Single pattern cams
Le Mans Master
Joined: Dec 2003
Posts: 5,727
Likes: 38
From: Fremont CA
The practice of using dual pattern cams comes from the fact that most cylinder heads have a lousy exhaust port flow compared to intake flow. If the exhaust port flow in in the 80% region of the intake flow, you can cut back on exhaust duration and build more power. There aren't many heads out there with good precentages, the AFR stuff is pretty good.......
Thread Starter
Drifting
Joined: Jun 2012
Posts: 1,990
Likes: 183
From: Port St. Lucie Fl
The practice of using dual pattern cams comes from the fact that most cylinder heads have a lousy exhaust port flow compared to intake flow. If the exhaust port flow in in the 80% region of the intake flow, you can cut back on exhaust duration and build more power. There aren't many heads out there with good precentages, the AFR stuff is pretty good.......
based that they are at the very minimum, wouldn't they benefit from a smaller dual pattern?
Race Director
Joined: May 2005
Posts: 10,674
Likes: 121
From: Millington Illinois
St. Jude Donor '08-'09
http://www.airflowresearch.com/index.php?cPath=24_25
based that they are at the very minimum, wouldn't they benefit from a smaller dual pattern?
based that they are at the very minimum, wouldn't they benefit from a smaller dual pattern?
Last edited by 63mako; Dec 20, 2014 at 10:41 PM.
Le Mans Master
Joined: Oct 2010
Posts: 6,900
Likes: 833
From: melbourne florida
2023 C3 of the Year Finalist - Modified
some factory heads were better than others, but guys ported heads back then more commonly than today. chevrolet because of input from racers like Smokey Yunick and Bill Jenkins got into hard racing parts more seriously. what we always called the Turbo casting was the first attempt at giving us a decent foundation. plus the layout of the small block sort of dictated to a degree the port size. And remember it was originally only 265 cu,in.
Race Director
Joined: Jan 2000
Posts: 13,011
Likes: 2,249
From: Corsicana, Tx
2020 C2 of the Year - Modified Winner
2020 Corvette of the Year (performance mods)
C2 of Year Winner (performance mods) 2019
2017 C2 of Year Finalist
This all depends on the RPM range you want to play in also. If you want it to hang on past peak HP...you're going to need some added exhaust duration in most cases.
JIM
JIM
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
2027 Corvette vs The World: Every Model vs Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
5 MOST and 5 LEAST Popular Corvette Model Years in History!
Joe Kucinski
2027 Corvette Buyer's Guide: Everything You Need to Know!
Joe Kucinski
10 Things C8 Corvette Owners Hate (But Won't Tell You)
Joe Kucinski
10 Best Corvettes Coming to Barrett-Jackson Palm Beach 2026!
Brett Foote
Every Corvette Grand Sport Explained! (C2, C4, C6, C7, & C8)
Joe Kucinski
Grand Sport & Grand Sport X Launch Alongside All-New 535hp LS6 V8!
Michael S. Palmer
5 Reasons Bad Drivers Crash & 5 Ways to Avoid a Costly Mistake!
Joe Kucinski
Drifting
Joined: Jul 2013
Posts: 1,299
Likes: 93
From: Tri-Cities TN
At 75% I/E ratio with a head sized to the CID and rpm application a cam will see the same duration at .050" for both intake and exhaust. Above this the duration will favor the intake. If you look at import cams and cylinder head flow the import stuff is in the high 80's on I/E ratio. Most import cams have more duration on the intake.
As CID grows and rpm grows this rule will change as these demands will change what the engine needs.
As CID grows and rpm grows this rule will change as these demands will change what the engine needs.