I have a 72 cutlass supreme 350. I rebuilt it awhile ago. It was around 8.5 compression so I shaved the block and had a little taken off the heads. I advanced the cam after degreeing it 4 degrees. It now has around 9.8-10 to 1. My question is where should I start the ignition timing. Right now I have 91 octane in it. But I will go higher. Thank you for any help. JIM

 

It all depends on how much mechanical advance is built into your distributor.

 

Most engines will work well with a total of 34 to 38 total. Initial comes down to how well you can tune. The most important part will be the timing curve. The variables all come down to where the total timing comes in and as I mentioned how fast it comes in. The overall combination plays a huge role gear, weight , converter.

 

Start with the total timing at 34º and see how it runs, then adjust up or down from there. The initial will just be whatever it ends up at - initial is the total minus the mechanical advance. If the initial seems wrong, then you would need to get into the mechanical advance and modify it accordingly.

I guess the first question should be what distributor do you have?

 

This thread is very interesting to me. I'm getting ready for a first start on my rebuilt '72 SBO and the timing settings have me puzzled. How do you know how much initial to start with? Is there a "rule-of-thumb" suggestion based on cam & compression or something similar to get you into the ballpark? I understand the overall timing limit, but you could reach that total timing with various combinations of initial + mech; i.e. 12 degrees initial + 22 mechanical = 34 total, and 20 degree initial + 14 mechanical = 34 total. These engines seem to idle better with more initial timing, but I'm not sure that is the correct approach to get the best timing curve. My engine is not a stock rebuild either, it has been stroked to 375cid based on guidance from Mark (CutlassEFI). I hope I'm not hi-jacking the OPs thread, but I think my questions are relevant. Thanks!
Rodney

 

Thanks for all of the answers. They help allot. Can I run the engine at 1800-2000 rpm and set the timing to 32 degrees then with no vacuum. Thanks and Merry Christmas and Happy New Year. JIM

 

No. Set your initial at 8°@1100 rpm with the vacuum disconnected. Now you will either need a timing tape on your balancer, or a dial back timing light to figure out how much mechanical advance is in your distributor. You will need to rev the engine until it stops advancing and then you will know what you have. If you were to set it to 32° @ 2000 rpm, there would be WAY too much initial and WAY too much total advance. The mechanical usually comes all in between 3400 and 3600 RPM.

 

To break in your cam, just set your initial timing at 7 if points, 12 for HEI. You can fine tune it once its broken in.