I'm trying to find a formula online to calculate exhaust gas flow but can't seem to find anything.

What I want to compare is 3" to a Y with 2x2.5" pipes to 2 2.5" inlet mufflers, compared to 3" to 4" where the Y would be and 4" back to a 4" muffler.

This is not for a Honda..

I think the snigle 4" flows more then the dual 2.5" but I'd like to play around with a formula and see...

anyone?

 

at the same pressure you can just use area of a circle.

your ? was kinda hard to read but im assuming you meant

4"--> pi * 2^2 = 12.57 in.^2
2 x 2.5"--> 2(pi * 1.25^2) = 9.82 in.^2

 

You have about 20% less surface area to lose heat thru and pile up boundary layers on with the single 4" exhaust compared to the twin 2.5". You'll also be packing roughly 20% less weight/foot with the 4". Not to mention the additional weight loss from reducing the number of hangers and mufflers with the single exhaust.

More effective flow area, less heat losses, less weight...seems like the single 4" is the better way to go.

 

Awesome.

My other car is a 98 Grand Prix GTP so it's a transverse V6 and it's only got 1 pipe that goes from the manifolds all the way back then it splits for the 2 mufflers..to me, that's gay, no reason there should be 2 mufflers on a car setup this way, just as bad as dual mufflers on a 4cyl.

Since I have a bunch of 4" I'll go ahead and use that.