Question: Setting of Timing on 327 - 300hp_Comp Cam

[hokie04]

I have a 64 Vette with a 327 - 300 hp engine. It was rebuilt by previous owner and he installed a Comp Cam 268H which I believe one step above stock. The question is stock timing is 8 BTDC. What should the timing be with this Comp cam and also the idle RPM. It seems to like between 700 and 800 RPM with vacum advance hooked up. Currently the timing is set a 8 BTDC and idles best at 800 RPM. With vacum plugged it will idle at 500 to 600 fine.

 

[gmjunkie]

I have a 64 Vette with a 327 - 300 hp engine. It was rebuilt by previous owner and he installed a Comp Cam 268H which I believe one step above stock. The question is stock timing is 8 BTDC. What should the timing be with this Comp cam and also the idle RPM. It seems to like between 700 and 800 RPM with vacum advance hooked up. Currently the timing is set a 8 BTDC and idles best at 800 RPM. With vacum plugged it will idle at 500 to 600 fine.

Are you sure that the Vacume advance is hooked to the right port??:confused

 

[hokie04]

The AFB carb only has one port a steel line coming from the front of the carb and converts to a hose near the distributor vacum horn. The carb pulls around 14 inches of vacum at idle with the carb line to the distributor plugged. When you hook up the distributor I didn't do a vacum reading but the idle increases by around 400 RPM. The timing at idle is 8 BTDC and with distributor hooked up the timing at idle is 15-16 BTDC.

 

[gmjunkie]

The AFB carb only has one port a steel line coming from the front of the carb and converts to a hose near the distributor vacum horn. The carb pulls around 14 inches of vacum at idle with the carb line to the distributor plugged. When you hook up the distributor I didn't do a vacum reading but the idle increases by around 400 RPM. The timing at idle is 8 BTDC and with distributor hooked up the timing at idle is 15-16 BTDC.

It's been along time since I messed with a AFB,But I thought it should not have any vacuum at Idle!

 

[BADBIRDCAGE]

It's been along time since I messed with a AFB,But I thought it should not have any vacuum at Idle!

VERY old school timing. You'll get other opinions on this one.

Warm engine up and shut down. Disconnect vacuum advance and plug vacuum source. Start engine and advance timing to fastest idle. Shut down. Restart engine. If too far advanced and engine fights starter back off timing until it does not. If engine starts without fighting starter reconnect vacuum advance and drive.

Rich

 

[JohnZ]

With that cam, anything between 8*-12* should work well for initial (base) timing, with the distributor centrifugal advance adding around 24* for about 36* total timing (measured with the vacuum advance disconnected).

When you connect the vacuum advance at idle, it should add about 15* of advance, not the 7*-8* you noted; I'd check the behavior of the vacuum advance with a Mityvac with the engine idling to see if it's either stuck, or if it requires more vacuum to deploy fully (to add 15*).

 

[hokie04]

Thanks for your info I will go back and check all the readings out.