Should my very non emissions engine vacuum advance be connected to full manifold vacuum or to ported vacuum?
Depends. Some cars came one way, some the other. Buick straight is/was ported. What engine are you inquiring about? Ben
It depends on what you like. In general, the engine doesn't care. Once you open the throttle, ported and straight vacuum advance operate exactly the same. I run straight vacuum on my nailhead because I have an automatic transmission and it gives me a soother idle.
Engine is a Willys 134L now making 140cuin Compression is now 7.2-1 Stock cam Carb is a Weber DGV-5A exhaust is a Tri Y design. Ignition is Points with a MSD-6D spark box the Distributor is a 1961 Autolite IAT-4405 (would have been stock in a 61 FC-150 with the 134F) I just changed it from Ported Vacuum to Manifold Vacuum and put my Fresh air intake on and added about 3 degrees of timing (now 12BTDC) and shaved a full second off my 1/4 mile time and gained 3mph its currently 23.6 sec. at 55mph. On the last Dyno run it showed 46.23HP at the rear wheels.
Am I correct that ported vacuum gives NO advance at idle and Manifold would be full vacuum advance at idle? Cruising will have max either way, wot will have min either way? Ben
I think it’s engine dependent. Many engines won’t start, or have a hard time cranking over with 15-18 initial, but will idle just fine at that, and even more. Other engines will get throttle tip in ping/detonation off idle with too much advance. Starting an engine with ported or manifold vacuum, should be about the same. I’d imagine the engine is making some vacuum when cranking over, never checked how much though. Really comes down to what the engine likes/wants?
I'm a sbc guy, and have always used manifold vacuum for my distributors. I like it all in around 2500 rpm. Just me. When timing it, I disconnect vacuum advance, if I'm using one, and bring rpm's up to 3000, then advance the distributor until the engine just starts running rough, then back it down slightly until it smooths out. Clamp the distributor tight and go. I only use a timing to verify that my advance is working.
Well Bob....I'm a SBF guy and I don't use vacuum advance, I have a timing tape on my balancer and I use a timing light to actually see what my engine /timing is doing. Nothing like KNOWING how many degrees of advance I have at a given RPM. I usta keep advancing the initial timing until the warm engine struggled to crank and then...back of a dab. Got tired of guessing where my timing was! Whatever works for you I suppose..... 6sally6
Mark - WHY....ask, really ? It takes three seconds to swap the vacuum line from one port to the other...right ? Do some driving (75+ miles), check your mileage carefully, pay attention to the seat of the pants "feel". Then, swap the vacuum line to the "other" port, and do the same. Check your mileage (the same 75+ miles), pay attention to your...seat of the pants feel. How does the engine perform, overall at each port ? How does the engine "run best"...at each port ? YOU pick..! Mike
I know use manifold vacuum on sbc. That allows a smooth idle at lower rpm, so it is easier to hold the auto trans in drive at a stop light.
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