4.0 performance mods

Eddie Greenlee

Eddie Greenlee

TJ Addict
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Hey guys, I know there will be some eye rolling on the 4.0 performance, and lots of opinions. I have spent the last 2 hours reading post that laugh, mock and say there are no modification you can do to the 4.0 6cyl. to improve horse power or torque.
Of course I've read a few positive reviews of a couple things that may give 5 to 10 HP gains along with torque gains too.
Has anyone here done testing on the cold air intake, headers and cat back exhaust mods and found a combined increase in HP and torque.??
I think that if you do several things that "improve a total combined HP/Torque" to the jeep then it may be worth the trouble.
 
Eddie Greenlee said:
Hey guys, I know there will be some eye rolling on the 4.0 performance, and lots of opinions. I have spent the last 2 hours reading post that laugh, mock and say there are no modification you can do to the 4.0 6cyl. to improve horse power or torque.
Of course I've read a few positive reviews of a couple things that may give 5 to 10 HP gains along with torque gains too.
Has anyone here done testing on the cold air intake, headers and cat back exhaust mods and found a combined increase in HP and torque.??
I think that if you do several things that "improve a total combined HP/Torque" to the jeep then it may be worth the trouble.
Click to expand...
If you are going to do a catback system and headers you should also spend the little extra cash and get a custom complete exhaust. It will probably make a big difference. I am thinking of doing this. I am going to have the shop install my new headers (haven't picked them yet) and then do custom exhaust from there. Eliminate the dual cats and do a single larger less restrictive cat further down the exhaust. Maybe I crazy, but I think it will give better results and will give better flow to the exhaust. Then I will install a "cai" which is really hard to do in that with the 4.0L jeep

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There are some very knowledgable people on this forum, Jerry Bransford, Mr Blaine, and several others. What I have learned, both here and elsewhere from having my LJ since 2005 (new) as well as a '83 CJ5 since new, is that the in-line 6 is a very durable motor and does not modify easily for increased performance. You put an exhaust on it (custom or out of the box) and all you will get is an increase in sound, the performance gains will be negligible at best and most assuredly $ per HP will be disappointing, same goes for the "cold air intake" stuff, as well as the "throttle body spacer" and the "tornado" stuff. In reality, the only thing I have seen that dramatically increases HP and torque is to either stroke it (making it somewhere around a 4.6 liter) or put a super charger or turbo charger on it. None of these three are inexpensive, but all three give significant boosts in HP and torque. My suggestion is to save your money for one of those or increase the capabilities through suspension, lockers, winch, etc. It is, after all, a JEEP, not a hot rod....... YMMV, just MHO
 
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FireJeep said:
There are some very knowledgable people on this forum, Jerry Bransford, Mr Blaine, and several others. What I have learned, both here and elsewhere from having my LJ since 2005 (new) as well as a '83 CJ5 since new, is that the in-line 6 is a very durable motor and does not modify easily for increased performance. You put an exhaust on it (custom or out of the box) and all you will get is an increase in sound, the performance gains will be negligible at best and most assuredly $ per HP will be disappointing, same goes for the "cold air intake" stuff, as well as the "throttle body spacer" and the "tornado" stuff. In reality, the only thing I have seen that dramatically increases HP and torque is to either stroke it (making it somewhere around a 4.6 liter) or put a super charger or turbo charger on it. None of these three are inexpensive, but all three give significant boosts in HP and torque. My suggestion is to save your money for one of those or increase the capabilities through suspension, lockers, winch, etc. It is, after all, a JEEP, not a hot rod....... YMMV, just MHO
Click to expand...
That ^^
 
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There’s a number of before and after dyne charts showing no substantial improvement with a cold air intake. The same can be said for an exhaust and headers as well.

You’re trying to “tune” a tractor engine. The only real way you’re going to get any noticeable power out of the 4.0 is forced induction, stroking it, a hotter cam shaft, or some good head work. Other than that, you’re simply burning money.

But hey, if you want to believe you’re going to gain some power from a cold air intake and exhaust, by all means, spend your money. You’re only fooling yourself though :)

On the subject of cold air intakes, please read this thread:
https://wranglertjforum.com/threads/cold-air-intake-faq.3087/

There’s before and after dynos there, as well as quotes from the Jeep engineers themselves.

As far as an exhaust goes, if your stock one is in need of replacement, then I would upgrade it with a new muffler and piping as well. But take it from someone who has had headers on a 4.0, they give you no power, they are a pain in the butt to get seated correctly, and if you do any sort of flexing offroad, they WILL crack usually in under a year. That’s not an if either, it’s a GUARANTEE! Mine cracked in under a year, as is the case with a lot of others as well.

I hate to see someone go down the wrong path, but believe you me, this is one of those situations that ends up being a major “I told you so”.

Headers = no
Exhaust = yes (it your stock exhaust is in need of a replacement)
CAI = no
 
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Chris said:
There’s a number of before and after dyne charts showing no substantial improvement with a cold air intake. The same can be said for an exhaust and headers as well.

You’re trying to “tune” a tractor engine. The only real way you’re going to get any noticeable power out of the 4.0 is forced induction, stroking it, a hotter cam shaft, or some good head work. Other than that, you’re simply burning money.

