Hello I thought I nailed down a tune for my recent swap to 868 injectors in my 2000 corvette however now I’m second guessing what I found. Data seems to be anywhere from 39.5 (Jake fuzion) to 42lb (FROST), for these at 4 bar. I saw several times that switching to these ONLY requires the IFR to be changed and not to touch the offsets etc however on the same hand I saw several tunes where the offsets were changed and even in those tunes they’re off from each other. I used data from an old FROST tune I found (fast 36 injectors), in mine and I was running about 3 and a half percent lean at WOT with it. His data was set for 42lbs and I used his offsets, min pulse width etc. The car is running leaner pretty much all around than it was with the previous 01+ 28lb injectors. Does anyone have these injectors and mind sharing their tune (hptuners)? I can’t upload my tune at the moment as my laptop isn’t with me but I can if anyone wants to have a look. Thanks for any help!

 

I did a little research online and, with a little AI assist, this is what I found. If those are Bosch 0280155968 Green Giants, Bosch rates them at 310 g/min at 3 bar (43.5 psi). They're commonly sold as 42 lb/hr injectors at 50 psi, and many listings show them as 440 cc/min at 43.5 psi. I also found older LS1Tech posts where guys were calling them 40 lb/hr injectors at 58 psi from GTP applications, which is where a lot of the confusion seems to come from. Using the pressure conversion formula, if they're truly 42 lb/hr at 50 psi, they would flow about 45.2 lb/hr at 58 psi. That would make me expect them to be somewhere around 45 lb/hr in a returnless LS setup running 58 psi (4 bar), not 39.5 or 42 lb/hr. What caught my attention is your observation that the tune is set up for 42 lb/hr injectors and the car is running about 3.5% lean pretty much everywhere, including WOT. That points more toward the IFR being off than the offset data, since offsets mainly affect idle, startup, cruise, and transient fueling rather than WOT. Before touching offsets, I'd verify actual rail pressure with a gauge and make sure it's really 58 psi with the vacuum reference disconnected. A lot of people assume they're at 58 psi and later find they're actually at 54-56 psi. If pressure checks out, I'd try setting the IFR closer to 45 lb/hr, dial in the VE and MAF, and see where the trims and wideband land. Once fueling is correct, then I'd start worrying about offsets, short pulse adder, and minimum pulse width. One other thing I'd want to know is whether you're running a vacuum-referenced regulator or a fixed 58 psi returnless setup on the P01 PCM, because that changes how the IFR table should be configured.

 

That references 968’s where I have 868’s. I’ll check out the rest though. I have static 58psi returnless and pressure was verified. Thanks.

 

This is an Ai response, some dont like it but honestly its helped me a ton on my truck.

I dug around some more and I think I found the reason you're getting conflicting answers. The Bosch 0280155868 is an older Bosch Design III injector that FAST sold as a 36 lb injector. There is plenty of flow-rate information out there, but very little verified offset, short pulse, and injector characterization data. In fact, I found several forum threads of people looking for the exact same information and not finding a definitive answer.What does seem to be consistent is the flow rate. Most sources list them at roughly 36 lb/hr at 43.5 psi (3 bar), which works out to about 42 lb/hr at 58 psi (4 bar). I also found a Holley discussion on the exact 0280155868 injector that calculated them at about 42.4 lb/hr at 60 psi, which again puts them right around 42 lb/hr at your verified 58 psi fuel pressure.Based on that, I don't think the IFR is wildly wrong if you're already using 42 lb/hr. The bigger issue seems to be that Bosch never published complete characterization data for these injectors, so a lot of people have had to piece together their own offset and short pulse data from various sources. I even found an old Corvette forum discussion where a guy was building his own offset curve because he couldn't find verified data.Since you've already verified static 58 psi returnless pressure and you're only about 3.5% lean at WOT, I'd honestly say you're probably closer than you think. If it were mine, I'd trust the wideband more than random injector tables pulled from old tunes. Unless someone can post a known-good HP Tuners file using 0280155868 injectors, I'd be more inclined to make small adjustments based on actual wideband feedback than keep mixing and matching offset data from different sources.Sources I found:
ThirdGen.org - Need Help Bosch III Injector Data EECTuning.org - Bosch 0280155868 Injector Discussion Holley Forums - Injector Data Bosch 0280155868 CorvetteForum - Injector Offsets for Bosch III 0280155868