Cam for 2.5?

[Peanut_butter_mj]

Has anybody put one of these in a Comanche? Is it a good idea to put one in?  If so what was it like driving after?  Thanks.

[eaglescout526]

Probably not. Not may Jeep owners stick with the 2.5L like you and I. There is a 2.5L dedicated performance group on Facebook you can ask. Some guys have gone as far as to stroke and bore out the 2.5L to get up to a 3L engine. One of our very own members supercharged his or something of the nature. 
 

If your going for performance, you can give it a shot. If your just replacing it, then stick with stock. 

[Peanut_butter_mj]

19 minutes ago, eaglescout526 said:

Probably not. Not may Jeep owners stick with the 2.5L like you and I. There is a 2.5L dedicated performance group on Facebook you can ask. Some guys have gone as far as to stroke and bore out the 2.5L to get up to a 3L engine. One of our very own members supercharged his or something of the nature. 
 

If your going for performance, you can give it a shot. If your just replacing it, then stick with stock. 

I don’t want to build just want a little more power not anything crazy I just want to have a little bit more get up and go

[eaglescout526]

For the 2.5L if you want some pep, make sure your sensors are reading within spec, mostly the TPS, and make sure your ignition system and fuel system is clean and free of corrosion and blockage(fuel lines and filter and injector). Then if you’re still not satisfied with making sure everything is up to snuff then I’d say go for the cam. Knock out the free stuff first before getting a new part. 

 

also converting to an electric fan, dropping power steering and AC will probably help gain some power too. 

I'm guessing where you want pep is take off in first gear huh?

 

Honestly when AMC made the 2.5L, they did it for three reasons. New engine, ditch the Iron Dimwit from GM and to have a Jeep oriented engine. 

[Peanut_butter_mj]

3 hours ago, eaglescout526 said:

For the 2.5L if you want some pep, make sure your sensors are reading within spec, mostly the TPS, and make sure your ignition system and fuel system is clean and free of corrosion and blockage(fuel lines and filter and injector). Then if you’re still not satisfied with making sure everything is up to snuff then I’d say go for the cam. Knock out the free stuff first before getting a new part. 

 

also converting to an electric fan, dropping power steering and AC will probably help gain some power too. 

I'm guessing where you want pep is take off in first gear huh?

 

Honestly when AMC made the 2.5L, they did it for three reasons. New engine, ditch the Iron Dimwit from GM and to have a Jeep oriented engine. 

Thank you, I’m gonna give it a little tune up.  Hasn’t had one in awhile.  Thanks for the help much appreciated:)

[eaglescout526]

No problem! Good luck!

[Eagle]

6 hours ago, Peanut_butter_mj said:

Has anybody put one of these in a Comanche? Is it a good idea to put one in?  If so what was it like driving after?  Thanks.

 

Years ago there was a guy in NAXJA from one of the Rocky Mountain states who had a cam in his 2.5L. Not that exact cam -- he had one of the factory cam kits. He loved it. He said it greatly improved performance and -- paradoxically -- also improved his gas mileage.

[Peanut_butter_mj]

On 2/23/2023 at 4:07 PM, eaglescout526 said:

Probably not. Not may Jeep owners stick with the 2.5L like you and I. There is a 2.5L dedicated performance group on Facebook you can ask. Some guys have gone as far as to stroke and bore out the 2.5L to get up to a 3L engine. One of our very own members supercharged his or something of the nature. 
 

If your going for performance, you can give it a shot. If your just replacing it, then stick with stock. 

How did the 4 banger hood up to being stroked?  Is it a good option or good idea?

[eaglescout526]

Not many folks have stroked the 2.5L as most dump it and go for the 4.0L since it basically has the previous 4.2L crank shaft to help stroke it out. 
 

I say if it’s something you’re going to do, research the idea and do more research until your comfortable with stroking it out. I can’t say if it’s a good option or a good idea cause it just more depends on what you want to build and how you want to do it. A friend of mine and I want to stroke out the 2.5L. I have a spare block I’d like to try this with but don’t have time or funds at the moment. 

[cruiser54]

I know 2 people who stroked their 4 cylinder engines. Both very disappointed and spent tons of money.

 

I think an aftermarket "performance" cam would be nice. The one in the Jeep now is for emissions anyway. 

[Eagle]

If the old Mopar Performance catalog is still available, the factory used to offer two cam kits for the 2.5L Jeep engine. I'm sure the cams aren't available, but the old books (from when the Performance Catalog was a printed catalog rather than a web site) had the cam specs.

 

[eaglescout526]

8 minutes ago, Eagle said:

If the old Mopar Performance catalog is still available, the factory used to offer two cam kits for the 2.5L Jeep engine. I'm sure the cams aren't available, but the old books (from when the Performance Catalog was a printed catalog rather than a web site) had the cam specs.

 

I have one of these books. It sadly didn’t offer the 2.5L performance cam but it offered the 4.0L one. 

[Eagle]

I still have the printed books from 2000 and 2002. There were three performance cams for the 2.5L -- Phase I, Phase II, and Phase III

 

Phase I -- P4529656

Duration: 240/240

Overlap: 24

Centerline: 108

Lift: .430/.430

 

Phase II -- P4529657

Duration: 248/248

Overlap: 32

Centerline: 108

Lift: .440/.440

 

Phase III -- P4529658

Duration: 256/256

Overlap: 40

Centerline: 108

Lift: .450/.450

 

The Phase I cam is supposed to be good for 900 - 5400 RPM.

