Overlap in cams is good for FI cars
02-07-2005, 10:27 PM
#1
0.0 BAR
Thread Starter
Join Date: Jun 2003
Posts: 0
Overlap in cams is good for FI cars
I stole this from Jeff Evans at www.Boosted-hybrid.com I thought would be pretty good info for this site since lots of people here are running log manifolds;
"Its been a trend lately to just "run gsr/itr cams without cam gear adjustment". Most cars that i tune do not have cam gears, so adjustment is not possible in most tuning sessions. After experimenting with cam gears on the last few cars i have been pleasantly shocked picking up 30-50whp, and 30-40 ft-lbs of torque at the same boost level with just cam gear adjustments. Gains were able to be made all over the place. Basically free horsepower. Here is an example of a car that i tuned on Sat with some cam gear adjustments:
The intake was +4, exhaust was -2. This is opposite of what people recommend for tuning turbo cars. I am dialing in overlap, not out. The other engines have been anywhere from +3 to +5 on the intake, and -1 to -3 on the exhaust. My thoughts on the matter are that with log manifolds (this car was using one), scavenging goes to crap. Increasing the breathing of the engine opens up the engine with the higher exhaust pressure from running the log manifold, and allows for less exhaust gas contamination to occur. I noticed that the plugs burnt much better after the cam gear adjustment, as well as less ignition advance needed to be run (and not because of retarding the ignition timing since the intake cam was advanced)"
"Its been a trend lately to just "run gsr/itr cams without cam gear adjustment". Most cars that i tune do not have cam gears, so adjustment is not possible in most tuning sessions. After experimenting with cam gears on the last few cars i have been pleasantly shocked picking up 30-50whp, and 30-40 ft-lbs of torque at the same boost level with just cam gear adjustments. Gains were able to be made all over the place. Basically free horsepower. Here is an example of a car that i tuned on Sat with some cam gear adjustments:
The intake was +4, exhaust was -2. This is opposite of what people recommend for tuning turbo cars. I am dialing in overlap, not out. The other engines have been anywhere from +3 to +5 on the intake, and -1 to -3 on the exhaust. My thoughts on the matter are that with log manifolds (this car was using one), scavenging goes to crap. Increasing the breathing of the engine opens up the engine with the higher exhaust pressure from running the log manifold, and allows for less exhaust gas contamination to occur. I noticed that the plugs burnt much better after the cam gear adjustment, as well as less ignition advance needed to be run (and not because of retarding the ignition timing since the intake cam was advanced)"
02-07-2005, 11:34 PM
#5
0.0 BAR
Join Date: Dec 2002
Posts: 0
Re:Overlap in cams is good for FI cars
Originally Posted by Kyle
Originally Posted by Whitey
Most cars that i tune do not have cam gears
oh wait thats gm. i guess he pushes the chromoly pushrods up and down
02-07-2005, 11:35 PM
#6
3.0 BAR
Join Date: Jan 2003
Posts: 7,082
Re:Overlap in cams is good for FI cars
Originally Posted by random-strike
Originally Posted by Kyle
Originally Posted by Whitey
Most cars that i tune do not have cam gears
oh wait thats gm. i guess he pushes the chromoly pushrods up and down
and yes, I was being sarcastic, I know the timing belt just hooks up the the vtack cylenoyed, duh.
02-07-2005, 11:36 PM
#7
0.0 BAR
Join Date: Dec 2002
Posts: 0
Re:Overlap in cams is good for FI cars
Originally Posted by Kyle
Originally Posted by random-strike
Originally Posted by Kyle
Originally Posted by Whitey
Most cars that i tune do not have cam gears
oh wait thats gm. i guess he pushes the chromoly pushrods up and down
and yes, I was being sarcastic, I know the timing belt just hooks up the the vtack cylenoyed, duh.
yea a lil. im tryni to get stoned so i can fall asleep tonighit.
02-08-2005, 12:06 AM
#8
3.0 BAR
Join Date: Apr 2003
Posts: 2,579
Re:Overlap in cams is good for FI cars
This is confusing because more overlap causes less cylinder pressure. the reason people raise compression, use nitrous, or turbos is to increase cylinder pressure. now he says he uses more over lap and less timing. So thnk about having a car that has too much boost or compression, and you're detonating, you would use more overlap or less timing to fix the problem. How would more overlap (less cylinder pressure) and less timing cause more power. That doesn't make much sense unless the initial tune was so bad that the spark was blowing out. I don't know but taht doesn't make much sense to me.Maybe hes got it backward and hes actually getting less over lap.
02-08-2005, 12:11 AM
#9
0.0 BAR
Thread Starter
Join Date: Jun 2003
Posts: 0
Re:Overlap in cams is good for FI cars
Originally Posted by fork
This is confusing because more overlap causes less cylinder pressure. the reason people raise compression, use nitrous, or turbos is to increase cylinder pressure. now he says he uses more over lap and less timing. So thnk about having a car that has too much boost or compression, and you're detonating, you would use more overlap or less timing to fix the problem. How would more overlap (less cylinder pressure) and less timing cause more power. That doesn't make much sense unless the initial tune was so bad that the spark was blowing out. I don't know but taht doesn't make much sense to me.Maybe hes got it backward and hes actually getting less over lap.
Did you read that the increased overlap might be preventing contamination from the reversion effects of the log manifolds?
p.s. Can the drunks go ---- up G.D and not the tech threads, thanks.
02-08-2005, 12:17 AM
#10
0.0 BAR
Join Date: Dec 2002
Posts: 0
Re:Overlap in cams is good for FI cars
Originally Posted by Whitey
Originally Posted by fork
This is confusing because more overlap causes less cylinder pressure. the reason people raise compression, use nitrous, or turbos is to increase cylinder pressure. now he says he uses more over lap and less timing. So thnk about having a car that has too much boost or compression, and you're detonating, you would use more overlap or less timing to fix the problem. How would more overlap (less cylinder pressure) and less timing cause more power. That doesn't make much sense unless the initial tune was so bad that the spark was blowing out. I don't know but taht doesn't make much sense to me.Maybe hes got it backward and hes actually getting less over lap.
Did you read that the increased overlap might be preventing contamination from the reversion effects of the log manifolds?
p.s. Can the drunks go ---- up G.D and not the tech threads, thanks.
but i bet he is thinkin about a really free flowing good system looking for max power potential
