Why round exhaust pipe?

[SuperBuickGuy]

Ignoring the above babble a minute...
We know a road race car (Corvette) needs some torque.. Thus it needs some back pressure... Remember drag cars are different animals..
Would it help to "tune" the exhaust to have some back pressure by having a set size pipe front to rear
Actually something that flows equal cfm all the way thru...
The drag cars that go on the street seem to have 4" collectors then go down to 3.5", wouldnt that be backpressure needed to be streetable or a semblence of it?
While hp is cool.. Shouldnt a roadrace car be set up for max torque rather than hp?

I know when I put smaller mufflers (by 1/4" diam.) I felt a little more driveability.. The car could go lower in the rpm range before downshifting was required and was easier to take off with.. Fenderwell headers with straight pipes to the turbo mufflers.. No turns except right at the collector.. And after the muffler.. Before rear tires..

You folks talk like I have all sorts of space underneath the car.... so tell me, what kind of flow can you get from an exhaust pipe that's been pinched flat? that's the issue to be resolved. By going out the side through 1x5 tube, I am removing 3- 45* bends and the 1 hard 90 plus several 30* bends. Now I'm no vizard, but I'm pretty certain that removing those bends will mitigate any issue I might have with backpressure (my suspicion is I'll have less restriction). And those numbers are PER side. The issue is this - where the pipe goes under the IRS, that space can get mighty scarce when you hit a bump at (laugh) 170. As it is, there's maybe 2" of space at rest between the pipe and the ground... now, as added benefit, I have a fiberglass rear spring. The driver's side pipe runs 2/3 of the length of 1 side within 1" of that spring.... remind me again, what does heat do to plastic? IIRC, bad juju happens.

[TC]

Ignoring the above babble a minute...
We know a road race car (Corvette) needs some torque.. Thus it needs some back pressure... Remember drag cars are different animals..
Would it help to "tune" the exhaust to have some back pressure by having a set size pipe front to rear
Actually something that flows equal cfm all the way thru...
The drag cars that go on the street seem to have 4" collectors then go down to 3.5", wouldnt that be backpressure needed to be streetable or a semblence of it?
While hp is cool.. Shouldnt a roadrace car be set up for max torque rather than hp?

I know when I put smaller mufflers (by 1/4" diam.) I felt a little more driveability.. The car could go lower in the rpm range before downshifting was required and was easier to take off with.. Fenderwell headers with straight pipes to the turbo mufflers.. No turns except right at the collector.. And after the muffler.. Before rear tires..

An engine needing back pressure to create more low end torque is pure myth...... Back pressure only limits cylinder filling and thus costs you power........

[yellomalibu]

You folks talk like I have all sorts of space underneath the car.... so tell me, what kind of flow can you get from an exhaust pipe that's been pinched flat? that's the issue to be resolved. By going out the side through 1x5 tube, I am removing 3- 45* bends and the 1 hard 90 plus several 30* bends. Now I'm no vizard, but I'm pretty certain that removing those bends will mitigate any issue I might have with backpressure (my suspicion is I'll have less restriction). And those numbers are PER side. The issue is this - where the pipe goes under the IRS, that space can get mighty scarce when you hit a bump at (laugh) 170. As it is, there's maybe 2" of space at rest between the pipe and the ground... now, as added benefit, I have a fiberglass rear spring. The driver's side pipe runs 2/3 of the length of 1 side within 1" of that spring.... remind me again, what does heat do to plastic? IIRC, bad juju happens.

Side pipes.
Bolt them on as they come (round) and make some passes or do some laps, then cut off the round pipe and fabricate a square pipe - see if it makes a difference, and note what differences it may make.
Report back with your findings.

[milner351]

Yup - side pipes - there's good reason the track cars all had them back in the day - and you're finding out why.

The chambered exhaust guys sell side pipe mufflers in varying designs, all made here in Michigan.

[SuperBuickGuy]

Yup - side pipes - there's good reason the track cars all had them back in the day - and you're finding out why.

The chambered exhaust guys sell side pipe mufflers in varying designs, all made here in Michigan.

Have you priced side pipes? I'd literally double the amount of money I have in my vette to go that route - all for the benefit of burning my leg every time I extract myself from the car.

and yes, I could build them - and I did have a sick thought of doing rectangular ones (to keep them inside the door frame) - but the way I've scoped out has the benefit of being easy, cheap, and not a danger to myself (or small children though the children bit probably isn't a benefit?)

all that said, if I build a Cobra, it'll have pipes

[dieselgeek]

Its not "Vizzards assertion" there is well known intake and exhaust pressure wave /pressure recovery(Helmholtz) I think the first I know trying to bring it into Drag Racing was Billy Shope ( High and Mighty Ram Chargers) . Pipemax with show the best size and lenght as a baseline of both. But its just a baseline not the rule of law, there is no magic number.

To add to this, you can "see" what the pressure wave does on simulations like Dynomation.

Or if you are very very lucky, you can observe in-chamber pressure monitoring on a running engine and see it also.

It's said that the exhaust pressure wave can move more air (by pressure differential) than the piston itself moving up and down the bore. That one is a Vizard assertion.

We've been using Dynomation to optimize some things on a v-twin engine I am helping tune, and so far it works really good.

[milner351]

I was assuming you'd build them.... the side pipe mufflers were around $80 each if I recall correctly.

[STINEY]

Cost?

So you take 4 or 6 glasspacks (depending on length), cut the ends off, weld them together, paint them black and burn your leg on those.

Cost....pffftt!

[SuperBuickGuy]

Cost?

So you take 4 or 6 glasspacks (depending on length), cut the ends off, weld them together, paint them black and burn your leg on those.

Cost....pffftt!

there ya go again with your high-falutin ways. Everyone knows that 3" conduit is what the big city manufacturers use for side pipe material.... glass packs? we don't need no stinkin glass packs; plus, I saved them from my first car; I'll just reuse them... then I'll be cool like you city slickers!!!

[STINEY]

City slicker....

If you could experience my day so far - anything but.

(How are the owls doing, by the way?)