I was reading the make the most outa ur engine with wat u have, how do i go about the vaccum advance deal? Its a 75 LT.

Two biggest drawbacks to a stock 75 year engine are the heads and camshaft. A set of Vortec heads and a mild mid range power camshaft would feel like an added hundred horsepower.

Yesh I know. But How do I set the vaccum advance to be at full advance when its supposed to be instead of it being retarded?

Vacuum advance is designed to be used at light power draw, that is when you are cruising down the highway. That's why it is vacuum operated and pulls in under high vacuum/low load situations. When you accelerate, vacuum drops, advance drops, and the dizzy is operating on mechanical advance. The advance you are getting at that point is controlled by weights and springs, and should be in the 36* range. If you try to introduce more advance at that point, you will introduce spark knock and loose power.

Keep in mind that (most) drag racers don't even use vacuum advance, since they are under constant acceleration. If you suspect that vacuum advance is not pulling in at light cruise, try plugging the advance can and take it for a spin or check it with a timing light.

theres a few things you need to look at

Timing at idle
Total timing
Rate of mech. advance
Amount of mech. advance
Amount of vac. advance.

With older heads you want your total timing between 34-38* depending on your compression ratio.. With lower compression 36 to 38* is norm. the best..

Thats with out the vac advance line hooked up.

Most HEI's gives 18-22* mech. advance.. 19/20* being the most common..

So just going by that 36 - 20 = 16.. So you will want idle timing to be 16* w/o the vac advance hooked up.

Now lets get to the rate of mech advance.. This is controled by the weights and springs under the rotor button. In stock form the mech advance aint fully in untill 4000 to 5000 RPM.

You will need to buy a re curve kit.. Under 10 bucks. It comes with 6 springs. 2 light, 2 med., and 2 heavy.. 2 weights, and a center plate.

Most kits the weights and center plates aint worth using, so just clean up and grease your stock weights.

Now try diff springs on it to get the total mech advance to come in sooner. You want your mech. advance to be fully in at 2800 to 3200 rpm depending on your compression, gearings, trans type, etc.

In most cases 1 light and 1 med. spring will get you in that range..

Now you get to vac advance. Theres 2 types of vac advance cans out there. Stock non adjustable
adjustable pull off/in based on vac leavels
adjustable amount of timinging added by the can.

With low compression you can and will want more vac advance, so really the stock can may be fine.

As your compression goes up, you will not beable to use as much vac advance timing because it will cause part throttle detonation. Then thats when you need a vac can you can adjust.

Most stock cans gives 15 to 25* of vac advance, which again is fine with lower compression.

When compression gets into the mid 9's you will only be able to run about 15* of vac advance, once compression gets into the 10's you will only beable to use 12* or less of vac advance timing.

push it off the side of a mountain, with tube doors it will be slower though..

JK

Check out this web page, http://www.hotrodders.com/forum/distributor-tuning-theory-part-1-a-59033.html