.

Putting a throttle body spacer in has got to improve performance, right? Nope, with the port injection there are no gains to be had with increasing plenum volume with a throttle body spacer. This is especially true of the magic throttle body spacers that promise miracle gains from swirling the intake air. That trick is a left over from the days of carburetors, and even then it wasn't effective. The length of the intake runners and the plenum volume needs to be matched to the engine's displacement, HP and torque bands. The Jeep engineers did that already. No gain to be had there.

Cold air induction has got to give me something, right? After all, cold air is denser than warm air! This is a true statement, as far as it goes. BUT, the difference in air temperature and air density going into the engine with a cold air induction system compared to the stock system is minimal at best. I have never seen or heard of a temperature difference greater than about 10 to 15 degrees F between a cold air system and the stock system. Most of the time the temperature difference is lower than that. The engine realistically doesn't see a difference and any power gains are unnoticeable.

High flow air filters will get more air into my engine, right? Sorry, the stock paper element and air box flow as much air as the engine needs. It also does a much better job of filtering the intake air than any of the aftermarket air filters. It's cheaper as well, and readily available.

So, how about relocating my IAC sensor to the air box? Again, this is only going to show a difference of a few degrees in temperature between the relocated position and the stock position. Once the engine reaches operating temperature and the ECM goes into closed loop mode, the O2 sensor takes over anyway as the ECM controls the air fuel mixture at 14.something to 1. No gains to be had there.

High flow four hole fuel injectors are the clear ticket, right? More fuel = more power! Not going to happen, sorry. Once the engine warms up and the ECM goes into closed loop operation, the amount of fuel injected is based off of the signal from the O2 sensor. The ECM will maintain that roughly 14/1 ratio no matter how much the injectors will potentially flow.

Now about the exhaust system:
Headers will give me more power! Uh, no. The TJ SE exhaust system is not restrictive. It will easily flow all of the exhaust gasses that the 2.5 will generate. The only thing you will gain is noise. And probably exhaust leaks from gasket miss-matches and failures. Headers will also put more heat into your engine compartment. The chances of the tube diameter and tube length matching the power band are also probably lower than the stock cast header.

Cat back exhaust systems are the cat's meow for performance gains. Not really. The Jeep engineers designed the exhaust system to flow the right amount of exhaust and generate the correct amount of back pressure for the 2.5. You can over scavenge the cylinders and kill performance and gas mileage with an ill designed exhaust system.

What about an electric fan? Let's get rid of all that parasitic drag! All the new cars have them. There are reasons to have an electric fan, but for the most part, no. It takes X amount of energy to move Y amount of air through the radiator to keep the 2.5 engine properly cooled. The stock fan does a good job of that, and doesn't generate a ton of parasitic loss at normal speeds. That's what the fan viscous coupling does. There's just not enough gain there to make it worthwhile.

A power chip will rock my 2.5! Nope, not really. You're already getting optimal air flow and the correct fuel mixture. Any gains from additional spark advance are minimal at best and will restrict the octane requirements for the 2.5.

Now we're getting into the more old school hot rodding tricks for generating more power out of the 2.5. Forced air induction, displacement changes, compression ratio increases, that sort of things. These will increase power, but the cost goes through the roof quickly.

Let's step back a moment and talk about what generates power. Power comes from burning a specific amount of gasoline and air at a specific ratio. We are starting out with 2.5 liters of displacement. That's not a lot of air / fuel being burned in the grand scheme of things, and it will only generate so much power. Let me repeat that. You can only burn a certain amount of the proper air / fuel mixture in the 2.5. That's all the power available out of the engine.

We can increase the amount of power generated by increasing the compression ratio and by extension the efficiency of the engine. Doing so increases the octane rating required to prevent detonation and the destruction of the engine. One of the bonuses of the 2.5 is that it will happily burn anything that looks and smells like gasoline. So we may not want to go there.

Another way to increase efficiency is to eliminate as much parasitic drag in the engine as we can. We can try to make as much power go to the transmission as possible. One of the ways to do that is with roller cams and roller rockers. With a four banger, that is a loosing proposition because there really isn't enough parasitic loss there to justify the expense. A full roller valve train would be expensive and result in an almost unnoticeable gain.

