4.0 power adders

[inVERt'D]

The 4.0 is a great motor for a Jeep. It's reliable, durable, has tons of low-end power, but if you want a hotrod motor, you'd better just swap in a V-8. All that high-flow intake and exhaust crap is really just overpriced, gimmicky B.S. for a Jeep--you'd have to modify the motor before you'd even begin to get your money's worth out of it.

I agree with those that suggest a gear change to compensate for larger tires. Larger tires are essentially equivalent to running taller gears, so that only makes sense. Besides, even in the hotrod world, it's well known that a proper gear change will yield better bang-per-buck than just about anything else. If I were looking for something to bolt onto my engine, I'd get some full roller rockers in there, which will give you more power and reliability by taking more friction and flex out of the equation. That's a good bolt-on upgrade, and Summit has Harland Sharp for about $330.00.

If you're thinking of paying $300.00 to $1,000.00 or more for engine performance, but aren't willing to open up your engine or regear, I'll sell you a case of snake oil engine treatment...

[Ol Man]

An interesting thread. My experience is with a friends' CJ7 vs mine when we both put the Hesco fuel injection on. He also did Borla headers and his CJ was noticeably faster accelerating than mine.

Now, I have a couple of friends in the KOH race in a couple of weeks. Both are running 40s on XJ buggies. One is the original high mileage engine and the other has a new stroker. Last weekend on Melville Lake Bed they both could only get up to 62.5 MPH! That really surprised them; not only the low top speed they could attain, but that the stroker did not do better.

[inVERt'D]

Allow me to qualify what I said...all that stuff is gimmicky crap for an otherwise stock Jeep TJ 4.0 HO engine, which is what Commandoman is driving, and presumably what he wants to upgrade. The only way you're going to get significantly more airflow (which, with more fuel = more power) through an otherwise stock TJ 4.0 is forced induction, i.e., turbocharger or supercharger. Then you're going to want to limit boost so you don't blow up your stock engine, so you're still limited there.

If I had to choose between a good set of headers and a K&N (etc) intake for a Jeep TJ, I'd take the headers for sure. Some other vehicles or powerplants, that might not be the case, but from what I've seen, the high-flow intake doesn't do much for a Jeep TJ, considering the $250-$300 retail price. It seems that the 4.0 HO is a pretty balanced air pump. If you have both the exhaust and the intake, they'd compliment each other to make the engine a more efficient pump...at least at high revs...you've now spent $600-$800 or so. But then you need the fuel flow to match that, so in with the high-flow injectors. Of course, you'll need to replace or recalibrate your ECU to really get the potential out of that other stuff... and what you have for that $1500 or so is a marginally improved powerplant. I'm sure at this point, assuming you'd done things right, you'd have noticeable improvement, but in my opinion, not one worth the money you spent. For some, money may not be and issue, but then why not throw in an LS-1 or LS-2? Then again, how fast do you really want to go in a lifted Jeep with 35s?

Since Commandoman is asking the question, I'm assuming he's concerned that he get the most out of his money. I'd say regear and spend the money on a good rollcage, 'cuz if you want to go fast, you're gonna need it.

[Commandoman]

Wow, nice comments everyone.....

I think there are several good comments out there. I've had several 6 bangers in my life in all kinds of vehicles including a 69 dodge charger believe it or not. All of them were reliable engines. One of my goals in posting this thread was to find a consensus among those of you who have tried bolt on items to see what worked. I wasn't looking for a hot rod, just something that would keep me in top gear just a little longer before having to downshift or turn off my overdrive (I'm running an auto trans). I agree more efficiency in air movement both in and out of the engine is the best solution. I’m already running the gear I want and for now I’ll just keep things as they are until I hear a better mouse trap has been invented. I won’t cross my fingers though as the 4.0 being an engine on it’s way out probably wont cause the aftermarket to keep developing new items.

[Kodiak Spirit]

you might have a new option of engine sooner than you think, I predict the V-6 they threw in the JK doesn't stay there long... maybe thats just wishfull thinking though.

[Willard]

I doubt with the financial crisis Chrysler is in that they would sink any more money into the Jeep line, especially for a new engine.