CIJeep

If that were true then the rice rockets would never benefit from it either.

CIJeep

You need the cam and timing to back up those mods.

On our 3.8's you need someone to take a serious interest in developement. There have been high HP renditions of these engines.

I'm wondering why you just didn't go with dual and enlarged pipes/exhaust tips behind a muffler that fits the standard exhaust pipe. Half of the rice burners on the cheap are doing it that way for the sound.

RedrockX

I had the same issue with my Harley a few years back, the 02's with fuel injection wouldnt run worth a crap with the large pipes...

but, you stick "torque cones" in the head pipe to get the back pressure back (its only a couple of inches of smaller restriction) and the rest of the system can still look good and be functional (and sound better).

chuck45

Of this same engine? Where, when and who? What were the results?

JMP8562

well im one of the people that got the duel exhaust "gibson" and lost mpg not sure on the torque because the lack of power to begin with but i like the look and sound "at easy throtle" if you gas it it sounds like a ricer but when you pay that much for it you sure as heck aint going to trash it but thanks for the info , im going to contact gibson and see if i can coax them out of the restrictors thanks again zhuskers1

JPop

Losing exhaust velocity is what causes a loss of power. There is a need to create a certain amount of back pressure to keep the scavenging effect intact and exhaust gas speed high. Dual exhausts exits for the JK would require 1.75" exhaust tips to maintain velocity, and that pretty much blows away any cool factor.

A true dual exhaust running 2.5" pipes would need to be in the 4-500 hp range, a very far cry from the JK. The single 2.5" pipe covers you to around 250 hp which would be a stretch to get to with all the third party widgets available short of a supercharger.

guybergeron

... and if we do a muffler relocation with a 2.5 straight true muffler under the driver seat and end the exhaust at the rear with a smaler tube would it be better for torque? like 2 inch or 1 1/8 at the end?

JPop

2.5" pipe is where you want to stay unless you are correcting for the lost velocity offered by dual exits. A 2.25" exhaust might work better if you weren't planning on running anything more than stock, but as soon as it's opened up to breathe better on the intake side or with a programmer a 2.25" pipe becomes restrictive.

About the only other thing you could do to moderately improve exhaust performance (after a free flowing can) is some sort of thermal barrier coating or exhaust wrap to hold the heat in and that is way more dollars than what it will ever buy you in performance. A dual exit exhaust will need to be restricted to 1.75" on both sides to maintain exhaust velocity.

I hope that helps.

guybergeron

ok ok so the problem is only on dual exhaust and now i understand its like having a 5 inch exhaust single. well not really but something like that.so a single 2.5 is allright. that is interesting.

JKChad

I see a little mis understanding in here.

The catback is not causing our JK's to lose power. Like earlier stated, it's just the change in back pressure shifting the powerband higher up in the rpms..

So, an exact example of why it would negatively affect us is cruising on the highway. example, Say our JK's make 200ft-lbs of torque at 2300 rpms with stock exhaust and peak at 240ft-lbs of torque at 3100. I roughly cruise around 2200-2300 rpms on the highway.

With an exhuast system, and no engine tuning, The lose of backpressure could easily bump our torque curve way up and only be making say 180ft-lbs of torque at 2300, but by 2600rpms be back up past the 200ft-lb range and the surpase our 240ft-lb mark a couple hundred rpms after the 3100 mark. this would directly affect our MPG.

With some type of engine management system. This could be easily correct and actually improved. I have seen thing like this first hand. My 1.96l engine that was in my honda civic easily benefited from 3.5" exhaust system, only because I had plenty of air moving through the engine, 23-25psi from a 61mm turbo.

Tuning is everything when it comes to effeciency and usable power. That's why you have to do a little research when you look into performace parts. Sure something might add 15,20, maybe 50 hp, but if it's so high up or down lown in the rpms that it's not even being used. Your just wasting you time and money.

-Chad-