Me and a friend who is pretty good at small engines got into an argument about back pressure. Basically I was just defending myself about running open cutout and another friend running a straight pipe. He said what i did was stupid because i have no back pressure. I can see that it may be a problem not having any but, i still have the manifolds, cats, and all the stock tubing all the way to the cutout. I was wondering why exactly you need backpressure, do I lose power by not having as much? Do I have enough with the open cutout?

I also want to know, I was thinking about lts and !cat. I hear that the cats are pretty restrictive but is it a bad thing to remove them? Will it cause trouble to go lts, ory, open cutout? At that point iwill probably actually use my catback though.

 

I ran open long tubes for a long time, made a little more power than my true duals did.

 

If backpressure was all that good--Prostock would be running mufflers,so would John Force.
Backpressure has NO good use at all.Some gonna disagree but that's a fact,seen it on the dyno Toooo many times.

 

Yea, back pressure is bad. This has been thoroughly discussed before. Removing any restriction in the exhaust system will always be a positive gain. Low end torque as a result of back pressure is an age old myth. What it comes down to is exhaust velocity. The faster the better. When you're producing too little exhaust for the volume of the exhaust pipe, the gas will expand, drop in pressure and decrease in speed. To prevent this and maintain exhaust velocity one could use a smaller pipe. Some people believe this is proof that back pressure was needed for low end torque. What is really happening is the exhaust velocity has increased because the pressure has increased in the exhaust system. Great, you say, why not run really small pipes? Well, once your pipe's flow potential is less than your engine's flow potential, you being to labour the engine. It takes energy to compress that exhaust and push it out, so you're losing power.

If you're going with a smaller diameter pipe to make low end torque, you're going to be hurting on the high end. Always robbing peter to pay paul.

 

Ditto, has anyone seen a car run good with a stopped up converter.That's to the extreme but the principal is the same.

 

Tell me if this setup is optimal....

I've got a 355 w/6" rods 11.2:1 CR w/a gm847 cam, hooker longtubes, and true duals with custom x-pipe and dynomax bullets. I believe it is a 3" system, but it may be a 2.5".

 

Backpressure bad, tuned scavenging good.

The quicker and more efficient you get that exhaust out the better, backpressure actually hurts this.

 

This is the question that's been beat to death on Advanced Tech... might be worth a "search"

http://web.camaross.com/forums/showt...t=backpressure

 

Ok, now i was wondering, this next, does a closed cutout hurt exhaust velocities over just having a regular pipe in its place?

 

I would imagine so. When the exhaust hits the closed cap it compresses in that area, and then reflects backwards through the pipe. Although how much of an effect it has, I'm not sure, it's probably very little. But it definitely does create some restriction in the pipe.

 

i agree. i think that it may be different story for a four cylinder engine trying to move a 3000 pound vehicle, but in the case of a v8 any flow restriction at all will cost power.

 

I believe that the only type of cutout system that would provide max power would be one where you could open or close the cutout and it could be completely smooth. i.e., an electric cutout. It would be tough to make one that would flow smoothly both ways. Perhaps the best possible solution to make the most power would be to make the mufflers easily detatchable for when you go to the strip. Thats pretty much how mine are. I've got hooker LT's going into an x-pipe, then the rest of the exhuast (3" into dynomax bullets) is slip-fitted onto the x-pipe, so it comes right off when I want.