I was just wondering if it made any difference about how far back a restriction in any given exhaust system was? For example, if i put a mufflex 3" to 4" y-pipe and then ran 4" pipe back as far as i could but then reduced it from 4" to 3" piping into my GMMG, would this make any flow difference over just going with a true 3" y-pipe, straight to the 3" GMMG exahust system? If you have any facts or flow data on this, let me know.

Brandon

 

I could be wrong so someone correct me if I am. I believe that the exhuast will only flow as well as its weakest point, therefore having 4 inch all the way to the back with 3 inch after the axle will only flow as well as having 3 inch all the way from the y pipe.

 

bingo

 

Exhaust gas waves and resonance come into effect. Normally if your stepping down though, all your going to get is a super raspy sound like a unmufflered old truck.

-Shannon

 

Might be wrong, but thats deffinatly how I see it.

I pretty much think of it as a garden hose that flowing water. Whether you pinch the hose at the beginning, middle or end, doen't matter. The end flow result will be the same.

Of course there are probably a million little details that alter this like rpms or whatever. But on the whole.. I think it's a pretty good analysis.

 

if i were you i would install a nice 4" cutout just before you state the 3" pipe. then you'd be flowing like crazy when you want to uncap it at the track.

QTP makes 4" e-cutouts now i think

 

Actually, as you move the step-down in size farther back on the exhaust system, the restriction goes down. Pressure loss (or backpressure in the case of an exhaust system) is caused by frictional losses as the gasses pass through the pipe. Frictional losses are approx. related to gas velocity. In an exhaust system, as the gasses cool down the density of the gasses increases and the velocity drops. The farther you are away from the engine, the less volume of gas you have to handle, and the less affect a smaller diameter pipe will have. A 3" pipe at the muffler will have less restriction than a 3" pipe at the "y".

You can't just say that a single restriction becomes the definitive limit on the capacity of the system. It depends where you locate it. An example I like... a buddy of mine had a decent exhaust system... Hooker LT's, custom Mufflex 3" Y-pipe, Mufflex 4" catback. And at the back of the system, he cut the turndown off the 4" exhaust pipe, and welded on the little dual tips from his 30th SS covertibles two-on-the-left system. Had no affect on the ability of the 3,900# car to run consistant 9.0X, 155mph 1/4- miles....