2.5L Performance Mods That Work - JeepForum.com
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post #1 of 39 Old 04-23-2012, 09:22 AM Thread Starter
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2.5L Performance Mods That Work

Before I get started, let me get this out of the way. I know the motor is an underdog. Some have gone so far as to call it worthless. I know a motor swap would be better. I know selling it for a 4.0 would be easier and cheaper. Turbo's for the 2.5 aren't practical or cost effective. This post isn't about all that. This post is about practical improvements to the existing 2.5L motor. I bet someone posts something from the above anyway.

None of my conclusions are scientific. My Jeep has never been on a dyno. Really, if I had the time and money to dyno everything added to my 2.5, would I be driving a 2.5? ECU was reset after each installation.

All conclusions are just my real world observations, operated to allow adjustments and break in and averaged over several months. The decision to keep or remove a mod was based on long term, repeatable, real world improvements. If it didn't help to a noticable degree, it came off.

K&N drop in filter
I've tried them with other vehicles with some degree of success. Out of the box, throttle response felt better, but don't confuse throttle response with horsepower. I think many do. Honestly, I don't know any instance where an increase in throttle response has helped me.

I've alternated between a paper Fram and the K&N many times. Usually while waiting for it to air dry after dusty trails. Using the same interstate on-ramp for my "control" study, I noticed no change in average MPH. Flooring it from ramp start to the ramp end was always within a mile or two per hour.

Conclusions: With no significant improvement or difference between paper or K&N, I saved myself the trouble of regular cleaning, gave it away and use paper filters exclusively.

High Flow Exhaust (Banks Monster)
Again, another felt throttle response when first installed, but after a few weeks, I noticed it was slower off the line. Using that same on-ramp for averages, it left the line faster, but after the initial start there was a noticable flat spot in the lower RPM's. It was able to reach the same averages by the end of the ramp, but averaged no better than the stock exhaust.

Initially, I did notice a slight improvement at highway speeds, but any improvements were either in my head or corrected by sensors or ECU.

Conclusions: With no significant improvement or difference over stock, I traded someone my high flow exhaust for his stock exhaust. He got a great deal and I got a quieter Jeep.

Jet Stage II Performance Chip
The Jet Chip suggests the use of a high flow exhaust and cooler thermostat. Both of which were used with and without the Jet Chip. My first observation was "This is great!". I was so convinced that my Jeep was renewed because of it. The reality was there was no noticable improvement at all. I would suspect that any improvement would be from the high flow exhaust, but as stated previously, there were no noticable improvements from that either.

Averages on that same on-ramp remained unchanged. I removed the Jet Chip and without resetting the ECU observed no changes for the worse either. My Jeep didn't seem to care if it was on or off. It was completely invisible as far as my Jeep knew.

Conclusions: It sits on a shelf in my garage. The only reason I still have it is because I'd feel bad about selling it to someone knowing it did nothing and I paid too much for it to just give it away.

Yellow Top Injectors
I can't remember the specific part # or year injectors used. The information was obtained from this forum. I believe they were from a Mustang or Crown Vic. I can honestly say that I did notice some improvement, but improvements were short lived. After initial install, I saw a 1-2 MPH increase using the same on-ramp. A week later, after the Jeep settled, any improvements went away.

I suspect the ECU didn't want the extra fuel in there and corrected it. I believe I confirmed this by reinstalling the stock injectors. After a week of letting the Jeep settle in with whatever settings it looks for, I swapped in the Mustang injectors without resetting the ECU. Again, I saw the slight MPH increase, but again it went away a short time later after the ECU made adjustments.

Conclusions:
This mod made sense to me. More fuel should translate to more power. Sadly, this improvement was only good for a few days. If there were a difference, no matter how slight, there should also be a related change in fuel economy. There was not. If there was a way to reprogram the ECU or allow it to continue to high flow the injectors, this might work. At this time, I know of no way to accomplish that. The stock injectors are back in place and the "upgrade" is on a shelf for backup purposes only.

4.0 Throttle Body
This one I had really high hopes for. After pulling the throttle body from a 4.0 Cherokee and comparing them, I thought this one might really work. The 4.0 throttle body was significantly larger. I figured this point would be the bottle neck preventing any high flow filter or CAI from working. For the sake of full disclosure, I did not port match the intake like some suggested, but from research most have said just the swap itself would show some improvement. If I saw a noticable improvement, I'd take the time to port match.

