Pushing the LT4 fuel system and still holding....recent build.

[MikeOD]

Ethanol is definitely going to play a big part in it...you need so much more fuel mass it's just very taxing on the setup.

That said, I tuned a car last night, max airflow was about 70 lb/minute, not as much as you, but it's got no problem even thinking about maintaining 20MPa through the pull.

[Higgs Boson]

Ethanol is definitely going to play a big part in it...you need so much more fuel mass it's just very taxing on the setup.

That said, I tuned a car last night, max airflow was about 70 lb/minute, not as much as you, but it's got no problem even thinking about maintaining 20MPa through the pull.

LT4 or LT1?

[MikeOD]

LT4, tuned another tonight, 85lbs of air. 20 MPa.

Can you run all LT4 stuff or is it still some LT1 stuff in your car.

[MikeOD]

I would say these cars are stubborn... But it's not that. I think we all still don't know enough about them... And I think we're missing a lot of things we need in the tune.

[Higgs Boson]

LT4, tuned another tonight, 85lbs of air. 20 MPa.

Can you run all LT4 stuff or is it still some LT1 stuff in your car.

LT4 HPFP, rails, and injectors
two lift pumps at 70 psi under load

the ethanol just demands too much. I am going to run it out and see what happens on 93.

if you don't mind, what SOI did you use on that car?

Keep in mind also I am getting that much air at maximum cylinder pressure.....it will go up from there over the next 2000 RPMs.....the calculators show I should be over 100 lb/min up top.

[LSChev]

Everything mechanically checks out on that 2015 LT1 with the HPFP issue. I haven't had any time to look at the tune yet, going to try playing with the SOI and see what that does.

[LSxpwrdZ]

I would guess that there is a cylinder pressure vs crank angle characterization that helps determine pulse-width, otherwise there is no way to determine injector delta pressure. This leads me to believe the LT4 engine obviously has a different cylinder pressure characterization being that it comes with a blower from the factory which increases cylinder pressure significantly. I may be shooting out in left field but that's the only ideas I have on the subject.

[Higgs Boson]

I would guess that there is a cylinder pressure vs crank angle characterization that helps determine pulse-width, otherwise there is no way to determine injector delta pressure. This leads me to believe the LT4 engine obviously has a different cylinder pressure characterization being that it comes with a blower from the factory which increases cylinder pressure significantly. I may be shooting out in left field but that's the only ideas I have on the subject.

So I wonder if it is better to use, on an LT1 with LT4 fuel system, the original LT1 injector and HPFP data....?

[DSteck]

Realistically, the cylinder pressure during the compression stroke is negligible compared to the fuel pressure in the rail itself and barely has an impact on the delta. That's not to say that GM doesn't do a hidden calculation, but I don't know that it's creating that much of an effect.

[LSChev]

Finally had a chance to look at the tune on that LT1. Not sure who was tuning it before but the EOI was changed quite a bit. Set that back to stock and did some very minor tweaking on the SOI and its running great now. Holds 2000psi right to 7k. Made 660/580 hp/tq. Looks like we can put more power in it now.

Has anyone played with the EOI on these?

[Higgs Boson]

The EOI description says it is for the second pulse, which doesn't apply as all the ones I have seen have split pulse disabled.

Therefore, EOI is just a function of SOI minus pulse width....when it still doesn't have time to finish, DC shoots up.

Are you seeing something else? What was the minor tweaking to SOI? How high did you go?

[LSChev]

Honestly I don't know exactly what I'm seeing haha. But the EOI tables were changed by close to 100 degrees and it was losing pressure at the rail bad (started falling off desired around 4k and was not able to rev past 6k due to pulse width being so high.) All I did was put the EOI back to stock, ran it again. It was about half a point richer but was able to rev cleanly to 7k. Then I leaned it back out to 12.2ish and crept up on the boost until I had to change the SOI to maintain rail pressure again. Increased the SOI by about 15 degrees between 4 and 6k rpm, ran it a few times for repeat-ability and then left it there.

Interesting, it never occurred to me that there would only be time for one pulse per cycle, are you sure about that?

[LSChev]

Just did some quick math and I can confirm that you are correct. Definitely only time for one pulse per cycle. Weird that the EOI made a difference in this case then. Maybe it's using a split pulse even though it's set to disabled. Or perhaps the EOI description is wrong and it is more of a "hard shutdown" for fueling in a cycle. (ie you're commanding a pulsewidth that would still be injecting fuel during the expansion stroke.) I will double check tomorrow but I am almost positive the only thing I changed was the EOI, and it was a drastic increase in rail pressure between the two (commanding 2300psi, eoi stock=2100psi eoi weird=1200psi)

[Road]

Duel pulse is used mainly for cold start emissions I never seen it to be a factor at wot