chevy small block timing

[ERIC87442]

well my cars put away for the winter but im still wondering things. my signature says everything my car has. i got my total timing set at about 30-31 degrees at about 3000-3500 rpms. which seems great but i just cant get the base timing part down, maybe im just not reading it right. i got it at 650rpms in gear and i set my timing gun on it and it says im some where around 20 degrees. is that normal? or maybe im reading it wrong. so anyone got any ideas?

 

[turbo78]

i would set the total timing alittle higher, like around 34-36 degrees total at 3500rpm and then adjust carb to get idle where you want it. are you running a vacuum advance dist? if you are, i would set total with vacuum attached to about 34-36. i dont ever use vacuum advance because it sends my turbo car into ping fits on top end due to the amount of air being forced through the venturies.

 

[MD13ailey]

you want your totall timing without the can to be at 34 degrees or so. and set your idle were you want it.

 

[ERIC87442]

you want your totall timing without the can to be at 34 degrees or so. and set your idle were you want it.

i dont under stand what you ment

 

[turbo78]

you want your totall timing without the can to be at 34 degrees or so. and set your idle were you want it.

i dont under stand what you ment

he means without the vac advance hooked up. then hook it up and set your idle

 

[Doober]

you want your totall timing without the can to be at 34 degrees or so. and set your idle were you want it.

With a stock distributor at idle and vacuum hooked up, that would put the motor at over 50º advance, way too much at idle (unless I read your post wrong). Initial timing at idle would be around 10-16º with the vacuum line disconnected, that's how I typically set mine. I believe what M.Bailey means is set your advance when timing is all in (at 3000-3500rpm like you mentioned), you'll likely see better mileage with it set around there too.

well my cars put away for the winter but im still wondering things. my signature says everything my car has. i got my total timing set at about 30-31 degrees at about 3000-3500 rpms. which seems great but i just cant get the base timing part down, maybe im just not reading it right. i got it at 650rpms in gear and i set my timing gun on it and it says im some where around 20 degrees. is that normal? or maybe im reading it wrong. so anyone got any ideas?

That seems a little low for a stock vacuum canister. With the vacuum disconnected, set the timing to 15º or so, then hook it back up, it should read 30-35º. Stock vacuum canisters aren't adjustable, and they typically have a number stamped into them designating the amount of advance they give. If you take the rotor off the distributor you will see the rod from the advance canister, and you should be able to move it with your finger (and hear air moving in/out of the canister).

The springs/weights take over when there isn't enough vacuum to provide advance anymore. The mechanical advance curve can be tailored by different spring weights (most kits I've seen have 3 different weights, and you can combine them for different curves).

 

[ERIC87442]

i do have an adjustable vacuum advance, i have been playing with the springs, i have medium weight springs in there right now. with my vacuum advance untouched from when i bought it and this is what i got though, at idle (650) with the vacuum advance disconnected my initial timing is at about 20 degrees.(seems high to me but it runs good still) and then at 3000-3500 with the vacuum advance disconnected I'm at about 30 (what my gun is reading). I have found with the cam i have my degrees at idle should be some where around 14-16. im reading this stuff that says initial timing plus mechanical advance plus vacuum advance = total timing if this is right id be well over 50 degrees advanced like doober wrote. this shouldn't be this confusing... haha i know where i need my initial timing now. ive heard vortec heads don't like over 32 degrees of mechanical advance. and thats where im standing right now. i just wanna get this total timing, initial timing, vacuum advance and mechanical advance stuff squared away. i guess my deal is i thought total timing ment total mechanical advance at 3000-3500? am i right? because i see this stuff saying inital + mechanical + vacuum = total timing im lost.

 

[MD13ailey]

Sorry for the confusion. Unplug your vaccum canister. Bring the rpm up until all the mechanicle advance is in (around 3000 3500rpm) set the timing at about 33 or 34 degrees. plug your vaccum canister back in and set your idle.

 

[ERIC87442]

good deal, now vacuum advance... manifold or ported, ive been always told ported, my holley carb has a spot thats for a vacuum advance and its ported.... (if i set the timing at 3000-3500 rpms with the port disconnected n pluged higher then 30 my inital timing is way up there)

this is what my instructions for my distributor said about vacuum advance

"vacuum advance is regulated by manifold vacuum which is a function of
the load placed on the engine. Under light loads, such as when cruising
at a steady speed on the highway, an engine can tolerate more spark
advance than it can when under a heavy load such as when climbing a
hill or accelerating at wide open throttle"

then this is what i found online

"Vacuum canisters control part-throttle timing. By igniting the spark sooner during part-throttle operation, the combustion process is aided. When vacuum canisters first appeared on distributors, the factory designed them to employ a nonadjustable amount of predetermined advance at maximum engine vacuum. As an engine accelerates and vacuum decreases, the canister slowly pulls timing from the engine until it reaches zero vacuum advance. The factory vacuum canisters were designed to work with individual engine combinations. HEI systems were designed to employ less mechanical advance to help control emissions, while point-type distributors featured high amounts of mechanical advance. When engines are altered and modified, their timing demands also change, which is why Crane Cams and Moroso designed adjustable vacuum-advance kits. By simply inserting a 3/32-inch Allen wrench into the end of the canister, the internal vacuum-advance springs can be adjusted to control the engine’s rate of vacuum advance. The system is also designed to work with a vacuum-timing limiter plate. This plate allows its user to preset the total amount of vacuum timing at maximum engine vacuum."

 

[turbo78]

i like the little plate in there stopping the amount of vac advance. 😀
i usually just disconnect the vac advance all together and leave it off. that way when the ventury vac comes up, i dont detonate. by not using the vac adv at all, you can more accurately set your total timing , which is way easier than messing with that vac crap.not running a vac adv makes it so you can run more initial timing without detonation on topend under hard accel.