Edelbrock w/Vacuum advance? Please explain?

[myasylum]

This wasn't even for my car, but for a friend. He was told to look for a Edelbrock Performer with Vacuum advance. Which is that??
I just assumed the vacuum line went from this disturber to the carb, and that was that? I didn't think that the carb had it own advance???

Do you know what he might mean?

Thanks!

 

[Burntorange70]

Sounds like he ment Vacum secondaries?

 

[chasduster]

yup I am w/ burntorange....vacuum secondaries...On the carb..vacuum holds the sendondaires shut..until you drop the throttle, no vacuume at WOT...then secondaries kick in...I like mechanical better..

 

[myasylum]

Whats the secondarys for? (I'm obviously not to good at this myself!)
Thanks!

never mind, I just read the above post

 

[dgc333]

yup I am w/ burntorange....vacuum secondaries...On the carb..vacuum holds the sendondaires shut..until you drop the throttle, no vacuume at WOT...then secondaries kick in...I like mechanical better..

Actually a spring holds the secondaries closed and the vacuum generated by air rushing through the primary venturis open the secondaries against the spring. You would get a huge bog if the secondaries just opened when the throttle went to WOT.

Myaslum, a 4 barrel carburetor has 4 venturis that allow air and fuel into the engine. Two of the venturis have throttle blades on the same shaft and the other two have throttle blade on a second shaft. The pair that is directly connected to the throttle cable are the primaries and the other pair is refered to as the secondaries.

On a vacuum secondary carb the secondaries are operated by vacuum. There is some linkage between the two that will prevent the secondaries from opening until the primaries are opened a minimum amount but whether they do or not is controlled by the vacuum generated in the venturi. The linkage will also force close the secondaries when the throttle on the primaries close.

A mechanical secondary carb (commonly refered to as a double pumper because of the two accelerator pumps) has a mecahnical linkage between the primary and secondary venturis. The linkage ratios are typically not one to one so the primaries will open more than the secondaries but by the time the primaries are fully open the secondaries will be two.

Which is better? That argument will never be settled. But generally a vacuum secondary carb works better on the street, is more tolerant of being to big for the engine and is generally easier to tune. A mechanical secondary will typically generate a little more power through the rpm but is harder to tune, needs to be sized more accurately and typically on a street vehicle won't be as economical.

 

[myasylum]

Hey, thanks! That's great info!!