No, this isn’t me asking about how to make more power out of this 2.5 tractor engine. This is me buying, testing, and concluding what works and what doesn’t when it comes to making 4 angry squirrels more agitated.
Now, full disclaimer. I don’t have access to a dyno, and I have no 100% foolproof method of testing actual gains, if there are any to be had. What i’m going to describe is based mostly on just driving around, which I do a lot of. I’ve also done some 0-60 tests, but i’m having a hard time getting all the variables right to exclude any inconsistencies in the testing, which isn’t easy to do when you drive something that’s about as aerodynamic as a barn on wheels.
Okay. Let’s start with what i’ve done so far, and what has come of it.
The first thing i’ve done in regards to getting more power is… wait for it… maintenance. Since i’ve swapped out most of the sensors in my XJ, before the modding, that’s where I’ve noticed gains. Now, i’m not making more power than stock with just replacing old sensors, rather i’m helping the PCM with timing the injector pulses and AFR.
Anywho, after replacing the MAP, TPS, CKPS, and IAC, I noticed a moderate increase in the way it acts going uphill and taking off.
Now, as far as mods go, i’ve only done two as of right now. Upgraded 4 hole injectors, and long tube headers.
4 hole injectors:
I didn’t noticed any actual increase in power. It pulled the same up hills, drove around like it normally does. But, I did notice better throttle response and a bit of an uptick in gas mileage. By better throttle response, I mean that when you lay on the throttle in 1st gear, it doesn’t kind of go, it instantly gets up and goes.
My conclusion: If you buy the right injectors that fit, it’s worth the 70 bucks to upgrade from stock.
Long tube headers
Wow. What a difference!
I’m serious. Adding long tube headers to this 4 banger really woke it up. It takes off a hell of a lot quicker, and it really helped with low end torque. I normally shift at 2k every gear, and it used to kind of bog down and lug after after every gearshift on a straight road, but now, shifting at the same time as before, it pulls a lot stronger and a lot more healthier. It no longer bogs down, and I can go up most hills with ease in 5th gear. As a matter of fact, there is this really steep hill on this road I take every day, and normally I have to downshift to 4th to overtake that hill, but when I went up it yesterday after the install, I didn’t have to downshift to 4th. I mashed the pedal down and held 55 all the way to the top.
I also ran around with my A/C on, and for those who don’t have a 2.5, when you have the A/C on, this thing becomes an absolute DOG driving around. But, after installing those long tube headers, it’s actually not that bad. It still slows down, but it’s not as bad as it normally is. I guess I could say that upgrading to long tube headers actually makes driving around with the A/C on tolerable, and not “do I really need my A/C on right now?”
My conclusion:
Buying long tube headers isn’t some “snake oil”. I actually felt the difference when accelerating, it pulls harder in 2nd and 3rd on the low end, and in 5th gear, it seems to have more power to maintain and even accelerate on some hills. Plus driving around with the A/C on is a lot better.
That’s all I have for now. My plans for the future is as follows:
Relocate IAT to the air box
Install a ported intake that’s been bored to fit a 4.0 TB
Install Harland Sharp roller rockers
Install an upgraded ignition kit along with iridium spark plugs
I also want to mention, my goal here is to test various different items that are said to increase power on really any engine, and some that are surrounding the 2.5 in general, like the 4.0 TB conversion.
Please take everything I’m saying here with a grain of salt. Since I don’t have access to a dyno to see the actual gains, everything i’m testing out isn’t going to be accurate. BUT, a dyno will only tell you what kind of power you’re making all the way to redline, but that doesn’t really translate into driving around. A dyno only measures power at the rear wheels (or front wheels), and that’s when it’s stationary. Driving around and having wind, humidity, temperature and other factors affect what kind of power you make. Plus, no one looks at their tach and says “yeah, i’m making X# of horsepower right now”
Also, here’s the links to the items i’ve purchased right now:
Thanks for posting, I bought a really clean, '99 2wd w/5sp for cheap with a blown head gasket. Pulled the engine and had it bored .030 over and replaced the head and the cam. Added 4 hole injectors and I can't tell how much it was improved because I never drove it stock. But I will be following this thread and would consider long tube headers if they make that much of a difference, especially if they will bolt up to my stock exhaust. I also have a 4.0 and the power difference is considerable but I have gotten 22 mpg out of the 4 banger on the highway and it's my daily driver. My next mod will be a posi rear.
Can anyone with math skills tell me what my new displacement is with a .030 bore?
Advancing the timing helps. What is your altitude pineapple?
Somewhat near sea level, around 600 feet or so.
Also, I know you’re the guy that knows damn near everything about these XJ’s, but I thought that timing was handled by the PCM and it’s non adjustable?
