cam experts step inside.
Thread Starter
Melting Slicks
Joined: Sep 2000
Posts: 3,150
Likes: 1
From: Carlsbad, CA CA
cam experts step inside.
For those of you that are cam experts, how much overlap is too much? Is 14 degrees too much?
Also, Should a blower cam have more lift on the intake side or the exhaust side?
TIA,
Paul
Also, Should a blower cam have more lift on the intake side or the exhaust side?
TIA,
Paul
Le Mans Master
Joined: Jan 2001
Posts: 5,786
Likes: 6
From: Lafayette Colorado
Normally S/C cams have more exhaust duration and lift. This is because the S/C is forcing the air into the cylinders, so it is more important to have more exhaust duration and lift to help remove the combusted fuel/air. As far as how much overlap, it really depends on several factors: CID of motor, flow rate of the S/C, overall power goals, and so on.
Keith
Keith
Pro
Joined: Nov 2003
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From: herminston oregon
overlap
Originally Posted by zelement
For those of you that are cam experts, how much overlap is too much? Is 14 degrees too much?
Also, Should a blower cam have more lift on the intake side or the exhaust side?
TIA,
Paul
Also, Should a blower cam have more lift on the intake side or the exhaust side?
TIA,
Paul
Thread Starter
Melting Slicks
Joined: Sep 2000
Posts: 3,150
Likes: 1
From: Carlsbad, CA CA
Originally Posted by Loboost
I think he meant 114 degrees.
Les
Les
is everyone on the same page here?
I am talking about overlap not lobe seperation.
From what I understand, the more overlap a cam has the more the lumpier the idle and less vaccum because all the air is getting blown out the exhaust. I seriously doubt a stock cam will have 50 degrees or 114 degrees of overlap.
All I am asking is what is an acceptable amount of overlap for a blown motor?
Last edited by zelement; Feb 18, 2005 at 02:19 AM.
Drifting
Joined: Jun 2002
Posts: 1,340
Likes: 1
From: hamilton nj "Life's tough......It's even tougher if you're stupid."-John Wayne
it will probably sound like a model a ford. i could be wrong
What he ment to say was:
The period when both valves are both a little bit open at the same time is called "overlap." Small overlap produces more torque at low engine speeds, but not so much at high speeds. Large overlap produces lower torque and low engine speeds, but more power as the engine runs faster.
As overlap is decreased, the engine loses the ability to run at high speed, but it might pull like a tractor at low speeds. Small overlap prevents exhaust from entering the intake manifold at slow speeds, but can't pull that extra intake charge at high speeds.
As overlap is increased, the engine produces more and more power at high speeds, but it has more and more trouble idling and running smoothly at low speeds. Large overlap can allow exhaust to be pushed backwards into the intake at slow speeds, but serves to charge the cylinders with more fresh air/fuel mixture at high speeds.
What he ment to say was:
The period when both valves are both a little bit open at the same time is called "overlap." Small overlap produces more torque at low engine speeds, but not so much at high speeds. Large overlap produces lower torque and low engine speeds, but more power as the engine runs faster.
As overlap is decreased, the engine loses the ability to run at high speed, but it might pull like a tractor at low speeds. Small overlap prevents exhaust from entering the intake manifold at slow speeds, but can't pull that extra intake charge at high speeds.
As overlap is increased, the engine produces more and more power at high speeds, but it has more and more trouble idling and running smoothly at low speeds. Large overlap can allow exhaust to be pushed backwards into the intake at slow speeds, but serves to charge the cylinders with more fresh air/fuel mixture at high speeds.
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Drifting
Joined: May 2001
Posts: 1,770
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From: IL
So, after reading Budmonts professional explaination, I might add, to answer you question, on a SC car, you want less overlap, otherwise you will bleed off boost. Good Luck....
And BTW this doesn't make me a cam expert, just my .02
And BTW this doesn't make me a cam expert, just my .02
Team Owner
Joined: Jul 2002
Posts: 37,048
Likes: 69
From: This city NEVER sleeps! Frank's back yard!
Originally Posted by 3XBlack6spd
So, after reading Budmonts professional explaination, I might add, to answer you question, on a SC car, you want less overlap, otherwise you will bleed off boost. Good Luck....
And BTW this doesn't make me a cam expert, just my .02
And BTW this doesn't make me a cam expert, just my .02
Yes - less overlap, more duration on the exhaust - fine line.
