ported heads technical question
 

has anyone installed ported heads, especially ones with oversized valves, noticed a decrease in engine vacuum at idle? if yes how much? thanks

Where more aggressive cams used also?

well, i had stage 2 patriot performance heads and i upgraded to stage 3 heads with larger valves and more porting. i used the same cams in both but i have lost about 8 in of vacuum. i do have a more efficient intake manifold also with a slightly larger supercharger. i upgraded from an m90 to an m112. the low vacuum is giving me a rough idle. i suspect the heads are at least helping with the loss.

they are cms (vt) stage 2 blower cams so the are a little aggressive