I finally have my new MSD 8383 installed in my 59 292. It runs so much better than the original dizzy with pertronix. I am now at the point where I'm dialing in the timing perfectly. I am using the blue stop bushing which gives me 21° centrifugal advance with RPM. Also the blue springs in the dizzy so its all in before 2500 rpm. I am toying with 10 and 12° initial advance which seems to be ok. I have an isky cam, headers and 500 cfm edelbrock AVS2 carb. I read that with a performance cam a lot of guys like around 16° of initial advance which would give me a total of 37°. My question is when i hook up the vacuum advance ( manifold vacuum ) I am getting around 38° at idle. Is that too much advance while idling?

 

There's no load on an engine at idle, so there's no cause for concern there. It won't pass smog though, if that's an issue. It will run a lot cooler in stop and go driving. If it idles well, try it.

Usually any problem with this setup is tailoring the vacuum advance canister for a full time or manifold connection. If you've a real performance camshaft engine, manifold vacuum tends to be fairly low. An OEM or factory type vacuum advance canister on the other hand, therefore will not be getting the signal it expects, and it doesn't expect to get it at idle anyway. It will tend to "flutter", setting up a kind of negative feedback deal - uneven idle RPM because the breaker plate is changing the igntion timing right? And that changes the engine vacuum. Which changes ... Rinse lather repeat.

If it runs good you're in good shape. My Y runs fantastic around 52° BTDC at cruise. I use the factory ported distributor connection and around 12° or so initial and around 36° or so "all in" total. I would not want to use a manifold connection if I couldn't achieve the correct cruise timing. It does take a lot of experimenting if you get off the reservation.

 

Here in a few I'll be back out there messing with it. My next move will be to try 16° initial and swapping between manifold and ported vacuum. Also with the light spring installed in the dizzy I am temped to try it without vacuum advance at all. That much initial should come close to covering the low rmp low load burn? Thoughts?

 

Definitely, disconnect and plug vacuum advance. Forget it even exists for the moment, and setup your mechanical curve. They work together but are tuned separately. Mechanical advance is always done first. Take some test drives, without vacuum advance connected. It's definitely a "cut and try" thing without access to a dyno.

Y-blocks in stock form like a lot of advance, and will tolerate quite a bit coming in quickly too. Low compression. OHV V8 in general like anywhere from say 32 to maybe 40 degrees total advance before 3000 RPM, it depends on combustion chamber design, compression ratio, aluminum or iron heads, vehicle weight, altitude, fuel quality etc. But the idea is to give your engine what it wants, not what somebody else thinks it should want, just short of engine knock or ping. Leave some on the table for safety, or a bad bag of gas.

Then, when that's straight, and you're satisfied, re-connect the vacuum advance and go for another test drive. At this point adjust only the vacuum canister. You're done with the first part, if it was done correctly. A lot of people bungle this part, because when they get ping city with vacuum advance reconnected and they don't understand how vacuum advance works they cripple the ignition timing curve by taking the advance out of the initial distributor or mechanical timing instead of tuning the vac canister. Make sense?

You're looking again for the point just short of engine rattle or ping, but here only under part throttle or cruise conditions. Wind the vac advance up all the way to max to start with and back it off from there. Excessive vacuum advance can be identified because under acceleration it actually goes away from a steady cruise condition, pretty much the opposite of the mechanical advance. Inspecting spark plugs carefully should show ignition timing is in the zone. The ground strap will show a color change about halfway.

Black specks on the plug ceramic are often oil splotches, but look carefully with a magnifier for tiny spherical silvery globules. Those are no bueno, evidence of excessive initial ignition timing. It isn't always audible.

 

i believe the vacuum advance that came on the msd 8383 is non-adjustable. It sounds like it adds quite a bit of timing too. I have plugged it in while running and rpm goes from 600 to 800. i will be checking all of this in a matter of minutes and report back. The good news is I checked the balancer with a piston stop and 0° on the balancer was perfect. I also got the dizzy installed perfectly with rotor pointing exactly at #1. Shes running amazing I am just obsessing on perfect timing. Also this is a shortbed 59 f100 with the original T-98 4 speed. I have a bit larger wheels on and I think the stock 9" rear has 3.0 gears. Its got to be somewhere right in there.

 

It gets involved, I messed with mine for a while. One thing, the Ignition itself, has to be a good HOT spark, or it will not run right at cruise. It will act just like it's too lean, or too much advance, which in a sense it is I guess. The factory ignition curve depends on a fully functioning ignition system. They used to use pretty hot plugs for around town driving. Points ignition. If a high voltage hot ignition is installed, consider stepping down a heat range for highway use especially. The plug itself can cause detonation or pre-ignition or whatever, if it gets too hot. Carbon deposits will do this too. So it can take a while to figure out what you're really observing.

The timing curve or advance is a different animal for the mechanical part under load, and the flat ground cruise under part throttle, is a whole 'nother deal. Keep that in mind. That's why vacuum advance was invented in the first place, there was no way to achieve the amount of ignition advance required just using weights and springs. 10 to 15 "extra" degrees is pretty typical for vacuum advance canisters.

Whenever the go pedal is depressed, vacuum advance goes away, and the ignition advance timing reverts to whatever the mechanical advance is doing at that particular point, till the load levels off, and vacuum comes back up. This happens in just a split second, if you watch a vacuum gauge driving around under different driving conditions it is educational.

 

well 15° initial it is. Thats where it feels good. Drives amazing. the idle rpm does shift just a small amount but hey, its an isky cam. its not the real rowdy one either its the 4444. I'm at about 31° advanced at idle with the vacuum advance plugged into manifold vacuum. RPM at idle is 650.

 

I forgot to add that I am using NGK Iridium IX WR5IX 7510 spark plugs. The are pre-gapped at .039" Also Taylor pro series 8mm wires.