Are they the same thing? What's the difference?

NO they are not the same Vacum advance is off engine vacum(ie. carb or intake) Centrifuagl is Motor RPM advanced. Hope this helps }[oooooo]

A guy doing some work on my 235 says that I should go with a cent. advance for a boost in horsepower. Does this make sense? How would this be done?

Preferably you'd like to have both. I'm not an expert on the 235 though, not sure what kind of ignition they came with. Ignition is determined largely by 1. RPM and 2. Engine Load (detected by vacuum). If you can accurately cover both of these variables you make more power due to more precise burns.

Patrick sales a Mallory dizzy with centrifugal only and a prepared curve for the 235, that might give you a slightly boost but hurts economy and tends to ping under load.

Frank

Tom Langdon's Stovebolt Engine Company's website has a good expanation as to why one would want both cent. and vac. advance for a street engine.

The purpose of vacumn advance is to give easier starting. In other words, the timing is retarded when there is no engine vacumn. After the engine starts to run there is manifold vac. and the distributor advances.It also retards the timing under heavy load conditions when the mainfold vacumn drops low.In the performance world more accurate,constant timing that relates to engine RPM is nessecary, so I prefer to use mechanical only. Its largely preferance and a person's use application of the vehicle when making a decision pro or con. Maybe this will help--Paul

Hi Paul,

When you are under "performance conditions" vacuum is low and vacuum advance is not advancing the ignition, just the centrifical advance is working as RPMs increase. This the same as having a centrifical only distributor. When you get back to high vacuum conditions, you are off the throttle. The vacuum advance puts more advance into the distributor cleaning the plugs and increasing fuel milage. This is truely the best of both worlds - at least until you go for computer controlled ignition timing.

Jim

P.S. Centrifical advance is what retards timing for starting conditions.