We can balance and blueprint the engine, so that it operates closer to it's theoretical efficiency. Again, that's a lot of expense for not a lot of gain. I estimate that you are only going to gain 15 - 20 HP at the top end with both a roller valve train and a balanced and blueprinted engine. And you'll only see that gain in the higher RPM ranges.

What about camming the engine? There's the possibility of gaining a little here, but we want a nice, flat HP and torque curve for the way we end up using the 2.5. Going with a lot of duration and overlap on the cam generates HP, but the power curve move up in the RPM range. Not what we are looking for. What about higher lift on the cam? We can get some gains there, and it can be done with rocker arms of a higher ratio. The longest rocker arms that will fit under the valve cover are approximately 1.6 to 1. We also have to be careful to not drive a valve into a piston doing this. Especially if you rev it and float a valve.

How about a stroker engine? That increases the amount of fuel / air mixture being burned and generates more power! Yup, it sure does. I've seen 2.5 stoker engines go for $3000 and up. That puts you in the same HP and torque range as a stock 4.0.!That's a lot of money to turn an SE into a stock Sport or X. If you can pick up an SE for $7000 and add in $3000 for a stroker, you're not far off from a decent Sport or X. Plus you still have the AX5 to deal with in the SE. It does solve the riddle of how to burn more fuel / air.

There's always head modifications as well. These work best in conjunction with a high lift and long duration cam. It will get more fuel / air mixture into the combustion chamber, but you'll only see the increase at higher RPM's. You can do things like bigger valves, CC'ing the heads so that all four combustion chambers are as close to the same size as possible, polishing the combustion chambers, raising the intake ports and port matching, contouring the intake valve bowl, lots of tricks to tried there. My take is that there just isn't enough displacement in the 2.5 to really make any of this worthwhile at the lower RPM ranges.

Forced air induction. Now this works. More fuel / air into the engine = more power. My preference would be something like a roots type positive displacement blower. It would generate power from idle to wherever you lifted the throttle. With supercharging and turbocharging the 2.5, you are faced with replacing the ECM with something that would control spark and fuel management. It's out there and available, but man is it expensive and hard to find. Plus you need to program these controllers from scratch to match your engine parameters. It's a good way to end up buying another 2.5. Good thing 2.5's are cheap!

Wet shot nitrous injection. This technology has been around since WWII, but it has nothing to recommend it to an SE owner. Just don't.

Repeat this as many times as it takes to sink in. You CAN NOT get more power out of these 2.5 liter 4 bangers unless you want to spend some serious coin.

All of the bolt on mods are a complete waste of money, most of them offering no performance gain at all, only an empty wallet (i.e. intakes, headers, etc.).

The ONLY real way to improve these 4 bangers in terms of power output would be to dump $3000 plus into a stroker engine, or dump $5000 plus into a supercharger system and custom standalone engine management system.

When you start putting that in perspective, you're better off selling your SE and getting a clean 4.0 model Wrangler. Either that, or if you really don't want to sell it, invest in a V8 swap and call it a day.

I see it asked all the time, "How do I get more power out of my 4 cylinder?", and the way to answer that is with this simple question: "Are you prepared to spend $3000 or more?"

And we know the answer to that question, so it's almost senseless to even ask.

OK, now let's talk about what you can do to increase the performance of your 2.5 powered TJ SE...

Keep the weight down. The 2.5 is perfectly happy pushing a 3,300 – 3,500 pound TJ around, especially on 31” tires. Around town, off road, on the Highway. Keep it Light for true Jeeping bliss!

Tires, Tires, Tires. Keep your tires to 31”, 32” or 33” tires. This effects the lift you require, the weight of the rotating mass involved and keeps you in the range of available gearing for the Dana 35 / 30 that comes with your 2.5.

Gears. You will end up changing gears out for one of two ratios. 4.88 or 5.13. That may sound pretty extreme, but those are the gear ratios that normally work the best with the 2.5 SE. Remember that the 2.5 is happy at 3,000 RPM.

The 2.5 SE is a good little Jeep that can be purchased economically in good condition. Use it within it's performance parameters and you'll be very happy with it!
Click to expand...
I've learned so much from this post! I have a 95 YJ with the 2.5 in it and been looking at possibilities. Let me say that not only is your response highly informative, but very well set out. I found it easy to understand everything you were telling me and im not a "car guy". The end goal for me is a V8 swap, however, now that I know my little 4banger won't be more than a glorified go-kart, I will save all of the money I may have spent on countless mods and bolt-ons and just go straight for v8
 
StG58 said:
TJ SE's and the 2.5 liter engine

There's a lot of discussion around the Jeep 2.5 liter engine and how to increase horse power and torque.

