I just sprung for a complete MSD setup (6AL, Pro-Billet, Blaster 2) But I'm not sure if I should go Vacuum advance or Mechanical advance. I have always only used vacuum so I'm not sure what the mechanical will do for me. Please help.

 

Mech only will probably lose you a few MPG's.

If the car is track only or race only, then Mech is fine, since the engine will be living at WOT blasts and not using Vac advance anyways...but you want Vacuum advance n a street car so you have more timing at cruise.

 

What Mike said.

A vacuum advance distributor STILL has "mechanical" advance (i.e. centrifugal or RPM-compensated advance) but it also adds in vacuum (or "load-compensated") advance on top of that which helps out quite a bit on a street engine. Better mileage, longer plug life, less fouling and carbon buildup inside the chambers.

If you're running on the street with a cam that pulls ANY kind of vacuum you'll want to run vacuum advance. Race engines or street/strip engines that see little street duty or don't ever pull much intake manifold vacuum due to a VERY large cam, stick with a mechanical advance-only distributor.

 

get the vac advance.


worse case, you'll turn it into a all strip car.... then you can plug the vac advance, and adjust the mechanical advance to take up all the timing.

if it sees street use at all (even only on the weekends an such) get a vac advance.

the only time you should have a mechanical advance (IMO) is when you cant use a vac advance at all.

 

Typical non-computerized distributors have both. It's not an either/or situation. They use mechanical advance to provide the correct timing vs. RPM curve, and then add additional advance at high speeds when the vacuum is high (cruise conditions) for better gas mileage.

The mechanical part will provide around 20-24° of advance to get the timing from the static setting at idle (around 10° in a typical performance-oriented setup) to around 34° at about 2500 RPM. Vacuum advance will add around 12° on top of that, under cruising conditions.

You want both.

 

Most certainly answers my question. Once again, ThirdGen.org to the rescue.