Jet Power chips?

Waste of money IMHO. Any HP they may get you will only be in the high RPM band and will require that you run higher octane gas, from what I understand.

Ditto, a complete waste of money. They only help a little and then only at WOT (wide open throttle) and high engine rpms... not exactly how a Jeep is driven by anyone but a 16-17 year old. ;) Plus they then make your engine start demanding no less octane than 89 or 91 to keep it from pinging.

Jerry

BNB7 did pass the time by typing:

Save your money.

Best first steps would be

1) cat-back, gibson, borla, etc. 2) new exhaust headers 3) bored over throttle body.

You don't give an engine size so be aware of this gotcha. If you have the 4 banger, the TB from a I6 is the largest you want to go. If you put a bored out TB for the I6 on your 4 it will run so lean the engine will melt. :) Well, maby not that lean, but it will run like crap cause you essentially overtook the injectors.

A larger throttle body *may* help at WOT. For normal driving, the PCM will simply adapt to it the same way it adapts to vacuum leaks. It adds more fuel and you gain no performance.

bllsht did pass the time by typing:

Actually it changes the whole power curve, not just the top end with the net result being the engine can breathe easier at higher revs. By itself you might be looking at 2-3HP gain, the benefit comes when your moving more air like I do with the supercharger. Within limits anything that lowers intake and exhaust resistance improves efficiency. I say "within limits" because resistance is necessary for the engine to scavenge properly. Most modern engines use the O2 sensor to set the mix, with the TPS acting as a sanity check and WOT signal.

I'd throw in my two cents and agree with Doug on the TB issue. I put a bored out 4.0L TB on my 2.5L and it SUCKED. Well, literally and figuratively. I could only use a fraction of the throttle before it started bogging down (i.e. running WAY lean). I sold it to a buddy with a 4.0L and took his stock TB. Everything is better now. :-)

I have the 2.5L and have done the following intake mods:

1. Cold air intake and TB spacer. Results: TB spacer is probably a HUGE waste of money. I had not found this forum yet, so I learned the hard way. I would say the intake made a difference. I live on a hill and can do it in higher gears than I could before putting it in.
2. 4.0L TB swap Results: Small change, but noticeable. Note that I went from the bored out 4.0L TB (which at times was GREAT... only on heavy acceleration, really, and only if I found the "sweet spot" on the throttle) to the stock 4.0L TB.

Overall: I like the CAI and the 4.0L TB. I'd do it again. However, if I had the 4.0L, I wouldn't have touched it. It has enough power and I wouldn't want to let all of the other crud in through the intake. I will eventually sell my TJ for a Rubi anyhow.

I will be swapping out exhausts this summer as I seem to have already developed a leak in my muffler (at 39k miles!). If my manifold has cracked by then (as they tend to do, so I am told) I'll replace it too.

Eric

99 TJ SE

By using a larger throttle body, you're just increasing the maximum amount of air that can get into the engine at WOT, so you may get more top end power. Less than WOT, and it's the same as opening the throttle a little more on a stock TB, or pulling off a big vacuum hose to allow more air in. Yeah, the RPM goes up, but has there been a hp gain? It may be "perceived" as more power because it takes less throttle action to let the same amount of air in. The same perception could be gained by changing accelerator linkage geometry.

A supercharger is a different ball game, and would probably benefit from a larger TB.

Eric, How did you do your cold air intake? Why do you refer to letting "crud" in? I fabbed a "cowl snorkel" or "cold air induction" intake for my TJ SE. It made a significant improvement on the highway. I also installed a 4.0L TB and that helped, too. My "CAI" pipes the air from the cowl box into the stock air filter box. I get the colder air and take advantage of the higher pressure area under the windshield to effectively increase the max manifold pressure available. The stronger the headwind, the more power it adds. :-) It also gives me some additional protection against ingesting water during a deep crossing (like water half way up the hood).

With a 2.5L on the highway, you spend more time at WOT. It does help in that situation. It effectively gives you another inch or two of pedal. Funny, though. I don't seem to have that problem with my Grand Waggy... ;-)

Maybe they let too much crud in using cloth filters instead of paper filters. Who knows. Maybe they're just cheap. Have any of the new "motorsports" types (i.e. NISMO -- Nissan Motorsports --, Subaru, Toyota, Honda, etc) offered cold air intakes as add-ons. I'm sure they have, or will.

As for a bigger throttle body, there probably isn't enough people wanting it to justify selling it. Again, big corporations, who knows.

Mine is actually just a cone filter setup from AirAid.

Eric

I wonder how many people have even taken a 2.5L on a road trip... or done any mods to it to see how well it performs. Interesting that the majority of comments on what it can/does/should do come from those without one. Could just be my skewed perspective. If I could do it over again, 4.0L, no doubt. But I still like my lil' SE. It's great in town. Just those highway trips are KILLER.

Should be interesting when I tow my bike over 900 miles.. *cringe*

Eric

David C. Moller did pass the time by typing:

EPA/Smog/Fuel Mileage mandates/production limits.

Vehicle makers have to keep an average economy across their whole line. So to offset performance vehicles they produce tinfoil slugmobiles.

Now for the far extreme, blueprinting, porting, etc. The improvement comes from extra time spent on the engine that the maker considers inefficient use of production time.

Interesting to note the first V8 ZJ (93) suffered from an intake restriction between the intake snorkel and TB. Several aftermarket vendors came up with a spacer. In 94 Jeep changed the intake snorkel to improve performance.

Depending on the dealer, some will do this. Some actually specialize in turning daily drivers into street legal monsters.

Agreed, it would probably be helpful in those situations, but I think you might be being a little generous with "another inch or two of pedal". :-)

That doesn't sound like fun. Aside from the obvious power difference, I just can't wait to get out of a 2.5L after listening to it scream and vibrate during a short road test. The 4.0L is a much more comfortable ride.

Maybe I'm just gettin' old. :-)