what is the difference between a mechanical and vacuum advance distributors?

Question

i dont know what distributor would work better for my chevy 383 stroker motor.

would a vacuum advance be easier or a mechanical my chevy 383 is in a 1970 pontiac gto .

Answer 1

Mechanical advance distributors use weights to advance the timing. The weights are connected to springs that regulate how quickly the timing advances. Different size weights cause the advance curve to vary. A vacuum advance causes the timing to advance when there is a load on the engine. Mechanical advance distributors only sense engine RPM, and as a result they are not as responsive as they would be if there was a vacuum advance unit attached. Vacuum advance units sense the increased engine load (which causes a drop in vacuum) the moment you open the throttle. There is not as much lag like there is with just a mechanical advance system, which has to sense increased engine RPM in order to advance the timing. Lots of race motors use just mechanical advance, because it's simpler and much more consistent, but for drivability, you probably need a vacuum advance as well because you will be driving under much more varied conditions than just flat-out racing. Get yourself a good Accel, Mallory, or MSD distributor. Summit Racing is a good source. It is simply not true that all distributors are mechanical advance, or even that they have any kind of advance feature built in to them. My Ford Ranger four cylinder had two distributors that were controlled by a computer, and were not mechanically connected to the engine. The timing was controlled only by the computer, which read inputs from a number of engine sensors and told the distributors when to fire the spark plugs .
It is a mistake to take answers you read here as gospel truth, especially from people who claim to have years of experience or who just want the points. You need to read tons of literature from reliable sources.

Answer 2

Vacuum advance uses the engine's vacuum (a vacuum hose attaches from a vacuum advance unit in the distributor to the bottom of the carburetor) to advance the timing in unison with the increased rpm

Mechanical advance uses weights and springs inside the distributor, to advance the timing.

In the old, old days, the timing was controlled by the driver, by a lever , sometimes on the steering wheel.

Application applies here. For street you really want a vacuum and mechanical combination. It gives you way better fuel economy. Pure mechanical distributors are for the race track where wide open throttle is the normal mode of operation. I would recommend an HEI distributor, however, I think it will not fit, due to firewall limits. My friend ran a stock distributor in his 1965 El Camino hot rod 350, and it worked just fine. I run a stock Chevrolet distributor in my 1974 Nova 350. No problamo.

Answer 3

Mechanical Advance Distributor

Answer 4

Biker-Dude, stick to motorcycles. An automotive distributor is normally a mechanical advance mechanism, with a vacuum trim. The way it operates_ the mechanical advance(MA) advances to a fixed point, where the engine will usually make max torque under full load. At full load, there is very little vacuum. As load decreases, the vacuum advance(VA) increases the advance, to the point determined by the builder to be the max the engine requires. This gives greater fuel effeciency. This is a breif summary of the operation. Some current engines have all electronic control, does the same thig, just fewer moving parts, quicker, and lasts longer (we hope). Tomcotexas

Answer 5

You ALWAYS have mechanical advance on a distributor, and usually you also have vacuum but you can disconnect the latter.

Mechanical advance is controlled by weights on springs, spinning on the dist. shaft. They advance timing as RPMs increase. Mechanical advance is necessary if you want to rev over 2000 RPM, so it's always there even if you don't think you have it. ALL distributors have it.

Vacuum advance is there purely for efficiency. It forwards the timing based on engine load. High vacuum = low engine load, so the engine can run more timing with no problems and deliver better fuel economy. The round vacuum can on the side of the dist. does this. You can disconnect the vacuum line (and plug it) to do without the vac advance if you want.

Answer 6

This Site Might Help You.

RE:
what is the difference between a mechanical and vacuum advance distributors?
i dont know what distributor would work better for my chevy 383 stroker motor.

would a vacuum advance be easier or a mechanical my chevy 383 is in a 1970 pontiac gto .

Answer 7

Vacuum Advance

Answer 8

i own a repair shop,and you need a msd ignition system on it with a vacuum,and mechanical advance unit on it,,and you don't have to keep adjusting the timing on it,i do this 6 days a week and i have a stroker engine,,i haven't set the timing on it in months,,and it runs fine,,ask at any advance auto parts they can show you what you need to make it run good,,hope this help,s.

Answer 9

I would use a vac advance on that vehicle ,be easier than adjusting timing periodically.