351W initial timing

[83gt351w]

Messing with the timing on my 351W. I’m running the vacuum advance to the metering block. Once the car is warmed up, it really seems to like the initial timing with vac advance unhooked set at 10 degrees btdc. When I start going higher, the idle isn’t as smooth, and at 16 degrees the best way to describe it, is the engine bucks back on the starter. Any lower than 10, it idles terrible.

Its an aluminum headed engine with a 296/302 duration cam. Checking the net, it seems initial timing recommendations are all over the place. Is this as simple as “well, this is what my engine likes.”?

IIRC, my total advance was 30. Which I believe can be adjusted as I have a dizzy that looks like the vac advance cap can take a wrench.

Thanks

[78futura]

Messing with the timing on my 351W. I’m running the vacuum advance to the metering block. Once the car is warmed up, it really seems to like the initial timing with vac advance unhooked set at 10 degrees btdc. When I start going higher, the idle isn’t as smooth, and at 16 degrees the best way to describe it, is the engine bucks back on the starter. Any lower than 10, it idles terrible.

Its an aluminum headed engine with a 296/302 duration cam. Checking the net, it seems initial timing recommendations are all over the place. Is this as simple as “well, this is what my engine likes.”?

IIRC, my total advance was 30. Which I believe can be adjusted as I have a dizzy that looks like the vac advance cap can take a wrench.

Thanks

What is your CR? Read about recurving duraspark distributers.
I have mine set to -2deg retarded inital any more will ping in 2 and 3. I have only 15 deg of mechanical advance and my advance does not start till 3k plus. I chalk it up to aftermarket balancer prob not right who knows and who cares.
You want to set it up initial till it pings under load then back off 2 degrees. Absolutely whatever works will be your initial setting. Do not try to set up to someone elses magic number as it most likely will not work for you.

[erratic50]

Basically if the distributor’s mechanical and vacuum advance are at all close to right, you should be able to loosen up the distributor so you can just turn it then start the car. Turn it to advance and retard to find where the idle starts to creep up and where it slows down, etc. Advance until it just starts to speed up then back just a freckle.

Put a timing light on it and see where you are

Shut the car off. Try starting it. If it kicks back against the starter as you crank it the timing is too far advanced.

Pull the vacuum advance and see what it does. See where you are at with a timing light

Youll end up wanting to run as much advance as you can with the vacuum advance hooked up without it kicking back generally

now rev it up a bit. See how many degrees the timing jumps when you rev it.

A lot of factors like compression and spark gap and head swirl, etc, all influence how much timing an engine will want. A decent rule of thumb is not more than 38 base advance plus vacuum and mechanical advance all in. But some motors I’ve helped turn up liked as little as 32 all in, one liked 42 which shocked me

and as stated if it pings back it off a few degrees

If you get it wrong it’s about guaranteed you’ll blow a head gasket or have some other dreaded failure so watch it

Fuel octane influences resistance to detonation.

where your air/fuel mixture is at greatly influence what timing a motor wants too. A lean mixture will want way less timing than a rich one will

Elevation is yet another factor

Stuff like this is somewhat a topic on why and how EFI shines so much.

Thats not to say a carburated engine can’t run great across the board - it can. But there are compromises

Ever notice how they sell lower octane fuel in the mountains and wonder why?

[erratic50]

Basically if the distributor’s mechanical and vacuum advance are at all close to right, you should be able to loosen up the distributor so you can just turn it then start the car. Turn it to advance and retard to find where the idle starts to creep up and where it slows down, etc. Advance until it just starts to speed up then back just a freckle.

Put a timing light on it and see where you are

Shut the car off. Try starting it. If it kicks back against the starter as you crank it the timing is too far advanced.

Pull the vacuum advance and see what it does. See where you are at with a timing light

Youll end up wanting to run as much advance as you can with the vacuum advance hooked up without it kicking back generally

now rev it up a bit. See how many degrees the timing jumps when you rev it.

A lot of factors like compression and spark gap and head swirl, etc, all influence how much timing an engine will want. A decent rule of thumb is not more than 38 base advance plus vacuum and mechanical advance all in. But some motors I’ve helped turn up liked as little as 32 all in, one liked 42 which shocked me

and as stated if it pings back it off a few degrees

If you get it wrong it’s about guaranteed you’ll blow a head gasket or have some other dreaded failure so watch it

Fuel octane influences resistance to detonation.

where your air/fuel mixture is at greatly influence what timing a motor wants too. A lean mixture will want way less timing than a rich one will

Elevation is yet another factor

Stuff like this is somewhat a topic on why and how EFI shines so much.

Thats not to say a carburated engine can’t run great across the board - it can. But there are compromises

Ever notice how they sell lower octane fuel in the mountains and wonder why?