enkeivette

I just got off the phone with a Procharger tech. He told me that I needed to have my distributor locked out (so there is no advance, mechanical or vacuum) and have 26 degrees of timing to start and 32 when I get it tuned.

Is this true?! I can't imagine having 26 or better yet 32 degrees of timing at idle! And is this necessary or is there a better way to do it?

BigBlockk

You're not going to have any vacuum advance under boost so you don't need to worry about that. As far as the rest of it goes, put the initial at about 12 BTDC and put in a slow mechanical advance curve. Like all in at about 4000 RPM. You can also limit the amount of mechanical to hold the total down at first. Tune from there.

BigBlockk

Later.....

69427

The tech support advice doesn't make any sense to me. At a single advance number (26* or 32* or whatever), you are running at an inefficient point for 99% of your driving. It might be tuned right for when you are at one level of boost, but the rest of the time your fuel economy, drivability, and exhaust valves are going to suffer. His recommendation will work, but it is brute force crude. Put some time and effort into it, and you can get a system that will give you driveability and performance.

yellow 72

I'm a big fan of running alot of initial but not locked out at total.
I would shoot for something like 22 initial and 10-12 mech in at 2500-3000 to start with...

norvalwilhelm

You know I run a 8-71 and this year I am running it 27% overdrive.
I set initial timing at 24 degrees, have a short 12 degree advance curve, all in my 3000 and another 16 degrees of vacuum advance.
Blower motors like advance. I also believe in vacuum advance.
I get great mileage and the motor runs great.

enkeivette

Are roots blowers different than centrifugal superchargers when it comes to vacuum? Could I simply leave my vacuum advance attached? Do I have to modify something to make it work properly? I will be going with a centrifugal supercharger by the way.

BigBlockk

Vacuum advance only works when the intake manifold is under vacuum. When the intake manifold sees positive pressure (boost) there is no vacuum to cause the canister to advance. If you are running a blow through system hook the vacuum advance to the "manifold" tap on the carburetor. If you are running a draw through system you'll want to get the vacuum signal from the intake manifold not the carburetor.

BigBlockk

Later.....

shafrs3

I would think if the vacuum advance mechanism was modified to do so it could also provide any necessary retard under boost.

69427

I've been curious about the same thing. Does anyone know if there is anything internal to the vacuum canister that would prevent it from moving the opposite direction when pressure is applied to the port?

norvalwilhelm

I also wonder about this. I never got around to testing this but next spring I will do testing. I will put a timing light on the motor and check timing with the motor running at say 2000 by turning the idle speed up, then pull the vacuum line and recheck timing at the same rpm, then take shop air, set the regulator at 5 pounds and hook it to the vacuum diaphragm and recheck timing. Turn the regulator up to 10 pounds and again check timing.
This will tell if you can push a vacuum advance into retart.
Vacuum operates against a spring in the housing so maybe pushing it with positive pressure will just cause it to retart.
I sent this question to mallory twice and both times they ignored me.
While I run a mallory ignition I am not a fan of the company.

shafrs3

It works good with the right mechanism, I did it on a Ford Capri that I fitted with a turbo many moons ago (German V6). The distributor didn't require mods on this application. Got the idea from Ak Miller who sold turbo kits in the early '70s. You should be able to pull the cap and watch the advance plate as you apply pressure for a quick check.

norvalwilhelm

That's a great idea. something I can do right now without starting the motor. A good visual will tell the story. Thanks

enkeivette

Sounds like a possible cheap substitute for a boost retard box. You've sparked my interest...

Couldn't I just stick an oral syringe in the vacuum hose going to the distributor advance and apply pressure? Then watch the idle with a timing light...

Matt Gruber

put down the crack pipe u will have to take it apart and re-design it.
they did sell them in '73. not cheap either, i passed over it due to cost

shafrs3

Glad I could help Norval.

enkeivette

These guys don't think it's such a bad idea. And it wasn't mine to begin with, why do I get the insult?

yellow 72

Nope, no worky.
I just tried it on my accel adjustable canister. When no vacuum is applied the diaphram is bottomed out against the back of the can and can only move one way.