kdf1986

I was at a car show and saw one car with the vacuum advanced plugged. Why would you make this mod? Is there some other way to create the vacuum advance?
kdf

jdmick

I'll take a stab at this one. You can just increase your initial timing by the amount of the vacuum advance BUT, the purpose of vacuum advance is for retarding the advance under load. So in order to reduce the chances of detonation under load you wouldn't be able to utilize as much total advance without the vacuum advance which would hurt performance. So I guess I'm not sure why you would want to do this.

greyghost79

if you drive at WOT (wide open throttle) all the time (ie on the strip/track) it makes sense to plug or "lock out" vacuum advance. for normal driving, it usually makes the car miserable to drive. as per post above, vacuum advance only comes in to play during partial throttle. if you don't believe it, plug your advance cannister as in the picture you posted and try driving the car around town. you won't like it. even if you increase initial timing to compensate the performance won't be as good. plus increasing initial timing that much causes other problems (ie. detonation, hard starting, etc.).

hope this helps. my .02.

427basketcase

In California in the 80's That was a smog thing. I brought a car from Washington to California. To register and smog it you had to purchase a "NOX" kit, It was 2 vacuum caps and a sticker you put in the corner of the windsheild, somehow this made the car pollute less? The car was a 1970 Impala, 350 ci, if that makes a difference.

gerry72

Vacuum advance has its place. You won't die if you don't use it but whether you benefit from having it depends on your engine. Some of the early HP Corvettes didn't have vacuum advance from the factory so you can see that it's not exactly new.

Higher compression (around 11:1 and higher) won't really see any benefit from vacuum advance due to the effect of the compression on VE. What you're trying to do with vacuum advance is to boost cylinder pressure under very low VE.

Of course, everything is in the tune up. You can run a low-compression engine fine without the vacuum advance by carefully tailoring the centrifugal advance but it's so much easier to just use the vacuum advance. And by the way, many folks concentrate strictly on the amount of vacuum advance with the adjustable canisters. It's also important to look at the can's active range (when it comes in and when it goes out).