Im looking to get a cold air intake and performance exhaust for a 4.0 grand cherokee wj are there any suggestions for the best increase... And are there any other ways to gain power...

Only regearing your axles will attain more power! Increasing the rpm at a given speed is what you should be after..
Changing the intake or (and) exhaust will do nothing for horsepower gain at low rpm.
If you have oversized your tires you should also undersize your gears.
These things ain't sport cars they are designed for off road use.
One of the WORST additions would be a supposedly "cold air intake" Leave the wonderful stock intake system on there for long engine life.
There are lots of folks that will SELL you something...all to no avail, you will simply have spent your money for no gain.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

I agree with BJ. You don't get something for nothing in this world, particularly the world of Jeeps. Most add-ons only help, if at all, at the high end of the rpm range, which you will hardly ever use off-road. In fact, some of the things that people ordinarily do to increase the horsepower of an engine at high rpm will kill it at low rpm. For example, racing cams installed in an off-road machine will ruin it's low end grunt, which is want you want when four-wheeling. Some exceptions to this are desert racing, sand drags, and hill climbs, which few of us do.

I don't know if I entirely buy the cold air intake concept... I guess it could help a tiny bit in theory. If you ask me, it is probably the case that hte stock exhaust is somewhat restrictive. You want to try and reduce restriction without significantly raising the power band rpm range... so in other words, a 3" exhaust = bad. <img src="/forums/images/graemlins/smile.gif" alt="" /> But you might think about a freer flowing muffler and catalytic converter. I base this on my own experience with AMC V8.

The only thing is, if flow is too free, the computer may not be able to 'learn' the right mix (ie, richen it up enough). That is one PITA with the computerized vehicles as they aren't as easy or cheap to retune as carb. I agree, gearing will help if you have increased tire size. If gearing is already optimal, Just going with lower gears won't necessarily help unless the power band is altered. Also tire and wheel weight reduction will help.

I guess I should've first asked... what specifically are you trying to fix? Off-the-line acceleration? WOT acceleration? Part throttle? Hwy ? Hill climbing?

Michael

if you want power the best and only ways to get it is stroaking your engine and regearing. cold air intakes (aftermarket) do nothing but suck oil and dirt into the throttle body. I had my share of that then trashed it.

My big problem is when i have a trailer on the jeep with just a fourwheeler and i cant hardly tow, feels like a house behind me... also without the trailor take off is a drag

You describe a need for GEARS! What size tires are you running? With 31/32's on there even with a V-8 engine those 3:07 gears would bog down on the hiway with a small trailer..
It is all about keeping the rpm up in the power range of the particular engine. Get the proper gears and a whole new world will reveal itself to you.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

im running 32" and i have the I6

Yep! You need gears.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

4.10's and 32's would be ideal and put you right back around stock performance for your jeep. If you plan on going any bigger than 32's OR you want a bit more grunt towing or accelerating you should get 4.56's but your Highway RPM's would be pretty high if you stick with the 32's (around 2800-3000 RPM's going 65).

Fred R.