Timing Q - Mechanical Distributor

[84ZZ4]

Anyone on here running a older distributor with the centrifugal advance on a N/A 3.8L? I'm wondering what you've got the base timing set to and what springs you're using.

I'm running 16* Base and one medium and one light spring. It runs good but I'm encountering some very light pinging when the outside temperature (not engine temperature) gets hot.

 

[fc227]

What Octane fuel are you running ?

 

[84ZZ4]

Argh, I thought I posted it, but it must have been on one of the other boards I posted the same Q.

I'm running 87. Factory base timing with the computer controlled dualjet was 16* in case that means anything.

 

[fc227]

You might want to try and run (2) mediums springs and see where that leaves you.

 

[84ZZ4]

Okay, I'll try that, thanks!

 

[84ZZ4]

Update:

I had to reduce the base timing to ~12*. Even with no vacuum advance and the heavy springs it still pinged. A can of top engine cleaner helped, but didn't get rid of the problem.

 

[fc227]

You might want to try some 89 octane.

 

[b4black]

How's your EGR valve? What temp thermostat and what does it run at?

 

[84ZZ4]

I'm sure '89 might take care of it, but this is sort of my daily beater. I don't really want to pay more at the pump if I don't have to and I'm willing to lose 5hp not to have to .

As far as the EGR, I hooked it up when I was having a problem and the only thing it accomplished was causing a surge at cruise. It didn't help the detonation one bit. Applying vacuum to the valve at idle killed the motor after one or two pumps on the vacuum pump, so it clearly works. I disconnected it again after realizing it didn't stop the ping.

Let's see, 180* thermostat, and I've not seen the temp above 190* (as viewed by Diacom)--even though I'm not running the ECM, I can still read a few values with the tool, most important being the temp and the O2 sensor reading. Interestingly enough, it pinged even when I had the fuel mixture richer, though the ping wasn't quite as bad.

One other interesting thing... one of my books show the 231 as using 12* of base timing up until 77 and then changing to 15* for 78 and later. Does anyone know what prompted that change? Was it the switch from odd to evenfire?