So I just bought another Cherokee from this guy and he had it outitted with a Flowmaster straight pipe (no muffler).

My question is I've been hearing that a muffler actually is better for the engine because it creates a certain amount of "back pressure" the engine needs for better performance. The guy I bought it from claims that a straight pipe is the best way to go because it restricts the least amount of airflow.

So what do guys think? Aside form the roar aspect of it just performance wise which is better?

Also I was looking into putting in a flowmaster 40 series muffler because they claim to increase horsepower and torque while reducing internal noise and still giving you the roar externally. I was thinking i like the sound of the roar of the straight pipe (its kind of badass) however sometimes while cruising on the highway the constant resonance/rumble in the cabin gets annoying after a while when I'm trying to listen to music or talk on the phone.

Thanks in advance!

Search. Backpressure is a myth. You need to keep velocity.

Basically as long as you keep your cat installed and the local PD doesn't have an issue with the noise, everything will be fine.

Yes I absolutely have a cat installed it wouldn't have passed emissions inspection without one nor would i want to pollute the air like that. So backpressure is a myth. hmmm thanks for the input.

Do you know anything about the Flowmaster 40 series mufflers? would you say their claims of increased power & torque is also b.s.?

With regard to power/torque, a performance/free flowing muff is going to be somewhere between a stock muff and a straight pipe......and sound level will be somewhere between stock and straight as well.

The only other thing in exhaust that will really increase power are tuned headers. The exhaust pulses help pull the exhaust. Scavenging.

Yes!

Seems like more are starting to understand!!

Scavenging and velocity go hand in hand.

I think you'll find that if you run your tailpipe straight out the back with no turndown, it will be quieter inside. I'm running a Magnaflow that is straight through with a louvered core, and its quieter inside the passenger compartment than it was with the original muffler.

I don't think an XJ exhaust without muffler will be obnoxiously loud if the pipe is routed out the back. It will be a bit more raspy than would be with a glasspack, louvered core, or chambered performance muffler, but not as loud as the ricers with their fart cans.

OK. Having said that, Flowmaster states that their mufflers create this "scavenging" you guys are talking about. Therefore increasing power.??

Is it an advertising gimick or can a well engineered muffler actually create scavenging?

They say the.design.of.their muffler helps pull the exhaust out. The.actual difference with our motors and.single exhaust is marginal. One way besides tuned headers though is to get a header with.two.collectors and run it into an x pipe. Thesis creates.a.situation similar to 180 degree headers. Don't think there's room for that though unfortunately.

The pipe on mine runs straight out the back. I dont know what you mean by downturn... It has a slightly wider mouth at the tip which looks really cool however i don't know if it is doing anything for performance, or considered a "tuned head"

So your saying your straight pipe is quieter than with the stock muffler?

What is a louvered core?

Magnaflow muffs do not have louvered cores....they have perforated, straight thru cores....no baffles or chambers that deflect or re-route the exhaust flow. Scavanging occurs where the manifold tubes begin to merge together.

Flowmaster straight pipe???

I hope it was at least a resonator and he/you are just confused. Otherwise it sounds like he probably paid way too much for a 5 dollar piece of pipe.

He said it was a Flowmaster straightpipe with a chrome time welded to the body. He paid $200 total for it.