Hi, guys. I have a 1991 Chevy Camaro Z28 with 350 TPI. Two and a half weeks ago, I installed the distributor and started it up last week. During initial start up, the car's idle was somewhat rough then it smoothed out and let run to operating temp. I was reading the Helm's manual, it said I should use an inductive timing light and a tachometer tool to set the timing to 6 degrees BTDC at 600 RPM in drive. What is the purpose of the tach tool? Is it necessary?

 

The tach is just to verify the idle speed.

 

no it isnt nessecary it is just used to get the most accurate rpm reading... i have never heard of seting timing in drive though sounds like it would be fun...but i remind you that stock timing isnt the key to performance... alittle more advance might be nice.

 

Ok, thanks. I was reading the label underneath the hood. It said 600 degrees BTDC (DR). Your right, timing is set in park. Why would GM say 600 degrees in drive on the label? Thanks for responding.
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Ok. Thank you.

 

you mean 600 rpm right? i dont know... but 6 degrees i think is standard for the automatic tranny but again that is just a suggestion not a rule set it where ever the engine likes it

 

Yes, you are correct. It is 6 degrees BTDC at 600 rpm. My apologies. I should have been more of what I was typing.

 

Steve- remember that you have to set timing with the EST (timing) wire disconnected to remove all computer-supplied timing. It's the one-wire weatherpack connector sticking out of the wiring harness just above the heater box. When this wire is disconnected you get your true "base" timing. THAT'S when you set it to 6* BTDC. And, by the way, it won't matter what RPM the engine is turning or what gear you're in- it will read the same regardless with the computer supplied timing taken out. This is the ONLY way to correctly set your base timing on GM EFI engines of this era.

Unplug the timign wire, start the motor, set the timing, shut it off, plug the wire back in. When you start it back up you'll notice that the timing is significantly more than 6*- this is normal.

Also- your idle speed is not adjustable. It idles at whatever the computer programming is set for in the chip.

Dwell is also non-adjustable on these computer controlled distributor and varies with RPM.

 

Thanks Damon. I really appreciate it.

 

All right guys. I was setting the timing on my car and seems to run better. But my question is where on the saw tooth indicator is six degrees BTDC, should it be on left or right side of the "big V" on the indicator looking at it from the top? The groove on the harmonic balancer was in the middle of the "big V" on the indicator with the timing light. I am assuming that is zero degrees TDC, is that correct? I am sending you a picture of the timing indicator. Another question, does each individual hash mark mean 1 degree? All right guys, thanks for posting and hope to hear from any of you and I'll keep you posted on what's going on.

 

The bottom of the "big V" is 0*. The tip of each point to the left of it is 4* advance. First one is 4*, next one is 8*, third one is 12*.

So 6* BTDC is in between the 4* and 8* point. The difference between running 0* (what you have right now) and running 6* on a TPI (what it should be) is a real nice bump in power. You'll like the results when you get it set right!

There's illustrated pictures of this floating around on the board somewhere. I'm sure somebody will post them.