2 1/2" or 3" exhaust ???

[Elohim1]

The 502/502 I am using came with a 850 holley and I have upgraded to edelbrocks MPEFI. I am using 1970 corvette exhaust manifolds (off a 454) which are designed for 2 1/2" exhaust pipe.

I think I will be going with the 2 1/2" exhaust so the exhaust guys can get tighter bends and probably tuck it in better. plus less expensive. Not that it matters to much at this point.

However, I wander if 3" would allow things to run cooler ? I do not think there would be any benefit to air flow since the hole at the manifold is 2 1/2".

Thoughts please?

[2ndA]

An exhaust is just like the ductwork on your house(ok, not "just" like, but similar). The outlet of your furnace is smaller than the ductwork and this allows an increased volume of air. The more volume it has to fill, and the straighter line it has to travel, the more easily it will flow(and the larger the amount). So just because your manifold outlets at 2.5 doesn't mean 3" pipes the rest of the way out won't help.

I'm not explaining that right, but I'm tired and it's been a very, very lousy day.

[BCOWANWHEELS]

2.5 is plenty with low restriction mufflers & dual exhst. or 1- 3" pipe would do nice also . think i,d do 1-3" with a flowmaster

[stanman]

Thats the debate thats been going on since the beginning of time, is it better to have smaller duals with an H pipe/ X pipe or a larger single? I myself am a fan of dual w/glass packs

[fisherman]

I'm gonna run 3" single all the way back and either a flowmaster or magnaflow. Try to keep it near stock in configuration.

[BCOWANWHEELS]

single 3" does good on a bb. 2 1/2" from engine to y-pipe.

[Hammer]

A 502 HP big block with a single 3" exhaust? That seems way too small.
It will work good, but you will be choking off the mid to upper range like that.
Dual 2.5" would be GREAT if you could use mandrel bends.

One reason to run dual 3" exhaust would be to make up for the crimps and crushing effects the bends will have on the pipe. But the sound difference is very noticable with the dual 3" pipes. This sound isn't for everyone (or their neighbors).

If I had to choose, dual 2.5" exhaust with either Flowmasters, or another chambered muffler (I like the sound, and the flowmasters are made VERY tough!).

[poolmike]

What gets sucked into the engine, must get blown out. If I was running a 502, it would be 3" duals with single chamber Flowmasters. I have no love for my neighbors

[brute4c]

If we go on the cross sectional area of 2-2.5 inch pipes, one needs almost 3.5 inches of cross sectional area in a single pipe to have the same flow capability.
A single 3 inch pipe would reduce the aiflow through the system....a single 3.5 inch pipe would keep it right at the same amount.

[Hammer]

Run a single 4" exhaust!
I love the one on my diesel

The real answer come down to usage, fitment, and preffered sound quality.
If this was an end all be all truck, with moderate usage of the engine, but still wanting clean sound and can take duals. I would get the mandrel bends and build my own exhaust. And believe it or not, you could problably still do it cheaper then most 'performance' shops will charge.

And remember, cheap exhaust shops will put in some badly crimped pipes. You are wasting your time if you get those with such a nice motor.