The short answer is, you can't. No one likes that answer, but it's the truth. The 2.5 is what it is. There are a lot of reasons to purchase an SE. Lighter weight, lower purchase price, successfully burns anything that looks and smells like regular pump gas, simpler and slightly less expensive to maintain are among of them. Oh, and they last bloody forever!

The common modifications that are attempted to gain performance are:
4.0 Throttle body
Throttle body spacer
Cold air induction
High flow air filters
IAC sensor relocation
Ford yellow top, 4 hole injectors
Headers
Cat back exhaust system
Power chips
Electric fans

Some of the less common modifications are:
Roller rockers
High performance cams
Ported and polished heads
Stroker kits
Turbocharging
Wet shot nitrous injection

Let's start with the common modifications first.

Intake modifications:
The TJ SE intake system is designed, and comes from the factory, to flow more air than the 2.5 liter engine needs to produce maximum HP and torque at wide open throttle and maximum load. True fact. There are no meaningful restrictions to air flow. The engineers did a good job of designing the intake system from the start. The only way to get additional air and fuel into the combustion chambers is to put a cam with higher lift and / or longer duration in, bigger intake valves, some form of forced air induction or a wet shot nitrous system on the engine.

Putting a 4.0 throttle body on will give me an extra 10 HP, right? Nope, sorry. Even with port matching the TB to the intake manifold, all you are gaining is the potential to flow more air. The 2.5 is really only an exotic air pump. The head will only flow so much air, and that amount is the air required to fill the combustion chambers at bottom dead center. That is especially true at lower RPMs, where our TJ SE's normally operate on the trail.

Putting a throttle body spacer in has got to improve performance, right? Nope, with the port injection there are no gains to be had with increasing plenum volume with a throttle body spacer. This is especially true of the magic throttle body spacers that promise miracle gains from swirling the intake air. That trick is a left over from the days of carburetors, and even then it wasn't effective. The length of the intake runners and the plenum volume needs to be matched to the engine's displacement, HP and torque bands. The Jeep engineers did that already. No gain to be had there.

Cold air induction has got to give me something, right? After all, cold air is denser than warm air! This is a true statement, as far as it goes. BUT, the difference in air temperature and air density going into the engine with a cold air induction system compared to the stock system is minimal at best. I have never seen or heard of a temperature difference greater than about 10 to 15 degrees F between a cold air system and the stock system. Most of the time the temperature difference is lower than that. The engine realistically doesn't see a difference and any power gains are unnoticeable.

High flow air filters will get more air into my engine, right? Sorry, the stock paper element and air box flow as much air as the engine needs. It also does a much better job of filtering the intake air than any of the aftermarket air filters. It's cheaper as well, and readily available.

So, how about relocating my IAC sensor to the air box? Again, this is only going to show a difference of a few degrees in temperature between the relocated position and the stock position. Once the engine reaches operating temperature and the ECM goes into closed loop mode, the O2 sensor takes over anyway as the ECM controls the air fuel mixture at 14.something to 1. No gains to be had there.

High flow four hole fuel injectors are the clear ticket, right? More fuel = more power! Not going to happen, sorry. Once the engine warms up and the ECM goes into closed loop operation, the amount of fuel injected is based off of the signal from the O2 sensor. The ECM will maintain that roughly 14/1 ratio no matter how much the injectors will potentially flow.

Now about the exhaust system:
Headers will give me more power! Uh, no. The TJ SE exhaust system is not restrictive. It will easily flow all of the exhaust gasses that the 2.5 will generate. The only thing you will gain is noise. And probably exhaust leaks from gasket miss-matches and failures. Headers will also put more heat into your engine compartment. The chances of the tube diameter and tube length matching the power band are also probably lower than the stock cast header.

Cat back exhaust systems are the cat's meow for performance gains. Not really. The Jeep engineers designed the exhaust system to flow the right amount of exhaust and generate the correct amount of back pressure for the 2.5. You can over scavenge the cylinders and kill performance and gas mileage with an ill designed exhaust system.

