Distributors?

I got a MSD 6A ignition for Xmas and I want to change my distributor while I am at it. Here is my question: is a vacuum advance needed or can I go with the MSD Billet without a vacuum advance work fine for me. The 302 has been rebuilt with 11 1/2:1 compr, race cam, and other goodies. It is on the street some (good weather months maybe 1 a week) and raced on the strip 1-2 times a month.

So my question will the MSD Billet work fine for me even on the street or should I get a distributor with a vacuum advance.

Thanks ....Todd

 

Vacuum advance is only used at idle or just off. You dont need it. I have the complete MSD set up and have had no problems starting mine.

 

Thanks......think I will get the Billet from MSD....is that what you have? That way its all MSD. The car might get 300-500 miles a year..if its lucky...lol

 

Thats what i did .Just went with all MSD that way its neat easy to install.And works like a charm

 

While vacuum advance is not strictly necessary, it does help with low speed and cruise situtuations. If you put more miles on it cruising to and from the track, and around town, get the vacuum advance Billet Distributor from MSD. If you really use the car mostly for race, forget the vacuum.

Improved drivability at part throttle as well as slightly better milage make it worth the extra $20 in my opinion.

 

the vacuum advance Billet Distributor comes with all the stuff to lock it out so try it if you don't like it lock it out
unless your geting a great deal on it I would get the vacuum advance unit

 

I do not have vacuum advance and cruised over 500 miles in about 6 months with no problems. The car will go from a dead stop or partial throttle till it hits the rev limiter with no hesitation whatsoever. Vacuum advance is mainly use for easy of cranking the motor over. You can start it with only about 4-6 degrees of timing which makes it crank easy. Once started, the vacuum kicks in and advances it somewhere around 12. Without the vacuum, you will be setting your initial timing around 10-12 degrees. If your running a standard starter, you may have a little difficulty turning the motor over with 12 degrees of timing set. I have one of those mini torque starters which doesn't have any trouble turning over the motor with this much timing.

 

Vaccum advance is for cruising is helps with gas milage and that's about it. You are not suppose to have vaccum at an idle if you do you have the hose on the wrong port on the carb. All carbs have a ported vaccum line wich means the port is above the butterflys so at idle the vaccum is minimal. At cruise speeds the manifold vaccum runs around 15-25 psi because your don't have a load the engine can handle more advance once you stomp on it the manifold vaccum drops and you run straight mechanicle. It would also advance any time you have high manifold vaccum except at idle, so for performace aplications it's not a good idea but, street cars it's a great idea.

Most of the after market distributors have adjustable vaccum advance so you can tune how much manifold vaccum is needed to activate.

PS being towed in a trailer doesn't count as cruising.............LOL

 

Ouch!!! I still say there is vacuum at idle for the reasons I stated, other wise, you wouldn't have to disconnect it to set timing like all manuals say.
Although the Sprint travels alot of miles resting comfortably in a trailer (almost 4000 so far), it does have over 500 actual miles on it so far. (honest!)

 

So how much snow did you have to shovel to take that picture of your odometer?

 

None. The 57 is out in the trailer. The Sprint and 77 is in the garage. The 71 however is another story.

 

Could you shoot a picture of the '71's odometer for me real quick? lol

 

Should not have vacuum at idle on the advance or it will pull full advance in at that time and be useless. The advance has to be feed from a port on the carb that is above the throttle plate so that it can see vacuum at low throttle opening for advance. As the throttle is opened farther the vacuum is reduced (in the manifold) and the advance is allowed to retard as the centrifigal weights take over the advance duty above about 2500 rpm or the curve setup.
For street use and better fuel milage, vacuum is needed but can always run with out it.
The 302 engines should not have a problem turning over at 10 to 12* inital timing. Starter, battery or cabling has a problem if the engine is hard to crank over with less than 10:1 compression.

 

Vacuum

Ken, you have hit it right on the button, the cranking problem is usually, in my case, caused by the headers being to close to the starter and to small a wire size in both the positive and ground cables. Now use a mini-starter and very large size cables. Again, size does matter!

 

Well, I musta goofed somewhere...

"Pegasus" has the MSD 6A box, with a new MSD 8479 vacuum advance distributor and Holley 80457S (4 barrel, vac secondary) and absolutely will die if I connect the vacuum advance!

Timing is set (no vac) at 10 BTDC and, while idling, will die if I connect the vacuum advance to EITHER the full manifold or above the throttle plate. What gives?

On top of that, I have had to play around quite a bit with the colored cams and jetting to get rid of the off-idle stumble (tip-in backfire). I am wondering if I can get the vacuum to work right and maybe come down a bit in jet size for fuel economy?

Of course most of this will be moot when I install the 6-71 blower with Intercooler

Tracy