I've now got an 05 LLY with 28,000 miles on it, and also an 06 LBZ with 67,000 miles on it.. Someone called me this morning telling me I should go with the LLY instead of the LBZ as a motor for my camaro.. Aren't the LBZ's supposed to hold up to much more power? He said the LBZ's have had a problem with the rods shortening around 550 hp.. Any help is appreciated.. Thanks....

LBZ's have a weaker piston

LBZ's have a weaker piston

A weaker piston???? How do you support that, it is also the exact same piston used in the LMM. All the Duramax pistons are forged aluminum and use the same basic design. Plus having a lower static compression ratio has no effect whatsoever on the overall strength of the material.

A weaker piston???? How do you support that, Read link below. Pack a lunch, diner and some beers yor gonna need them
it is also the exact same piston used in the LMM. Yes

All the Duramax pistons are forged aluminum and use the same basic design. No. Cast piston. See link below.Plus having a lower static compression ratio has no effect whatsoever on the overall strength of the material. [COLOR=red]In theroy yes. But you have to remove materail to lower compression. If you remove it from where you should not it can be weaker.


http://www.dieselplace.com/forum/showthread.php?t=114322&highlight=piston

You will find all different kinds of opinions on the pistons.
Here is mine. :)

LBZ/LMM pistons are the devil!

Ah, they are not forged. They are cast.

Reduced compression also reduces the loading on the piston.

The LBZ and LLY pistons are significantly different designs.

http://www.dieselplace.com/forum/showthread.php?t=114322&highlight=piston

You will find all different kinds of opinions on the pistons.
Here is mine. :)

LBZ/LMM pistons are the devil!


I don't mean to come off sounding like a jerk, but your statement [quote=JOHNBOY;2446635]But you have to remove materail to lower compression. If you remove it from where you should not it can be weaker.
Isn't entirely correct. While some engine builders will mill small amounts of piston dome material to balance and lower compression slightly, it does not mean the lower compression pistons were milled from a higher compression pistons.

A ton of engineering goes into the design and refinement and so much more is involved than just milling the top of the piston.

Anyways, the pistons were redesigned but to accomadate larger pins and the connecting rods were also beefed up to handle the increased power. With that said the combustion chamber of the cylider head was also redesigned to aid in lowering compression. So putting in cast pistons wouldn't make any sense.

I could go on and on, but since I haven't destroyed my pistons yet I'll take the word of someone who has and can actually verify the piston material and whether or not it was forged or cast.

Here's some good reading for everyone:
http://media.gm.com/servlet/GatewayServlet?target=http://image.emerald.gm.com/gmnews/viewmonthlyreleasedetail.do?domain=74&docid=16955

In closing I'll just leave it be from here on in and avoid coming off as even more of an a$$!!

Peace

I don't mean to come off sounding like a jerk, but your statement [quote=JOHNBOY;2446635]But you have to remove materail to lower compression. If you remove it from where you should not it can be weaker.
Isn't entirely correct. While some engine builders will mill small amounts of piston dome material to balance and lower compression slightly, it does not mean the lower compression pistons were milled from a higher compression pistons.

A ton of engineering goes into the design and refinement and so much more is involved than just milling the top of the piston.

Anyways, the pistons were redesigned but to accomadate larger pins and the connecting rods were also beefed up to handle the increased power. With that said the combustion chamber of the cylider head was also redesigned to aid in lowering compression. So putting in cast pistons wouldn't make any sense.

I could go on and on, but since I haven't destroyed my pistons yet I'll take the word of someone who has and can actually verify the piston material and whether or not it was forged or cast.

Here's some good reading for everyone:
http://media.gm.com/servlet/GatewayServlet?target=http://image.emerald.gm.com/gmnews/viewmonthlyreleasedetail.do?domain=74&docid=16955

In closing I'll just leave it be from here on in and avoid coming off as even more of an a$$!!

