Is this a good way to go? Engine is a n/a 350 with probably a 650 cfm holley. Dual 3" exhaust with super turbos rated at 410 cfm each. I'm looking to hit about 400-450 with it. Would these mufflers hurt much?

They were on my camaro, but I swapped them out for ultra-flos to match the new engine.

 

You mean like the way intake valve size is matched to exhaust valve size?

 

I don't think your going to make 450hp with a 650 carb.

 

Hmmmmmm, if your making a point, I think I follow. I've forgotten why the exhaust is smaller. Perhaps due to the pulling force of scavenging? But by the time the exhaust gets to the mufflers....it just needs to get out.

450hp with a 650? Not the best choice, yes. Impossible, hell no. Im toying with the idea of high compression and E85. It may also end up as a nitrous motor, which like carbs on the smaller side........

So do you guys think these dynomax super turbos would hold back much? I know they are good mufflers, but to what limit? I also dont want this engine to be too loud, its going to have a big cam. A just for fun engine.

 

A couple of good reads regarding exhaust and muffler flow.


http://www.superchevy.com/technical/...t/0505phr_exh/


http://www.broaderperformance.com/mu...flow_tests.htm

 

There are so many variables between the carb and exhaust that I don't think there can be a rule of thumb between the two.

 

Thanks that was some good info. Dynomax says their turbo flows 410cfm for an unknown diameter. Your article said 268cfm for 2 1/2 if I remember correctly.
Nevertheless, I think these will be ok for 400hp.

I do wish all mufflers were rated in cfm......

 

And if they were, what good would that do?

How many CFM of hot exhaust gas is produced by some number of CFM of cold air? Given that exhaust gas is roughly twice the temperature in Kelvins as intake air, then its CFM should be roughly double. Eh? But it's not exact, and it would depend on ALOT of variables beyond the control of the muffler itself; like, where in the system it was installed, whether the engine had headers or manifolds, and so forth.

What pressure would you like to "rate" the muffler's CFM at? I guess the first question is, what pressure is appropriate within an exhaust system? We can all agree that we want as little as possible; but, what pressure would we consider "acceptable", if for instance it turned out that we had to have dual 8" exhaust to make it "negligible"? That is, if we consider some number, let's say 2%, of power loss "acceptable", what pressure would that be? 1 psi? 10 psi? 100 PSI? I haven't a clue. But needless to say, whatever pressure that is, is where you'd want the CFM "rated" at. Remember also, at the carb side of things, all the pressure you have available to push air in, EVER, is atmospheric (14.7 psi or less); but how much pressure can the engine generate on the exhaust? Again I don't have a #, but I'd bet it's AHELLUVALOT more than 14.7 psi.

All in all, it doesn't seem to be a very useful thing, in a practical way; and certainly not tied directly to carb CFM (the optimum value of which is also affected by a number of variables, such as plenum size, runner size, and so forth.

What's your air cleaner's CFM "rating?

I just don't see where there's much "matching" to be done there.

 

I think you nailed it on the pressure. Different engines produce different pressure and it doesnt matter much on the carb cfm. But one good thing to look at is at a given pressure, the cfm of a straight pipe compared to a muffler. I think that gives you a good indication of a muffler's restriction.

I suppose the best way to go, would be to get some cut-outs, and see how much of a power increase I got with them open.

For the best power, I think some smaller diameter tube and better flowing mufflers would be optimal, but this is what I have laying around.

I believe your correct, there is no matching to be done in relation to carb and exhaust.

But keeping all the engine parts the same, and decreasing carb size, would you notice less of a drop in overall torque if you also decreased your exhaust size?