Lets talk valve timing....

[AZ3.8Camaro]

I want to know some of the specs on stock cam as far as the intake and exhaust opening and closing points.

On our engines...
What is ideal for the intake opening point?
A very little bit before the piston reaches TDC?
maybe 4 degrees? Or would it be best to open right at TDC?

Exhaust closing?
just a tad after TDC? We want to create that vacuum effect, but don't want to overdo it.

Exhaust opening?
I know that an early exhaust opening can create a more pronounced exhaust tone, but I want to go for performance. So I am thinking around 35-40 degrees before BDC.

Intake closing?
I am guessing a number similar to the exhaust, or around 30-35 degrees Above BDC? This is very important to compression so, I think a lower intake closing might be benificial to our already low compression motors. But then again, the flow of the air is still coming in after BDC, so you could get more air in...

Anyone want to get a good discussion going?
[img]graemlins/thumbsup.gif[/img]

[Dominic]

The problem with looking at it like that is everything is interrelated. If you stop for a moment and decide on a set lobe size (lift/dur) for int/exh, you'll be able to play with the valve timing.

I've found that retarding the cam by pushing up the intake centerline is better on the 6, wheras a more advanced cam seems to work better in old school V8s or LS1s. Its an oddity... The little Honda 4 bangers like straight up cams, LS = IC essentially... Then of course they have VTEC, which is nothing more than valve timing [img]smile.gif[/img]

Anyone who thinks valve timing isnt important, tell that to Honda with their VTEC, or VVTi if you like yodas. IMO Valve timing is more critical than actual lobe sizing, especially the intake closing point.

[AZ3.8Camaro]

<blockquote>quote:</font><hr>Originally posted by Dominic:
IMO Valve timing is more critical than actual lobe sizing, especially the intake closing point.<hr></blockquote>

Agreed. It is important becuase it is actually what determines compression. What do think would be a good number for Intake closing? I know it should be after BDC (which seems like it would waste compression) but you can still ram some air in there from the "momometum" (if you will) or the incoming air. It is crucial to find a balance there.

Another question I have is about clearance...
How do I find how much I can deck the heads?
I want to shave as much as I can off.
The intake doesn't really open until TDC So I don't think there will be much of a clearance problem.

The exhaust valve should be the only problem.
It closes at 8 degrees before TDC, which shouldn't really yeild too many problems.

What would stop me from milling the heads .040"?

[ September 25, 2003: Message edited by: AZ3.8Camaro ]

[ September 25, 2003: Message edited by: AZ3.8Camaro ]</p>

[Ex-5.0]

<blockquote>quote:</font><hr> I've found that retarding the cam by pushing up the intake centerline is better on the 6, wheras a more advanced cam seems to work better in old school V8s or LS1s. Its an oddity... <hr></blockquote>

Advancing the cam helps low RPM torque but reduces high RPM torque. Retarding the cam helps high RPM torque to the detriment of low RPM torque.

Regarding cam timing, it all depends on RPM range. On stock engines more duration will probably not help much because of the restrictions in the stock intake and exhaust tracts.

[AZ3.8Camaro]

I want a higher rpm range powerband, I will be shifting around 6500 rpms or so.