What about an electric fan? Let's get rid of all that parasitic drag! All the new cars have them. There are reasons to have an electric fan, but for the most part, no. It takes X amount of energy to move Y amount of air through the radiator to keep the 2.5 engine properly cooled. The stock fan does a good job of that, and doesn't generate a ton of parasitic loss at normal speeds. That's what the fan viscous coupling does. There's just not enough gain there to make it worthwhile.

A power chip will rock my 2.5! Nope, not really. You're already getting optimal air flow and the correct fuel mixture. Any gains from additional spark advance are minimal at best and will restrict the octane requirements for the 2.5.

Now we're getting into the more old school hot rodding tricks for generating more power out of the 2.5. Forced air induction, displacement changes, compression ratio increases, that sort of things. These will increase power, but the cost goes through the roof quickly.

Let's step back a moment and talk about what generates power. Power comes from burning a specific amount of gasoline and air at a specific ratio. We are starting out with 2.5 liters of displacement. That's not a lot of air / fuel being burned in the grand scheme of things, and it will only generate so much power. Let me repeat that. You can only burn a certain amount of the proper air / fuel mixture in the 2.5. That's all the power available out of the engine.

We can increase the amount of power generated by increasing the compression ratio and by extension the efficiency of the engine. Doing so increases the octane rating required to prevent detonation and the destruction of the engine. One of the bonuses of the 2.5 is that it will happily burn anything that looks and smells like gasoline. So we may not want to go there.

Another way to increase efficiency is to eliminate as much parasitic drag in the engine as we can. We can try to make as much power go to the transmission as possible. One of the ways to do that is with roller cams and roller rockers. With a four banger, that is a loosing proposition because there really isn't enough parasitic loss there to justify the expense. A full roller valve train would be expensive and result in an almost unnoticeable gain.

We can balance and blueprint the engine, so that it operates closer to it's theoretical efficiency. Again, that's a lot of expense for not a lot of gain. I estimate that you are only going to gain 15 - 20 HP at the top end with both a roller valve train and a balanced and blueprinted engine. And you'll only see that gain in the higher RPM ranges.

What about camming the engine? There's the possibility of gaining a little here, but we want a nice, flat HP and torque curve for the way we end up using the 2.5. Going with a lot of duration and overlap on the cam generates HP, but the power curve move up in the RPM range. Not what we are looking for. What about higher lift on the cam? We can get some gains there, and it can be done with rocker arms of a higher ratio. The longest rocker arms that will fit under the valve cover are approximately 1.6 to 1. We also have to be careful to not drive a valve into a piston doing this. Especially if you rev it and float a valve.

How about a stroker engine? That increases the amount of fuel / air mixture being burned and generates more power! Yup, it sure does. I've seen 2.5 stoker engines go for $3000 and up. That puts you in the same HP and torque range as a stock 4.0.!That's a lot of money to turn an SE into a stock Sport or X. If you can pick up an SE for $7000 and add in $3000 for a stroker, you're not far off from a decent Sport or X. Plus you still have the AX5 to deal with in the SE. It does solve the riddle of how to burn more fuel / air.

There's always head modifications as well. These work best in conjunction with a high lift and long duration cam. It will get more fuel / air mixture into the combustion chamber, but you'll only see the increase at higher RPM's. You can do things like bigger valves, CC'ing the heads so that all four combustion chambers are as close to the same size as possible, polishing the combustion chambers, raising the intake ports and port matching, contouring the intake valve bowl, lots of tricks to tried there. My take is that there just isn't enough displacement in the 2.5 to really make any of this worthwhile at the lower RPM ranges.

Forced air induction. Now this works. More fuel / air into the engine = more power. My preference would be something like a roots type positive displacement blower. It would generate power from idle to wherever you lifted the throttle. With supercharging and turbocharging the 2.5, you are faced with replacing the ECM with something that would control spark and fuel management. It's out there and available, but man is it expensive and hard to find. Plus you need to program these controllers from scratch to match your engine parameters. It's a good way to end up buying another 2.5. Good thing 2.5's are cheap!

Wet shot nitrous injection. This technology has been around since WWII, but it has nothing to recommend it to an SE owner. Just don't.

Repeat this as many times as it takes to sink in. You CAN NOT get more power out of these 2.5 liter 4 bangers unless you want to spend some serious coin.

All of the bolt on mods are a complete waste of money, most of them offering no performance gain at all, only an empty wallet (i.e. intakes, headers, etc.).