The Phase II cam is supposed to be good for 1100 - 5500 RPM

The Phase III cam is supposed to be good for 1300 - 5600 RPM

 

For what it's worth, the factory performance cams for the 4.0L have exactly the same specs as the cams for the 2.5L.

[Eagle]

I don't know nearly as much as I should about camshaft design and selection. That Melling cam has longer duration but less lift than any of the Jeep factory cams. What does that translate into as far as the performance characteristics are concerned?

 

I found this: https://www.hemmings.com/stories/article/the-right-camshaft-choice

 

Based on that article, it appears all three of the Jeep factory cams are more performance-oriented than torque and fuel economy oriented. The Melling cam looks like more of an RV type cam, which should be good for fuel economy and street driving applications.

[ghetdjc320]

Gears will be the best mod for a seat of the pants increase. And forced induction is typically the best bang for the buck if you want the engine to make more power. Having modded several 4.0’s now, I can say that most mods do not produce an appreciable power increase. 

[gogmorgo]

X2 on gears, although yours is an automatic so it might already be geared pretty deep. 

My 2.5 with 4.10’s on stock size tires is decent at low speeds even with a full load in the bed, but it does need the beans fed to it to climb hills at highway speeds. And gears isn’t likely to correct that one without making the highway experience less pleasant than it already isn’t. I’d be looking to open up the midrange, 3-4k rpm.

But if you’ve increased tire size and you’re looking to get performance back, gears is going to be the way to go. It’ll have a way bigger effect on drivability than getting an extra ten horse out of an engine. 

 

Getting more air into an engine isn’t going to increase fuel economy. Ever. More air increases performance because it allows you to burn more fuel. Burning more fuel won’t save you fuel.

[Eagle]

7 hours ago, ghetdjc320 said:

Gears will be the best mod for a seat of the pants increase. And forced induction is typically the best bang for the buck if you want the engine to make more power. Having modded several 4.0’s now, I can say that most mods do not produce an appreciable power increase. 

 

That doesn't hold true for the 2.5L. The 4-speed manuals had 3.54 gears, the 5-speeds had 4.10s. The stock 2.5L doesn't have any low-end torque. Unlike the 4.0L, which in most years reached the torque peak by around 2200 RPM, the 2.5L peaks at 3200 RPM -- and it's very much a "peak," not a flat curve like the 4.0L torque curve. The 2.5 engine is a reliable engine, but in stock form it's pretty anemic. (And that torque chart is from 1997, with the newest Chrysler multi-port injection. The '86 thru '90 2.5 with the throttle body injection was even worse.)

 

With the little tires the 2.5L typically came with, the 4-speed would be turning 3000 RPM at 65 MPH. Gear it up to 4.10s and that becomes 3482 RPM. 75 MPH becomes 4000 RPM. That's churning the engine pretty fast, and for what? You're way beyond the torque peak at that point.

 

Look at the 5-speed, with overdrive but 4.10 gears, and it's not too different. 2600 RPM at 65 MPH in 5th gear, 3000 RPM at 75 MPH. That's on the torque peak. What gears would you swap in? 4.56 isn't much of a change, so you'd probably have to go to 4.88s. Now you'd be looking at 3100 RPM at 65 MPH and about 3600 RPM at 75 MPH. I've owned three 2.5L MJs and two 2.5L XJ. More gear can't create a miracle. That's why I think an RV cam could be a game changer. It won't turn a 4-cylinder into the equal of a 4.0L, but I think it could make a significant improvement.

[ghetdjc320]

It will be interesting to see the results of a cam swap but ultimately, I have my doubts that it will do much. Gears could help with low end but as you pointed out, you’ll be high up in the rpm band without more transmission gearing. I’m sure some have done forced induction. How well does the 2.5 respond? I would think it would be a reliable little performer

[gogmorgo]

Per OP's registry post, we're looking at a 2.5 mated to a 904 auto. I don't know what gear ratio it would have come with, given the build sheet said 4.78 and that's not an available ratio in any of the factory axles.

I've spent some considerable time finding other examples to try to establish what axle ratio would come with that drivetrain combo, and I only found two where I could confirm the gear ratio before I decided it was a pointless endeavour when the OP would probably want to investigate their own truck regardless. But at any rate, one had 3.55 gears and the other had 4.10's. I can't count it as a hard data point due to the uncertain vagueries of memory, but I remember encountering another in a wrecking yard with the 3.31 gears. But from that very small dataset and the knowledge that 4.56 ratio was standard I'm sure we can establish that gear ratio is maybe lacking a bit in this particular instance. It's not really a sample size worth mentioning but there's a strong chance that truck was set up for something other than acceleration.

 

We can speculate all we want, but I don't think we can discount gears without know what gears are in the truck.

 

2 hours ago, Eagle said:

 

This is still a pretty flat torque curve. Other than the spike at 3200 it's what, 10% difference from 1500 to 4500 rpm?

 

Personally I wouldn't go to the effort of putting a performance cam in unless I was having to change out the camshaft anyhow, but I guess it's cheap enough. Certainly cheaper than regearing.

[Eagle]

Let's see if I can post the 4.0L torque curve for comparison ...