[gtofreek]

Originally Posted by pastry_chef

Yes, exactly.

The intake valve close event is by far the largest factor. Second would be the exhaust valve open event.

I would disagree with that statement. I've made many engines quit detonating by advancing their cams.



Instead, I would restate that comment as the biggest factor in detonation would be the valve opening difference between the intake valve and the exhaust valve at TDC during overlap. Retarding the cam causes the exhaust valve to be open more, and the intake open less at TDC so when the piston starts down the hole, for the first few degrees it is sucking harder on the exhaust port and trying to suck hot exhaust gasses back in which I feel are the main ingredient for detonating. I like to see the intake valve open between .035 and .040" more than the exhaust at TDC during overlap on 110° LSA cams. Wider lobe seps will bring these numbers closer so with 112 LSA the difference will be more like .025"-.035". If your exhaust valve is open close to the same amount as the intake at TDC during overlap, then your engine will almost certainly detonate without low compression. Looking at it this way, I have built quite a few 10:1+ iron headed engines that ran fine on 91.