The ONLY real way to improve these 4 bangers in terms of power output would be to dump $3000 plus into a stroker engine, or dump $5000 plus into a supercharger system and custom standalone engine management system.

When you start putting that in perspective, you're better off selling your SE and getting a clean 4.0 model Wrangler. Either that, or if you really don't want to sell it, invest in a V8 swap and call it a day.

I see it asked all the time, "How do I get more power out of my 4 cylinder?", and the way to answer that is with this simple question: "Are you prepared to spend $3000 or more?"

And we know the answer to that question, so it's almost senseless to even ask.

OK, now let's talk about what you can do to increase the performance of your 2.5 powered TJ SE...

Keep the weight down. The 2.5 is perfectly happy pushing a 3,300 – 3,500 pound TJ around, especially on 31” tires. Around town, off road, on the Highway. Keep it Light for true Jeeping bliss!

Tires, Tires, Tires. Keep your tires to 31”, 32” or 33” tires. This effects the lift you require, the weight of the rotating mass involved and keeps you in the range of available gearing for the Dana 35 / 30 that comes with your 2.5.

Gears. You will end up changing gears out for one of two ratios. 4.88 or 5.13. That may sound pretty extreme, but those are the gear ratios that normally work the best with the 2.5 SE. Remember that the 2.5 is happy at 3,000 RPM.

The 2.5 SE is a good little Jeep that can be purchased economically in good condition. Use it within it's performance parameters and you'll be very happy with it!
Click to expand...
I've learned so much from this post! I have a 95 YJ with the 2.5 in it and been looking at possibilities. Let me say that not only is your response highly informative, but very well set out. I found it easy to understand everything you were telling me and im not a "car guy". The end goal for me is a V8 swap, however, now that I know my little 4banger won't be more than a glorified go-kart, I will save all of the money I may have spent on countless mods and bolt-ons and just go straight for v8
 
TJKarr said:
I've enjoyed this read. I agree that most of these mods are useless. The fact that you put new parts, on an old Jeep, makes it better anyway??

The best modification I have done, is re-gearing to 4.88 and going with a Ford 8.8 rear axle. That axle already has the same bolt pattern as the stock Jeep, plus you get LSD, disc brakes, larger axle shafts, etc. I run 285/75/16s on mine. Yes, I drive comfortably at 3000 RPM, 60-65 mph down the highway.

The performance on and off-road, with all the benefits from this mod, is unrivaled in my opinion.
Click to expand...

Just bumping this old post to ask for a bit more information on this mod. Are those axles easy to find? What trucks did they originally come on? Was the swap very difficult?
 
Last edited:
StG58 said:
TJ SE's and the 2.5 liter engine

There's a lot of discussion around the Jeep 2.5 liter engine and how to increase horse power and torque.

The short answer is, you can't. No one likes that answer, but it's the truth. The 2.5 is what it is. There are a lot of reasons to purchase an SE. Lighter weight, lower purchase price, successfully burns anything that looks and smells like regular pump gas, simpler and slightly less expensive to maintain are among of them. Oh, and they last bloody forever!

The common modifications that are attempted to gain performance are:
4.0 Throttle body
Throttle body spacer
Cold air induction
High flow air filters
IAC sensor relocation
Ford yellow top, 4 hole injectors
Headers
Cat back exhaust system
Power chips
Electric fans

Some of the less common modifications are:
Roller rockers
High performance cams
Ported and polished heads
Stroker kits
Turbocharging
Wet shot nitrous injection

Let's start with the common modifications first.

Intake modifications:
The TJ SE intake system is designed, and comes from the factory, to flow more air than the 2.5 liter engine needs to produce maximum HP and torque at wide open throttle and maximum load. True fact. There are no meaningful restrictions to air flow. The engineers did a good job of designing the intake system from the start. The only way to get additional air and fuel into the combustion chambers is to put a cam with higher lift and / or longer duration in, bigger intake valves, some form of forced air induction or a wet shot nitrous system on the engine.

Putting a 4.0 throttle body on will give me an extra 10 HP, right? Nope, sorry. Even with port matching the TB to the intake manifold, all you are gaining is the potential to flow more air. The 2.5 is really only an exotic air pump. The head will only flow so much air, and that amount is the air required to fill the combustion chambers at bottom dead center. That is especially true at lower RPMs, where our TJ SE's normally operate on the trail.

