cam question
Safety Car
Joined: Aug 2000
Posts: 3,711
Likes: 43
From: San Antonio TX
In some cases. But it depends. Two cams with the same duration and one with a wider LSA will retard the intake closing point which bleeds off low rpm cylinder pressure but has a lower overlap event. Tighter LSA also doesn't unto itself cause low vacuum. With a tight LSA, you can loose vacuum due to the overlap and the more duration you have, the greater your overlap event. This overlap pollutes the intake mixture and causes weak cylinder pressure, which means lower vacuum. This charge dillution, by the way, is also what gives the cam the rumpty-rumpty sound at idle. A cam with modest duration (say around 220 at .050)with a wide 114 degree LSA will have higher idle vacuum than the same duration with tight 110 LSA because you still have efficient combustion at idle. But one component that matters is compression ratio. It kind of skews the result.
My best take on this is that it's hard to use absolutes on the affects of a cam unless you specify all the parameters.
My best take on this is that it's hard to use absolutes on the affects of a cam unless you specify all the parameters.
Thread Starter
Team Owner
Joined: Apr 2002
Posts: 62,198
Likes: 1
From: All humans are vermin in the eyes of Guru VA
Cruise-In IV Veteran
Cruise-In V Veteran
234/242 duration at .050
I have a choice of 112 or 110 LSA
110 LSA was recommended because I want to start roadracing.
If I move to 233/244 I can adjust my LSA anyway I want, plus the lift is more inline with what I am looking for.
I have a choice of 112 or 110 LSA
110 LSA was recommended because I want to start roadracing.
If I move to 233/244 I can adjust my LSA anyway I want, plus the lift is more inline with what I am looking for.
Thread Starter
Team Owner
Joined: Apr 2002
Posts: 62,198
Likes: 1
From: All humans are vermin in the eyes of Guru VA
Cruise-In IV Veteran
Cruise-In V Veteran
Yes that is the conundrum.
I am thinking the 112 or a 114. The corners well will be tire limited more than engine limited.
I am planning on keeping my 3.55 rearend and 2.5" ramhorms.
I am thinking the 112 or a 114. The corners well will be tire limited more than engine limited.
I am planning on keeping my 3.55 rearend and 2.5" ramhorms.
Thread Starter
Team Owner
Joined: Apr 2002
Posts: 62,198
Likes: 1
From: All humans are vermin in the eyes of Guru VA
Cruise-In IV Veteran
Cruise-In V Veteran
I am theorizing. I havent driven the car in a couple of years. I am building an engine, rebuilding the suspension, and putting in new brakes and seats this winter.
I think having working brakes and a smoother idle will trump a little bit of torque in the corners.
I will be running 255/50-17 tires, so the amount of torque will be limited by the tires.
I think having working brakes and a smoother idle will trump a little bit of torque in the corners.
I will be running 255/50-17 tires, so the amount of torque will be limited by the tires.
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Le Mans Master
Joined: Jul 1999
Posts: 9,206
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From: Sewell NJ
I have a Crane Powermax dual pattern in my car. It's got 216 degrees intake and 228 degrees exhaust duration at .050 and 112 degree lobe centers. The idle is noticeable but the engine will idle down to a lumpy 750 rpm. I usually keep it at 800~850 rpm at idle and I get about 14~15 inches of vacuum and have no problem with the vacuum systems on the car.