348 Chevy exhaust sizes?

Hi all, I'm building a car in Aus with a 348 chevy W block. The motor should have around 450hp and the same in torque. It's a full size street car. Just wondering what size exhaust guys are running on these things? I was thinking 1 3/8 for the pipes and either 2.5 or 3" for the rest? Also, I want to get that cool old tone out of it. What's a good muffler combo? Needs to be Roughly 91db or under..

Also, it will have a T700 w/2800 stall & 4:11 diff ratio.

Build thread here http://www.facebook.com/60minus

Cheers, Justin...

 

I checked out your facebook, you have some sheet metal skills. Great looking build. To the exhaust I would recommend a metal pack such as porter or brockman mellow tone mufflers.

 

1 3/8 pipes, I'm guessing you mean headers, go with 1 5/8 or 1 3/4, with a 2.5 or 3 inch exhaust.

 

Cheers Lucky, I'll look them up...

Headers Indy, yeah. And I actually meant 1 3/4 too, 3/8's small. Would a half inch difference in the 2.5 - 3 make a bit difference with these motors? The exhaust is running under the diff (heaps of room) so it's going to be pretty much a straight length the whole way through. Should flow fairly decent.

 

W engines like to breathe try and make your headers 1-7/8 if you can

 

2.5" duals should be fine. I run 2.5" duals with a 464c.i. Chevy, and works fine.

 

Doesn't oversizing the headers and making exhaust flow too freely, i.e., not enough back pressure, actually reduce low end torque? I thought this is a general truth in naturally aspirated engines. I don't know what a dyno would show, or a trap speed or well-calibrated **** dyno for that matter, but larger than 1-1/2" dia. primary on a 348/450hp engine sounds too large to me.

 

1-1/2 is way to small block hugers are 1-3/4" aleast

 

If you want to build some good torque with it build some tri-y headers. 1-3/4 primaries into 2-1/2 secondaries into 3" collectors.

 

Your signature speaks for itself so I'm not arguing with proven success.

 

1 7/8 is probably good for your drag car. But this will be a street car/cruiser. So I won't be holding the throttle open very often. that size, even for a 348 might be a bit big? Maybe i should go with a 1 3/4 - 2 "hot rod" style design feeling into 2.5" collectors. Simmilar to the pic below. I want low end power and no drone when using on the hwy.

Thoughts?

 

An experienced header builder once told us as a rule of thumb that the primary tubes should be the same diameter as the exhaust valve. I am thinking for a street car
1 5/8" primary tubes with 2 1/4- 2 1/2" pipe. 3" pipe would be overkill and harder to route the exhaust.