Injector Spray Pattern - LMM

[kidturbo]

Was talking about what size just yesterday. I drilled them on a LLY some years ago with stock pump. No issues. 5/32 drill bit comes to mind, but don't take that as gospel. So long as you leave the spring and check ball alone, they only spray at above 27psi.

I can say the LML squirters are considerably lager than you could even drill out the older ones. So GM found it benificial to
Increase cooling of pistons for some reason.


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[rcr1978]

Was talking about what size just yesterday. I drilled them on a LLY some years ago with stock pump. No issues. 5/32 drill bit comes to mind, but don't take that as gospel. So long as you leave the spring and check ball alone, they only spray at above 27psi.

I can say the LML squirters are considerably lager than you could even drill out the older ones. So GM found it benificial to
Increase cooling of pistons for some reason.


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Thanks for the info if I can squeeze the LML pump in mine like you did I will try the LML squirters to.

 

[rcr1978]

Have you guys tried the Diamond forged pistons with a steel insert in a boat build yet? Looks like these boats really purt the hurtn on the pistons in a hurry so i'm curious to see how the fingers one do on your current build.

 

[malibu795]

I talked to JJ at diamond last year about them.. but wasn't sure what I was doing this year..
Forgde with a keystone top ring sounds promising but they are a good ~50% more than mahle with good reason.. when I talked to him

 

[kidturbo]

I talked to JJ at diamond last year about them.. but wasn't sure what I was doing this year..
Forgde with a keystone top ring sounds promising but they are a good ~50% more than mahle with good reason.. when I talked to him

Met JJ at Indy while checking out those pistons. Certainly solves one of my biggest concerns about forged. We've chatted about a monotherm dyno test. Which is what's really needed to have sustained power, and survive the occasional injector misfire or A/F related mishaps.

I firmly believe if you can keep any decent cast piston cooled, they should hold 700-800hp for short bursts without issue. In single day I beat a Mahle set hard as anyone. 10+ 1 mile WOT passes at well over 1500EGT. After that ya know if they are gonna hold up or not..

Guess why so pee'd to find a key trick to this combo was overlooked. Makes it impossibly to isolate why an identical piston failed, when all comparative data is based off different cooling volumes...

 

[rcr1978]

I talked to JJ at diamond last year about them.. but wasn't sure what I was doing this year..
Forgde with a keystone top ring sounds promising but they are a good ~50% more than mahle with good reason.. when I talked to him

This is why I went with the regular race cast and the diamonds were not really tested yet I did talk to them on the phone and they had a few sets in boat builds just no test time yet.

 

[kidturbo]

Remember the boat Wagler built that beautiful Duramax with transparent valve covers to go in? Then it all just fell off the radar bout a year ago. That guy ditched the Dmax plans for a pair of standard 500hp marine Cummins. After some testing, he realized there's a big difference between 500hp and 1200hp. So now according to his latest post, Industrial Injection is building a pair of big HP Cummins for it. Being a Mono is actually available for that engine, I'm curious to know which piston style they choose...

Back on topic, thanks for everyone's input on the spray pattern question. I posted it very vague cause I wanted some honest opinions to how they looked with a crap load of timing on decent size sticks. While only about 2-3deg more advance than my boat ran happily, [plus pilot and less oil cooling] I know now the race casts still contain weak points that can't take extended heat and pressure. If anyone has similar std bowl race cast failure pics, please do share the data.

:hug:

 

[Fingers]

The problem with pistons cracking is not a cooling issue.

 

[kidturbo]

Okay I'm all ears...

But my first question is, why did I crack two stockers back to back when a pieces of rubber shot up the main oil passage and restricted flow?

Load, and EGT was at a minimum when all mine let go. While those same stock pistons took more heat and abuse for way longer periods of times before it spun two rods due to oil starvation. Nothing else changed in that setup between those tear downs.

What's your best analysis of that race Mahle above with no cracks, but hole in the bowl? We know LML's crack too, so the increased oiling / cooling that GM modified everything for obviously wasn't the main issue was it?

 

[Stingpuller]

Pistons

I see more LML's with holes in the pistons than any other years. Between the pumps blowing up and pistons with holes I will stick with my LBZ.

