21,000psi on big tune with lbz regulator

[diesel-don]

Getting 21,000 psi actual on max effort tune when desired is 26,000.

In tune 4 the desired fp is in line with actual. Is my best bet to add a 2ND cp3 or is 21,000 acceptable?

 

[hondarider552]

well you are loosing power at 21k but that's borderline for me.

 

[A. Stock Lbz]

Have you datalogged it and sent it for rob to look at?

 

[NC-smokinlmm]

Meh, it's not bad. I'd probably swap in a sportsman 750 and roll with it if I did anything. Personally, I think rob tuned them like this on purpose. The engines will last longer with lower pressure, I think he limits power that way, I told him I wanted mine to live and I bet you did too...

 

[Cknight199]

Meh, it's not bad. I'd probably swap in a sportsman 750 and roll with it if I did anything. Personally, I think rob tuned them like this on purpose. The engines will last longer with lower pressure, I think he limits power that way, I told him a wanted mine to live and I bet you did too...

If desired is 26k and actual is 21k then it's not the tune holding it back. Plus running rail at below desired is not what I would do since atomization would suffer and could hurt the motor IMO.


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[JoshH]

There will not be any atomization problems at 21k psi of rail pressure.

 

[A. Stock Lbz]

Op do you have stock injectors in the truck? My lbz did this same thing with the first set of tunes rob sent me. I datalogged it and he looked it over and sent me a new tune that didn't pull rail pressure down so quick and it picked up a while bunch of power. Held 26k on the big tune

 

[Cknight199]

There will not be any atomization problems at 21k psi of rail pressure.

I must have been told wrong. Will big injectors have a problem?


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[N2BRK]

running rail at below desired is not what I would do since atomization would suffer and could hurt the motor IMO.

^^^ That's why Mark said he stopped my tune at 25,500psi.

 

[JoshH]

I suppose it depends on how big you go, but I would have a hard time believing you would have any atomization problems at that pressure. If you do, I would question the quality of your injectors.

 

[JoshH]

^^^ That's why Mark said he stopped my tune at 25,500psi.

He said you would hurt the motor because of poor fuel atomization or you would lose power?

 

[N2BRK]

Poor atomization. Hard on the motor and also working the hell out of the pump, so he suggested that it was time to stop;I was "out of fuel".

 

[JoshH]

Poor atomization. Hard on the motor and also working the hell out of the pump, so he suggested that it was time to stop;I was "out of fuel".

If you have poor fuel atomization that can damage the motor at less than 25,500, does that mean the motor never runs below that?

 

[diesel-don]

Op do you have stock injectors in the truck? My lbz did this same thing with the first set of tunes rob sent me. I datalogged it and he looked it over and sent me a new tune that didn't pull rail pressure down so quick and it picked up a while bunch of power. Held 26k on the big tune

Stock injectors for now. I didn't want to bother Rob with something I could find on the forums. I was thinking about adding another cp3. I just did the studs and turbo upgrade and I really don't want to tear into this thing again until I have rods and pistons ready to go in.

If it's desired 26,000 and actual 21,000 I don't think it's in the tune on purpose.

 

[Dozerboy]

If you want more power then it's a problem. I wouldn't daily drive on a tune that can't hold 24k+ RP. Your just taxing the engine and cp3 running it on the ragged edge.

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[N2BRK]

If you have poor fuel atomization that can damage the motor at less than 25,500, does that mean the motor never runs below that?

At max pulsewidth...?

At what point does the LMM go into limp mode at WFO for low rail pressure? I always thought it was around 24k. Are they protecting the engine with that fuel limp? I also seem to recall that a max effort tune will run down as low as 24-25k but no lower, so is that to protect the engine? I'm asking because I'd like to learn. I ASSumed until now

 

[N2BRK]

google is my friend, lol. It looks like it depends on the genre to run "well", but no mention of safety or hard on the engine kinda stuff I was looking for.

Dustin (ATP):
23-24 is actually about perfect for a Lbz/lmm on a max effort tune. They dont really run well with less than 23k


On lb7/Lly they can run good even in the 19k range

Tony (Moonshine):
Here are some facts, my 2002 LB7/LBZ-CP3 will pull down to 18,500psi and still run 12.6's

I did a lot of track testing and although the LBZ/LMM trucks want as close to 26K as possible to run well, the LLY and LB7's are more forgiving.

Pressure is better, but sometimes they just like the extra fuel, especially when that fall air is crisp and dry

 

[JoshH]

I have never heard of and cannot come up with a scenario allowing low rail pressure can damage an engine. The reason low rail pressure causes a limp mode is because they think there is a problem with the truck if the rail pressure goes a given amount below desired, and on a stock tune, they are correct. Fuel coming out of the injector nozzle is going to atomize the same at a given pressure regardless of how much you are pushing the accelerator pedal. There could possibly be other factors involved with cylinder pressure, pulse width, timing, boost, or any other number of things that could cause problems because of low rail pressure based on how the tuning is done, but I cannot imagine how fuel atomization could be one of them.

 

[N2BRK]

so it's more about efficiency than damage, then? Does that translate into higher cyl pressures/temps perhaps? Or should I shut up and keep reading :thumb::rofl:

 

[JoshH]

so it's more about efficiency than damage, then? Does that translate into higher cyl pressures/temps perhaps? Or should I shut up and keep reading :thumb::rofl:

That really all depends on how the tuning is done. If the pulse width table is written in such a way that pulse width stays the same or drops as rail pressure drops at max fuel, there shouldn't be any ill side effects from running low rail pressure, but you would have to discuss that with your tuner. Like I said, I'm not saying you can't have problems from running low rail pressure, but I don't see how fuel atomization could be the cause.