runs better with advanced base timing

[KFred 513]

So I know a lot (almost all up to date threads) say to leave base timing at 5*btdc When using the 1g cas. I found that no matter what I do with timing set to 5* btdc I cannot get the car to run right at low rpm.

I got my car running better than ever down low at idle and light cruise by adjusting my cam gears along with spending some time on link.
I realized this must have been partially due to my base timing changing with the intake cam. I bought a timing light and set my base timing to 5* btdc and the car would not run right no matter what.

Idle was choppy, it had a slight 150 rpm surge from erratic timing adjustments. Also low speed manners were horrible. I idle my car in open loop so I made timing changes from 5* up to 12* in the DA table. Adjusted AFR from 13.0-14.0. I made all sorts of dead time/ VE corrections to get airflowperrev to where it should be but nothing worked.

I decided to adjust the cas "by ear" and my idle immediately smoothed out. I advanced it some, I still need to check to see how much but the car is running great again. I had to get my tune back in order but it only took a few minutes compared to the failed hours spent with the cas at 5*.

I guess my reason for this novel is to ask if anyone knows why/how base timing can have such an effect that I couldn't get it to run right with link. It just seems like something else may be going on that the added base advance masks?

 

[Calan]

You are running a COP right? If you are clipping the light to one of the coil wires, are you sure you have been looking at base timing off the correct side of the coil?

Coils are inductive devices; switch the timing light pickup to the other coil wire and see what happens. On one of the wires, the spark will be out of phase and the timing light can be off by 5-15 degrees.

 

[KFred 513]

Hm very interesting, I am running cop. I actually set the pickup on top of the coil rather than on any wires. When you say to put it on the other coil wire, do you mean coil 3 since they fire together? Shouldn't I just get 2x the amount of signal and "ignore" every other flash?

 

[Calan]

No... I'm talking about clipping the timing light pickup to either of the two signal wires coming off the top of a coil. Some people connect the light that way, others can get it to trigger by laying it on top of the coil.

Regardless of how you trigger the light, with a COP you have to be careful that you are seeing what you think you are seeing.

 

[KFred 513]

OK i follow you now. I set it off the cam marks with an adjustable timing light too, not the crank so I had a perfect line of sight. Since I was getting signal from the coil itself, the signal had to be coming at the right time? If that is the case that I was correctly set at 5* I'm still left wondering about the poor running condition.

 

[Calan]

How much overlap are you running on the cams?

 

[KFred 513]

Intake is advanced 2*, exhaust is retarded 4* I tried to eliminate as much overlap as possible because my cold starts were terrible. I run a q45 throttle body the right now but I have a 1g to replace it once I machine an adapter for my smim.

When I had my base timing at 5* I played with the exhaust cam and brought it back to 1* retard with no improvement. Its worth mentioning that my cams weren't degreed to factory specs. I'm just referring to the cam gear marks from 0*. My idle no longer has a lope with the cams at -2*,+4* so the overlap is not much at all. Has a smooth, seemingly stock cam idle with about 15-30 rpm fluctuation