View Full Version : Beefing up the 4.0???

April 17th, 2004, 21:43
I have some questions about getting some more power out of my 4.0. I just needed some reinforcement with my plans..What do you guys think.

Headers (Borla)
TBS (Airaid)
Jet Performance TStat
Bigger Fuel Injectors (Dont know what kind do get yet though)
I wont be doing any intake mods b/c I will be fabbing my own with a snorkel.
Spark plugs/cap,rotor/spark wires --probably accel

Any other suggestions on bolt on mods. My goal is to gain about 50 hp at the end. Ive heard that some people use the mustang 5.0 liter injecters (is that true). Any input would be greatly appreciated. Thx

April 17th, 2004, 22:01
That will not net you 50 hp. (header maybe 20hp TBS +/-3hp) Oversized injectors are used to compensate for running lean because of intake mods, I run the 5.0L injectors on my stroker with ported heads, bored TB, TB Spacer, header, and an msd 6 ignition. It runs way rich and I had to build a MAP adjuster to dial it in. Plus an engine makes more horsepower at a leaner mix. Your biggest bang for the buck would be a DIY port and polish (see Dino's website), and a cam swap, That shouldn't run you more than $400 if you do a lot of the work yourself, and it will reach your 50 additional hp goal.

Dr. Dyno
April 17th, 2004, 22:20
I've added a long list of performance mods to my 4.0 (including a ported/milled head) to gain anything close to 50hp so you'll need to do the same if you're going to achieve that goal.
I also gained about 40lbft and that's about as much as I can gain without tearing into the engine's internals and replacing the camshaft. Even then I'm near the limit of the 4.0's maximum torque potential and the only way I can gain significantly more (apart from forced induction) is by adding more cubes.
I've decided that I can gain another 45-50lbft by building a 4.6L stroker and this is eventually going to replace my strong (but ageing) 4.0.
- 1992 4.0 XJ Laredo UpCountry with modifications (http://www.jeep4.0performance.4mg.com/mods.html) - 173k miles - AX15 (http://www.off-road.com/jeep/tech/trans/ax15.html), NP231 (http://www.off-road.com/jeep/tech/xfer/np231.html), D35c (http://www.off-road.com/jeep/tech/axle/d35c.html), D30 (http://www.off-road.com/jeep/tech/axle/d30.html)
Estimated 240hp@5250rpm/280lbft@3500-4000rpm, 1/4=14.98@93.1, race weight 3465lb
- Future mods -
4.6L stroker (under construction)
- Websites -
Jeep 4.0 performance (http://www.jeep4.0performance.4mg.com), 4.6L stroker build-up (http://www.angelfire.com/my/fan/stroker.html)
- Tech Webpages -
CTS resistor trick (http://www.angelfire.com/my/fan/CTS.html), Dual electric fans (http://www.angelfire.com/my/fan/electric.html), IAT sensor relocation (http://www.angelfire.com/my/fan/IAT_sensor.html), Intake manifold heatshield (http://www.angelfire.com/my/fan/manifold.html), MAP adjuster (http://www.angelfire.com/my/fan/MAP_adjuster.html), Oil temp. gauge install (http://www.angelfire.com/my/fan/oiltemp.html)
- Info Pages -
Automotive formulae (http://www.angelfire.com/my/fan/formulae.html), Jeep 4.0 cam specs (http://www.angelfire.com/my/fan/Jeep4.0Camshafts.htm), Jeep engine dyno graphs (http://groups.msn.com/desertxj/dynocharts.msnw)