Melting pistons.

[Mike]

I'd think the opposite actually. More pressure creates better atomization, which means more surface area on the fuel droplets. this would mean the fuel absorbs more heat faster in its transition into vapor, and would cool the cylinder better. Just like crushed ice versus ice cubes. The crushed ice cools faster but is gone quicker too, while cubes cool slower but last longer.

My point is the ice cubes not evaporating fast enough and sitting on the piston. And of course the ice cubes being hot.

 

[Fingers]

I'm absolutely drunken with information. 'Bout get a chub reading all this stuff! Thanks guys! :hello:


How bout that CP... obviously it peaks. But how important is the curve before and after the peak. I mean how steep the curve is. How important is the ramp up to peak an ddown from peak in relation to the actual peak number? Is the peak number actually the most important number or what? Is it better for the ramp up and down to be flatter (within reason, I know it's not gonna be flat like a HP or TQ curve fro a dyno unless the sampling rate is astronomical) or is it ok to be steep? What tuning changes change that rate of increase and decrease up to peak?


Shoo. That's ^^^ a lot in one question. :angel:



C-ya

I don't know how important a sharp peak is or isn't, but a rounder peak makes more power from what I have seen so far. And the engine likes it better too.

A quick rise is an indication of either too much timing or a dead fuel shot going off all at once. A steep decline indicates that the burn is petering out. A bump, or knee in the rise usually means you need more timing, but this is only true above about 2000 RPM. Below, that you have to lower the rail pressure too much to keep the knee out and still apply enough timing.

In general, a "chubby" curve is a happy curve.

Attached is plot of a dead load going off all at once on a low compression engine. The timing is too far advanced or the rail pressure was too high and did not light when injected. When it did go off, the whole charge went at once. This was during a defuel/shift.

 

[Accelerator]

If that theroy was correct than it would also mean that any fuel pressure that could be used ( enough to make decent power anyway 20K min ) would be too much also , and that kills the theroy behind what you believe will fix it . It does re-inforce the decisions Pat has made to correct the problem though

Hence my answer "A" primary cause of piston failure but 20 k may be within the threshold of failure while 29k may not be...., who knows for all i know it could be the late or even long duration of diesel fuel burn during the power stroke....

 

[RKTMech]

Holy sht......Do any of you people work.....I cant help but think there is a room full of Isuzu engineers laughing their ass's off on there lunch 10mins at the amount of speculation and theory that has been displayed by the immense amount of intelligent and not so intelligent posts and counter posts to this thread on how to maintain 800 plus HP on STOCK parts.

That was the original idea right, cracking stock pistons, I got lost some where between the red trailer guy threatening to take his ball and go home if any one picked on him and the other guy that was getting drunk while he was posting tech info... I think there was someone touching himself at one point too!!!

When the simple truth is there will be no cheap snake oil part or tune that will keep stock motors from crumbling like ice cubes in combustion chambers (really guys, ice cubes as a metaphor) when you double their HP.

But keep it coming boys, maybe some of us tards will make hide or hare of the info spewed here and hope for an actual dura-max engineer, who knows all this shat already, to hear about this monster thread and land here and answer all our dreams.

I love you guysopcorn:

 

[Accelerator]

Holy sht......Do any of you people work.....I cant help but think there is a room full of Isuzu engineers laughing their ass's off on there lunch 10mins at the amount of speculation and theory that has been displayed by the immense amount of intelligent and not so intelligent posts and counter posts to this thread on how to maintain 800 plus HP on STOCK parts.

That was the original idea right, cracking stock pistons, I got lost some where between the red trailer guy threatening to take his ball and go home if any one picked on him and the other guy that was getting drunk while he was posting tech info... I think there was someone touching himself at one point too!!!

When the simple truth is there will be no cheap snake oil part or tune that will keep stock motors from crumbling like ice cubes in combustion chambers (really guys, ice cubes as a metaphor) when you double their HP.

But keep it coming boys, maybe some of us tards will make hide or hare of the info spewed here and hope for an actual dura-max engineer, who knows all this shat already, to hear about this monster thread and land here and answer all our dreams.

I love you guysopcorn:

:rofl::rofl: great post! :hug:

 

[JoshH]

I don't know how important a sharp peak is or isn't, but a rounder peak makes more power from what I have seen so far. And the engine likes it better too.

A quick rise is an indication of either too much timing or a dead fuel shot going off all at once. A steep decline indicates that the burn is petering out. A bump, or knee in the rise usually means you need more timing, but this is only true above about 2000 RPM. Below, that you have to lower the rail pressure too much to keep the knee out and still apply enough timing.

In general, a "chubby" curve is a happy curve.

Attached is plot of a dead load going off all at once on a low compression engine. The timing is too far advanced or the rail pressure was too high and did not light when injected. When it did go off, the whole charge went at once. This was during a defuel/shift.

