Vacuum advance issues

[davepl]

I thought 307s were very low compression... doubt it should ping on 87 octane. You really want vacuum advance, it's not just an emissions thing. Without it you're going to have very retarted timing at idle which will heat up valves, heat up the engine, and suck for driveability. You might be able to get it to work with a lot of base timing and less mechanical advance, but then you'll be fighting part-throttle issues.

[cppursell]

Originally Posted by davepl

I thought 307s were very low compression... doubt it should ping on 87 octane. You really want vacuum advance, it's not just an emissions thing. Without it you're going to have very retarted timing at idle which will heat up valves, heat up the engine, and suck for driveability. You might be able to get it to work with a lot of base timing and less mechanical advance, but then you'll be fighting part-throttle issues.

As I mentioned above, I conquered the 307 doggie-ness by using 283 power-pak heads, giving a higher 9.9:1 compression.

Yes I agree vacuum advance is valuable. This mechanic told me to just run without vacuum, and now after my research I wholeheartedly disagree with him.

[mud.man.rj]

Originally Posted by cppursell

As I mentioned above, I conquered the 307 doggie-ness by using 283 power-pak heads, giving a higher 9.9:1 compression.

Yes I agree vacuum advance is valuable. This mechanic told me to just run without vacuum, and now after my research I wholeheartedly disagree with him.

The mechanic is right if it is an all out mostly race engine but not a street or part time srip engine, the vac advance is there for a reason, besides part throttle it helps a lot for economy because as stated you would be running it pretty retarded and then low power and kind of gutless. Start with heavy stock springs for initial advance then reconnect vac advance and readjust when driving, just make sure it is ported only not full vacumn that way it starts off with no vacumn adv until the throttle is just part way open then it helps as you accelerate so it is mech only until the throttle starts to open, if it was full vac then the advance would give extra timing at idle and cause ping not what you want as noticed.