How would I calculate(what tables) total timing with tunercat & 91 tbi bin?

 

I'm not positive (I only had a brief moment to play with a 7747 this summer), but I think it is similar to SD where you need to add the base along with the Main Spark and PE to get your total spark advance in PE.

MAF is different in that the Main Spark Table also includes the base spark amount in the number, while SD is strictly the "relative" spark amount.

 

Thats what I thought but why is the tbi table so different than tpi.I was thinking of turning off the main spark bias.Would thid be a good idea?

 

The main spark bias in a tbi bin is set to 20, except in the 454tbi where its closer to 10.
From what I understand a lower number increases total spark and a higher number lowers it.
Is it a one to one ratio. if I move my main spark table down to 19 my overall spark goes up 1 degree?
Does the 20 mean 20 degrees of spark plus the main spark table plus the WOT spark table(only at wot of course)
How you you figure if it went to 19? Would I now have 21 degrees plus the main spark table plus the WOT?

 

What is the main spark bias?

 

I'm actually working out how to have winaldl display the total timing. I'm editing the eprom in the aldl stream to display the timing instead of the prom id.
I'll keep you guys posted when I get it to work.
, Jon

 

At DIY_EFI, Incoming is a tech paper on how the 747 figures timing. Might snag a copy of it to read.

 

thanks

 

I have already read that article. According to that you subtract the main spark bias form the the main spark table and WOT.
This can not be right.
Stock tbi RS's have a main spark bias of 20
WOT spark added of ~5 degrees
Last value at 100KPA and 3200RPMS of 16degrees on the spark table.
So 16+5-20=1
So a stock tbi runs 1 degree of advance, plus a couple more for coolant temp and extend spark slope. So maybe 5 degrees MAX timing.
I don't think so. So once again I ask what the main spark bias table does and how it effects timing