[gto19]

Hi guys

I have 67 gto that just got the original motor rebuilt to stock specs pretty much , original distributor and running points .. I remember the engine builder saying to set the total timing at 32 . When I set it to that number do I unplug the vacuum line from the distributor Vacuum advance and plug it at the carb to check ? Or leave it alone and check ?

Thanks

[Gary H]

Unplug the vacuum advance and check it. Total advance as described doesn't include the amount added by the vacuum canister. Also, you may know this but when checking total advance you need to raise the rpm's until the centrifugal advance is all the way in, then set it.

[Navy Horn 16]

What Gary H said.
My advice would be to run check initial, then total and find the difference. Then set your initial timing to what it needs to be in order to get that "total" number.
Lock it down, then verify total.
Trying to dial in total timing with the engine spinning 3000+ rpm is some unnecessary excitement.

[694.1]

670 heads are closed chamber and like lots of timing. This sounds pretty stingy, how about it, experts?

[lust4speed]

What is the new compression of the engine? 32° sounds a little conservative unless compression is over 9.3:1. My engine is exactly 9.3:1 and I run 38° and don't have pinging even with the A/C on high on a really hot day.

The other problem is if you have the original stock springs in the distributor the advance might not fully come in until 4,500 RPM or more. Just depends on whether they did any work on the distributor with lighter springs. As said above, even 3,000 RPM with my head stuck under the hood is about the edge of excitement for me.

Bottom line is come as close as you with the timing light and then road test. If you hear pinging retard the timing, if you don't hear pinging advance it a little at a time until you do - and then take 2° or so out of it.

As far as total timing. I purchased another 67 GTO and when I purchased it we couldn't run anything above 28° because of carbon buildup and such. So bottom line is to see what the engine really wants. After a rebuild that engine also really liked 38°.

[TCSGTO]

With a points distributor you can take the advance springs out and it will go to full total advance at idle speed. Adjust that then put the springs back in and check initial timing. If it’s not at at least 10-12 degrees btdc you can add a bushing to the limit pin.
Most stock Pontiac distributors had around 26-28 total without a bushing so if you want 36-38 degrees total you may not need a limiter bushing.

[amcmike]

Originally Posted by 694.1

670 heads are closed chamber and like lots of timing. This sounds pretty stingy, how about it, experts?

Very true. 32 degrees would make more sense if it were the later model open chamber heads.

If he's still running the factory closed chamber heads, stock compression, 93 octane, and keeping the timing curve stock, he should be closer to 38 degrees.

[PontiacJim1959]

Originally Posted by amcmike

Very true. 32 degrees would make more sense if it were the later model open chamber heads.

If he's still running the factory closed chamber heads, stock compression, premium fuel, and keeping the timing curve stock, he should be closer to 38-40 degrees.

Agreed with all this, but I think the key is as you pointed out, premium or the need for an additive to the gas with 10-to-1 compression or better. 32 may be better to start with and then advance upward from there.

[gto19]

Thanks guys
Yes original 670 heads and original distributor. I think the compression is the same as stock or a little lower . I’ll ask him Tommorow to get a exact answer. I’ll also ask my friend what exactly he did to my original distributor

Thanks again

[steve25]

The early heads chambers ( 67 and prior) and even the slightly different but still closed chamber in the 670 heads need way more the 32 degrees to burn and run right!

You builder told you 32 degrees to be on safe side of things to start with I would say!

When you test your cranking compression you need to take the 7th or 8th hit reading and all the plugs must be out of the motor with it warm and the Carbs primary open all the way.

[flat-bill]

You need to disconnect the line from the distributor and plug at the carb so there is no vacuum leak into the carb.


QUOTE=gto19;6158789]Hi guys

I have 67 gto that just got the original motor rebuilt to stock specs pretty much , original distributor and running points .. I remember the engine builder saying to set the total timing at 32 . When I set it to that number do I unplug the vacuum line from the distributor Vacuum advance and plug it at the carb to check ? Or leave it alone and check ?

Thanks[/QUOTE]

[Kenth]

Originally Posted by gto19

Hi guys

I have 67 gto that just got the original motor rebuilt to stock specs pretty much , original distributor and running points .. I remember the engine builder saying to set the total timing at 32 . When I set it to that number do I unplug the vacuum line from the distributor Vacuum advance and plug it at the carb to check ? Or leave it alone and check ?

Thanks

With stock 1967 GTO engine and stock distributor i would not alter the ignition curve at all. Just see that bushing is present at advance stop pin.

The 1111250 distributor starts with 0-4°@1000 rpm, has 21-25°@2000 rpm and max 26-30°@4400 rpm. Add to that 6° initial and you have the total centrifugal advance.
The vacuum advance (engine load sensor) 1115365 starts @ 8-10 in/hg and gives max 20°@15-17in/hg.

FWIW