I have a question about timing and how it relates to PROM tuning:

The mechanic that built the engine for my '87 vette (383, mini ram, AFR195s, 240/240 @ .050, .580 lift, 112 lsa, +4 deg adv), put it on a dyno and burned a chip for it. He advised me that the best numbers were made with BASE timing set at 17 degrees advance.

While this number seems a lot higher than most of what I've read on the forum, it truly did start up and run it's best with base timing (EST disconnected) set at 17 degrees advanced. I tried to bring it down, but the engine would start to run worse and die by 10 - 12 degrees, so I set it at 17.

Anyway - the original chip that came with the engine was far from ideal, and was really only tweaked for WOT. Long story short, after talking to another tuner on CF, I went with a Formato chip and it is much closer.

My question is (FINALLY) - Is the base timing something that would / should be specific to each individual tune, and therefore need to vary with each tune?

Or, based on my engine combination and how it runs with the EST disconnected, should it always be set at 17 degrees (which is where it seems most comfortable, no matter what chip I put in)? Then I would just need to deal with the additional advance built into the chip, etc.

Hopefully I made some type of sense... Thanks!!
Dan

 

Or, asked differently:

Would a different tune change what BASE timing the engine operates best at (with EST disconnected)? That is simply a function of mechanical set up, how the cam was installed, etc, correct?

It is my understanding that the base timing is a global starting figure that the programmed timing in the chip would be added to.

Is my thinking correct?

Thanks for your help!!
Dan

 

There are two areas that are affected by the base timing: crank, and min/max timing at the crank (while running).

The distributor is only able to affect the timing by so many degrees. This is relative to the base timing. Also, when cranking, the engine is using the base timing. So changing the base timing changes the cranking timing.

Once running the timing min/max is relative to the base. The physical base timing needs to be (and should be!) set to the same value in the BIN. In this manner the scan tool will report the correct timing. And, the ECM is not being lied to. For a hot-rod it isn't unusual to have a base timing set to 10-14 degrees. After that hot crank can tend to be difficult.

RBob.

 

That helps me to understand the relationship!

Dan