hey i have a 70' cleveland with boss heads 10.7:1 comp ratio...cam intake carb headers all that crap..but it seems like ive been having a trouble with the timing. I converted it to one of those australian pro comp hei ignitions..ive been setting the intitial 10-15 degrees and the mechanical advance ups it to about 25-30 btdc...the problem may be with the vacuum advance ..do i hook it up to the manifold vacuum port or the top of the carb port....when its all said and done what should the total degrees btdc be with initial, mechanical and vacuum advance? thanks
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The quench head Clevelands (and that's what you have if you have the Boss heads with 10.7:1 compression with flat top pistons) like about 36 to 38 degrees total timing without vacuum advance.

The best way to set the timing is to run the engine at about 3000 rpm so that all the mechanical advance is in and set the total timing with the vacuum advance disconnected to 36 or 38 degrees. The purpose of vacuum advance is to give the engine better gas mileage so when you're cruising with some engine vacuum, it advances the timing more to give you better mileage. It should be hooked up tomanifold vacuum port. When the engine is under full throttle, vacuum is zero. When you let off the gas, the vacuum is maximum.

Hope this answers your questions and doesn't sound too confusing.

 

Initial should be about 10* to start, with the vacuum disconnected. The vacuum advance should be hooked to a ported vacuum source. Varies from carb to carb which one this is, so take a gander online or let us know which carb you have.

 

[align=left]yeah ill have to try that tomorrow..thanks fosters and its got a holley 850 double pumper
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