initial timing?
 

i was wondering what you guys would suggest for timing. Not sure what octane gas i want to run but i have 87 89 92 where im at. also is there a big dirrerance between 87 and 89? i usally put either 87 or 92. i have ben told that set initial timing to 14-18 degrees before TDC (while running the motor at 2000 RPM) and check the timing again at 2000-3000 rpm and see where the timing is at. Should be around 45-50 degrees before tdc. sound good to me but i would like more specific numbers and what octane to use.

I know a lot of people ask this question but iv tried what others tell me and it never seems to run like it should.. sometimes it runs good at low rpm and then i have power loss after 4000. other times it runs good but i have problems starting it like its pinging or something.

also does anyone have a adjustable vaccume advance canister and know what direction with the allen wrench is advance or retard? i currently have it 6 full rotations counter clockwise and it seems to run pretty good.

2 things to think of, one is your total timing after all the advance is in shouldn't exceed 36-38 degrees. 45-50 is too much for anything short of Japanese sportbikes.

The octane you should use is largely a function of whatever your compression ratio is. I saw your running 302 heads on a 289 and IF they have larger combustion chambers your compression would be lower allowing you to use the cheaper gas, but pistons, deck height, etc, all affect this. Just use the seat of your pants and run what it likes.

Keep on tuning!

any more sugestions? anyone have a similar setup? if so what r u running as far a timing goes and what octane do you run? any thing is a big help. thanks

my compression is 122psi. and iv decided to use 92 octane from now on. anyone have similar compression and use 92 or any other gas. if so what is your timing set at. i can use any suggestions possable. i will try every number you guys can throw at me and i will see what works best and just stick with that.

i don't know what my compression is but i have my car set at 12 degrees BTDC at idle, and my car runs much better than it used to. I have the original 289 heads on my car so my compression would be higher due to that fact, but i try to use 92 octane whenever it is feasible for me, but once in a while i have to use 87 or 89 when money is tight. give it a try, good luck.

Jason

I didn't mean to mislead you guys on compression but to some extent we're talking apples and oranges here. The biggest factor to consider when selecting an octane rating is your compression ratio, not the cranking pressure you obtain form a compression test. Two different things.

The cranking pressure is affected by the compression ratio but it's also affected by cam timing. If you have a big rumpity-rump cam in there the intake will be staying open for a longer period of time and the piston can't develop any pressure while the intake valve is open. So you get less cranking pressure on a compression test.

For a comparison, I had a 10-1 motor developing 215 psi on a compression tester because it had a stock cam. Now that motor is at 12.5-1 but because I have more cam it's only cranking 155 psi.

Assuming a fairly stock cam 122 psi would indicate a lesser octane is fine and the higher octane gas probably won't make any difference at all. I'd try both tho.

Good Luck. Hope I cleared that up.