Cam experts? Need Help.
Thread Starter
Racer
Joined: Apr 2003
Posts: 349
Likes: 0
From: Katy TX
Cam experts? Need Help.
I want to change out my cam, currently I have a 502/516 238/244 duration 106 lob seperation, it has a pretty bad rough idle. I want to go with something like a 562/580 248/254 duration with a lobe seperation of about 112 . Will the higher lobe seperation result in a smoother idle? What gives it a rough idle, the lobe seperation or the duration? By the way this is all @ 0.50
Race Director
Joined: Sep 1999
Posts: 11,360
Likes: 382
From: Plano TX
Re: Cam experts? Need Help. (bhmyers)
Rough idle is caused by overlap, which is the time that both intake and exhaust valves are open at the same time. Exhaust gets pushed back into the intake causing irregular mixtures.
Overlap is increased when lobe separation (LSA) is decreased. Lower LSA means the intake and exhaust lobes are closer together, which makes the time they are both open longer.
Longer duration also increases overlap since the lobes are "wider".
To answer your question: The new cam you listed will also have a very rough idle due to the long duration. If you post all your specs (size, compression, heads, intake, exhaust, gearing, tranny, intended usage) there are several people on the forum that can give you recommendations.
Overlap is increased when lobe separation (LSA) is decreased. Lower LSA means the intake and exhaust lobes are closer together, which makes the time they are both open longer.
Longer duration also increases overlap since the lobes are "wider".
To answer your question: The new cam you listed will also have a very rough idle due to the long duration. If you post all your specs (size, compression, heads, intake, exhaust, gearing, tranny, intended usage) there are several people on the forum that can give you recommendations.
