LLY: Bent rods!!
- Thread starter THduramax
- Start date
Man, some of you guys are just freaking crazy.I dont feel so bad any more. :rofl:
Tom, I still can't believe the power your truck was putting down. You don't hear of many stock charger guys bending rods. Did you ever play with the calculator on this site to figure out what the truck was making when you ran your 12.1?
Calc here figured 567 to hit my ET, 575 to get my MPH. CompD's calc figured 591 using ET, 601 using MPH. All @ 6450lbs. Thanks for the compliment.
Except when you put lbz rods in a lb7 then you have the power to bend them
I plan on testing these theories in the 1/2 ton next year. :rofl:
They are the same Rod per GM Spec. Its a myth that LBZ/LMM rods are stronger than LB7/LLY's. Typically a Z or M will crack a piston before bending a rod, thanks to the wrist pin bushing jeopordizing the cross sectional strength over the wrist pin area. Except when you build them right and keep the duration short and sweet, you skip cracking the pistons and go straight to bending rods. Ive got a 600RWHP LMM in the shop now thats got short rod syndrome. Averaging between 260 & 280 PSI on a compression test... But hes had his fun...
Caleb
They are the same Rod per GM Spec. Its a myth that LBZ/LMM rods are stronger than LB7/LLY's. Typically a Z or M will crack a piston before bending a rod, thanks to the wrist pin bushing jeopordizing the cross sectional strength over the wrist pin area. Except when you build them right and keep the duration short and sweet, you skip cracking the pistons and go straight to bending rods. Ive got a 600RWHP LMM in the shop now thats got short rod syndrome. Averaging between 260 & 280 PSI on a compression test... But hes had his fun...
Caleb
Interesting this would be the first time I have heard the 06 and up had the same rods.
so are they the same part number but the contract was different so they were better? I have always been told by people with a lot of know how that LBZ rods were stronger than LB7s.They are the same Rod per GM Spec. Its a myth that LBZ/LMM rods are stronger than LB7/LLY's. Typically a Z or M will crack a piston before bending a rod, thanks to the wrist pin bushing jeopordizing the cross sectional strength over the wrist pin area. Except when you build them right and keep the duration short and sweet, you skip cracking the pistons and go straight to bending rods. Ive got a 600RWHP LMM in the shop now thats got short rod syndrome. Averaging between 260 & 280 PSI on a compression test... But hes had his fun...
Caleb
While the weight on the LB7/LLY rods is nearly identical to the LBZ+ rod, the beam (shaft) has about 10% more cross sectional area, and larger radii. In theory, it's harder to bend at the beam, which is where they bend.
But it's not like something that can be easily tested.
Some LBZ pistons crack and others don't. My guess is they have a process problem with the press fitting of the bushings, and are microfractured from the factory. Ditto for Dmax crankshafts when they roto forge them.
But it's not like something that can be easily tested.
Some LBZ pistons crack and others don't. My guess is they have a process problem with the press fitting of the bushings, and are microfractured from the factory. Ditto for Dmax crankshafts when they roto forge them.
Pat do you have data to reflect the difference between the LB7/LLY's and the LBZ's? Id like to see it. Everything Ive found suggests its the same road. And considering we are seeing rod failures at the same points on an LBZ as the LB7's and Y's...
Regardless a stock Duramax rod is not the solution for a budget build. You would not be fixing anything, just swapped parts around.
Caleb
What I did was digitized the rod beam on a LLY and a LBZ when the LBZ came out. I measured the sectional area.
The material is in the radii. I'll check for the CAD models.
The material is in the radii. I'll check for the CAD models.
I didn't find the file with a quick search. It was over 5 years ago, and I've got thousands of CAD files. I'll look again later or re-shoot a couple.