Widening the LSA can be tuned to decrease the chance of detonation and improve low end and idle quality..

The duration of the cam must be adjusted for any major rpm range changes..

The lift and size of the valves, will effect the flow potential and velocity of any given head design and cam duration.. Too much flow and duration, without enough compression to keep the velocity up, will cause poor performance and poor intake vacuum.

It goes on and on... .. It's best to tell the cam maker exactly what you are putting it in and what you want out of the combination.. They have computers to take the guess work out of it..

quote:

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Originally posted by Clevo377:
If everything else stays the same. What effects would changing the LSA of a cam be. Say, if you went from 104��to 106�� to 108�� to 110�� to 112�� Is 2��going to make a noticable difference? if so what effect will 8��have?

Paul

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You want some overlap because the exiting exhaust gases have a velocity, and the momentum of them leaving draws intake gases in more effectively than if the valve was shut before the intake opened. Of course you do not want intake gases exiting out the exhaust port either.

How much overlap is sort of a black art, I'll leave it to the cam manufacturers. But generally more overlap will bring your power peak to a higher RPM.

So if I had two cams, one with 250��and 104��LSA, and the other 260��with 108 or 110 LSA. Would they be similar? (given they are installed on the same intake centreline) i.e how much effect does a couple of ��in the LSA make. Is overlap the main thing that is affected?

I guess an application for this would be if I wanted to obtain higher lift, but given the profiles available I had to go for a longer than optimal duration, I could custom grind the specific cam at a wider LSA to make up for the lost bottom end.

Alternatively, If I wanted more top end but wanted to keep the lift at a reasonable level for reliablility/maintenance reasons, I could grind less LSA into the cam to get where I want to be.

http://www.nightrider.com/biketech/camlsatable.htm

Here's another one:

http://www.wighat.com/fcr3/confusion.htm

Decreasing lobe seperation:
1. narrows the powerband
2. moves the powerband lower
3. makes the idle choppier
4. makes more power
5. pumps up the midrange

Increasing lobe seperation
1. widens powerband
2. makes the idle smoother
3. takes away from the midrange
4. produces less maximum power

Racers usually use tight lobe seperations. The only exceptions are Pro-Stock, where 500+ ci are revved to the moon with cams so HUGE, tight LSA's produce too much overlap, and nitrous/blower/turbo applications where overlap sends all that extra fuel mixture out the tailpipe!

Tight lobe seperations increase overlap and can help increase velocity in overly huge intake ports (4bbl 351C). This will pump up the midrange, and make the engine feel less "lazy". Some 351C drag race cams have lobe seperations as low as 102-104 degrees. Automatics generally need a tighter lobe seperation for extra midrange.

Small engines with big ports LOVE tight lobe seperations, large engines with small ports work better with wider angles between the lobes.

A tighter lobe seperation also allows you to use a slightly larger cam in a lower rpm range. If you want maximum valve timing without revving the engine to the moon, a tighter lobe seperation can make it happen.

Good Luck!