Duramax Monotherm Pistons

TrentNell

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Jul 7, 2008
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slc tuah
Pat this may be a stupid question and i am almost positive you did but, but did you change all the Bidi controls in the TCM tune ? Most are set to over ride / ignore other commands over at a anything over 4k ( D5040 - D5047 )
 

McRat

Diesel Hotrodder
Aug 2, 2006
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Come on Ben. All you need to do is control the valves, manually. No TCM brain to figure out if you should be in "fifth" just align the clutches for "fifth" and let her fly. Even one of your little computers can do that!

I'll make one for you Pat. You like it, you buy it.

I think there would be a market for a manual controller.

Dyno testing, trans testing on a stand, sled pulling, LSR, and perhaps even drag use.
 

McRat

Diesel Hotrodder
Aug 2, 2006
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Pat this may be a stupid question and i am almost positive you did but, but did you change all the Bidi controls in the TCM tune ? Most are set to over ride / ignore other commands over at a anything over 4k ( D5040 - D5047 )

I'd have to look. I know I normally shut off that stuff so I can dyno.
 

Fingers

Village Idiot
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Apr 1, 2008
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The hard part is controlling the apply and release to avoid hang ups. Fixed table would work for drag, LSR, maybe sled pulling.

On Topic=> Is the wrist pin length the same on the monotherms? Are there oil passages for cooling?
 

duratothemax

<--- slippery roads
Aug 28, 2006
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The hard part is controlling the apply and release to avoid hang ups. Fixed table would work for drag, LSR, maybe sled pulling.

On Topic=> Is the wrist pin length the same on the monotherms? Are there oil passages for cooling?

Should have been more clear...this is what I meant...it would be impossible to make a "full-manual valve body" in the traditional sense that everyone thinks of when they think of a "full-manual transmission valve body"...IE, no electronics, all shifting is done with a manual shift lever.

Its easy to make it HOLD a gear steady-state with no TCM. For example if you want the trans to do 5th gear, and only 5th gear... Trim A, Shift solenoid C, shift solenoid D...leave those wires "floating" (off), and ground the wires going to Trim B, and shift solenoid E. That would get you a steady-state 5th gear.
 

duratothemax

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Aug 28, 2006
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Ben,

The LML piston bowl volume is the same as the LBZ/LMM at 41cc. So I believe the compression ration is 16:8 just like the LBZ/LMM.

Guy

Hmm interesting. Maybe GM originally planned a lower compression ratio, and thats why the service manual/documentation says 16.0:1 for the LML? It certainly wouldnt be the first time that the GM docs were wrong...for example when the LMM came out the GM info/docs said that it had an electrically-controlled cooling fan (like the current LML). Obviously, as we all know, the LMM does not have an electronically controlled fan clutch; its the same as the 01-06 duramax's.
 

gmduramax

Shits broke
Jun 12, 2008
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Rounded up some pistons this morning and ran them across the scale. These are pistons only, no pins or rings.

LB7/LLY +.020 Piston 845-860 grams. (Cut and Coated 16.8:1 compression)

LBZ/LMM Std. Bore Piston 918 grams. (16.8:1 compression)

LML Std. Bore Piston 834 grams (16.8:1 compression)

Forged Stock Stroke +.020 Piston 847 grams. (16.5:1 compression)

Duramax Billet Monotherm +.020 Piston 1064 grams. (16.5:1 compression)

So if I wanted to run the Monotherm pistons but not add weight to the rotating assembly would it be possible to take 25 grams out of each wrist pin?
 

TrentNell

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Jul 7, 2008
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slc tuah
So if I wanted to run the Monotherm pistons but not add weight to the rotating assembly would it be possible to take 25 grams out of each wrist pin?

X2 , also if you made sure to run a real light rod like a Carrillo , lightened wrist pins , ect i wonder how close you could get each rod and piston assembly to that of an aluminum setup ?
 

TeaBagger2006

Im a Garrett Nut Swinger
May 11, 2008
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so there is roughly around 3.7 lbs difference between the steel pistons and the aluminum pistons(talking about a whole set).
 

TrentNell

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Jul 7, 2008
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That would be the last place I would want material removed from. I bet you could get 25+g out of the bottom/inside of the piston.

The wrist pins in my motor have been lightened , there is a safe amount that can be removed , whether its enough to make a difference or not I dont know , I was told how much mine were lightened but cant remember now .
 

Slammed2007Lbz

Super Spicy Tunaz
Feb 1, 2009
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After looking at the weights of all these,pistons is it possible that all the lbz piston issues are because they are much heavier than all the other years? Just kinda odd that we had no piston issues and then they came out with the heavier lbs pistons and we have failures.
 

paint94979

Beer Nazi
Sep 18, 2006
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After looking at the weights of all these,pistons is it possible that all the lbz piston issues are because they are much heavier than all the other years? Just kinda odd that we had no piston issues and then they came out with the heavier lbs pistons and we have failures.

No. They went from Mahle to a cheaper Asian manufacture
 

Dirtymaxx03

Active member
Aug 4, 2009
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After looking at the weights of all these,pistons is it possible that all the lbz piston issues are because they are much heavier than all the other years? Just kinda odd that we had no piston issues and then they came out with the heavier lbs pistons and we have failures.

thats what i was thinking. but that is when they made the switch from mahle to overseas garbage. but that still doesnt mean that the weight couldnt affect it...? idk too many variables to know a real answer
 

McRat

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Aug 2, 2006
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LBZ's were the first dmax pistons with pressed in sleeves. Like crankshafts, not all LBZ pistons are weak. Some take lots of abuse without cracking or holing (core shift), others fail under stock loads.
 

Yellow Jacket

WannaBe Sled Puller
Feb 11, 2009
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Who makes the LML pistons? Would they be a alternative that would be better than the LB7/LLY pistons for a daily driver/sled puller dmax?
 

Yellow Jacket

WannaBe Sled Puller
Feb 11, 2009
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LBZ's were the first dmax pistons with pressed in sleeves. Like crankshafts, not all LBZ pistons are weak. Some take lots of abuse without cracking or holing (core shift), others fail under stock loads.

How do you know if you have good or bad? Is there a way to tell or test?