[i82much]

msd ready to run ... spendy but sure easy to use. heard there were some module failures early on but that has been resolved.

i run mine with a programmable 6AL2 but have not tried programming the timing, i just used the weights and bushings on the ready to run. Quite happy.

[Formulajones]

Originally Posted by i82much

msd ready to run ... spendy but sure easy to use. heard there were some module failures early on but that has been resolved.

i run mine with a programmable 6AL2 but have not tried programming the timing, i just used the weights and bushings on the ready to run. Quite happy.

I saw that 6AL2 with that feature and thought that might be pretty cool, uses the laptop which I like much better than a phone. Plus all the regular features with a 2 step, rev limit, multi spark, etc.... and they made the box much smaller.
Thinking about trying one on the current build.

[uttergto]

Kenth, here are the distributor timing results:
Engine idle RPM 900
Vacuum at idle is 9 in. hg, it goes up to about 14 in. when the RPM is increased.
Initial advance at idle is 6 deg.
Initial + vacuum advance is 38 deg.
initial + centrifugal advance is 30 deg. (springs removed)
I set the initial + centrifugal at 36 deg. total, resulting in 12 deg. initial advance.

Does this sound about right? It starts fine.

Thanks

[Cliff R]

Initial plug vacuum advance it 38? That's adding WAY too much timing. I'd reduce the travel of the VA to provide closer to 10-14 degrees instead.

9" vacuum at 900 rpm's is horrible. What are the engine specs? CID, compression ratio, camshaft used, etc?

Setting the initial timing at 12 to acheive 36 degrees shows 24 degrees in the mechanical curve. So adding another 24 from the VA isn't going to work for chit since it brings the timing up to 60 degrees. Few if any engines I've ever worked on will tolerate anywhere near that much timing at light engine load, nor will they like it at idle if you add it to the initial timing of 12 degrees........FWIW.......

[Formulajones]

Cliff is correct, it appears that your vacuum advance is adding 22 degrees and that's way too much. Pretty typical of stock vacuum cans. You'll have to limit the slot on the can to about 10-12 degrees. That's really all you need.

We've had a ton of threads on this in the past. Your 12 initial is fine, and sounds like 36 total which is 22 centrifugal and that's okay as long as it's all in around 3000 rpm it'll work fine and be pretty happy there, but the vacuum advance will have to be dialed down a bit.

[Singleton]

I suspect the possibility that the vacuum advance isn't solely responsible for the jump from 6 to 38 degrees. Connecting the VA increased the idle rpm, which may have also added some centrifugal to that 38 total?

[Cliff R]

Correct, ....but one would certainly think the "tuner" doing that move would lower the idle speed at the same time, to drop out any of the mechanical curve that came in, but these days I'd don't assume anything when it comes to these sort of things......

[Half-Inch Stud]

Dual Task: Rotor-post phasing is thee task while reducing the VAV ADV advance. Need a spare cap with window to aim timing light to Post #6.

[uttergto]

The engine is a .030 over bore 1965 389 ci. Advertised compression ratio was 10.75, now it has thick head gaskets. The camshaft is an H-O Racing HC-02, 301 duration on the intake with a .465 lift, 313 duration on the exhaust with a .469 lift. It was installed 3 deg advanced when assembled.

[uttergto]

I have a new Standard VC-24A vacuum advance can, but I can't find any specs on it. The one on the distributor is the original 1965 unit. Another original vacuum advance has a 20 stamped on it.

[uttergto]

If the idle RPMs drop much under 900, the engine will stall.

[Cliff R]

Perfect "recipe" for low vacuum at idle and tuning issues........LOWERING compression, increasing quench distance/squish area, and going with a BIGGER camshaft.

Stalling at idle speed orf when you lower idle RPM below 900-1000rpms is typically either vacuum falling off and the vacuum signal to the VA falls below the point where spring tension inside the can hold the timing all-in (timing retards and engine RPM"s drop or engine stalls).....or dropping engine RPM's to get a "normal" or resonable idle RPM retards timing because the springs are too light and some of the centrifical advance is in at idle speed......or a little of both.

Not enough fuel at the carburetor idle mixtures screws is another contributor to that issue, and many times I see all three problems when troubled vehicles are brought here for custom tuning......

[uttergto]

Cliff, what would be a good camshaft for this combination? I have a GM 068 (RA II) cam, a Mellings SPC 3 (same as a GM 744, RA III), and a RV cam.

[Shiny]

Originally Posted by uttergto

I have a new Standard VC-24A vacuum advance can, but I can't find any specs on it. The one on the distributor is the original 1965 unit. Another original vacuum advance has a 20 stamped on it.

Does your VC-24A have a "B1" stamped on it?

I bought a VC-24A recently and it had a B1 stamp.

It is advertised to start @8-10 inches and be completed by 16 inches. The total advance is supposed to be 16 degrees. I measured mine and it was close on the vacuum levels but had significantly higher total advance. At the advice of many on the forum, I limited the total to 10 degrees but used an adjustable stop.

