[SD421]

Originally Posted by uttergto

I have been reading all of the comments about ignition timing. I have a 65 GTO, .030 overbore with an HO 744 cam, set 3 deg advanced. The tuneup specs say, with the vacuum advance hose disconnected, the timing should be 6 deg. advanced. My question what happens if it is set at 12 Deg. advanced. Does this cause the engine to overheat driving at 3,000 RPM and under a load?

Depends on what your mechanical advance is at 3000rpms and how many degrees does your vacuum can pulls at that rpm as well. For example.

12 initial
30 mechanical advance (stock w/o a bushing)
= 42 degrees at 3000 rpm’s
Add a stock vacuum can = 20 degrees

42+20= 62 total timing at part throttle/cruise

Yes, it’s going to overheat

42 degrees under load (no vacuum) will also overheat and probably ping too

You’ll need to shorten your mechanical to 24 degrees (by adding a bushing) & vacuum advance can of 14 degrees

12 + 24 = 36
Then add a vacuum advance that adds another 14 degrees
= total timing of 50 degrees for part throttle/cruising. No more than 52 degrees

I’d make sure to get the mechanical advance dialed in to get your 36 degrees at 3000 rpm’s
Then get an adjustable vacuum advance where you can back it off until there is no pinging at part throttle/ cruising speed

Here’s a great article http://www.camaros.org/pdf/timing101.pdf