[sjdiesel]

MSD 8528 with vacuum advanced
Pontiac 468 stroker (build in sig), ported 670 heads, ported factory intake, Holley stealth 4150 EFI, bla bla
Current distributor setup is two silver light springs and a green bushing.
Initial: 22*
Initial with VA: 35*
Total 34* all in by 2k

How does this sound? Do I have the timing coming in too early?

[Scott65]

I would be concerned with light cruise above 2000rpms with those numbers. 47 degrees may rattle when you ease in to it, depending on vehicle weight, gearing etc. With iron heads I'd think total in by 2800-3000 may be better, and maybe limit to 10 degrees vacuum.

[sjdiesel]

Ok good info. It’s a heavy car, full body, full interior, AC, 4l80e. I don’t have an exact weight.

How do you limit the VA to 10?

[sjdiesel]

Ok I’m an idiot... my notes were wrong. I have two lite blue springs. So all is in at 3k. Just pulled the cap and verified and put a timing light on it.

[Scott65]

There's different ways to limit it. Most involve limiting the travel of the rod. With mechanical not in til 3000, 13 may work ok. Drive it and keep close tabs on it. Maybe put the light on it with vacuum connected and see what it looks like above 1800-2000. 40 degrees should be tolerable on light load situations, maybe a little more. But less is better if there's doubt.

[BDH79TA]

If I'm not mistaken, that distributor comes with an adjustable VA. Takes a small allen head inserted in the vacuum port. If not, you can purchase one. That's one of the easier methods to limiting VA.

[ID67goat]

Unless you are set on running a vac advance distributor, I think you might be better off controlling timing with the EFI, if it has the capability. So much easier to tune with the laptop.

Are you using a Terminator stealth that also is controlling the 4l80e?

[lust4speed]

We both get to enjoy the same garbage gas. Engine in my 67 GTO is set up for 16° initial and 38° all in at 3,000. I've limited max vacuum advance to 14° but only sees about 11° at steady freeway speed. You have 9.5:1 and I have 9.32:1, but your cam is a little larger so think that total timing should be about the same with both our 670 heads having the Dave treatment. Your EFI will be much better at maintaining the fuel/air ratio over my Quadrajet, but have a suspicion that 38° is probably going to be the sweet spot.

[steve25]

It sounds like your motor has not even been fired for the first time yet?

If so I would put conservative timing in it , break it in and then do a hot cranking compression test to see what you have for cylinder pressure and then make base line timing settings from that empirical information.

A very safe timing setting for breakin with those stock 670 chambers is 32 and then a added 10 degrees of VA.

[sjdiesel]

BDH79TA, I’ll see if this VA is adjustable. Thanks for the tip!

ID67GTO, One day I’ll upgrade to the Holley distributor & box so I can control the timing via the EFI software but for now I’m stuck with my current distributor setup. And yes, the Holley terminator X max controls the 4l80e too. It is a nice setup.

Thanks Mick, I’ll bump up the timing to 38 and see how it runs.

Steve, I have about 5k miles on the engine now. Just finished up the EFI conversation so I’m playing with the timing and tuning.

[track73]

I bought a couple a stock AC Delco vacuum advance units that I believe came with Hi performance 427 Chevys. They were rated at 10 degrees of advance. I got one on EBAY and another on Rockauto.

[steve25]

Ok, but if you have not taken a compression test just for your notes and keeping track how well the motor is living you should.

In terms of the high rpm max power fuel to air ratio that the 670s want you will find that it wants to be on what’s going to be concidered on the fat side if your headers are scavenging well.

So if you have a knock sensor make good use of it!