Ignition Timing

[Brandon]

What are folks using for initial timing on 67 GT500's with the stock distributor? Book says 8 -- which is what I have marked in chalk and am still using.

[Bob Gaines]

What are folks using for initial timing on 67 GT500's with the stock distributor? Book says 8 -- which is what I have marked in chalk and am still using.

That's good. Octane of fuel is a big consideration if you go higher. Others may have a different opinion.

[Brandon]

Always use 91, with some percentage of ethanol nowadays.

[Bob Gaines]

Always use 91, with some percentage of ethanol nowadays.

If you go more then 8 on 91 octane I suspect you will get pre ignition/ping when you get on it.

[FL SAAC]

do your timing by ear

warm up the engine, loosen the distributor: just enough so it can be turned by hand

retard the timing first, then advance the timing by slowly rotating the distributor

listen for detonation: or "spark knock" and then back off the distributor slightly until the sound disappears.

secure the distributor, then take the car for a test drive.

listen for pinging under load or hesitation on when you start it.

make further adjustments the timing if needed.

retune your carb after setting the timing.

best of luck in your endeavors

[TLea]

do your timing by ear

listen for detonation: or "spark knock" and then back off the distributor slightly

Well, I agree with this in theory it definitely needs to be driven under load. As Bob mentioned there are many factors such as resurfacing of cylinder head in deck, combustion chamber, piston, size, etc., as well as the octane used.
I don't think you're gonna be able to hear that nation on an engine that's idling and not underload to a point where were really matter. I suggest you start with an initial around 10 to 12° and drive it and see if it does pain. If it does under a heavy load and back it off 2° and check again. I think you'll find you probably can get up getting around 12 if you go up to 93 pump gas.
The other thing that's a big factor is your harmonic balancer. Has it been rebuilt or checked? A lot of these balancers actually can shift a little bit overtime and spend which will make the factory timing Marks non-Reliable.

[Lincoln tech]

I wonder why someone decided to invent a timing light 

[Brandon]

do your timing by ear

listen for detonation: or "spark knock" and then back off the distributor slightly

Well, I agree with this in theory it definitely needs to be driven under load. As Bob mentioned there are many factors such as resurfacing of cylinder head in deck, combustion chamber, piston, size, etc., as well as the octane used.
I don't think you're gonna be able to hear that nation on an engine that's idling and not underload to a point where were really matter. I suggest you start with an initial around 10 to 12° and drive it and see if it does pain. If it does under a heavy load and back it off 2° and check again. I think you'll find you probably can get up getting around 12 if you go up to 93 pump gas.

I'm not sure where I'd find 93 pump gas.

The other thing that's a big factor is your harmonic balancer. Has it been rebuilt or checked? A lot of these balancers actually can shift a little bit overtime and spend which will make the factory timing Marks non-Reliable.

No, I haven't done that. Are these easy to rebuild or is there someone folks use?

[pbf777]

I wonder why someone decided to invent a timing light 

    +1! 

    Scott.

[98SVT - was 06GT]

I wonder why someone decided to invent a timing light 

Too true - I've done it by ear since the 60s. If it pings back off a couple degrees.

[TA Coupe]

He said, stock distributor but how about the cam? If it's not stock and has more overlap, you can run a little more timing. More overlap will bleed off a little bit of compression on the bottom end and build it as the rpms build up. Also have you checked to make sure your distributor is up to snuff?

     Roy

[Bob Gaines]

I use Octane Supreme  http://www.wildbillscorvette.com/octanesupreme01.htm  to doctor the 91 octane available around me so that I can run a little more timing (better performance) without the pinging problem.

[FL SAAC]

So true in a perfect world or just after a total rebuild a timing light and sometimes even then it's a NO....why?

On older engines with vacuum advance the timing more than likely will not be right with a timing light...close but not right.

Usually these engine have enough wear to have lower vacuum levels.

On mechanical advance if anything is worn, timing chain, springs, weights or pivot pins you are not going to get it right with a light.

Best cheap way to time them is hook up a vac gauge, advance the timimg until max vacuum is achieved.

Or use your PRO timing light

[Drew Pojedinec]

Wow.

So no one here adjusts the curve on their mechanical advance.

[rockhouse66]

Wow.

So no one here adjusts the curve on their mechanical advance.

I would say 2/3 of the time it needs help.  Maybe because it is all gummed up inside or maybe (more likely) it has been monkeyed with in the past by someone who just sticks a different spring inside.  I would plug the vacuum advance, set an adjustable timing light at around 35-36 degrees and set it to that at full advance (whatever engine speed that is) and see what you have.