Hot Rod Forum : Hotrodders Bulletin Board - View Single Post - Ported -vs- Manifold - Vacuum Advance Scenario
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Old 01-12-2009, 01:36 AM
techron techron is offline
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curtis, with all due respect, i stand by my statement. i have been messing with engines since the late 60s and was a professional mechanic for 30 years, so have probably built, tuned and modified more engines than most here with the exception of a few older guys who have been doing this for a living all their lives as i have. the OP asked a simple question and i gave a simple answer. while i agree with some of your statements, like each engine has to be tuned for what it likes-initial timing, total cintrifigal, total vacuum. i assume the OP knows this, otherwise i'm wasting my typing finger .

every car from any factory has an RPM controlled advance (centrifigal or computer controlled) advance curve to make the engine performs best at full throttle. the vacuum advance is to get the engine to perform best at cruise/high vacuum conditions, idle is a high vacuum condition with a stock or mild cam. the combo of centrifigal and vacuum works very well, just tweak them to suit your engine. don't try to outguess the factory engineers who designed these advance systems that are on millions of cars.

it sounds to me from your post like you are trying to use the vacuum advance for a substitute for centrifigal advance and locking the dist. at 36*. how does that engine crank with 36* advance without kicking back??? how is it at 1000/1500/2000 RPMs at full throttle with 36* advance???

i used to work on many 60s high compression, high performance corvettes in the 70s and they all used manifold vacuum. when the ported vacuum cars started showing up out here in cal. to meet smog regs. i would ALWAYS switch them to manifold vacuum-every customer would come back and say "HOLY CRAP, what did you do to my car, it runs tons better". out here in the early 70s the first smog regs. required all cars to have a kit installed on the upper rad. hose to lock out the vacuum advance until the engine reached hi temps. customers were pissed at the crappy performance. i would just tell them "come back after you pass the smog test and i'll hook you back up to full manifold vacuum"

SO, i stand by my earlier post:

ALWAYS use manifold vacuum...

PS: i still work on early vettes, i'm doing a body off resto-mod on my 64 coupe. i built a 383 stroker with 10.7-1CR (but i know how to make it live on pump gas) i'm also helping a friend/noob 65 vette owner build a late engine 383" stroker because he wants to be faster at the strip...

to the OP----> go with MANIFOLD VACUUM-->ALWAYS...
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