Cummins R2.8 97 TJ

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nuffsaid

nuffsaid

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I have had some time to put a few miles on the new engine conversion and all I can say is I have a big smile on my face. With 4.56 gears and 35-12.50 M/T's, the engine is really happy at 62 mph and is turning in over 20 mpg! When I get out on the two lane highway, I go through the gears ending up in 5th and don't have to shift out of 5th for grades that the 4.0 would have fallen flat on it's face. The engine is pretty responsive and has great torque. It seems to like to run around 200-210 degrees on the highway but quickly cools down when the speed is decreased. I haven't had a chance to run around in the hills alot yet, but I am sure it will be great. So far everything seems to be working great. I really like the intellitronix gauges, and the gps speedometer makes a nice add. Right now I am only up to 160 total miles and about 6 total hours of run time. At this point I have no regrets on this swap.
 

NDSpeed

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I have had some time to put a few miles on the new engine conversion and all I can say is I have a big smile on my face. With 4.56 gears and 35-12.50 M/T's, the engine is really happy at 62 mph and is turning in over 20 mpg! When I get out on the two lane highway, I go through the gears ending up in 5th and don't have to shift out of 5th for grades that the 4.0 would have fallen flat on it's face. The engine is pretty responsive and has great torque. It seems to like to run around 200-210 degrees on the highway but quickly cools down when the speed is decreased. I haven't had a chance to run around in the hills alot yet, but I am sure it will be great. So far everything seems to be working great. I really like the intellitronix gauges, and the gps speedometer makes a nice add. Right now I am only up to 160 total miles and about 6 total hours of run time. At this point I have no regrets on this swap.

What RPM are you running at those speeds?

I’m going to transition to 35s and I have the 4:10 gearing. Calculator says it should be happy at the 70mph
But I also have the 6spd transgender in my heap
 

rasband

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Can you post some under hood pictures? I am curious how everything laid out - since this is an eventual upgrade I'd like to do.
 

Ericshere03

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I have had some time to put a few miles on the new engine conversion and all I can say is I have a big smile on my face. With 4.56 gears and 35-12.50 M/T's, the engine is really happy at 62 mph and is turning in over 20 mpg! When I get out on the two lane highway, I go through the gears ending up in 5th and don't have to shift out of 5th for grades that the 4.0 would have fallen flat on it's face. The engine is pretty responsive and has great torque. It seems to like to run around 200-210 degrees on the highway but quickly cools down when the speed is decreased. I haven't had a chance to run around in the hills alot yet, but I am sure it will be great. So far everything seems to be working great. I really like the intellitronix gauges, and the gps speedometer makes a nice add. Right now I am only up to 160 total miles and about 6 total hours of run time. At this point I have no regrets on this swap.

I am surprised it gets worse mileage than my gladiator ecodiesel with 37’s … I get between 24 and 27 mpg on my JT. Stock I saw between 28 and 32mpg.

My LJ with 31’s gets 14-20mpg … I been dreaming of a diesel TJ/JL since they teased a mopar swap kit (2.8 VM Motori) back in 2006-ish…
 
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What RPM are you running at those speeds?

I’m going to transition to 35s and I have the 4:10 gearing. Calculator says it should be happy at the 70mph
But I also have the 6spd transgender in my heap

I am about 2300 at 65
 
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I am surprised it gets worse mileage than my gladiator ecodiesel with 37’s … I get between 24 and 27 mpg on my JT. Stock I saw between 28 and 32mpg.

My LJ with 31’s gets 14-20mpg … I been dreaming of a diesel TJ/JL since they teased a mopar swap kit (2.8 VM Motori) back in 2006-ish…
Engine is nowhere near broken in yet and having a soft top doesn't help aerodynamics either. If I can get over 20 with 4.56 gears and mud tires, I will say it is a win. A hard top would be cool, but I haven't stumbled on one for a good price yet.
 
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Can you post some under hood pictures? I am curious how everything laid out - since this is an eventual upgrade I'd like to do.

What are you looking to see? I have posted quite a few under hood photos already. If I get a chance, I will try and make a video.
 

eastbloc

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Do you feel like dropping ratio to 4.10 would not hinder your performance?
In every diesel swap i read, guys talk about going down to as far as into 3.XX to increase efficiency, seems like there is plenty of torque to allow that.
 

Ericshere03

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Engine is nowhere near broken in yet and having a soft top doesn't help aerodynamics either. If I can get over 20 with 4.56 gears and mud tires, I will say it is a win. A hard top would be cool, but I haven't stumbled on one for a good price yet.

I did a round trip from Phoenix to Albuquerque down to Hatch and back to Phoenix averaging 30.2 on a new gladiator. Front half of my top is soft plus vehicle is much bigger, heavier, powerful, restricted by massive exhaust and after exhaust treatments.

I believe peak torque for the 2.8 is 1800rpm. I think your way over geared. 3.73 or 4.10 might be better. The nice thing about a turbo diesel is LOAD causes the engine to make more power and apply more torque (works the turbo harder, allowing more fuel) … I would say my ecodiesel works better (gearing wise) with 37’s than the factory 32’s … with small tires the diesel was revving too much, bigger tires slow the RPMs and provide more boost and less shifting … it’s hard to convey over text … a good but extreme example is a semi doesn’t produce much boost unless it’s loaded.
 