I'm assuming the heavy black line is the cylinder pressure, the first small shaded green area is pilot injection, the second longer shaded green area is main injection, and the vertical red line is obviously top dead center, but what are the two thin blue curved lines?

 

[Fingers]

I'm assuming the heavy black line is the cylinder pressure, the first small shaded green area is pilot injection, the second longer shaded green area is main injection, and the vertical red line is obviously top dead center, but what are the two thin blue curved lines?

Both blues are adiabatic curves based on the cylinder pressure at 30* before and after TDC using the engine compression. The lower one is useful, but the upper not so much.

The lower one represents the expected pressure curve if there wasn't any combustion event and the number near the TDC line is the estimated effective boost to the cylinder. The boost estimate has proven to be very accurate.

 

[JOHNBOY]

like i said, before the 03-04 has no post injection (after TDC) event. this i belive is the main reason the 03-04's are not melting pistons, but yet the 04.5 and up have multiple shots and post injection, and there melting pistons faster than you can blink.

lets look at the 12 valve, it has no pre, or post injection cycle right, yet it make the most HP right now, with(1) main shot and no melting pistons........

this goes back to what i said in the prior post's making most of your fueling advance BTDC would make more since, and if timed right would save pistons and would act close to the CR dodge 03-04's..........which we both know is making over 1200HP and no melted pistons... get my point of veiw john?

Wade!:rofl: Man you totally missed what I said. What I said had NOTHING to do with a post injection shot. You need to read more before you post buddy. I was responding to what you said here in red.

I run injectors bigger than 99% of CR guys do and I can not pull that off.

every 03-04dodge CR opperates that way..

The "every 03-04 dodge CR opperates that way" statement. This just shows how little you actually know. Your correct 03-04 do not have Post injection. But the does mean they can get all the fuel in BTDC. Totally bogus statement. At a warm Idle a 03 does not start the main shot till -1*. It starts after TDC. That does not make it Post injection. Now to expand this point even further. A 03 WOT Main shot will start BTDC but the injector is still open after TDC. Just like a Dmax. If you have math skills you can figure it out. But first let’s start with some terminology.

Pilot Injection: A small fuel injection used to start a combustion event gently to reduce noise. It comes before the Main Injection.

Main injection: Just what it sounds. This is the main power generating injection, the largest.

Post Injection: A small injection after the Main injection used to raise EGT for emissions reason.

The names of these have nothing directly to do with TDC.:cool2:

Now to the math. Lets us some common timing and pulse width at progressive steps in rpm. For ease of example I will use a timing 1* per 100rpm (Very common in High output Stock injector tunes) and a 3000us main shot (again very common).


2000rpm, 20*timing, 3000us shot = at this rpm the shot takes 36* which means it ends at 16* ATDC

2500rpm, 25*timing, 3000us shot = at this rpm the shot takes 45* which means it ends at 20* ATDC

3000rpm, 30*timing, 3000us shot = at this rpm the shot takes 54* which means it ends at 24* ATDC

3500rpm, 35*timing, 3000us shot = at this rpm the shot takes 63* which means it ends at 28* ATDC

4000rpm, 40*timing, 3000us shot = at this rpm the shot takes 72* which means it ends at 32* ATDC




Now if you use less timing you push the end point of the main injection even further down the hole.

Cummins Main shot do not end before TDC. I don’t care what you think. That would take a huge injector! Cummins CR injectors are very similar size wise to a LB7. So no way the main shot is all in BTDC. I have seen the scanner with my own eyes it backs up the math. Which proves your talking out your behind.:cool2:

 

[Accelerator]

Wade!:rofl: Man you totally missed what I said. What I said had NOTHING to do with a post injection shot. You need to read more before you post buddy. I was responding to what you said here in red.

The "every 03-04 dodge CR opperates that way" statement. This just shows how little you actually know. Your correct 03-04 do not have Post injection. But the does mean they can get all the fuel in BTDC. Totally bogus statement. At a warm Idle a 03 does not start the main shot till -1*. It starts after TDC. That does not make it Post injection. Now to expand this point even further. A 03 WOT Main shot will start BTDC but the injector is still open after TDC. Just like a Dmax. If you have math skills you can figure it out. But first let’s start with some terminology.

Pilot Injection: A small fuel injection used to start a combustion event gently to reduce noise. It comes before the Main Injection.

Main injection: Just what it sounds. This is the main power generating injection, the largest.

Post Injection: A small injection after the Main injection used to raise EGT for emissions reason.

The names of these have nothing directly to do with TDC.:cool2:

Now to the math. Lets us some common timing and pulse width at progressive steps in rpm. For ease of example I will use a timing 1* per 100rpm (Very common in High output Stock injector tunes) and a 3000us main shot (again very common).