 

[IOWA LLY]

I see more LML's with holes in the pistons than any other years. Between the pumps blowing up and pistons with holes I will stick with my LBZ.

I agree. The LLY kinda got labeled the bastard child of the duramax family, but I think in a short amount of time the LML is gonna take over that position. Just my opinion of course. But they have some of the most expensive inherent issues of any duramax to date.

And the L5P, at least on paper is gonna dwarf the LML in every aspect. The only reason the LML platform has held on as a decent engine is because it was still being produced, and none of them were that old. That's all changing.


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[RidinHigh99]

I agree. The LLY kinda got labeled the bastard child of the duramax family, but I think in a short amount of time the LML is gonna take over that position. Just my opinion of course. But they have some of the most expensive inherent issues of any duramax to date.

And the L5P, at least on paper is gonna dwarf the LML in every aspect. The only reason the LML platform has held on as a decent engine is because it was still being produced, and none of them were that old. That's all changing.


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What have you heard about the L5P? Everything I've heard is pretty good consensus


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[IOWA LLY]

What have you heard about the L5P? Everything I've heard is pretty good consensus


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So far so good. Only really negative I've heard is a few tuning quirks. Most of which have been discussed on this forum.


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[gmduramax]

The problem with pistons cracking is not a cooling issue.

I could be wrong and I don't know the correct name for it. But isn't the problem with the piston the silicon(sp) that's part of the casting process? From what I read the silicon expands at a different rate than the aluminum causing stress fractures from fluctuating temps. I understand the pistons are going to see a huge fluctuations in temperature. But wouldn't keeping them cooler help? But who knows if opening up the squirters is even to even keep them cooler.

 

[kidturbo]

The only common operational factor shared by the all failures I've personally witnessed is; engine was at operating temp, shut down for aprox 5-10 minutes, then started and immediately subjected to normal getting on plane loads. Every piston failed within 30 seconds under light to moderate load. I actually have video of the one above letting go I'll toss a link up to.

The OEM's all went quickest. Tally is at, 2 stock LLY, 1 stock LMM, and the race Mahle above. Ah, and can't forget those Mahle forged, 8 at once they claim..

So is it a temperature shock from much cooler oil hitting a heat soaked piston, a lack of oil cooling volume as I lean towards, or some strange metallurgy factors?

They don't seem to exhibit this problem if you bring them up to temp slowly, or keep em good and hot. All but the forged set shared that exact failure scenario. While none had any improved oiling mods.

The engine still running some 300hrs later, a 16.5:1 LLY Mahle race, polished bowls with valve reliefs, drilled out sqirters, running no pilots above 2400. That's the basic facts we have to work with. After 5yrs and a good chunk of $ in blocks and scrapped pistons...

 

[kidturbo]

Here is the video of engine above when piston let go. Total time of original video from engine start to the end was just over 2 minutes.

Also remember this boat has a 6sp Allison with std converter in there. So about as close to your typical truck setup as you'll find, in a boat.

EFI screenshots above are from previous run on same day.

[YOUTUBE]qH4jx4AWEl0[/YOUTUBE]

 

[Fingers]

I could be wrong and I don't know the correct name for it. But isn't the problem with the piston the silicon(sp) that's part of the casting process? From what I read the silicon expands at a different rate than the aluminum causing stress fractures from fluctuating temps. I understand the pistons are going to see a huge fluctuations in temperature. But wouldn't keeping them cooler help? But who knows if opening up the squirters is even to even keep them cooler.

No, the silica does not cause the problem. It enhances the thermal stability of the aluminum, but does reduce the ultimate strength. In other words, it helps control the thermal expansion of the piston.

Oil cooling does help keep the pistons cooler. But they are not melting, they are cracking.

 

[Fingers]

The only common operational factor shared by the all failures I've personally witnessed is; engine was at operating temp, shut down for aprox 5-10 minutes, then started and immediately subjected to normal getting on plane loads. Every piston failed within 30 seconds under light to moderate load. I actually have video of the one above letting go I'll toss a link up to.