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Do you feel like dropping ratio to 4.10 would not hinder your performance?
In every diesel swap i read, guys talk about going down to as far as into 3.XX to increase efficiency, seems like there is plenty of torque to allow that.

If I had a tranny with a deeper first gear I would consider it, but right now I think it is geared perfect.
 
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I did a round trip from Phoenix to Albuquerque down to Hatch and back to Phoenix averaging 30.2 on a new gladiator. Front half of my top is soft plus vehicle is much bigger, heavier, powerful, restricted by massive exhaust and after exhaust treatments.

I believe peak torque for the 2.8 is 1800rpm. I think your way over geared. 3.73 or 4.10 might be better. The nice thing about a turbo diesel is LOAD causes the engine to make more power and apply more torque (works the turbo harder, allowing more fuel) … I would say my ecodiesel works better (gearing wise) with 37’s than the factory 32’s … with small tires the diesel was revving too much, bigger tires slow the RPMs and provide more boost and less shifting … it’s hard to convey over text … a good but extreme example is a semi doesn’t produce much boost unless it’s loaded.
If I had a stronger transmission I would consider turning up the power, but as it is my transmission will last longer with lower gears. I use my Jeep for offroad adventures, hunting and such and cruising around in town in the summer. It really isn't a great highway vehicle, so going slow is my priority.
 

Ericshere03

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If I had a stronger transmission I would consider turning up the power, but as it is my transmission will last longer with lower gears. I use my Jeep for offroad adventures, hunting and such and cruising around in town in the summer. It really isn't a great highway vehicle, so going slow is my priority.

Boom, there ya go! Makes sense.

I know your wallet is still recovering, but have you seen the Tremec TR4050? 6.16 first! They make an ax15 replacement … I saw them last time I considered a 5 speed OD for my old Vette.

https://shiftsst.com/1997-2006-jeep-tj
 

Wildman

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Boom, there ya go! Makes sense.

I know your wallet is still recovering, but have you seen the Tremec TR4050? 6.16 first! They make an ax15 replacement … I saw them last time I considered a 5 speed OD for my old Vette.

https://shiftsst.com/1997-2006-jeep-tj

Watch the video of them installing on in a TJ and see how much it hangs down. They have to cut the crap out of a STOCK skid plate to make it fit. So if you have any type of tummy tuck/belly up skid it'll be hanging down 3" at a minimum. It's a great transmission for the gearing offered but not for a 0ff-road Jeep.


@nuffsaid I couldn't find it so how do you have the speedo hooked up? You're using a GPS sending unit that sends a signal to the dash?
Thanks.
 
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Boom, there ya go! Makes sense.

I know your wallet is still recovering, but have you seen the Tremec TR4050? 6.16 first! They make an ax15 replacement … I saw them last time I considered a 5 speed OD for my old Vette.

https://shiftsst.com/1997-2006-jeep-tj

I am aware of the tremec 4050, but since I already have a doubler and an atlas II, it doesn't fit my build. When I swapped a 24v cummins 5.9 into a 85 suburban with one ton running gear, I kept peeling the splines off of the NVG 4500 output shaft due to the low speed torque. The 1 3/8 32 spline shaft wouldn't hold up as I ate two of them in 10,000 miles. I ended up going to a 23 spline dodge output shaft and never had another problem.
 
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Watch the video of them installing on in a TJ and see how much it hangs down. They have to cut the crap out of a STOCK skid plate to make it fit. So if you have any type of tummy tuck/belly up skid it'll be hanging down 3" at a minimum. It's a great transmission for the gearing offered but not for a 0ff-road Jeep.


@nuffsaid I couldn't find it so how do you have the speedo hooked up? You're using a GPS sending unit that sends a signal to the dash?
Thanks.

I got a speedometer gps sender from intellitronix and it was an easy 3 wire hook up. The module is mounted behind my gauge cluster and it has an antenna that I have sitting on the dash, works great, speedometer is accurate as well as the odometer. This was the simplest solution I could find.
 
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I did a round trip from Phoenix to Albuquerque down to Hatch and back to Phoenix averaging 30.2 on a new gladiator. Front half of my top is soft plus vehicle is much bigger, heavier, powerful, restricted by massive exhaust and after exhaust treatments.

I believe peak torque for the 2.8 is 1800rpm. I think your way over geared. 3.73 or 4.10 might be better. The nice thing about a turbo diesel is LOAD causes the engine to make more power and apply more torque (works the turbo harder, allowing more fuel) … I would say my ecodiesel works better (gearing wise) with 37’s than the factory 32’s … with small tires the diesel was revving too much, bigger tires slow the RPMs and provide more boost and less shifting … it’s hard to convey over text … a good but extreme example is a semi doesn’t produce much boost unless it’s loaded.

One thing to note about the R2.8 is that it has a very flat torque curve, pretty much comes on at 1800 and carries through close to 3000. It's not like a 4bt with a very narrow torque curve. Horsepower peak is around 3k.
 
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NDSpeed

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I got a speedometer gps sender from intellitronix and it was an easy 3 wire hook up. The module is mounted behind my gauge cluster and it has an antenna that I have sitting on the dash, works great, speedometer is accurate as well as the odometer. This was the simplest solution I could find.

So your Speedo is connected to factory instrument cluster?

If so very nice.