The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - Header or Not To Header That Is The Question

*lakeroadster* · 04-14-2011, 12:20 PM

One thing to add in regards to Ram Horn manifolds, they are not all created equal. The stock manifolds range from 2" to 2-1/2" outlet sizes. The stock 2-1/2" Corvette style are said to be about 66% as good as headers on a mild SBC. The more radical the motor, the more you will benefit from headers. Some people are porting the 'vette ram horn and getting within 10% of headers, but those ported manifolds cost as much or more than a set of headers. Why? Well in certain drag racing classes stock, means running stock parts. But the classes allow modifying the stock parts, thus you end up with high dollar stock manifold modifications.

Here is a link to a company that sells stock and modified Ram Horn manifolds, as well as late 60's "log" style manifolds. Again, this stuff is very pricey, but the data in this website is very educational in regards to flow. Much to be learned here...

http://www.castheads.com/faqs_exhaust_manifolds.php

Log Style Manifolds:

GM built the 2-1/4" outlet size "log" style manifolds for better flow. Stock exhaust manifolds that pre-date the log manifolds were very restrictive. Don't use those older pre-log style manifolds on any performance built motor, unless you are going for a concourse restoration on the vehicle you are building. Just remember for good flow 2-1/4" outlet size is the absolute minimum and 2-1/2" outlet ('vette style ramhorns) are better.

And here is some actual data posted in regards to a '72 LT1 motor, rams horn vs. headers.:

http://forums.corvetteforum.com/c3-t...s-headers.html
The difference between a fully ported set of 2.5" dia rams horns and Hooker Super Comp 1.75" headers was about 10% of my power on my 1972 LT-1 motor during a dyno test of the motor (394HP manifolds/426HP Hookers.) The testing was done with a set of DynoMax Ultra Flow 2.5" mufflers on a simulated exhaust system. The difference at the Drags 12.60@113.8 MPH with rams horns (I had a lot of porting labor in them and broke over $90 of carbide burrs porting them, they were better than Brezinski manifolds) and 12.28@117 MPH with the Hookers (both runs through the mufflers)

04-14-2011, 12:20 PM	#21
lakeroadster Account Suspended Join Date: Sep 2009 Location: High Plains of Colorado Posts: 2,485	Re: Header or Not To Header That Is The Question One thing to add in regards to Ram Horn manifolds, they are not all created equal. The stock manifolds range from 2" to 2-1/2" outlet sizes. The stock 2-1/2" Corvette style are said to be about 66% as good as headers on a mild SBC. The more radical the motor, the more you will benefit from headers. Some people are porting the 'vette ram horn and getting within 10% of headers, but those ported manifolds cost as much or more than a set of headers. Why? Well in certain drag racing classes stock, means running stock parts. But the classes allow modifying the stock parts, thus you end up with high dollar stock manifold modifications. Here is a link to a company that sells stock and modified Ram Horn manifolds, as well as late 60's "log" style manifolds. Again, this stuff is very pricey, but the data in this website is very educational in regards to flow. Much to be learned here... http://www.castheads.com/faqs_exhaust_manifolds.php Log Style Manifolds: GM built the 2-1/4" outlet size "log" style manifolds for better flow. Stock exhaust manifolds that pre-date the log manifolds were very restrictive. Don't use those older pre-log style manifolds on any performance built motor, unless you are going for a concourse restoration on the vehicle you are building. Just remember for good flow 2-1/4" outlet size is the absolute minimum and 2-1/2" outlet ('vette style ramhorns) are better. And here is some actual data posted in regards to a '72 LT1 motor, rams horn vs. headers.: http://forums.corvetteforum.com/c3-t...s-headers.html The difference between a fully ported set of 2.5" dia rams horns and Hooker Super Comp 1.75" headers was about 10% of my power on my 1972 LT-1 motor during a dyno test of the motor (394HP manifolds/426HP Hookers.) The testing was done with a set of DynoMax Ultra Flow 2.5" mufflers on a simulated exhaust system. The difference at the Drags 12.60@113.8 MPH with rams horns (I had a lot of porting labor in them and broke over $90 of carbide burrs porting them, they were better than Brezinski manifolds) and 12.28@117 MPH with the Hookers (both runs through the mufflers) Last edited by lakeroadster; 04-14-2011 at 12:42 PM.