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.
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02 lightning all stock
99 mustang gt Tork Tech terminator kit making a little boost
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