If you can, measure what yours does!

[uttergto]

Yes, it has a B1 stamped on the mounting bracket. I could not find any information on this unit.

[KGTO]

Originally Posted by Cliff R

Good plan. Total potential timing at cruise is right for what you are doing. I've tuned hundreds of older high compression engines to run on this new fuel and they ALWAYS like about 10-15 degrees additional timing at light engine load. They NEVER like, want or respond well to super quick all-in timing curves right off idle (many show up here that way).

Most folks do NOT understand the mechanical advance portion of tuning. These engines require a timing advance curve simply because we are bound by the laws of physics with these things. To accomplish complete/efficient combustion the timing must start sooner with increased engine RPM because we have LESS time to get it done as the cycles per second are increasing as well. With a very well thought out engine build, optimum compression, cam making good cylinder pressure, tight squish, etc you will NOT need a quick curve or "all-in" early. Well thought out engine builds will like LESS timing everywhere as they are more efficient. On the other end of that spectrum you have the guy who "lowered the compression for pump gas", then installed a cam on a tight LSA that bleeds off more cylinder pressure with it's added overlap, so it will LIKE, WANT, NEED, and RESPOND WELL to a LOT of initial timing, plus a really quick timing curve to help it be more efficienty at low engine RPM's.

It's just physics with these things, and ALL of these N/A engines end up with simliar if not near identical timing curves no matter what brand they are. It's all about CID, static compression ratio and cam events for the most part. Of course some engines are simply more efficient than others based on design, and some older varieties had HORRIBLE combustion chambers designed for emissions, so in those applications you may find yourself pouring more fuel to them, and throwing more timing at them to make them happy........

Really great info in this thread. I fall into this category, used to race the car and run all initial with a MSD pro-billet. Swapped the original heads back on which are mildly ported with some chamber work from SD. Solid cam, tight LSA. Spent time with the PV, IFR and bleeds, the car runs, starts and performs very well, but has always bucked, though it's a bit smoother now. So I've been thinking of changing the timing and utilizing the mechanical advance (no VA). The engine has always responded well to a lot of initial advance (obviously). Since it gets smoother above 2500 I thought 16*-18* base and bring in the total (36-38) in by 3000. Would that help and does it matter that I don't have VA in this instance. Box has a start retard so starting the car is never an issue with a lot of lead.

[Formulajones]

16-18 initial should not be a problem unless you have some other underlying issue. I have a couple here that I run that much initial with and it's fine cranking without any start retard. Usually when that becomes a problem it's a result of a starter that has a worn armature, draws too much amperage, or wiring that has built up some resistance from age, or even an ignition switch with too much resistance. Pretty easy to diagnose all that if necessary.

No reason really to "not" run the vacuum advance. It only has advantages, and no disadvantages. But...you have to dial it in correctly. With your total of 36-38 it would work well with about 10-12 degrees additional vacuum advance at light cruise.

[KGTO]

Not opposed to running VA, the pro-billet just doesn't have it. So is it realistic to assume some of the "chugging" can be tamed with the timing? I don't lug this around, but under 2500 becomes noticeable.

[Formulajones]

Originally Posted by KGTO

Not opposed to running VA, the pro-billet just doesn't have it. So is it realistic to assume some of the "chugging" can be tamed with the timing? I don't lug this around, but under 2500 becomes noticeable.

The MSD pro billets have the ability to accept the vacuum advance if you want one. They are machined, drilled and tapped if you peak under the breaker plate.

Yes the chugging can be tamed with the timing. How much depends on some variables and becomes more of an experiment with each engine. Typically what I find on a very rambunctious engine is the vacuum advance works well when added at idle using manifold vacuum, so you would have an additional 8-10 degrees or so while idling on top of your initial of 16-18 degrees. That way it cranks on the 16-18 and once running idles on 24-26-28 degrees.
It's basically the same thing the EFI tuners do these days with electronic ignition control on a rowdy engine, only you're doing it with a mechanical distributor. The electronic control is cleaner and more efficient with the ability to really tweak and fine tune, but very similar results can be had with the mechanical stuff this way.

I've been able to tame pretty darn radical engines this way to a point that they become very docile to drive, smoother, especially beneficial with a manual trans, and just all around more pleasurable to drive. The added benefit is that now you don't have to get too crazy with carb adjustments, especially in the idle and transition circuits that normally would require extensive rework using a very radical camshaft. They kind of go hand in hand. Carb tuning is still important to make a radical engine behave nicely, but in a lot of cases timing plays a bigger roll, and why I always like to tackle the timing side first, get that squared away, then get into the carb stuff.

[KGTO]

Alrighty, that's promising and worth giving it a shot. Might even need to consider another distributor to add the vacuum advance later if it works well. Will it still be as snappy? Its very crisp right now. I assume I'll need to then go back to the carb and play with IFR, mixture and maybe bleeds to compliment the ignition curve.

Looking at curves I figure it should start coming in around 1300 RPMS and all in by 3000. It idles best about 1050-1150