I dont have a distributer VAC advance on my distributer. I have a sbc 355, with a holley 750 DP. It has the sec vacume line, but nothing connected to it. So how important is it to have one, and what are the effects, if i need one how hard is it to put in.

 

You need one.

If you still have the stock distributor in your car left over from when it was computer-controlled, but no computer, then your ignition timing is NEVER varying from the "static" setting; which is costing you BIG TIME in power and gas mileage.

To give you some idea of the effect, you have your static timing set to 6° or 10° or whatever. The centrifugal advance part of a non-computer dist begins advancing the timing at around 1200-1500 RPM, and adds about 25° by the time the RPMs get to 3500 or so, for a "total" advance of around 32-35°. Then the vacuum advance adds another 10-12° ON TOP OF THAT whenever the gas pedal is off idle and the vacuum is higher than 12" or so (i.e., cruising, basically). So your "final" "total" ignition timing right now, is 40° OR MORE retarded from where it really needs to be, while driving down the road.

Distributors are like just about anything else; you get, AT BEST, what you pay for. Meaning, if you pay the least, you get, AT BEST, ..... what you paid for. You can easily figure out what that will be.

Get one from here for a truly premium unit. www.performancedistributors.com

Very easy to put in. One bolt, one 12V plug, one tach plug, 8 spark plug wires.

 

how do i know if it is computer controlled? cant i just order a vac, they sell them from summit.

 

Has vac advance = non-computer-controlled

Has no vacuum advance = computer-controlled

Sounds like you have the CC type. Particularly if it's the stock distributor in your car left over from when it was computer-controlled.

 

is that good or bad. if its good, what do i do with the vacuume on the carb. is it bad to have both?

 

I'm not sure what you're asking, "both"....

But yes, if you're running your stock computer-controlled distributor, as it sounds like you are, without the computer like it sounds like, then that's bad, as detailed above. Makes a car run REAL lazy and sluggish, no throttle response, poor high-RPM power; tends to make it overheat at high speeds (even highway cruising); and makes it suck gas without mercy.

The carb supplies vacuum to the distributor, which then responds by changing the timing according to the vacuum. You hook the vacuum port on the carb (source) to the one on the dist (destination). Has nothing at all to do with the secondaries.

 

If the computer wasnt controlling it, probly wouldnt run very well at all then right? It would sputter and everything else right. Can you even use the left over distributor and be fine, or will the computer not be able to control it? It runs good, very fast. I just didnt know what to do with the port on the carb.

 

That's what has happened to you.

Get the right dist, hook it up right. You think it runs good now: you ain't seen nothin yet.

 

it is possible that he has a truck dizzy in it....they didnt have Vaccum Advance b/c they were governed......if it is a cc dizzy....more than 2 wires not counting the wires from the coil to the cap....then u should change it asap.....seems like it ruins plugs too....detonation perhaps? not very sure but you can run any cc stuff on a non cc engine

 

ok, i got the distributer opened and saw that the vaccum advance, hardware was all there, but the advance tube itself was not, i dont know what the guy that owned it before me was thinking, but i got an hei upgrade kit from summit on order, so i will let you know what happens when i get it installed, thanks for all the help, and advice.