Pro
Joined: Nov 2003
Posts: 532
Likes: 0
From: herminston oregon
overlap
Originally Posted by budmont
it will probably sound like a model a ford. i could be wrong
What he ment to say was:
The period when both valves are both a little bit open at the same time is called "overlap." Small overlap produces more torque at low engine speeds, but not so much at high speeds. Large overlap produces lower torque and low engine speeds, but more power as the engine runs faster.
As overlap is decreased, the engine loses the ability to run at high speed, but it might pull like a tractor at low speeds. Small overlap prevents exhaust from entering the intake manifold at slow speeds, but can't pull that extra intake charge at high speeds.
As overlap is increased, the engine produces more and more power at high speeds, but it has more and more trouble idling and running smoothly at low speeds. Large overlap can allow exhaust to be pushed backwards into the intake at slow speeds, but serves to charge the cylinders with more fresh air/fuel mixture at high speeds.
What he ment to say was:
The period when both valves are both a little bit open at the same time is called "overlap." Small overlap produces more torque at low engine speeds, but not so much at high speeds. Large overlap produces lower torque and low engine speeds, but more power as the engine runs faster.
As overlap is decreased, the engine loses the ability to run at high speed, but it might pull like a tractor at low speeds. Small overlap prevents exhaust from entering the intake manifold at slow speeds, but can't pull that extra intake charge at high speeds.
As overlap is increased, the engine produces more and more power at high speeds, but it has more and more trouble idling and running smoothly at low speeds. Large overlap can allow exhaust to be pushed backwards into the intake at slow speeds, but serves to charge the cylinders with more fresh air/fuel mixture at high speeds.
you can go to vinci web site, he list the amount of overlap for each cam. a cam with 212 in, 218ex.....550in lift, 550ex lift, on 114 lobe centers has 52 deg of overlap. that would be at 50 thousands. i could be wrong on lift numbers, but that would make a good mild SC cam. also the stock LS6 cam works good. 
Thread Starter
Melting Slicks
Joined: Sep 2000
Posts: 3,150
Likes: 1
From: Carlsbad, CA CA
Originally Posted by budmont
it will probably sound like a model a ford. i could be wrong
What he ment to say was:
The period when both valves are both a little bit open at the same time is called "overlap." Small overlap produces more torque at low engine speeds, but not so much at high speeds. Large overlap produces lower torque and low engine speeds, but more power as the engine runs faster.
As overlap is decreased, the engine loses the ability to run at high speed, but it might pull like a tractor at low speeds. Small overlap prevents exhaust from entering the intake manifold at slow speeds, but can't pull that extra intake charge at high speeds.
As overlap is increased, the engine produces more and more power at high speeds, but it has more and more trouble idling and running smoothly at low speeds. Large overlap can allow exhaust to be pushed backwards into the intake at slow speeds, but serves to charge the cylinders with more fresh air/fuel mixture at high speeds.
What he ment to say was:
The period when both valves are both a little bit open at the same time is called "overlap." Small overlap produces more torque at low engine speeds, but not so much at high speeds. Large overlap produces lower torque and low engine speeds, but more power as the engine runs faster.
As overlap is decreased, the engine loses the ability to run at high speed, but it might pull like a tractor at low speeds. Small overlap prevents exhaust from entering the intake manifold at slow speeds, but can't pull that extra intake charge at high speeds.
As overlap is increased, the engine produces more and more power at high speeds, but it has more and more trouble idling and running smoothly at low speeds. Large overlap can allow exhaust to be pushed backwards into the intake at slow speeds, but serves to charge the cylinders with more fresh air/fuel mixture at high speeds.
thanks for the explanation.
I know what overlap is and I know a lot of "overlap" is not recommended with FI cars. However, the question is, what should be a good amount of overlap for FI cars.
VortechC5,
Yes, I believe it is 14 degrees @ .050. Is that too much?
Do you know the amount of overlap on your cam?
Drifting
Joined: Jun 2002
Posts: 1,340
Likes: 1
From: hamilton nj "Life's tough......It's even tougher if you're stupid."-John Wayne
[QUOTE=zelement]Bud,
thanks for the explanation.
I know what overlap is and I know a lot of "overlap" is not recommended with FI cars. However, the question is, what should be a good amount of overlap for FI cars.
Had no doubt that you knew, was just trying to explain why MYBLACKC5 said "it will probably sound like a model A Ford"
thanks for the explanation.
I know what overlap is and I know a lot of "overlap" is not recommended with FI cars. However, the question is, what should be a good amount of overlap for FI cars.
Had no doubt that you knew, was just trying to explain why MYBLACKC5 said "it will probably sound like a model A Ford"