initial advance.

[Gilles]

I don't know how much advance to use on my internally stock 1973 350 SBC. The ignition is a HEI and the engine runs exactly the same with, 6, 8, 10 or 12 degrees of initial advance.
Actually I run 12° and no pinging or any problem. Isn't too much?

Gilles

[462cid]

Do you have the stock specs? It probably recommends 8*

Personally, when I got my 455, I alsways advanced it to about 10*. The engine liked it there

When i got a new HEI, the card that came with the unit told me that it had been tested on an oscilloscope and I should make it 13* initial advance. 14* is better, I pull more vaccum at idle and thw car responds better in general I find, but that took some trial and error

A couple questions:

Is this an old HEI? the bushings wear out and the shaft oscillates a bit, so your needing 12* might be a case of a worn out unit

How old is your balancer? I'm not a Chevy expert, but old balancers can "walk" and make your advance timing marks incorrect

Are you running a non-stock camshaft?



One last thing I'd do if I were you is to check engine vacuum. I don't know how high your local elevation is or what cam you use, but about 15" Hg (Mercury) at idle or higher, with a pretty steady needle, is "good". It depends on several things including carb adjustment as well as cam selection (high performance cams typically make less vacuum) and timing, but you get the idea. On my mild performance engine I pull 18-19" Hg, but I am close to the ocean here.

If you find you get more vacuum at 8*, I'd leave it there. Just becuase the engines "sounds better" at idle when your at 12*, that doesn't mean that the engine will like that extra advance later on in the rpm range.

A vacuum gauge is the simplest and one of the best engine diagnostic tools for us old car guys. They are cheap and easily available

Just some thoughts to get you going. Tell us how it turns out

[Gilles]

Thanks fot your advice. The cam is stock, I live at a near ocean level. I don't know which year my HEI is. The 600 cfm Edelbrock carburetor is rejetted 8% leaner than stock. The balancer is old as the engine and maybe worn!I have a vaccum gauge and will try what you suggest.

Gilles