[timbergrove]

I have just completely rebuilt the 389 for my 65 GTO. As soon as gas got to the carb, it started and after setting the timing (6 degrees BTDC) and idle speed, it has been running fine so far. Broke in the new cam for 1/2 hour at 2000 just fine. There is no hood, doors, trunk lid, or windows yet, I just set the body on the frame and started it up so I cannot drive it anywhere but up and down my 1000 foot gravel driveway in first gear.

But when we checked the timing at high rpm, we found it only went up to 19 degrees. I think it is supposed to go much higher, perhaps up to 32 BTDC at 3000 rpm.

I cannot find any spec on the max timing of the distributer, vacuum disconnected. Can anyone tell me what the max timing should rise to at high rpm and what my options are if this is much greater than 19 degrees?

Your help is greatly appreciated.

[timbergrove]

I have just completely rebuilt the 389 for my 65 GTO. As soon as gas got to the carb, it started and after setting the timing (6 degrees BTDC) and idle speed, it has been running fine so far. Broke in the new cam for 1/2 hour at 2000 just fine. There is no hood, doors, trunk lid, or windows yet, I just set the body on the frame and started it up so I cannot drive it anywhere but up and down my 1000 foot gravel driveway in first gear.

But when we checked the timing at high rpm, we found it only went up to 19 degrees. I think it is supposed to go much higher, perhaps up to 32 BTDC at 3000 rpm.

I cannot find any spec on the max timing of the distributer, vacuum disconnected. Can anyone tell me what the max timing should rise to at high rpm and what my options are if this is much greater than 19 degrees?

Your help is greatly appreciated.

[WDCreech]

I remember that my old 389 liked a total of 37 to 38 deg total, with stock 716 heads, for drag racing, but that was before unleaded gas. Vacuum advance is only for milage on the street, so just bump your timing up to give you a total of 32 to 38 degrees. Good luck!


Bill

[timbergrove]

After talking to three machine shops, I learned that the distributer mechanical advance can be adjusted by a shop to give a fairly linear ramp in advance vs rpm for about $50. They actually have a machine dedicated to this work. From what I hear, Pontiac did not pay much attention to the ramp curve. This is a performance issue if you want to get the most horsepower out of your engine and is probably not mandatory for a street machine. However, now that I know that the weights and springs can be adjusted for a linear performance curve, I plan to have it done while my goat is laid up for the winter.

Bob

[hobbygto65]

Most auto parts stores carry a recurve kit for GM dist. They contain new weights and a choice of 3 different strength springs. Just cleaning your old ones may do the trick too.

[Old Man Taylor]

The stock distributor for that car had 12 distributor degrees (24 crank degrees) from the factory. Although the spec was 6 degrees at idle you will find it runs much better with 12-16 initial. This assumes your compression is low enough that it won't be a problem with gas. The old closed chamber heads needed more advance than the newer open chamber heads because the flame propagation was slower. Best performance could be as high as 42 degrees total. I would set it at 12-14 initial with 24 crank degrees in the distributor all in by about 3000.

http://www.jimspontiac.homestead.com/Index.html

[timbergrove]

Thank you for your replies.

I will try setting the idle advance higher, but I expect it will be hard to start. What did you experience with starting when you increased your advance?

[Old Man Taylor]

With a good starter it is no problem. My racecar is set at 18 initial. My old wagon was set at 16 and it used the factory high torque starter. Also no problem.

http://www.jimspontiac.homestead.com/Index.html

[Sun Tuned]

You may find you will need to either limit the amount of vac adv you currently have or change it to one with different values. This is in addition to turning up the initial setting. Be sure the mechanical advance mechanism is free and not binding and that the advance does not start until 1100 to 1200 crank rpm and like Old Man Taylor said about 3000 crank rpm will be about all you can do on todays gas with your heads.