The OEM's all went quickest. Tally is at, 2 stock LLY, 1 stock LMM, and the race Mahle above. Ah, and can't forget those Mahle forged, 8 at once they claim..

So is it a temperature shock from much cooler oil hitting a heat soaked piston, a lack of oil cooling volume as I lean towards, or some strange metallurgy factors?

They don't seem to exhibit this problem if you bring them up to temp slowly, or keep em good and hot. All but the forged set shared that exact failure scenario. While none had any improved oiling mods.

The engine still running some 300hrs later, a 16.5:1 LLY Mahle race, polished bowls with valve reliefs, drilled out sqirters, running no pilots above 2400. That's the basic facts we have to work with. After 5yrs and a good chunk of $ in blocks and scrapped pistons...

Marine applications are bastards for thermal shocking all engine parts. Blocks and heads too.

I thought you had run some Oval Bowls....

The main problem has to do with pressurization of the area above the fire ring. Think of a fire cracker in a paper cup and how it splits. If that area does not pressurize enough, the piston will fail under normal loads and applications. There is no margin.

 

[MarkBroviak]

Marine applications are bastards for thermal shocking all engine parts. Blocks and heads too.

I thought you had run some Oval Bowls....

The main problem has to do with pressurization of the area above the fire ring. Think of a fire cracker in a paper cup and how it splits. If that area does not pressurize enough, the piston will fail under normal loads and applications. There is no margin.

I agree and think there is more to this because of the constant load and duty cycle on the parts. Oval bowls should technically fix the problem I'd think because of the strength over the pin to keep them from cracking even with excessive surface temperatures on the pistons. Only one way to find out!

 

[malibu795]

The only common operational factor shared by the all failures I've personally witnessed is; engine was at operating temp, shut down for aprox 5-10 minutes, then started and immediately subjected to normal getting on plane loads. Every piston failed within 30 seconds under light to moderate load. I actually have video of the one above letting go I'll toss a link up to.

The OEM's all went quickest. Tally is at, 2 stock LLY, 1 stock LMM, and the race Mahle above. Ah, and can't forget those Mahle forged, 8 at once they claim..

So is it a temperature shock from much cooler oil hitting a heat soaked piston, a lack of oil cooling volume as I lean towards, or some strange metallurgy factors?

They don't seem to exhibit this problem if you bring them up to temp slowly, or keep em good and hot. All but the forged set shared that exact failure scenario. While none had any improved oiling mods.

The engine still running some 300hrs later, a 16.5:1 LLY Mahle race, polished bowls with valve reliefs, drilled out sqirters, running no pilots above 2400. That's the basic facts we have to work with. After 5yrs and a good chunk of $ in blocks and scrapped pistons...

Both my stock pistons failed towards bottom long grades, shortly after rolling back into the throttle to climb the next grade. Everything was heat soaked prior to coasting Down the grade
Both times in the spring.. and truck/Trailer where loaded towards capacity limit.
I'd say that's as close to duplicating what you did.

The LBZ lasted 40k miles in OEM cooler setup.. the LMM got a aux oil cooler before hauling.. lasted ~125k in stock form.. with substantually more HP 275-300fwhp vs 450-475fwhp..and grossing more weight as well 26,000 to 36,000lbs.

From experience...The aux coolers lowered the overall peak/valley swing and extended time between peak/valley temps.. might have something to do why the LMM lasted ~3x longer IDK

Usually see close to 10-20° drop from cresting the hill to rolling back on the throttle..for summer time(~80° temps)..seen upwards of 60° drops in the winter(~20° temps)
Longer the grade..greater the temp swing

IDK how much of a temp drop you're seeing during the 5-10 minute shut down.

What are you seeing for oil temps?

Further thinking out loud..
Hot fluid on a cold item= cracks item
And cold fluid on a hot item..= item lives another day..

ECT is almost always lower than EOT, and usually cools off faster then EOT as well...

While Engine is off pistons can transfer more heat to the ECT.. making them substantually? Cooler than normal.. fire engine back up, now you're pumping hot oil on a "cold" piston, put the thermal shocked pistons under a load and they crack...
Basic theroy...it makes sense...