Reason for Exhaust Bias of GM Cams?
#22
So if the ASA and GrandAm cam have been optimized by GM for max performance with headers, why do most aftermarket cams have designs with less exhaust bias? I'm sure GM did extensive testing.
#23
I wouldn't say most aftermarket cam's have less exhaust duration. There are a lot of traditional splits, and are getting to be more all the time. Traditional splits are about all Comp Cam's sells. Most of the reverse splits are custom grinds. The intake is more sensitive to lift, while the exhaust likes duration.
#24
For example, here is Futral's cam specs from their website.
Why is the relationship between the intake and exhaust durations so different from the GM max performance designs?
FM-F2 224"/224" .588"/.588" 112 or 114
FM-F4 226"/226" .575"/.575" 112 or 114
FM-F5 224"/228" .588"/.576" 112 or 114
FM-F6 226"/230" .575"/.595" 112 or 114
FM-F7 224"/230" .588"/.595" 114 *
FM-F9 232"/236" .585"/.600" 114 *
FM1-F10 228"/228" .576"/.576" 112 or 114
FM1-F11 228"/230" .576"/.595" 112 or 114
FM1-F12 230"/230" .595"/.595" 112 or 114
FM1-F13 230"/232" .595"/.585" 112 or 114
FM1-F14 232"/234" .598"/.598" 112 or 114
FM1-RJ 236"/239" .600"/.611" 111
* recommended for blower/nitrous applications
Why is the relationship between the intake and exhaust durations so different from the GM max performance designs?
FM-F2 224"/224" .588"/.588" 112 or 114
FM-F4 226"/226" .575"/.575" 112 or 114
FM-F5 224"/228" .588"/.576" 112 or 114
FM-F6 226"/230" .575"/.595" 112 or 114
FM-F7 224"/230" .588"/.595" 114 *
FM-F9 232"/236" .585"/.600" 114 *
FM1-F10 228"/228" .576"/.576" 112 or 114
FM1-F11 228"/230" .576"/.595" 112 or 114
FM1-F12 230"/230" .595"/.595" 112 or 114
FM1-F13 230"/232" .595"/.585" 112 or 114
FM1-F14 232"/234" .598"/.598" 112 or 114
FM1-RJ 236"/239" .600"/.611" 111
* recommended for blower/nitrous applications
#25
No Cam company's keep many reverse splits on the shelf. Why? Because there are very few cyclinders heads in the world where the exhaust side out flows the intake side. Most reverse splits that cam companys have are some of the turbo grinds and that is because of how a turbo works. A reverse split really wouldn't do you any good on a typical head.
#26
Check out what Ed "The Camfather" Iskederian has to say about longer exhaust duration:
http://www.iskycams.com/techtips.php#2003
http://www.iskycams.com/techtips.php#2003
#27
Originally Posted by Unaffiliated Racing
No Cam company's keep many reverse splits on the shelf. Why? Because there are very few cyclinders heads in the world where the exhaust side out flows the intake side. Most reverse splits that cam companys have are some of the turbo grinds and that is because of how a turbo works. A reverse split really wouldn't do you any good on a typical head.
Last edited by 66deuce; 02-04-2005 at 07:20 PM.
#29
Originally Posted by nuzee
Check out what Ed "The Camfather" Iskederian has to say about longer exhaust duration:
http://www.iskycams.com/techtips.php#2003
http://www.iskycams.com/techtips.php#2003
#30
i would also recommend the "Cam Disscussion" threads from awhile back.their long,but well worth the time for anyone that wants to learn about cams.
Last edited by 66deuce; 02-04-2005 at 04:00 PM.
#32
I find it funny...
Anti-reverse guys claim, they are only good for top end power. But yet, I've seen others claim they kink off power up top.
However, Ed Iskenderian writes:
Anti-reverse guys claim, they are only good for top end power. But yet, I've seen others claim they kink off power up top.
However, Ed Iskenderian writes:
At the drag strip it's a little different and I feel more honest. Here, racers have long enjoyed longer exhaust and longer durations across the board (If I may add specifically for the purpose of "killing" low-end torque) to keep the tires from too easily breaking lose. This has been successful and sometimes actually results in a slight increase in top end power - something you can actually use in drag racing since it is a full throttle endeavor through the lights. Keep in mind here though, it's quite possible that a longer duration cam overall would have done just as well or better. In other words if you needed that longer exhaust for top end, perhaps the intake could have benefited from such a lengthening as well.
#37
Well I've probably spec'd out more LS-1 cams than most people around....99% of the time I will use a traditional split unless it's a turbo grind. Yes, granted the LS-1 head has a very good intake to exhaust flow ratio..it still lacks a little on the exhaust side.
#39
Originally Posted by Cal
I think there is no question that a traditional split is better for a normally aspirated LS1, but the best split ratio may not be as big as those GM off-road cams have.
An intake crutch is in place once the intake valve is cracked open enough to where the head flows decent.
Any way it's put, it comes down to the setup and type of usage. There are to many varieties of normally aspirated setups to say, all will make more power with more exhaust lobe.
#40
Originally Posted by SportSide 5.3
Probably the most impressive, forum favorite ots grind. The F13, is a 230* 232* .595 .585 @ 112
An intake crutch is in place once the intake valve is cracked open enough to where the head flows decent.
Any way it's put, it comes down to the setup and type of usage. There are to many varieties of normally aspirated setups to say, all will make more power with more exhaust lobe.
An intake crutch is in place once the intake valve is cracked open enough to where the head flows decent.
Any way it's put, it comes down to the setup and type of usage. There are to many varieties of normally aspirated setups to say, all will make more power with more exhaust lobe.