Blow-Thru/vacuum advance????
I am running a Vortech S-Trim V-1 on a Dodge 360 Magnum in an old Valiant sedan and I drive it on the street a lot, with an occasional trip to the strip for some Bracket racing.
It's a blow-thru setup with a Holley 750 double-pumper, and the distributor is a Mopar Performance stock-type magnetic pickup unit that has a slightly modified curve in it.
It also has a vacuum advance diaphragm that was factory-calibrated for ported vacuum.
I am curious as to whether I might be able to access the ported vacuum signal on this Holley 4bbl and use it to increase spark advance at low-throttle (cruise) conditions.
I know that normally-aspirated engines, under cruise conditions, run cooler and get better gas mileage with an operating vacuum advance unit.
What I don't know is this: Will the ported vacuum in the fitting at the base of this blow-thru carburetor "go away" if the throttle blades open and the boost that is already in the supercharger air delivery pipe begins to enter the intake manifold, or, will there be some residual vacuum in this line at the fitting, since it's ported and not manifold vacuum???
It's a mystery to me, but somebody who knows Holley carburetors should be able to tell me the answer to that, I am sure.
If it's possible (yea, "feasible") to use a vacuum advance for cruising, yet have the vacuum signal DIE instantly, as soon as the throttle blades open, I'd like to try it.
But, if that vacuum signal doesn't go away imediately (if, indeed, there is EVER a vacuum signal at the ported fitting), then I think it's not going to be do-able.
Anybody got solid information about this tantalizingly confusing question???
If nobody knows, I guess I can put a vacuum gauge on that fitting, and run a line to the cockpit, and watch it as I drive the car.... but, I thought I'd ask, first.
Any information will be appreciated!
Thanks!