I think you could edit the ignition timing by using software that can flash the PCM, but that seems possible on OBDII, not OBDI.
If it’s possible on OBDI, then that’s awesome. It’s something i’ve been looking into if I run hotter plug wires and hotter plugs like iridium or whatnot, but it’s the fact that i’m running OBDI and not OBDII
Timing can be adjusted by sliding the CPS body on it's metal bracket. Mopar offered a "high altitude" CPS for the Renix models that advanced the timing a few degrees. The "slide it on it's mount" trick will work for any year, but do understand, you'll run into the need to run premium fuel as you advance it more and more...
Timing can be adjusted by sliding the CPS body on it's metal bracket. Mopar offered a "high altitude" CPS for the Renix models that advanced the timing a few degrees. The "slide it on it's mount" trick will work for any year, but do understand, you'll run into the need to run premium fuel as you advance it more and more...
Are you talking about the distributor pickup, (or camshaft position sensor) or the crank sensor?
Maybe 10 or 11 at idle. The change in cps location changes the base timing, meaning all the ignition load cells get increased. The 2.5L has a slightly higher compression ratio than the 4.0L so I would not go the full advancement. Send me a PM if you want to go that route.
Note the horsepower curve. Try shifting at 4 k at least if you want to get any idea of what that engine will do. The way you are shifting you have nothing when you get the next gear.
Based on your profile you have a 95. Does it have a "SIL" (shift indicator light) that you are using when your shift? Those things were on some manual transmission vehicles of that vintage to "force" the people driving the federal test procedure (FTP) to shift at those crazy low engine speeds to increase the fuel economy numbers that resulted from the test. Ignore that light , use the tach....that's what it's for
(I probably watched 500 of those tests being run back then)
You're talking about buying all this stuff that might get you a 2% HP gain when you could double your HP by learning how to shift. (I'm surprised Cruiser didn't pick up on your 2 k shift point, I'll bet he shifts his Alfa a bit higher than that.)
Well, I tried to shift at 4k each gear. I got up to 45 in 3rd gear and I felt like my engine was gonna toss something out.
Anyway, I finally got the new intake installed. It was ported, and it had the 4.0 TB on it and the intake was bored out to match. I had a lot of trouble mounting up the new tensioner design, but once I got it to work, it worked brilliantly. Now it takes 5 seconds to change a belt or remove it.
My alternator bracket also snapped, so that really set me back even more waiting on a new one.
But, I got it driving once again today, and I have to say…
WOW.
I mean it’s night and day difference. There’s not much gain on the lower end, but if I go higher in the revs, like merging onto the interstate, it really picks up speed.
I decided to try and accelerate for the first time on a hill on this one part of the interstate, and before this modification, I could only maintain 70 going up that hill. But I ended up accelerating to nearly 75, and that was in 5th gear up a hill!
I also found out that I can cruise at 80, and I don’t even have to peg it to the ground to do it!
I feel like the 3 mods i’ve done so far have complemented each other. The 4 hole injectors flowed a little more than stock, and they had a more precise spray. The long tube headers helped with getting exhaust gasses out of the head faster and more efficiently, and the ported intake with the 4.0 TB helped flow more air, and with the upgraded injectors that flowed more than stock helped create more boom. so to speak.
I am very happy with how this turned out. I’m happy I got everything to work again, aside from the one fuse that keeps blowing.
Next up, is the Harland Sharp roller rockers. I’ve heard that if you only add those and nothing else, then they don’t do much until the higher RPM’s, but adding them with other mods, such as what I did with my 2.5, then I could expect to get more from those roller rockers.
I finally got my Harland Sharp roller rockers installed today.
I also replaced all of the lifters and pushrods while I was at it.
Anyway, you came here to hear about what it did and didn’t do. Well, in this case, it did everything I hoped and more.
For starters, the power band on the 2.5l is all low end. After about 3k, it starts to fall on its face and just revs up without going anywhere. But with these new roller rockers, 1.7 duration, it carries out all the way to redline. It just doesn’t stop pulling.
It also ended up making my exhaust deeper, and I guess that’s because the valves are hanging open longer, and therefor letting more air in and more exhaust out as well.
Im really starting to love how powerful this engine is now. It doesn’t feel anything like when I first got it, and now, it’s really starting to feel like less of a burden to drive and i’m really really pleased with how far “The Little Engine That Could” has come
Thanks for the write up. I would like to see the dyno results instead of a seat of the pants opinion. I drove 300 miles home this weekend running 85-90. The 2.5 has a sweet spot around 3200 3400 rpm. Mine is basically stock with a .030 over bore and 4 hole injectors. I get up to 22 mpg.
