Gen 5 boosted target AFR
 

Anyone mess with gen 5/LT4 stuff or looked at a stock tune? I'm trying to understand how direct injection impacts target AFTER I for a boosted setup. I couldn't find much info searching online other than people saying it's leaner than port injection. An example would be port injected 93 octane ls1 may target 11.2 under boost, an LT4 direct injection on the same 93 octane may target 12.0 under boost. My understanding is that its due to cooling efficiency and that more of the fuel stays a liquid in DI as opposed to PI. Learn me.

I stop seeing gains leaner and richer than 12.5 ish on DI stuff

Thanks Cesar, thats what I was looking for.

12.2-12.5 depending on how much power and hard we are leaning on one.

Thanks. Do they typically handle more timing as well because of DI? Ps....not asking for anything GM related. I just posted on here cause guys like you that do this for a living would give me concise honest feedback.

We dont run alot of timing in them but 95% of the time when we re-tune something from another shop we run less timing and make the same power and go faster. They are sensitive to timing but I think that has more to do with the E92 ecm vs the DI.

Good to know, thanks for the tips. Excited to mess with DI now.

treat it like an ls3 engine

I didn't think the LS3 liked as lean an AFR as a DI motor?

in terms of spark advance**

:P

:jest: word. TY.

The gasoline and spark plug don't really know it's DI vs PFI. You just get an extra cooling process inside the cylinder as the fuel evaporates, so think of it as running in a cooler ambient temp. I see a lot of village wisdom claiming that the DI engines need to run leaner under boost than the previous (LS3/7) engines and that's simply not true according to the tests I've run where we were able to keep conditions constant.

Thanks Greg, was hoping you'd chime in. I'm seeing other platforms outside of gm where people are running boosted setups upwards of stoich with DI and it just didn't make sense to me.

We haven't ran any DI motors on a engine dyno (waiting on more support from holley on DI) where we can control the conditions and my chassis dyno room is defiantly not a controlled environment like what you have access to. On my chassis dyno with a LT4 car on there with just CAI and stock pulleys we tried the fuel from .75-.89, the plugs looked rich at .80 and it made less power than when it was at .84. The stock LT4's heat soak so fast it took a lot of time to try to do each run at the same temp so we wernt fighting multiple variables. Very interested in hearing what you have seen at your level of testing Thank you for sharing, it is really nice to have someone at your level share what you have seen.

^LSX- You said the plugs looked rich at .8 and made less power than .84....I assume that means the richer AFR didn't help with the heat soaking of the LT4? Sounds like the DI cools the charge enough that the impact of heat soak is minimized?

Always good to hear your input greg, but I will disagree right now solely on empirical data.

I actually did a Lambda sweep on a GM 4.3L DI V6 engine as part of our Calibrated Success Blu-Ray. We had a Bosch standalone ECU on it that let us dial Lambda in real time while we held everything else constant on the engine dyno. I don't think you'll get much more consistent than that. In that particular test, we saw torque peak MUCH richer than 0.84 Lambda - more like 0.76 actually. It surprised us as well, especially since we had not yet added the spark advance that we normally would at that ratio as well. There would be a little more torque yet with the added spark since the additional fuel helps push the knock limit higher as well.

The link above shows us on the same dyno, but it isn't the Lambda sweep. It's all in the disc though.

.76, as in ~10.7 on E10? Holy crap that seems rich.