Again, throttle response felt better initially, but after putting a few miles on it there was no noticable difference.

Conclusions:
This one didn't hurt or help so, this one will probably stay on the Jeep unless I feel any negative affects.

Hotter Ignition Coil (Screamin' Demon)
This one came as a set including:
Ignition coil
Plug cables
Cap & Rotor

Immediately, I noticed a smoother idle. Also, a faster throttle response, but again that never helped me in the real world. I did notice that there was a 1 to 2 MPH increase using that test on-ramp. Not a big increase, but I was thrilled to see any real improvement. Unfortunately, any MPH increases disappeared in a week. I'm pretty sure the ECU self adjusted something and the thrill was short lived.

Other than the smoother idle, the only long term improvement I did observe was an increase in fuel economy. It's not a significant increase. By increase I mean, instead of filling up every 4th morning, I now fill up half a day later. I would estimate the MPG to have increased by maybe a quarter mile per gallon if that.

Conclusion:
No performance gain, but a very slight increase in fuel economy. This one will stay on my Jeep because it didn't hurt and very slightly helps. I will concede that the fuel economy gains and smoother idle may only be the result of the new cap, rotor, plugs and cables. Let's assume for a moment that the improved idle and fuel economy are a direct result of the hotter ignition coil system. Given the costs of the system compared to the fuel saving, it's not something I would recommend or do again.


Summary:
I spent a lot of money trying to get as much out of that little motor as I could, but in the end it's already giving me all it has to offer. Nobody wanted to see improvements more than me, so in some instances, I convinced myself it was true. I suspect the same has and is happening to others reporting improvements with the same mods.

I thought for sure having all the above mods on at the same time would yield some improvement. I observed no noticable improvements with all mods together or using any combination of the mods. That really surprised me as I'm a firm believer of every little bit helps. Even after putting all the money and effort into my Jeep, I don't feel like it was wasted. If it's not a repair, I enjoy working on my Jeep as I'm sure many others here do as well.

As much as I've spent, I could have paid for a regear. If I could, I would take it all back and do just that. It's the only thing that I know would help. I'm not trying to talk anyone out of running their own experiments either. It's your Jeep. Have fun with it. Just don't expect "A's" from a "C" student.

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post #2 of 39 Old 04-23-2012, 09:39 AM
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Plenty of people have said it and now you know why. the 2.5 is worthless to try and upgrade. You can boost it and get good power but it won't last very long. Other than that a different motor is the only way to see any real gains, and now you've seen why.
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post #3 of 39 Old 04-23-2012, 09:47 AM Thread Starter
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Quote:
Originally Posted by youstupidbunny View Post
Before I get started, let me get this out of the way. I know the motor is an underdog. Some have gone so far as to call it worthless. I know a motor swap would be better. I know selling it for a 4.0 would be easier and cheaper. Turbo's for the 2.5 aren't practical or cost effective. This post isn't about all that. This post is about practical improvements to the existing 2.5L motor. I bet someone posts something from the above anyway.
Winner!!! I wasn't expecting it in the first reply though.
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post #4 of 39 Old 04-23-2012, 10:16 AM
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Haha! Thread title is a little misleading though. Apparently none of them work! That's a shame. My little 2.5 does it's job, but just simply is what it is. A good little motor. It's not really even under powered for what it is, just underpowered for how much weight it's being asked to move. Good post though, sorry none of that worked out for you. Might save someone some money reading this. Re-gearing to 4.88 made my 2.5 much happier!
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post #5 of 39 Old 04-23-2012, 12:17 PM
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$1200 regear is all you can do.

Quote:
Originally Posted by jeepinmichguy_ View Post
TheBoogieman is a jerk.
GOT IT BACK 6/17. 03' Rubicon/Zone 4.25" combo lift with 4" lift coils up front/Zone hydro shocks/5.13 gears/35" Mickey Thompson MTZ P3 tires/Black Magic brakes. Jeep #17 & 19.
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post #6 of 39 Old 04-23-2012, 12:51 PM
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Thank-you for taking the time to write-up your experiences; hopefully you've saved others from wasting their money on things that don't work.

