4L exhaust....no cat...muffler on headpipe

[fast_Z28_guy]

anyone done this as a cheap exhaust?

the head pipe on the 03 4L is 2.5", mandrel bent. then after the cat it necks down to 2.25" for the muffler, and compression bent tubing on the tailpipe.

looking to build some power on the jeep for towing the boat.

very few companies make a full 2.5" exhaust setup...and most are obnoxiously $$$ anyway.

was considering pulling the cat off the headpipe, throwing on a 2.5" in/out magnaflow straight thru muffler (have it on my Z28...love it) and then just dumping the exhaust under the vehicle ahead of the axle.

i realize it has the potential to be too loud...in which case i may put the cat back on but with an increased exit pipe (2.25 --->2.5").

just looking for input?

[Bounty__Hunter]

You won't be able to pull the converter on an '03 without throwing the check engine light. I don't think it would be worth the trouble as catalytic converters aren't all that restrictive these days.

All 4L jeeprs came with 2.5" necking down to 2.25 downstream. Keep in mind that exhaust will get more dense as it cools downstream, doesn't need as large a tube to get the same flow. Plus you need some backpressure so as not to lose low end torque.

I've heard a glasspack on a few newer 4L's with the cat in place, sounds really nice.

[fast_Z28_guy]

hmmm

when under it recently...i didn't notice a post-cat o2 sensor....i guess i'll have to look harder.

if thats the case i'll leave the cat in place i guess....untill i can find a simulator

as for the backpressure/low end power thing.....seen it discussed more times than i can count....and the educated consensous is that that its and old wives tale.

without doing the research to get specifics....i think it comes from the idea that less backpressure changes the power curve, therefor making it feel like you've lost power down low.

and before anyone jumps on it....
i'm not saying the solution is "zoomies" off each exhaust port on the heads. the engine needs some amounts of scavenging to help draw spent gases out of the cylinders.
although at WOT "zoomies" would probably outperform standard exhaust.....and probably sound awesome

[fast_Z28_guy]

info from some guys with a HELLOFA lot more knowledge than myself:

one thread

start reading at post 6....very good stuff

[SenorCole86]

If I'm reading your suggested reading material correctly, it seems that the guy in post #6 in the second link is confirming Bounty's claim. The engine will experience the best scavenging and the best torque at the point at which the exhaust gases have the highest velocity, which is dependent upon the tube's inner diameter and the other objects in the exhaust system causing minor head losses in the flow, such as cats, mufflers, bends, etc. As one decreases back pressure, one is moving the "best scavenging rpm" to a higher rpm and therefore losing that scavenging ability down low. I'm not pretending to be an expert on the subject, just an engineer taking a look at the suggested reading material.