Putting a throttle body spacer in has got to improve performance, right? Nope, with the port injection there are no gains to be had with increasing plenum volume with a throttle body spacer. This is especially true of the magic throttle body spacers that promise miracle gains from swirling the intake air. That trick is a left over from the days of carburetors, and even then it wasn't effective. The length of the intake runners and the plenum volume needs to be matched to the engine's displacement, HP and torque bands. The Jeep engineers did that already. No gain to be had there.

Cold air induction has got to give me something, right? After all, cold air is denser than warm air! This is a true statement, as far as it goes. BUT, the difference in air temperature and air density going into the engine with a cold air induction system compared to the stock system is minimal at best. I have never seen or heard of a temperature difference greater than about 10 to 15 degrees F between a cold air system and the stock system. Most of the time the temperature difference is lower than that. The engine realistically doesn't see a difference and any power gains are unnoticeable.

High flow air filters will get more air into my engine, right? Sorry, the stock paper element and air box flow as much air as the engine needs. It also does a much better job of filtering the intake air than any of the aftermarket air filters. It's cheaper as well, and readily available.

So, how about relocating my IAC sensor to the air box? Again, this is only going to show a difference of a few degrees in temperature between the relocated position and the stock position. Once the engine reaches operating temperature and the ECM goes into closed loop mode, the O2 sensor takes over anyway as the ECM controls the air fuel mixture at 14.something to 1. No gains to be had there.

High flow four hole fuel injectors are the clear ticket, right? More fuel = more power! Not going to happen, sorry. Once the engine warms up and the ECM goes into closed loop operation, the amount of fuel injected is based off of the signal from the O2 sensor. The ECM will maintain that roughly 14/1 ratio no matter how much the injectors will potentially flow.

Now about the exhaust system:
Headers will give me more power! Uh, no. The TJ SE exhaust system is not restrictive. It will easily flow all of the exhaust gasses that the 2.5 will generate. The only thing you will gain is noise. And probably exhaust leaks from gasket miss-matches and failures. Headers will also put more heat into your engine compartment. The chances of the tube diameter and tube length matching the power band are also probably lower than the stock cast header.

Cat back exhaust systems are the cat's meow for performance gains. Not really. The Jeep engineers designed the exhaust system to flow the right amount of exhaust and generate the correct amount of back pressure for the 2.5. You can over scavenge the cylinders and kill performance and gas mileage with an ill designed exhaust system.

What about an electric fan? Let's get rid of all that parasitic drag! All the new cars have them. There are reasons to have an electric fan, but for the most part, no. It takes X amount of energy to move Y amount of air through the radiator to keep the 2.5 engine properly cooled. The stock fan does a good job of that, and doesn't generate a ton of parasitic loss at normal speeds. That's what the fan viscous coupling does. There's just not enough gain there to make it worthwhile.

A power chip will rock my 2.5! Nope, not really. You're already getting optimal air flow and the correct fuel mixture. Any gains from additional spark advance are minimal at best and will restrict the octane requirements for the 2.5.

Now we're getting into the more old school hot rodding tricks for generating more power out of the 2.5. Forced air induction, displacement changes, compression ratio increases, that sort of things. These will increase power, but the cost goes through the roof quickly.

Let's step back a moment and talk about what generates power. Power comes from burning a specific amount of gasoline and air at a specific ratio. We are starting out with 2.5 liters of displacement. That's not a lot of air / fuel being burned in the grand scheme of things, and it will only generate so much power. Let me repeat that. You can only burn a certain amount of the proper air / fuel mixture in the 2.5. That's all the power available out of the engine.

We can increase the amount of power generated by increasing the compression ratio and by extension the efficiency of the engine. Doing so increases the octane rating required to prevent detonation and the destruction of the engine. One of the bonuses of the 2.5 is that it will happily burn anything that looks and smells like gasoline. So we may not want to go there.

Another way to increase efficiency is to eliminate as much parasitic drag in the engine as we can. We can try to make as much power go to the transmission as possible. One of the ways to do that is with roller cams and roller rockers. With a four banger, that is a loosing proposition because there really isn't enough parasitic loss there to justify the expense. A full roller valve train would be expensive and result in an almost unnoticeable gain.

