I am haveing a problem with setting the total timing on the new motor.The more I read about it, the more I am confused with it. I set the intial timing at 12 degress BTC at 900 rpm with the vacum hose off. Then I had my wife hold the rpm at 3000 (the vacum hose still off) and and checked my degree tape with the timing light and it read 24 degress, with all of the 24 degress coming in by 2800 rpm. Here is the part that I am confused about, do I now add the inital of 12 degress to the 24 degress to get my total timing of 36 degress? Or is the inital 12 degress already in the total 24 degress I have at 3000 rpm? If so,I have a problem because I should be up around 36 degress total, not 24. Can someone please clear this up for me. Thanks, Trey

It sounds like you are only getting 12 degrees of advance. It should be 12 initial + 24 advance = 36.

the 12degrees inital is in the 24 degrees you are reading at 3000rpm. give us some background, what distributor are you using and have you already modified it? setting the timing at 900 rpm you might be having the advance curve already kicking in. give us more info and i will tell you how to set the timing right

Crank,
You did not mention which distributor you are running. There are 2 possibilities.
1. Someone has worked on the distributor and it only has 12 degrees of mechanical advance in it. Or
2. Possibly the springs are so heavy that it is not getting to full advnace at 3000 rpm.
One other possibility, like mech said is that the springs are so light that it has already advanced some at 900rpm. Basically you take your initial setting (12 deg in this case) and add to it the amount of mechanical advance in the distributor, which is usually around 20 -22 degrees, to get your total of 36.
The best way to accomplish all of this is to have the distributor set up on a distributor machine, then its pretty foolproof.

I would try some lighter springs and and maybe bump your base up..you migh gain 3-5* by swapping to the lighter springs.While a distributor machine is nice,all you need is some springs,time and patience.You could also try flipping over the center plate to get a few more degrees too
I have 20* mechanical advance in my HEI,plus 16* base for *36 total by 3000

My stock 86 305 HEI only has about 12-14deg from the factory.

Steve

What heads are you using??

crankitup, Sounds like you have an HEI. What wanarace says is normal. About the only way to get more mech advance in those is do some careful grinding on the weights and weight cam. Those and the springs are what control the amount of mech advance, not the slot and bushing like on points type dist.

If he has 12 init and another 12 of mech with the vacume disconected wont the vacume give him the rest to bring it up to 34, as long as the vacume advances it 10. or am I missing something too

Originally posted by PUUU70:
If he has 12 init and another 12 of mech with the vacume disconected wont the vacume give him the rest to bring it up to 34, as long as the vacume advances it 10. or am I missing something too The mechanical advance should be 32-40° total, whatever works best for maximum power. The vacuum advance would be in addition to this from 10-20° depending on the engine, raising the part-throttle advance into the 45-55° degree range. Under full throttle there is no vacuum advance.

Sorry it took me so long to get back to my computer. You all are right ,it is an HCI. I have the usual 3 sets of springs for it. I had the black (the strongest springs) in it when I first checked the timing. I have since put in the gold springs (the weakest). Other then that the distributor is stock. I'm using open chamber oval port heads.I take it from what you all have had to say, I should be getting between 32-40 on the timing tape.

Yes 32-40, 36-38 ideal with vacuum advance temporarily disconnected. Most HEI's were used from the factory with port sourced vacuum advance for better emissions. That's why the mech advance is so little compared to the older point type distributors, which utilized manifold vacuum advance. I won't even open up that can of worms (manifold vs port vacuum advance). Do a search if you want to see the debates.

I've never seen a factory setup use manifold vacume for the distributor, only ported.