Mallory distributor question
 

I've seen some Mallory distributors (like the Comp 9000) that do not have a vacuum advance, but have only an adjustable mechanical advance....

Why are they offered like this, and why would you not want to have a vacuum advance...???

Would you want to run one of these on a street motor...???

thanks

I had a Comp 9000 with a Hyfire VI in my 73 Mustang Mach 1. It worked great on the street and when I worked for Super Shops we use to sell alot of them.They have a Unilite that has vacuum advance.

I am currently running a com9000 that just so happen I bought at a supershops years ago. I mainly ran it before for clearance with a tunnel ram. A properly modified HEI with vacuum advance is a great choice for a street motor, parts are easy to get and they are easy to rebuild and tweak, hard part is changing advance to fit the engine, not a big deal unless you have a high hp engine usually. Personnaly I like no vacuum advance and no vacuum hose. Also I get a know advance all the time.

thanks for the replies.... still trying to understand why vacuum advance is needed on some but not needed for these distributors....

what function does it serve on distributors that have it...???

Maybe this should be a seperate topic, but is there anyone who could give a quick clinic on vacuum vs. mechanical advance...???

thanks for the input...

Vac. advance does one thing--advances your timing while you are under cruise conditions which improves gas milage 2-4 mpg. When you step down on it the vac. goes away causing the time to drop back to whatever you have set your initial timing plus what ever the mechanical advance is adding at that rpm. An example--12* initial + 22* mechanical (most HEI have this much)=34* total advance at wide open throttle. Same setup at cruise--12* + 22* +vac. advance *'s (some GM's have as much as 20*)=54*. This assumes that you are turning enough RPM to have all the mechanical in. There is no way you could run this much advance at wide open throttle as it would ping itself to death. You can run one without vac. advance but you will lose gas milage and smoothness at cruise. Race engines are not cocerned with gas milage so no vac. advance needed. Hope this helps a little.

thanks for the info, I did some snooping around on the net and basically found the same explanation.... it's for non-WOT conditions and contributes to cleaner emissions.