I too have the 2.5 four cylinder engine, and changing to 4.88 gears is what has made it driveable.

I was disappointed the hotter ingnition didn't really do anything for you. Oh well... money saved.
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post #7 of 39 Old 04-23-2012, 12:58 PM Thread Starter
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Quote:
Originally Posted by armyRN View Post
hopefully you've saved others from wasting their money on things that don't work.
Probably not. I researched everything that I added and knew the common opinion was none of them worked. Yet, I did it all anyway.

It's like growing up. Your family tells you your girlfriend is no good, but you have to find it out for yourself.

Despite what it's lacking, my Jeep is still a fun ride. So was that girlfriend.
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post #8 of 39 Old 04-23-2012, 03:44 PM
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Quote:
Originally Posted by YouStupidBunny View Post
Winner!!! I wasn't expecting it in the first reply though.
I read the beginning and was simply saying, now you see why so many people have already told you that would happen. Some people just have to be stupid on their own and prove the masses right. Do you pour coffee on your lap to see if its hot too? I guess some people just can't take the advice of countless hundreds of people who have come before them and told them what would happen. This thread is nothing more than proving that you can't listen and prefer to waste money in the name of experiments. As you said, if you could do it over again you wouldn't do any of it but if you read much at all on any jeep forum you would have known long before doing any of this that it would net absolutely no gains.

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post #9 of 39 Old 04-23-2012, 03:55 PM Thread Starter
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Wow. Seriously.... you are soooooo right. Thank you for restating 3 of the 4 things I stated this thread was not about. Big help. Huge.
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post #10 of 39 Old 04-23-2012, 06:39 PM
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I appreciate it when somebody is willing to testify that they knowingly tried something that others have said would not work and got the same results.

As long as nobody was physically hurt or had their feelings hurt, or damaged their Jeep, it's all good. Just money that could have gone elsewhere.

I did the same thing with a Bestop underseat storage drawer. They said it wouldn't work with the tilt-and-slide seats, but I thought it might work with a 1.25" seat riser. Not. I ended up putting it under the rear passenger seat. And I wrote it up for others to add to the other threads that said it wouldn't work.

https://www.jeepforum.com/forum/f9/pu...-seat-1190828/
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post #11 of 39 Old 04-23-2012, 07:54 PM
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eek! i have a lot on my 2.5... i need to dyno it and see if any of it helped at all... all i honestly know it that it made it drivable with 4.88's and 33's... it is still 4 cylinders but a blast to drive!

motor has 40k on it/ tranny 50k (ax5)
jet stage 2 chip
64 mm bored tb from a 4.0
banks header
DIY cowl intake with AEM dry flow filter
cherry bomb glasspack with turn down - all 2.5 pipe
180 jet t stat
hyline hood louver panel
recent tune up on wires, plugs, cap, rotor
syn oil - royal purple 10w30 with k and n oil filter
mobil 1 syn gear oil in diffs
syn 10w30 in tranny

runs and drives smooth... rpm's are faster to spool up and does not dog out nearly as bad on hills on the highway... i have to say i like driving it around town even with a bunch of armor and stuff on it...

maybe one of these days i will dyno it...
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post #12 of 39 Old 04-23-2012, 09:39 PM Thread Starter
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Like you, I enjoy my Jeep most days. I love it in the mountains. It's just getting up there that I don't like. It's in deperate need of a regear.

Heading up a mountain, I was passed by a school bus. A few kids on the bus gave me the finger.
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post #13 of 39 Old 04-23-2012, 09:42 PM Thread Starter
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Quote:
Originally Posted by armyRN View Post
I appreciate it when somebody is willing to testify that they knowingly tried something that others have said would not work and got the same results.
Case in point: Everyone told me not to use heroin, but I had to see for myself. The things I have to do now for a fix would make a billy goat puke.
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post #14 of 39 Old 04-23-2012, 09:43 PM Thread Starter
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Since some people lack a sense of humor, I should add that I do not, nor have I ever used heroin.
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post #15 of 39 Old 04-23-2012, 10:20 PM
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Since some people lack a sense of humor, I should add that I do not, nor have I ever used heroin.
Thanks for clearing that up!
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