vaccum advance

[daveid]

i dont know much about vaccum advance but, on my 454 i just took off my dominator and am in the process of hooking up a holley 4150hp. This has vaccum advance as the dominator didnt and back before, they sold me a distributer with vaccum advance so now i can hook it up.
My question is, this is gonna help me and give me more air right? Cuz i moved up in altitude so i need as much air as i can get. And another is, do i have to do much to the timing or what do i have to do after i hook it up.

thanx
david

[curtis73]

A vacuum advance will actually give you less air, but that's what you want. Sounds backwards, but one of the worst things you can do for an engine is give it too much airflow through the carb; especially at higher altitudes. The nice thing about the vacuum secondaries is that it will only open the secondary air doors as much as the engine needs. Exactly what you want. The engine can only ingest so much air, which is limited by the atmospehere around you. If the engine needs 750 cfms and you give it 900, its only going to draw 750. The vacuum secondary carb will adjust for everything UP TO its rated flow, so if you need 750 and put a 900 VS on it, it will only open up the carb for 750. The vacuum secondary carb will also be more tolerant of altitude changes when you go on trips.

The ignition vacuum advance needs ported vacuum. Its designed as a fuel economy thing first, and a drivability thing second. You might not need to change anything since the vacuum advance adds nothing at idle or WOT. It will advance it during part throttle. If you have a properly tuned mechanical curve right now, adding a little at part throttle probably won't need too much extra tuning. Is it an adjustable canister? If so, hook it up and back the adjustment screw the whole way out. This will add the least advance. Get the engine up to full operating temperature and drive it while going up hill while playing with the throttle between 1/4 and 3/4. If you don't get any detonation, screw the adjuster in one turn. Repeat this test until you get pinging at part throttle somewhere. Then back it off 1/2 to 1 turn. You may have to adjust this more for hotter temps in the summer, or if you go back down to sea level, but just keep the little allen wrench in the car so you can adjust it when you visit other lower altitudes.

[daveid]

the canister? as in the thing for the vaccum advance on the distributer?
Also, I know when an engine sounds healthy and stuff but on my engine its so dam loud that i cant really tell if theres detonation.

thanx for all the info,
david