Help needed with ignition timing

Landon · Sep 3, 2016

Ok so I'm trying to dial in optimum ignition timing for my 340 setup, 9.5:1 compression, 360 j heads, 2.02, 1.60 valves, comp 268xe cam, edelbrock rpm intake, 670 holley, 6al mad and Mopar perf distributor. I recently had a little trouble out of my vaccum advance and while diagnosing it I started checking out my initial and mechanical timing thinking I may not have it setup for optimum operation. Right now it runs good. I have 12 initial and 42 total mechanical advance and i have never been able to detect any pinging or rattleing. While doing some reading I've seen several people say you should want your timing around 36 to 38 degrees total. I've always assumed you want as much timing as possible without detonation but now I'm rethinking that. What do some of you tuning experts recommend? And how should I dial in optimum timing without putting it on a dyno or going to the strip?

TrailBeast · Sep 3, 2016

First thing I did was look to see where you are geographically because each motor at all the different possible scenario's matters.
Do the plugs show detonation?
What elevation are you?
What fuel do you use?

All that asked 42 sounds pretty high for iron heads and 9.5
The cam is a weak spot for me, so it actually might need that much I don't know.

KitCarlson · Sep 3, 2016

Landon said:
Ok so I'm trying to dial in optimum ignition timing for my 340 setup, 9.5:1 compression, 360 j heads, 2.02, 1.60 valves, comp 268xe cam, edelbrock rpm intake, 670 holley, 6al mad and Mopar perf distributor. I recently had a little trouble out of my vaccum advance and while diagnosing it I started checking out my initial and mechanical timing thinking I may not have it setup for optimum operation. Right now it runs good. I have 12 initial and 42 total mechanical advance and i have never been able to detect any pinging or rattleing. While doing some reading I've seen several people say you should want your timing around 36 to 38 degrees total. I've always assumed you want as much timing as possible without detonation but now I'm rethinking that. What do some of you tuning experts recommend? And how should I dial in optimum timing without putting it on a dyno or going to the strip?

Reading the instructions suggests the distributor comes with 22 to 24 degrees advance. You are measuring 30, so that suggests you have vacuum advance of about 8 degrees in there too. Mechanical advance is done with vacuum pulled and plugged at carb.

Landon · Sep 5, 2016

I run 93 octane fuel. I did a little more checking on my timing marks at top dead center and they seem accurate. So I went ahead and double checked my timing and this is with mechanical only! No vaccum advanced hooked up! It read 12 initial and 42 total. Its always ran good at that and I've never been able to detect any spark knock. But I went ahead and retarded it to 10 initial and 37 total. It seems to drive about the same with maybe a little less low end torque and for the top end power I can't really tell a difference by just driving on the street. Can you still have to much total timing and not detect any spark knock? Or should I just set as much timing as possible with out detecting any spark knock for best power?

KitCarlson · Sep 5, 2016

To put the low end back, you want more base timing. It seems you pulled about 3 degrees out of the mechanical, or was that a reading error? Seems if you pull out about 5 more, the distributor would be as factory set, then adjust up base timing to 14, see how that works.

downsr · Sep 5, 2016

Disconnect the vac advance if you have one.Set your initial about 18 add 18 to 20 mech for a total of 36.If you have vac advance adjust it to add about 6 to 8 degrees if it is adjustable should be fine set at these settings