Reason for Exhaust Bias of GM Cams?
#1
Reason for Exhaust Bias of GM Cams?
Is the large exhaust duration bias for the following three GM cams to match up with the poor flowing stock exhaust manifolds (i.e., no headers)?
If not, why is this bias greater than what is typically seen for aftermarket cams?
Hotcam
219 228 0.525 0.525 112
ASA
226 236 0.525 0.525 110
GrandAm
239 251 0.570 0.570 106
If not, why is this bias greater than what is typically seen for aftermarket cams?
Hotcam
219 228 0.525 0.525 112
ASA
226 236 0.525 0.525 110
GrandAm
239 251 0.570 0.570 106
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#8
I dont think its any higher than any other cams.
A popular Lunati cam for the Fords is a 218/226 .498/.510
One of the most popular cams of all time is a 234/244 .488/.510
Most traditional cams are single pattern or split patterns with 10 degrees of split.
Nearly every Edebrock cam made is a either a single pattern or a 10 degree split no matter if its Ford or Chevy.
A popular Lunati cam for the Fords is a 218/226 .498/.510
One of the most popular cams of all time is a 234/244 .488/.510
Most traditional cams are single pattern or split patterns with 10 degrees of split.
Nearly every Edebrock cam made is a either a single pattern or a 10 degree split no matter if its Ford or Chevy.
#9
Originally Posted by Unaffiliated Racing
compared to other heads the intake to exhaust ratio is very good...like I said it was mainly because of emissions.
#12
most engines, heck ALL conventional piston engines, prefer more exhaust duration then intake duration for power.
think about this:
you're sucking in, 43.375ci of air (ideally).. but after the cyl ignites, you have much more then that to push out. the more exhaust you can get out, the more fresh air you can pull in.
most aftermarket cams (for any motor) are either straight (ie 224/224, 232/232, ect..) or split with more exhaust....
i see some guys on here with a "reverse" split.. why, i donno.. seems like they're shooting themselves in the foot, and the results go along with that, but whatever.
think about this:
you're sucking in, 43.375ci of air (ideally).. but after the cyl ignites, you have much more then that to push out. the more exhaust you can get out, the more fresh air you can pull in.
most aftermarket cams (for any motor) are either straight (ie 224/224, 232/232, ect..) or split with more exhaust....
i see some guys on here with a "reverse" split.. why, i donno.. seems like they're shooting themselves in the foot, and the results go along with that, but whatever.
#13
GM designs their cams to work on an engine with stock manifolds and exhaust. Therefore they hold the valve open longer to allow a decent amount of air to find its way out since its not a good exhaust system.
#14
Originally Posted by LSUxBlake
GM designs their cams to work on an engine with stock manifolds and exhaust. Therefore they hold the valve open longer to allow a decent amount of air to find its way out since its not a good exhaust system.
#16
Originally Posted by Cal
Not true. All of the GM off-road cams listed above are designed for use with headers. In fact, GM engineers will tell you that the Hot Cam will make less power than stock cam if you don't put headers and free flow exhaust on the car. The reason is these cams all have intake exhuast/overlap for scavenging action that you can only get with headers.
The GM Performance catalog I have specifically says the kit (12480033) is designed to be used on engines with no other modifications. And I don't believe that a GM engineer would tell you the hotcam will make LESS horsepower than the stock cam without headers.
#18
Originally Posted by LSUxBlake
The GM Performance catalog I have specifically says the kit (12480033) is designed to be used on engines with no other modifications. And I don't believe that a GM engineer would tell you the hotcam will make LESS horsepower than the stock cam without headers.
#19
i'm probably wrong, but i always through turbo cars used less exhaust duration to get the gas velocity higher. NA cars with more restrictive exhaust would want an exhaust bias to allow more time for the gases to escape.
#20
Originally Posted by LSUxBlake
I don't believe that a GM engineer would tell you the hotcam will make LESS horsepower than the stock cam without headers.
Last edited by Cal; 02-03-2005 at 07:28 PM.