Ok the ECU advances timing based on coolant temp, crank and cam position, throttle position, IAT, and MAP. Now when we run high boost we need to retard timing. The only things that would be directly related to boost is the MAP and, to a lesser extent, the IAT. Now if we use the missing link then we block the MAP sensor from seeing any boost. So all of the readings going to the ECU should be w/ in factory range right? So the question is what is the highest that the ECU advances timing NA? Because if it never goes above 21-22 then there should be no reason to retard timing because the ECU shouldn't see any readings different from stock. Is my reasoning all wrong? Someone please correct inform me if it is. Thanks.

I would like to know also. I need to learn as much as I can about timing and boost since I will be running 18 psi soon.

I've seen timing as high as upper 30's.

Damn :( well there goes that idea.

Ok so if the ECU never sees boost then why do we need to retard at 20psi and not 5psi? The ECU doesn't know the difference.

Actually, we need to retard from 10-ish to 15 psi. After that the stock maps do a fine job of regulating timing based on load, rpm's, intake temps, etc. That's why the timing retard modules are usually connected to a 2 bar MAP instead of a 3 bar MAP. I don't know the specific technical issue between 10 and 15 psi, but I do know the combo works. If I turn down the retard, I will knock until 15 psi. Then it goes away.....

OK let me see if I get what you are saying. So if I run 20psi will it have too much timing when it is building boost and goes through 10-15psi for a split second or will it be too quick to cause detonation? If it's too quick then I'll just leave it set at above 15psi all the time and not use any ignition system. If it does knock when going through the 10-15 mark is it enough to actually hurt anything?

You have a race gas pump in your garage?

Don't boost over 20psi on pump gas (please) especially w/o an ignition control.

The 10 to 15 psi stretch WILL hurt things if you don't properly retard ignition. And like he ^^^ said, I wouldn't go over 20psi on pump gas.

Ok guys thanks for clearing that up.

Greg- which timing retard module do you use? Also, which coil pack? Thanks.

I'm using the Crane TRC-2 Timing retard module and the stock coil pack.

In regards to the ML (or really any FCD) and how it interferes from the ECU seeing boost and thereby theoretically effecting timing, this really is a non-issue, as it being a distinct scenario only effecting ML-equipped 420a's.

Why?

Since all of these products sole purpose is to prevent the ECU from reading boost, if these devices are functioning correctly, the ECU will operate assuming an atmospheric level in any situation under boost. Really the only ones who can operate under a different scenario of the ECU reading "boost" and thereby possibly effecting timing are 95's or oddball 96+'s that CAN read boost without sending a MAP sensor CEL error accompanied with fuel cut.

Otherwise, any 96+ with any sort of boost blocking mechanism for the MAP sensor will only allow the ECU to read atmospheric pressures at best.

I am running 15 psi and I datalogged my car. My timing was at 19.5 mostly. I think thats pretty good isnt it? I dont think I am detonating.

I think maybe it's a car to car thing. Like Dave just got 20 degrees and that's like perfect. Dino doesn't use timing retard either and is running 15psi. I think I'll take my chances w/ out it. If I datalog and have too much timing then I'll buy an ignition.

running 8psi and my timing is around 20+ at boost so that must mean my car is running fine?

^ did you check out my datalog file yet?