Tweaking 2.5 4cyl For More Power/Torque

[wrangler88yj]

Hey I have a 1988 Jeep Wrangler w/ a 4 cyl 5spd and stock everything
I am looking for a way to gain more horsepower and torque out of the engine transmission and drivetrain i have 33 inch mtrs on it and 6 12 volt lights that also complicate the process they draw so much power they strain the altenator also looking for any advice on the lights or gaining horsepower/torque

[fredjacksonsan]

Intake. Exhaust. Camshaft.

Also, you may want to look into changing your axle ratios, with those big tires your engine's probably not in the powerband.

[wrangler88yj]

what gear ratio do u recommend
for the '88 i was thinking 4.10 or 3.55 any help would be appreciated

[fredjacksonsan]

I'm not sure about the '88, but both our '97 2.5L and the '04 2.4L have 4.11 gears. I've heard about people running 5.88's for really big tires. Do some ratios between the stock tires and revolutions per mile with the stock gears, then figure the revs per mile on the bigger tires and see what ratio would match.

[SpeedIsRelative]

I have a '91 YJ with the 2.5L 4Cyl with the stock 5-sp transmission, x-fer case, and axles. When I bought the Jeep 5 years ago I had it checked out by 2 repair shops. Both gave the engine and drivetrain a clean bill of health. As such I proceeded with 'modifications'.

The engine had torque but the Jeep has been lowered and was running undersized tires. I proceeded to install an Explorer Pro Comp Stage II 4.5" lift and 15x10 American Racing rims with 33x12.5" Michelin A/T tires. I removed the restricter in the air intake hose. This was a nice power change (but it was still lacking). The Air restricter reduced the air flow by more than 50% from what I was able to determine. Next I proceeded to change fluids throughout and grease everything. This is where the engine issues became apparent ... lol ... I drained the oil and got ~2qts. I removed the Oil pan to find it full of sludge ... and then removed the valve cover to find the same. I spent 3 days cleaning out the sludge and hard deposits. 2 Weeks later the engine began to use oil ... more and more as time went on.

This gave me the opportunity to work on the engine. The dealer and other local repair shops wanted $1500-2400 to rebuild the 2.5L. I chose to do it myself (took a little longer, but I am very satisfied). I spent ~$750 on parts and machine work (just over a week) and 2 Saturdays. When I finished the engine was bored .060 over (due to cylinders being out-of-round), has Badger racing pistons and bottom-end internals, a stage 2 racing cam, 3 way valve seat job on the head, head was polished out, the air intake system was changed out to a K&N cone filter with stock air hose. Results ... more than 50% torque and hp increase. It runs a little bit hotter (I use a 2-core radiator now) ... lol ... but I can run 85mph in 4th on the highway (clocked by AL State Trooper ... lol) and still pull an 8'x18' dual axle trailer with 3 motorcycles loaded on it at 70mph in 4th (lol ... learned my lesson with the 1st ticket ;P ).