I have settled on 15 degrees of initial static advance, 23 degrees of centrifugal advance (all-in at 2600 RPMs), and 12 degrees of vacuum advance at 15" or higher vacuum. I have found that this combination works well on Ford small blocks with up to a 9.5:1 compression ratio and a mild cam. With higher compression ratios you will need to back the initial static advance down a little.
My vacuum advance doesn't even begin to pull in until there is at least 8" of vacuum, an engine won't develop anywhere near this much vacuum during startup cranking.
One does not need to be concerned that much with detonation during warm-up because the engine is running so much richer when the choke is partially closed than it does at normal operating temperature when the choke is wide open.
I have very near this same timing setup and am pleased with the performance and cooler running engine. There is one issue I had to overcome that I think is worth mentioning: I had to back the throttle stop off to get the idle down to normal with the 27 degrees advance. After that adjustment, when I crack the throttle to pull off, the engine would stumble because I immediately lose the 12 degrees vacuum advance. My solution was to add a "slow bleed" check valve in the vacuum advance line. This allows the vacuum advance timing to slowly fall off over 3-5 seconds and until I'm moving and above idle. Problem solved
Funny, everything that I have read on the internet says that a nearly stock lower compression Ford small block can use as high as 50-52 degrees of TOTAL advance (static+centrifugal+vacuum) with 89-93 octane pump fuel. My personal experience bears this out.You should not run more than 33 degrees total advance in a Ford small block
and running as much as 45 degrees on the highway with vacuum advance for gas mileage if you are concerned with mileage seems to work on stock motors. My 302 is not even in the neighborhood of being stock @ 385 hp and what's a choke !!!....Detonation of any kind will damage your motor it just takes longer in a stock motor...
Moondoggie
Funny, everything that I have read on the internet says that a nearly stock lower compression Ford small block can use as high as 50-52 degrees of TOTAL advance (static+centrifugal+vacuum) with 89-93 octane pump fuel. My personal experience bears this out.
33 degrees of static+centrifugal would be about right for a high performance high compression Ford small block although I have read that some people run as high as 36 degrees. 33 degrees is what the factory dual point non-vacuum advance ignitions would be set at. If you are running vacuum advance, add 12 degrees to the 33 and you get 45 degrees, about the max you can run in a high compression engine using 93 octane pump fuel. Having a vacuum advance distributor is the way to go for street use.
After I did this I had to adjust the idle mixture settings in addition to adjusting the idle speed. If they are not richened up a little the engine will run too lean at idle and you will get a stumble. The problem with using a check valve like you have done is that the vacuum advance won't come down fast enough to avoid pinging during acceleration in the mid RPM range from having too much advance.
Thanks for your input...When I went to manifold vacuum the rpm's went up to 1,500. I had to back the idle stop screw (mixture volume) down to get back to 950. My wide band 02 gauge reads 12.5-13.5 at idle. Do you recommend I richen the idle mixture until the stumble is tolerable?
Well my 454 HP engine has 14 degrees static timing: 21 degrees of mechanical advance (all in by 2500): 10 degrees vacuum advance. So thats 31 degrees of advance at idle. Runs so cool that I may change thermostat and of course runs like a scalded dog on fire.
The engine has a 10.8:1 compression ratio.
Duke..
Your 454 number comes off a chassis dyno and you are pumping in what you think are losses and although that might get you in the ball park it is still a GUESS at best. My numbers come from a engine dyno that routinely tests race motors and is accurate. Again think about what is happening here, lower temps come from unspent fuel and that means less horse power it's just how things work. If your happy with less than perfect horse power so be it you should probably not try to run me......your getting to be a short timer over there when do you actually leave ???
Moondoggie
Your 454 number comes off a chassis dyno and you are pumping in what you think are losses and although that might get you in the ball park it is still a GUESS at best. My numbers come from a engine dyno that routinely tests race motors and is accurate.
Huh? You shouldn't be getting ANY of that 21 degrees of centrifugal advance at idle speed Duke, so 14+10=24. 24 degrees at idle is what I set-up Tom's car at, while mine is set at 27 degrees with a lower compression ratio.Well my 454 HP engine has 14 degrees static timing: 21 degrees of mechanical advance (all in by 2500): 10 degrees vacuum advance. So thats 31 degrees of advance at idle.
Huh? You shouldn't be getting ANY of that 21 degrees of centrifugal advance at idle speed Duke, so 14+10=24. 24 degrees at idle is what I set-up Tom's car at, while mine is set at 27 degrees with a lower compression ratio.