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making more power with 2.5

12K views 122 replies 58 participants last post by  moonshinefuel 
#1 ·
I decided to go to a 4.0 TB and a smooth TB spacer and a homemade cold air intake. I am also going to enlarge the intake were the TB mounts and down the line maybe port and polish the head. What other items can I do to improve the power on the cheap.
 
#41 ·
Copied from the 4banger website:

Quote from: "Gear Poet"
Yesterday a 4.0L TB from a '98 Cherokee arrived by UPS -- to be installed on a 2000 2.5L TJ. With the help of a neighbor who teaches auto mechanics at the local high school (absolutely cool woman who decided to make it a day project for some of her students), I dyno-ed everything in stages. Checked the air flow, too.

Results, with stock (2.5L TB & no spacer)as baseline:

(1) Poweraid spacer only -- +2 HP, 8% less airflow (Evidently, the helix bore, lips of which extends beyond intake & TB opening, actually cuts down on airflow. But the spacer does "cool" and extend air volume, hence horsepower increase.)

(2) 4.0L TB only -- + 6 HP, 16% more airflow (no surprise here)

(3) 4.0L TB & grind out intake opening to match lower TB opening -- + 13 HP, 29% more airflow (Wow! Grinding out the intake opening did make a difference!)

(4) 4.0L TB & Poweraid helix spacer & grinded-out intake opening -- +16 HP, 2% less airflow from #3 above(overlapping helix bore is still cutting off airflow, but spacer is still cooling & increasing air volume)

(5) 4.0L TB & grind out helix bore in Poweraid spacer to match lower TB opening & grinded-out intake opening (the Big Kahuna) -- + 24 HP, 39% more airflow (Wow again; the optimal configuration, obviously)

It should be noted that grinding out the helix in the Poweraid spacer still leaves a partial helix in the walls -- the main difference being that the helix now has rounded edges rather than sharp ones. My auto mechanics-teacher neighbor suggests that these rounded edges are actually more aerodynamic than the original sharp ones, and will still "spin air" -- so perhaps the "pulse-organizing" effect I mentioned in an earlier post will be retained, if in fact there is such an effect.

So, to reiterate, I ground out on the helix bore of the Poweraid spacer, and ground out the intake opening, both to match the lower opening of the 4.0L TB I swapped in. Dyno-ed & tested airflow, results: +24 HP, 39% more airflow.

Seat-of-the-pants impression: idles smoothly, more torque on the low end, smoother accleration through the midrange, and better performance above 2700 RPM. No hesitation, no engine codes.

One MAJOR suggestion: if you grind out your intake opening, be VERY CAREFUL about aluminum filings in the intake manifold. We stuffed everything with tack cloth -- sticky cloths which can be purchased at a hardware store -- rather than shop towels. The tack cloth caught about 95% of the filings, but there was still a small mess in the intake. We vacuumed a lot of the leftover out with a shopvac, but we still had to use tack cloth attached to a long, thin screwdriver to "mop out" the runners. On the TJ there are also four open plugs/hoses attaching to the intake below the TB -- you'll have to clean those, too. It took longer to clean out the intake than it did to bore out the opening, but it can and needs to be done.

Finally, should say that the TJ has a two-stage K&N filter system, an MSD ignition system & coil, high-gapped Champion truck plugs, a Flowmaster delta-40 catback, and a case-full of Mobil 1 synthetic oil. All or part of which may have a synergistic effect on my results, since mods usually affect each other.

Cheers, GP http://www.forumco.com/jeffy/topic.asp?TOPIC_ID=858&FORUM_ID=6&CAT_ID=1

More Info: (1) The intake is soft aluminum, so we used a medium tungsten rasp, followed by a fine fluted grinder bit, followed by a fine polisher. I'll admit it's not even -- hard to get consistency around the runner walls which are nearly flush to the intake opening. The spacer is a harder grade of metal, and trickier, even when clamped in a vise. Doesn't look pretty anymore, at least on the inside.

(2) Tested at 1800 RPM and 2800 RPM with an average between the two -- but the results were fairly similar.

(3) We figured the following: At 2800 RPM, torque was up by about 16% with #5 option above. At 1800 RPM, torque was up by about 14%.

Again, folks, consider the mods and the synergistic effects -- your numbers may be different depending on what you have your rig, mileage, mechanical conditions, altitude, etc. I give this just as a general indication.

Ambient air temperature: 74 degrees Humidity: about 35%

Here is the link, if it works.
http://4bangerjp.com/forums/index.p...6d3032b0deb86153dc6&topic=424.msg1887#msg1887
 
#42 ·
Theres a lot of information on 4bangerjp.com, I plan to turbo mine by spring. I love getting 17mpg with 35s and the fact that a turbo wont negativly effect my MPG around town when its not boosting is great. But when I need the power, its there. That and people are turboing for between $500-1000 depending how much power you want.
 
#50 ·
mines slow as is with 31s, highway top speed is around 55. Up hill is horrible. Im nevious that my junk wont move if i go with 35s but i might be getting a great deal on a set and im not a patient person.
 
#51 ·
I do 70 with 31s...i am still stuned at the dude that said his tac was around 1900 at those speeds. what era set up does HE have?!?
 
#55 ·
I am going to lose a bit out of the wallet
I am swapping an engine this week...i've got a nasty bearing noise
 
#56 ·
while were on the subject this will be perfect time to ask this question. i have a 91 2.5L wrangler, in august the motor was shot and had no compression with 201,872 miles on it. which i guess isnt too bad. my mom insisted on me 2 sell it. so i put a 4 sale sign on it and looked for a nice cheap sport car. :eek: but i felt so guilty trying to get rid of it and my mom is tired of me borrowing cars and said fine fix the jeep!!!! :) so my question is should i put another 2.5L motor in it or should i put the 4.0 in it. but i need to know what all will it cost and what would have to change? i.e. front end,rear end,transmission??? and would it be reasonable to do? im so glad i kept my jeep i dont think i really couldve sold it. and i think yall will agree:thumbsup:
 
#57 ·
tell mom to get you a motor with 100k on it and swap it in...then take your old motor and build it from the frame up. Hot cam, bored out, shaved head..slap that sucker back in and do the same with the 100 k motor

if you try the 4.0 swap, you ar going to move motor mounts, trannys, etc
 
#58 ·
Hey guys! I just got my 94 Auto YJ back from the shop as the head went. its a 2.5l 4cylinder with 146,000 miles and after reading the discussion in this forum i've recanted most of the mods i was planning. I really feel the exhaust needs a overhaul. Would it behoove me to get new headers, catalytic converter and the cat-back system? or just the cat-back?
 
#63 ·
Believe me, I still dont believe it. I went over my calculations a couple times and had my dad double check me too. I think it has to do that I never drive city. I pretty much drive at 45 for long periods of my 10 mile commute, only 3 stops. So theres very little stop and go, mostly just a light foot to maintain my speed.
 
#87 ·
First off, obviously there is a way I'm getting 20mpg..since I am. I'm not really sure how else to prove it, I did the math, my dad checked the math.

Secondly, if I could draw your attention to my sig line you can see that I have a 4in suspension lift and a 2in body lift. It also has 7/8in lift shackles, bringing my whole lift to 6.875in.

Here are the pictures you asked for...


 
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