i have herd that the only purpose of vacume advance was for economy reasons. now i always thought that it was both for performance. i thought that the higher octane gas being run the more advance you need or is that opposite?

oh well thanks in advance

Your vacuum is for part throttle ignition control. During part throttle operation you need more advance to properly burn the mixture. Otherwise you're on the gas more the get the same power, screwing over both MPG and emissions.

Depending on how the vacuum adv is hooked up it can also improve idle quality and throttle response. A street driven engine without a vacuum adv will also be more prone to overheating and detonation in stop and go traffic.

<font face="Arial,Verdana" size="2">Originally posted by Joekool:
Depending on how the vacuum adv is hooked up it can also improve idle quality and throttle response. A street driven engine without a vacuum adv will also be more prone to overheating and detonation in stop and go traffic. </font>

wow news to me! lmao. i disconected that vacume advance two months ago after looking into the manual that came with the zz383. Driven by my wife and I daily, and no overheating or detination what so ever.MPG is the same and since see half of the mid to early 90's toyotas on the road burning oil I could care less about emisssions * know im gonna catch flack for that) adn the car pulls much better. Belive it or not I was exspecting all the things that you stated to accure but I tryed to go with what GMPP wrote. I was suprised when to motor behaved so well, then again each motor is diffrent.

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72 RS, ZZ383- 770 Holley, HVH carbspacer and RPM Airgap manifold, flowmaster american thunder system modified with two 40 series mufflers, pro-billet distributer,6AL box, msd super conducter plug wires, powermaster 140 amp alternator and March serpantine conversion.

!!!Piss on C.A.R.B.!!!

I don't run any vac advance either. Just played with the spring tension in the HEI to get the mech advance I wanted, at the rpm I wanted it. It takes a little time, but works for me

Whatever works, but I know for a fact some (say 8deg) vacuum advance at idle will tame a big cam. On a 383 I put together with an XE274 I gained over 2 inches of vacuum at idle (same idle speed) with the extra timing and it would hold at 160 deg. at idle whereas it would not without the extra advance. To me that says you are more efficient.