2000rpm, 20*timing, 3000us shot = at this rpm the shot takes 36* which means it ends at 16* ATDC

2500rpm, 25*timing, 3000us shot = at this rpm the shot takes 45* which means it ends at 20* ATDC

3000rpm, 30*timing, 3000us shot = at this rpm the shot takes 54* which means it ends at 24* ATDC

3500rpm, 35*timing, 3000us shot = at this rpm the shot takes 63* which means it ends at 28* ATDC

4000rpm, 40*timing, 3000us shot = at this rpm the shot takes 72* which means it ends at 32* ATDC




Now if you use less timing you push the end point of the main injection even further down the hole.

Cummins Main shot do not end before TDC. I don’t care what you think. That would take a huge injector! Cummins CR injectors are very similar size wise to a LB7. So no way the main shot is all in BTDC. I have seen the scanner with my own eyes it backs up the math. Which proves your talking out your behind.:cool2:

I agree with you john, but i was talking about the post injection event starting AFTER TDC, basically chasing the piston down the hole, thats where the issue is with the 04.5's and up, and i assume the d-max is the same way, my concern was not the end of the main shot being ATDC, i understand how that works,i just came across wrong...again


BTW stock dodge timing advance is much lower than your chart, more like 10-12*.. i too have a scanner...DRB 3

Stock dodge 03-04 is 24LMP
Stock LBZ is 19LMP

5 LMP is a big difference in flow... about 90HP or so on a dodge!

 

[Accelerator]

I think that by getting rid of the post shot we have a win-win situation, JMO though

 

[Mike]

I think that by getting rid of the post shot we have a win-win situation, JMO though

For the LB7 and LLY guys there are no post injection shots period. LBZ and LMM does have post injection. Melting pistons is occurring with all CR engines.

 

[Accelerator]

the injectors in my truck NGM were 65 LMP (thats 170% over stock), the tune was 19* timing advance about 85% max duration, and RP 25.5K, never had a issue, with alot of NOS

But thats a 03-04 dodge, much different than a d-max

03-04 only has pre and main shot, and MOST of the fuel is in BTDC, like i implied about 5 pages ago, THAT i think is where tuning should take us to make a d-max more reliable, dont kill me for my thinking out loud.:cool2:

 

[Accelerator]

For the LB7 and LLY guys there are no post injection shots period. LBZ and LMM does have post injection. Melting pistons is occurring with all CR engines.

i thought the LB7 piston handle the stress and heat better, do you see less melting issues with those pistons?

 

[JOHNBOY]

I agree with you john, but i was talking about the post injection event starting AFTER TDC, basically chasing the piston down the hole, thats where the issue is with the 04.5's and up, and i assume the d-max is the same way, my concern was not the end of the main shot being ATDC, i understand how that works,i just came across wrong...againYes is that is what you meant then it came across wrong. The main shot still chases the piston down the hole a good bit.


BTW stock dodge timing advance is much lower than your chart, more like 10-12*.. i too have a scanner...DRB 3
I never said those numbers where stock.:rofl: I said they where common in High power tunes for both the Dodge and GM with stock injectors.
Stock Duramax LB7 timing will only get you to about 14* max.

Stock dodge 03-04 is 24LMP
Stock LBZ is 19LMP

5 LMP is a big difference in flow... about 90HP or so on a dodge!But Dodge has 6 GM has 8. 24*6 =144 where as 8*19=152

Answers in Red.

 

[Accelerator]

Answers in Red.

Agreed.


what do you think my 170% injectors add up to in your d-max world?

 

[Accelerator]

never mind i found my calculator... answers in LPM

lbz 80% over =34.2 x 8=273.6

Dodge 80% over = 43.2 x6 = 259.2

LBZ 170% over 51.3 x 8 = 410.4......WOW!

my dodge 170% over = 64.8 x 6 = 388.8

 

[JOHNBOY]

never mind i found my calculator... answers in LPM

lbz 80% over =34.2 x 8=273.6

Dodge 80% over = 43.2 x6 = 259.2

my dodge 170% over = 64.8 x 6 = 388.8

I have no idea what my 7 X.011s flow. Crap tons!:rofl:

FWIW big difference between LB7 and LBZ injectos in stock form.

 

[McRat]

i thought the LB7 piston handle the stress and heat better, do you see less melting issues with those pistons?

Both LB7/LLY(same) design pistons melt, as do the LBZ/LMM's(same). Cracking is the difference. LBZ/LMM are more prone to cracking. Seems there is a quality control issue with some of them. My best guess is that they have pressed in wristpin bushings. Press fitting parts into cast aluminum is always risky. If the process isn't perfect, the aluminum cracks, either right away, or over time. When I ran LBZ pistons in Casper, they didn't crack. They melted first. The only time I had a piston start to crack, was an LLY slug, but it was already destroyed by melting first.

 

[Accelerator]

I have no idea what my 7 X.011s flow. Crap tons!:rofl:

FWIW big difference between LB7 and LBZ injectos in stock form.

is the tale true...about 20% bigger than LBZ ?

 

[JOHNBOY]

is the tale true...about 20% bigger than LBZ ?

Not sure on the actual flow. From what I have seen tuning both them. I would say 20% to 25% difference