We can balance and blueprint the engine, so that it operates closer to it's theoretical efficiency. Again, that's a lot of expense for not a lot of gain. I estimate that you are only going to gain 15 - 20 HP at the top end with both a roller valve train and a balanced and blueprinted engine. And you'll only see that gain in the higher RPM ranges.

What about camming the engine? There's the possibility of gaining a little here, but we want a nice, flat HP and torque curve for the way we end up using the 2.5. Going with a lot of duration and overlap on the cam generates HP, but the power curve move up in the RPM range. Not what we are looking for. What about higher lift on the cam? We can get some gains there, and it can be done with rocker arms of a higher ratio. The longest rocker arms that will fit under the valve cover are approximately 1.6 to 1. We also have to be careful to not drive a valve into a piston doing this. Especially if you rev it and float a valve.

How about a stroker engine? That increases the amount of fuel / air mixture being burned and generates more power! Yup, it sure does. I've seen 2.5 stoker engines go for $3000 and up. That puts you in the same HP and torque range as a stock 4.0.!That's a lot of money to turn an SE into a stock Sport or X. If you can pick up an SE for $7000 and add in $3000 for a stroker, you're not far off from a decent Sport or X. Plus you still have the AX5 to deal with in the SE. It does solve the riddle of how to burn more fuel / air.

There's always head modifications as well. These work best in conjunction with a high lift and long duration cam. It will get more fuel / air mixture into the combustion chamber, but you'll only see the increase at higher RPM's. You can do things like bigger valves, CC'ing the heads so that all four combustion chambers are as close to the same size as possible, polishing the combustion chambers, raising the intake ports and port matching, contouring the intake valve bowl, lots of tricks to tried there. My take is that there just isn't enough displacement in the 2.5 to really make any of this worthwhile at the lower RPM ranges.

Forced air induction. Now this works. More fuel / air into the engine = more power. My preference would be something like a roots type positive displacement blower. It would generate power from idle to wherever you lifted the throttle. With supercharging and turbocharging the 2.5, you are faced with replacing the ECM with something that would control spark and fuel management. It's out there and available, but man is it expensive and hard to find. Plus you need to program these controllers from scratch to match your engine parameters. It's a good way to end up buying another 2.5. Good thing 2.5's are cheap!

Wet shot nitrous injection. This technology has been around since WWII, but it has nothing to recommend it to an SE owner. Just don't.

Repeat this as many times as it takes to sink in. You CAN NOT get more power out of these 2.5 liter 4 bangers unless you want to spend some serious coin.

All of the bolt on mods are a complete waste of money, most of them offering no performance gain at all, only an empty wallet (i.e. intakes, headers, etc.).

The ONLY real way to improve these 4 bangers in terms of power output would be to dump $3000 plus into a stroker engine, or dump $5000 plus into a supercharger system and custom standalone engine management system.

When you start putting that in perspective, you're better off selling your SE and getting a clean 4.0 model Wrangler. Either that, or if you really don't want to sell it, invest in a V8 swap and call it a day.

I see it asked all the time, "How do I get more power out of my 4 cylinder?", and the way to answer that is with this simple question: "Are you prepared to spend $3000 or more?"

And we know the answer to that question, so it's almost senseless to even ask.

OK, now let's talk about what you can do to increase the performance of your 2.5 powered TJ SE...

Keep the weight down. The 2.5 is perfectly happy pushing a 3,300 – 3,500 pound TJ around, especially on 31” tires. Around town, off road, on the Highway. Keep it Light for true Jeeping bliss!

Tires, Tires, Tires. Keep your tires to 31”, 32” or 33” tires. This effects the lift you require, the weight of the rotating mass involved and keeps you in the range of available gearing for the Dana 35 / 30 that comes with your 2.5.

Gears. You will end up changing gears out for one of two ratios. 4.88 or 5.13. That may sound pretty extreme, but those are the gear ratios that normally work the best with the 2.5 SE. Remember that the 2.5 is happy at 3,000 RPM.

The 2.5 SE is a good little Jeep that can be purchased economically in good condition. Use it within it's performance parameters and you'll be very happy with it!
Click to expand...
Thank you for this!!! Just saved me a bunch of time and money.
 
  • Like
Reactions: Chris
RG&A has had their 5.13 kit for Dana 30/35 listed as out of stock for many months now. And no email response regarding this... The waiting game continues😣
 
Top Bottom
Back