The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post

Super73 · 02-05-2010, 11:32 PM

Hmmm.. I must have too big of an exhaust for my 347ci motor..

BTW, bellow are a couple dynograph overlays showing a mild cam and bolt on 347ci 3rd gen motor (stock heads). The lower numbers are going through 3" exhaust to the cut out then necks down to the 2.5" exhaust to the mufflers. The higher numbers are with the cut outs open IE dual 3" straight open..

I have done several exhaust similar to this, some 3" all the way through, some necked down to try and quiet it down a little.. All of them showed gains in both TQ and HP under the curve with less restriction. I was proving a lot of people wrong back in 01 about back pressure. Even with stock cams, the gains were all over..

I think a well thought out set of headers make the biggest difference with exhaust scavenging.

02-05-2010, 11:32 PM	#12
Super73 Registered User Join Date: Nov 2007 Location: Bay Area, Ca Posts: 2,841	Re: 3 inch exhaust too much? Hmmm.. I must have too big of an exhaust for my 347ci motor.. BTW, bellow are a couple dynograph overlays showing a mild cam and bolt on 347ci 3rd gen motor (stock heads). The lower numbers are going through 3" exhaust to the cut out then necks down to the 2.5" exhaust to the mufflers. The higher numbers are with the cut outs open IE dual 3" straight open.. I have done several exhaust similar to this, some 3" all the way through, some necked down to try and quiet it down a little.. All of them showed gains in both TQ and HP under the curve with less restriction. I was proving a lot of people wrong back in 01 about back pressure. Even with stock cams, the gains were all over.. I think a well thought out set of headers make the biggest difference with exhaust scavenging. __________________ ------Motor---------------Bottle 60'---1.53---------------1.41 1/8---6.58 @ 105.92----5.87 @ 118.41 1/4---10.38 @ 126.97----9.24 @ 142.49 Last edited by Super73; 02-05-2010 at 11:35 PM.