I would like to thank everybody for your input on this thread. I think it is getting pretty interesting and I'm learning.
Quote:
Originally Posted by 68 P.O.S.
I take it you didn’t read the links I posted. Vacuum advance is only meant to be supplemental for when it is needed (in low load situations like idle and cruise so it can burn the lean mixture more efficiently, keep the engine cooler, and improve mileage and streetability), not used as your primary means of advance. That’s what the mechanical advance is for. What distributor do you have and how many degrees of mechanical advance does it have? How much vacuum are you pulling at idle? The crate engine heads you have on it, are they vortec or standard heads?
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I did read the links. I recognized all of them and I've had them bookmarked before. I can't say I understand all of it, but I think perhaps I understand a little more each time I read them. I'm a novice, and I show it at the beginning of this thread where I didn't have much of a clue about how to use the timing light or the timing marks and didn't know how many degrees per mark.
I have a GM HEI distributor that a friend gave me. I don't know what vehicle it came out of. I've been looking for a part number stamp on it but don't see it. Perhaps it is inside. I will look some more. The vacuum advance can was damaged and it didn't work. Another friend shade tree mechanic put the current vacuum advance on it, and I don't know how it was selected, I just know it was new from O'Reilly Auto Parts. He set the timing, had trouble figuring out the timing light, and the engine was working OK but pinging sometimes while driving. Then I picked up from there and started this thread late last year.
I am getting more involved with the mechanics of this truck. Now you guys are getting me interested in tuning. I don't have a vacuum gauge but now I'm interested in getting one. I don't know how much mechanical advance the distributor has. I don't know what type of heads the engine has. The casting number is 10147898. After reading all the great info on this forum that you guys offer up, I have recently moved my vacuum advance from ported to manifold vacuum.
When I brought this thread back to life the other day I was interested in knowing the technical details about
: if most total advance you can go with your timing without causing detonation is desirable, why is higher amount of vacuum advance not better than smaller amount of vacuum advance?
Please tell me if I figured out the answer from input from you guys and the links provided that I have been reading. I want the maximum total advance you can get at wide open throttle and heavy loads without causing detonation. If I have a lot of vacuum advance, and adjust the initial timing as advanced as possible to avoid detonation at idle and mid-throttle, it will be the appropriate amount of total advance at idle and mid-throttle. But the total timing will drop more than I want at wide open throttle, because all of the vacuum advance goes away at wide open throttle. On my engine, since I have 23 degrees of vacuum advance, I will lose 23 degrees of advance from my total at wide open throttle. Optimum performance may be realized if I "lost" a lower number of degrees. Do that by lowering vacuum advance and increasing initial advance by about the same amount. The engine with stock parts was designed for minimum warranty period repairs, pretty much without regard for performance, and severely limiting advance under load reduces the chances of my engine having any detonation problem, regardless of quality of fuel. Reducing the amount of vacuum advance is part of hotrodding the distributor.