vac advance or not for FE Cobra

[fordracing65]

What are the pros on not using vac advance??

[patrickt]

Originally Posted by fordracing65

What are the pros on not using vac advance??

I went with the 8594 Pro-Billet MSD all mechanical because I didn't care about gas mileage, and not having a vacuum advance unit on it is just one less thing to screw with when you're trying to get your curve just perfect.

[blykins]

And that's pretty much it.

In a Cobra, any benefits would be nominal. If you had an existing distributor that was curved well, I doubt you would see any difference in driving or efficiency.

A vacuum advance requires a vacuum source, which some engines won't have due to intake manifold or carburetor combinations. It also adds another tuning variable to the mix, which may be out of the capability of some users.

[patrickt]

Originally Posted by blykins

It also adds another tuning variable to the mix, which may be out of the capability of some users.

Like me. And even with the simplest Holley known to man (4160), the simplest cam known to man (SFT), and the simplest distributor that only has two springs and a cam to change, it still took me years to get it all just right.

[cycleguy55]

Originally Posted by fordracing65

What are the pros on not using vac advance??

It's simpler - one less thing to worry about.

OTOH, distributors with vacuum advance also have mechanical advance.

Mechanical advance is controlled by weights on springs, spinning on the dist. shaft. They advance timing as RPMs increase. Mechanical advance is necessary if you want to rev over 2000 RPM, so it's always there even if you don't think you have it. ALL distributors have it - except those used only as signals to an ignition box with timing curves.

Vacuum advance is there purely for efficiency. It advances the timing based on engine load. High vacuum = low engine load, so the engine can run more timing with no problems and deliver better fuel economy. The round vacuum can on the side of the distributor does this. You can disconnect the vacuum line (and plug it) to do without the vacuum advance if you want.

[fordracing65]

Very informative. This is a great site.

[lippy]

Originally Posted by cycleguy55

It's simpler - one less thing to worry about.

OTOH, distributors with vacuum advance also have mechanical advance.

Mechanical advance is controlled by weights on springs, spinning on the dist. shaft. They advance timing as RPMs increase. Mechanical advance is necessary if you want to rev over 2000 RPM, so it's always there even if you don't think you have it. ALL distributors have it - except those used only as signals to an ignition box with timing curves.

Vacuum advance is there purely for efficiency. It advances the timing based on engine load. High vacuum = low engine load, so the engine can run more timing with no problems and deliver better fuel economy. The round vacuum can on the side of the distributor does this. You can disconnect the vacuum line (and plug it) to do without the vacuum advance if you want.

Vacuum advance also makes the engine run cooler and provides better throttle response at most conditions.