Originally posted by Henry Rifle
Nice article, lots of good info. It brings up one question, however: If manifold vacuum is the real deal, why do the instructions for just about every Chevy crate motor on the market recommend connecting to ported vacuum?

I am not disputing your method or reasoning, just wondering . . .

I didn't know the Chevy crate motors came with that recommendation, but where part of the confusion (I think) comes from is that the Carter and Edelbrock instruction/install sheets recommend using the ported side.

The part I don't like about using ported vacuum - aside from the overheating problems it sets up in most cars - it keeps adding advance as air flow - pressure differential - through the venturi increases due to engine speed.
The pressure differential can be altered due to throttle settings as well.


I ran some interesting tests on my roadster as pertains to vacuum levels from each source.
Had a vacuum gauge connected to full time vacuum and another connected to ported.vacuum.
If I can find it, I'll post it.
Reason I say "if" is that I think it's in my old computer which seems to have a mind of it's own as far as giving up info goes....