cam size = x amount of vaccum

Originally Posted by 289nate

So nobody thinks things like cubic inches might play a role? I wouldn't put any faith in such a calculation unless it took a BUNCH of things into consideration. Bore, stroke, just about every aspect of the valve events, true compression, heads, intake, exhaust, etc, etc, etc...

It was a "general" question, of course I think all the things you listed would affect the vaccum,but, unless you have a custom ground cam that is way out of this world most cams such as the ones Spali and Baron have are going to be in the same ball park. My solid roller is a little bigger than Spali's but they are in the same ball park. Barons cam is slightly gigger than mine on advertised duration and wow, it ha slightly less vaccum. I was not asking you to solve world hunger or anything like that!
Fe,the same mechanical process that creates compression, creates vaccum. the N/A cylinder/piston will only compress the amount of air that it has drawn in. The cylinder/piston drawing in air is what creates vaccum.

If you feel confident in a couple people stating that their combo is (or they think is) a certain vacuum then good for you. Are you even curious about what rpm the vacuum was taken? I think Spali is about 1,100 rpm. Again, I wouldn't put much faith in a basic formula like you seem to be asking about. Maybe you'd get the same vacuum as these guys are talking about. However, nobody can tell you for sure without knowing a good amount of detail about your combo.

So we have a certain amount of vacuum with a stock 5.0L HO shortblock with stock heads and a regular performer carb intake with a 600 cfm carb. Now add an AFR 225 head with a super victor intake and 850 cfm carb with an appropriate exhaust. What happens to the vacuum at idle?

Oh I know for sure it was 9" of vacuum. Used a real vacuum gauge, I did.

Has anyone else actually hooked a vacuum gauge to their engine and checked the vacuum at idle? If so, what are your cam's specs? Just for shirts and giggles...