But hey, if you want to believe you’re going to gain some power from a cold air intake and exhaust, by all means, spend your money. You’re only fooling yourself though :)

On the subject of cold air intakes, please read this thread:
https://wranglertjforum.com/threads/cold-air-intake-faq.3087/

There’s before and after dynos there, as well as quotes from the Jeep engineers themselves.

As far as an exhaust goes, if your stock one is in need of replacement, then I would upgrade it with a new muffler and piping as well. But take it from someone who has had headers on a 4.0, they give you no power, they are a pain in the butt to get seated correctly, and if you do any sort of flexing offroad, they WILL crack usually in under a year. That’s not an if either, it’s a GUARANTEE! Mine cracked in under a year, as is the case with a lot of others as well.

I hate to see someone go down the wrong path, but believe you me, this is one of those situations that ends up being a major “I told you so”.

Headers = no
Exhaust = yes (it your stock exhaust is in need of a replacement)
CAI = no
Click to expand...
The reason I'm doing mine is because it looks like my exhaust was smacked with a hammer right below the cats, and in a few other places

Sent from my SM-G955U using Tapatalk
 
Chris said:
There’s a number of before and after dyne charts showing no substantial improvement with a cold air intake. The same can be said for an exhaust and headers as well.

You’re trying to “tune” a tractor engine. The only real way you’re going to get any noticeable power out of the 4.0 is forced induction, stroking it, a hotter cam shaft, or some good head work. Other than that, you’re simply burning money.

But hey, if you want to believe you’re going to gain some power from a cold air intake and exhaust, by all means, spend your money. You’re only fooling yourself though :)

On the subject of cold air intakes, please read this thread:
https://wranglertjforum.com/threads/cold-air-intake-faq.3087/

There’s before and after dynos there, as well as quotes from the Jeep engineers themselves.

As far as an exhaust goes, if your stock one is in need of replacement, then I would upgrade it with a new muffler and piping as well. But take it from someone who has had headers on a 4.0, they give you no power, they are a pain in the butt to get seated correctly, and if you do any sort of flexing offroad, they WILL crack usually in under a year. That’s not an if either, it’s a GUARANTEE! Mine cracked in under a year, as is the case with a lot of others as well.

I hate to see someone go down the wrong path, but believe you me, this is one of those situations that ends up being a major “I told you so”.

Headers = no
Exhaust = yes (it your stock exhaust is in need of a replacement)
CAI = no
Click to expand...

jeep_boss said:
A re-gear will buy you a lot of "peppiness".
Click to expand...

Both of these ^^^
 
talianslyr said:
The reason I'm doing mine is because it looks like my exhaust was smacked with a hammer right below the cats, and in a few other places

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Click to expand...

That’s a good reason to do it! I replaced the exhaust on my old TJ with a new one because it was worn and starting to develop a hole in it. I didn’t feel any real power gains from the new exhaust, but it definitely gave it a really nice and throaty sound! The sound alone was worth it.
 
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Chris said:
That’s a good reason to do it! I replaced the exhaust on my old TJ with a new one because it was worn and starting to develop a hole in it. I didn’t feel any real power gains from the new exhaust, but it definitely gave it a really nice and throaty sound! The sound alone was worth it.
Click to expand...
What do you think about eliminating the 2 cats by the headers and moving it down the line?

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talianslyr said:
What do you think about eliminating the 2 cats by the headers and moving it down the line?

Sent from my SM-G955U using Tapatalk
Click to expand...

You won’t gain anything by doing that. The other issue is that it will set off your check engine light and generate error codes that you won’t be able to get rid of. That will also mean you won’t be able to pass emissions testing if your state does that.
 
Eddie Greenlee said:
Has anyone here done testing on the cold air intake, headers and cat back exhaust mods and found a combined increase in HP and torque.??
I think that if you do several things that "improve a total combined HP/Torque" to the jeep then it may be worth the trouble.
Click to expand...

With the money spent, what useable increases would you really gain on a TJ? Will 15hp and 10ft/lbs of torque really make a difference?
 
I have my eyes on the Banks CARB approved turbo with intercooler. Supposed to be pretty easy to bolt on. The turbo is little over $3k, the intercooler is a little under $2k. I’m guessing it’s a weekend install. I have a 30k mile complete 4.0 sitting in the corner of my garage. I’ll probably do the swap first since I feel better about turbocharging a motor with 30k vs one with 123k... I chose 4.56 gears over 4.88s with a turbo in mind.
 
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Serbonze said:
With the money spent, what useable increases would you really gain on a TJ? Will 15hp and 10ft/lbs of torque really make a difference?
Click to expand...

Just me thinking , but 15hp and 10ft/lbs torque would be nice and would help in the overall function of the jeep. I know its not a big difference, but say you lost a little due to larger tires or maybe pulling a trailer, it wont win any races but it might bring some power back.
 
Does a cold air intake have a refrigerator attached to it?

I would guess that a less restrictive exhaust, with cats removed, and an ECU tune will add more power. Most of the other stuff mentioned above does nothing noticeable.

As others said, just buy a new engine to drop in...or realize this is a jeep and go buy yourself a 2000 BMW or Audi and tune the crap out of it.
 
Unless you go with forced induction, or a stroker motor, save your money. Cai,s do nothing but let more dirt get into the engine. A cat back will make it louder. If you went with taller tires, then re-gearing will get most of the stock power back, and make it easier on the entire driveline.
 
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