Ignition Timing

What am I not seeing here?

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Sep 22, 2017
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Waterloo
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1978 Corvette
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#1
I have greatly improved the performance of my 1978 C3 Corvette 350 with automatic transmission. I am happy with the car now but the work I did has brought about questions. The initial advance with vacuum advance hose disconnected and plugged is 16 degrees BTDC and that setting is fine as time has proven. Now we go to mechanical advance that is set with the appropriate springs, weights and plate to be all in at 2500 RPM and 20 degrees mechanical advance and this is fine also. The issue I have is all of this advanced timing is BTDC. It is difficult to check the timing beyond the 16 degree initial because the timing mark on the damper disappears - meaning if one stands at the front of the car looking down at the damper and the damper is turning CW it would be noticed that the damper timing mark will move in a CCW direction as engine RPM is increased and therefore not visible and out of sight for the timing light. Something is screwy here and I am not seeing it. Thanks for any help !
 

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nascar03

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Jan 27, 2009
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#2
16 degrees..! Seems like a lot.
I’m not a trained tech but never seen advance that high.
I believe you can get timing lights that will make up for this in their display .
Like this ...maybe...

Graham
 
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Sep 22, 2017
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Waterloo
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1978 Corvette
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#3
Thanks, this engine loves lots of initial advance which brings about controversy for sure. TDC is TDC verified with a piston stop. In my many , many hours of research about SBC 350 initial timing settings I have found mostly all experts agree that as much initial advance as possible is the route to go as long as there is no engine ping or knock or excessive starter load. 12, 14, 16, even 20 initial has been documented. I estimate a wild gain of 50 HP from playing with timing, keeping in mind the car did not perform well before.
 
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nascar03

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#4
Danny..
Is the motor ‘built’? Or stock GM..
What does your Cam builder recommend.?
I agree, if you can get more advance without issues, and make more HP..
but 16 ‘initial’ seems up there.

If you can feel more punch with your right foot than good on ya!

Graham
 
Jul 26, 2018
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#5
Sorry folks if this is way to late to join the thread since it was last active in March but I'm pretty new here.

Danny - provide some engine specs such as compression ratio, heads, cam specs as well as roller or flat tappet, fuel you have available there in Waterloo, read differential ratio, Auto/manual, etc. I assume running MSD with a mix of springs and stop bushings?

16 degrees initial is "common" on a built SBC so depending what you have in there, you could be in the ball park.

Sorry if this is a dead thread.

Cheers,

Ryan