cut outs are purely for sound. i promise. that and like i said about the racers. your 4.0 is NOT a race car engine

 

Cast Iron??? Your are High. Only 2000 and 2001 JEEP Cherokees come with a cast iron exhaust manifold. 1st year 87 models through 1999 model year are ALL tubular exhaust manifolds.

 

Really? So every race league in the world run cut outs or straight open exhausts (cut outs a nice when you want to drive home after the race) just cause they like the sound? What about the cut outs on new vets that open at full throttle to bypass the muffler? They only did that for the sound and not to squeeze a few more ponies out of it

The 4.0 can be a race motor if i raced my jeep like some of the prerunner jeeps out there. I know theres a difference between a nascar 350 that revs to 9k rpm and the 350 in a vet/camaro/trans am but you cant say the run of the mill sbc isnt a race motor if its used for racing.

 

The importance of backpressure has nothing to do with the fuel delivery system and nothing to do with a lean running condition. Carburetors can adjust A/F ratios by means of accelerator pumps and power valves, granted they can't adjust it "on the fly" like a EFI system can.

The importance of backpressure has everything to do with cam profile and exhaust scavenging affects. The importance of backpressure is no myth and is still considered by todays automotive engineers.

You don't think backpressure is important because you don't understand it.

 

Agree with him, too much back pressure and like stated before when the intake and exhaust cam are overlapping ( both open at same time) or as most call is scavenging there will be hot exhaust gas in the chamber and you will not get as much fuel into chamber and cause pinging knocking detonation or uneven burn pattern to little back pressure can effect your fuel economy, when the overlap is happening the incoming air fuel mix will actually push out the exhaust valve and not be trapped in the combustion chamber as designed, hence why in dump pipe race cars you see the after burn of raw fuel in the exhaust, this is also due to there cam profiles but that is a whole different story,

By the way i have a pacesetter i like it, sounds good with my super 40 and i actually gain about 2 mpg. my .02 cents