MaxLean

I've been doing some dataloging and tuning on my dads '90 and noticed that there is approx a five degree discrepancy between whats in the various tables and what is reported by Datamaster at any given point. For example, at 5500rpm, 100kpa, the timing table commands 28.8 degrees, but datamaster reports 22-23 at the same conditions. It even does this with the closed throttle spark advance. Set it to 20 and you get approx 15. In other words, everything seems to be retarded 5 degrees from whats commanded. This isn't due to knock retard, as there is none of that going on, and a Tech 1a reports the same as Datamaster. In my experience with my '94 LT1, it actually went the other way. Whats reported by a scan tool (or datamaster) is approx 4 degrees more than whats commanded. Popular opinion in the LT1 scenario is that there is an unknown table thats adding the timing. Is this the case with the LT5 as well?? Which do I believe, what I'm commanding or whats reported. If I go by what's reported, I'm leaving alot of performance on the table. Does anybody have and explanation for this????
Thanks
Scott

Graham Behan

Scott,
There is a 6 degree, advance, offset in the LT5. This is taken into account in the calibration, the base offset is a calibratable value at address 1B in the cal. The scan tool does not reference this offset.

Graham

LS7redhot

Hello there..
visit this site and Zr1 folks going to give you the answers
http://www.zr1netregistry.com/forum/...splay.php?f=14

glass slipper

I know you're new here, but the guy before you is the most qualified person in the world to answer that question. Graham worked for Lotus on the LT5 project in the '80s/'90s. We're fortunate he steps in here every once in a while to share his wealth of knowledge.

I agree the registry is a great place, but he won't get a better answer than he already got here.

MaxLean

I've seen spark bias tables for open and closed port throttles as well as spark bias for coolant temp vs map, but not this offset that you mention. I assume this offset is not present in the standard $8EA XDF file that I'm using for tunerpro then? So what is reported by logging software or scan tools is really six degrees off. I guess everything is correct then. Thank you all for the responses!
Scott