Makes it sound dirty? Lol... Is that a good or bad thing? Haha

 

Can I see proof of that concept?

backpressure improves cylinder filling of the air/fuel mixture...if you lower back pressure the air/fuel charge does not fill the combustion chamber as well, but simply flows through, resulting in less power. It's like filling a bucket with water....if the bucket has a huge hole in it, it takes longer to fill it. Back pressure is like a wall in the exhaust port that the air/fuel mixture hits when entering the combustion chamber so it fills up more....resulting in more complete filling and more power on detonation. There are other important considerations regarding back pressure, especially for racing engines, but you get the idea. And we won't even touch the concept of pipe size and it's effect on exhaust velocity.....


Point is, DO NOT remove your cat, it is ILLEGAL. That should be enough. Then it negatively affects your engine, most likely.

I run a flowmaster 50, its a little quieter and much deeper/mellow. If i had to choose, the 44 does have a much cleaner sound than the 40. The 40s sound metallic and hollow.

 

Your logic is a bit... Flawed on this concept. What you want is NEGATIVE pressure, i.e., vacuum, to help fill the cylinder. The valve acts as a wall, not the backpressure. Valves in a 4-stroke engine have springs to close the cylinder, and do NOT rely on backpressure. More backpressure in a properly tuned engine DECREASES HORSEPOWER AND TORQUE.

http://www.veryuseful.com/mustang/te...Scavenging.pdf

Backpressure requirement is a very old, often logically flawed concept. Freer exhaust flow, up to a certain point, increases power out of an engine. Each exhaust pulse needs to be able to flow to the end of the low-pressure pipe (opening at tailpipe) without expanding too much in the exhaust pipe.

 

I believe we are explaining two different concepts. I still don't see proof, just a curve. I lost a lot in a house fire, but I may still have the dyno sheets for my ranger's old V6. I lost horsepower AND torque when we tested open headers. It was a significant amount better (+6hp IIRC) with the back pressure of the exhaust to create the scavenging effect you describe in a properly designed exhaust system (stepped down pipe/minimal smooth bends)

We should start another thread instead of hijacking this one if we continue.

 

Look at top fuel dragsters, they have nothing to cause back pressure and they run freaking amazing and hard. Back pressure isn't what does a engine good, but exhaust tubing does, just like what the guy said about creating a vacuum. You want suction to pull the exhaust out and get less scavenging. Back pressure is just dumb

 

I would venture that your engine was either tuned incorrectly or the headers were not engineered correctly for that V6.

 

Check out the Cherry Bomb Xtreme:

 

I would agree as I think every dyno run I've ever seen usually makes those peak numbers on the open header pull.

 

Ok let's settle this... pull your exhaust off and tell us how it runs..... I can tell you it will run like crap and have a lot less power. Everything you are talking about pertains to high powered and propperly tuned engines. Not the tractor motor that comes in the XJ. When you buy an after market exhaust that says it frees up the exhaust flow basically all it is doing is removing the parts of the exhaust that limmit power in order to keep it quiet. So yes I will agree too much back pressure will lower over all performance (like the back pressure caused by the sound dampening parts of the factory exhaust), but saying a 4 stroke engine doesn't need back pressure is not correct.
back on topic though....
the 44 sounds great on the Jeep I6. I had that and a high flow cat on my ZJ and got tons of compliments on the sound. It's not going to sound like the rumble of a V8, but it's a nice deep and smooth sound. quick note though, dont expect any major performance gains from it. if your exhaust is clogged up or has a bad leak at the moment, you'll notice an actuall difference after the install, but if your exhaust is fine, you might only gain about 3 to 5 hp and maybe if you are lucky 5 to 6 ft/lbs. It will sound much nicer though and that will put a smile on your face.

 

Its a good thing... il post a vid then maybe...

 

I will inform Ford that they used an incorrect design. The 2.9L had a tendency to float the valves under high rpm pulls. Adding the exhaust back provided the resistance needed to stabilize the mixture in the combustion chamber and settle out the valves Seeing as neither my 2.9L or 4.0L are designed with high rpm screaming performance in mind, flow for the regular guy will be just fine with a new cat, muffler and properly stepped pipe.

With an XJ, it's all about the sound. That's what we're going for.

 

Yes, it would run like crap, because it needs the O2 sensor to calibrate air/fuel ratio. The Chrysler L6 is not a tractor motor. It traces its heritage to such, but the 242 is a light-duty passenger car engine. Please explain to me why it needs backpressure. My engine is properly tuned, and engines that have little to no backpressure run with more power than one that does have backpressure.

http://www.nsxprime.com/FAQ/Miscella...austtheory.htm