I've wanted to address fueling on my primary LT1 car for a while. The dyno tune from 2009 was good on power and driveability but pretty rich all over. I started checking the tune after learning a lot more about it over the last several years and found some things that needed doing. Primarily, O2s weren't relocated, the VE tables weren't touched. I stumbled across Injector offset voltage and realized I could have some noticeable fuel waste and rich condition. Those that played with it and got it close with Bosch-style Ford 30# reported better all over the place.
Searching for the answer from someone else's hard work (hey, I admit it) I came up with no clear answers. I have attempted to do this with fairly simple math and Excel's scatter chart functionality to get what I needed, pretty close. Unless I just completely don't get it.
Ford gives us 8 data points of offset vs voltage. GM uses 32. GM is missing 3 values that Ford gives (11V, 13V, 15V). Ford gives us fuel pressures closest to GM's 43.5 with 39.15psi and 44.95psi. So I divided that into chunks to make up some increments in between to get close to 43.5psi. Then figured out the corresponding multiplier for 43.79psi (close enough, and way better than leaving values meant for the much faster response Rochester 24#ers). That estimated multiplier is 1.05512.
Next, I laid out 35 values, knowing I'd not use 3 of them (11V, 13V, 15V) but graphing the voltage vs offset curve would help me to find the in-between values I needed to generate and paste into TunerPro.
Here's the shape with 8 data points, as Ford hands it to us for the M-9353-BB302:
Ford-8pts.jpg
Now with 35, but with 27 unknowns as zero:
Ford-35pts.jpg
So I left the chart open while I played with the values in the column. I threw some meaningless fudged numbers in below 6V so that end of the chart is not relevant. Hey, at 6V, it's not even running, right?
Ford-35pts-filled.jpg
Next, I multiplied these values by 1.05512 to get offsets for those voltages at 43.79psi: EDIT: ***I changed this to 1.0538 when I resumed work on this at post #3***
GM-35pts-filled.jpg
I've attached the spreadsheet I created, tried to make notes on it as to what I was doing. 2 sheet workbook. Feedback welcome. Column F- red numbers are multipled, blue values are filled to make the graph smooth between REAL DATA points.
I changed offset voltages, dropped the low pulse adder by an arbitrary 11% and added the O2 relocation values. The car noticeably rips better and harder than before. Throttle is more responsive, revs quicker. Definitely less fat at idle and part throttle. I left PE mode alone as it was already really good. I also dropped the idle from 875 to 800 and it's stable, though I may bump it up a hair. I do plan to datalog it as soon as it stops raining again, to make sure all is good, not leaned out where it shouldn't be. Car is as follows:
94 M6 Formula 76k mi.
ported 374 casting heads with 1.94/ 1.56 valves + appropriate springs, 7/16 studs, raised plates
Comp Ultra Pro Mag 1.6
short travel 875-16 Comp lifters
Comp 503 cam
approx. 10.9+:1 ish SCR
properly ported stock intake
TPIS 58mm TB
Stock bottom end + resize big end + ARP
Ford Racing 30# M-9353-BB302
better than stock pump but not overkill 255lph, lol
Stock regulator
44psi @KOEO
Pacesetter long tube headers
mandrel bent true dual exhaust/ X pipe with glasspacks tucked/ stacked into the old muffler location
SLP CAI
TFS ceramic elbow
retains unmodified (clean) MAF
Stock 3-channel ABS 10-bolt with 3.42s
LCAs/ relo brackets
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