Peace

Hey easy know.;)

No one said above you where an ass. I certainly did not. :D

What is wrong IMHO with the LBZ/LMM piston is that even though GM lowered its compression ratio and used longer wrist pin is that they added the bronze wrist pin bushings. These bushing forced the internal oil cooling gallery upward. This combined with the fact that the oil gallery is larger along with the bowl being wider means the pistons cross section is a good bit less then the LB7/LLY piston makes it weaker.

It is not forged. It cast. Because of two reasons. One: The piston as a hollow ring inside it that oil is squited into to cool it. That is the oil gallery I mentioned above. Two: The top ring rides in a steel liner to help take the abuse caused by the forces of combustion and the fact that the top ring rockes slightly as the piston direction changes. The top ring is designed to rock in the groove in order to keep the groove clean so the ring does not stick.

I have taken both varities of stock pistons and cut them to bits. I am not just spouting. I beleive the LB7/LLY to be stronger and so do many others. Some beleive differnet. To each his own.

Somemore crappy news those beefier rods still bend.

I am glad you like you LMM. I like my LBZ.:) 16,000 and no cracked pistons.:rockit: Am I going fuel the crap out of it and beat it like I did my LB7? Most likely not. Honestly them darn pistons scare me. I almost bought a Cummins intead because of those pistons. But good GM 0% kept me from the darkside.

That link you gave is just and ad. I really recommend you go back and read that thread I linked. It is long and you to read past some the egos but there is a ton of good info in there.;)

First off let me just mention that your reasons listed for supporting a cast piston doesn't make any sense. Reasoning being, I work with castings and forgings every day for a living - I'm a metallurgical engineer, and neither of those two "reasons" restrict design strictly to casting and both characteristics can be achieved with a forging process.

regardless my argument is pointless so 'nuff said!!! like you said, to each his own.

I have an '07 Classic LBZ with 23000+ miles on it and love the engine. Way better than my '04 LB7 Sierra and miles ahead of the '05 LLY I had and exchanged for the '07.

The LLY I had was a joke and I consider it an engineering goof!!!!

I would be interested to hear about the forging process that could be used to form the oil gallery void inside the piston.

FWIW, we don't support a cast piston, the stock ones just are.

First off let me just mention that your reasons listed for supporting a cast piston doesn't make any sense. Reasoning being, I work with castings and forgings every day for a living - I'm a metallurgical engineer, and neither of those two "reasons" restrict design strictly to casting and both characteristics can be achieved with a forging process.

regardless my argument is pointless so 'nuff said!!! like you said, to each his own.

I have an '07 Classic LBZ with 23000+ miles on it and love the engine. Way better than my '04 LB7 Sierra and miles ahead of the '05 LLY I had and exchanged for the '07.

The LLY I had was a joke and I consider it an engineering goof!!!!

i would be interested in any thing you could share coming from the tehnical side of things its my understading that the reason our pistons lbz Lmm pistons are weaker is due to the origin of manafacturing. ie China and to be more exact the same company that make handuai pistons. Just curious if this could be one of the maine reasons for the weaker pistons.

I've now got an 05 LLY with 28,000 miles on it, and also an 06 LBZ with 67,000 miles on it.. Someone called me this morning telling me I should go with the LLY instead of the LBZ as a motor for my camaro.. Aren't the LBZ's supposed to hold up to much more power? He said the LBZ's have had a problem with the rods shortening around 550 hp.. Any help is appreciated.. Thanks....

The LBZ rods will handle more than the LB7/LLY rods

If I need different pistons and rods, I'd rather go ahead and do it now while the motor is sitting in the shop and not in the car. Who offers decent pricing and is very knowledgable? If someone is near KY, that would be great.

If I need different pistons and rods, I'd rather go ahead and do it now while the motor is sitting in the shop and not in the car. Who offers decent pricing and is very knowledgable? If someone is near KY, that would be great.

IMHO It will be alot cheaper and easier to do it now. Get forged pistons and some good rods and be done with it.