Good information!

durallymax

durallymax

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Apr 26, 2008
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Nothings 100%.

That article bugged me, kept talking about catastrophic failure from injectors leaking. Class action lawsuit? Maybe, the original extension was a Special Policy. Unless we've all been lied to. I know people have tried filing Class action suits later though.

Not the point of why you posted it though. Nitriding was discussed in the crank thread some.
 
motoking_1990

motoking_1990

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May 9, 2011
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Idk I just ran across it and thought the crank part was intresting. It listed all the dimensions for bore and stroke does it calculate to the compression ratio they say? I don't remember how to calculate compression.

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durallymax

durallymax

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motoking_1990 said:
Idk I just ran across it and thought the crank part was intresting. It listed all the dimensions for bore and stroke does it calculate to the compression ratio they say? I don't remember how to calculate compression.

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Click to expand...

It's a longish process process, easiest to just google a calculator. Summit has one as do others. I like math though, and for those who like numbers as well, here's the paper way to go about it. If it seems hard or confusing just lookup common core math:thumb:

The bore and stroke for the Duramax has never changed, the piston design has which is why the compression is lower later. The reason for a compression drop I assume is emissions based. Cooler combustion produces less NOX. Most OEM's did the same thing.


Displacement = (Bore/2)^2*3.14*Stroke*16.387
Head Gasket space = (Bore/2)^2*3.14*Gasket thickness x 16.387
Deck Height space = (Bore/2)^2*3.14*Deck Height x 16.387
Compressed Volume = Head Gasket space + Deck Height space + Piston Bowl volume + Cylinder head volume
Uncompressed Volume = Compressed Volume + Displacement
Compression Ratio = Uncompressed volume/Compressed volume


So for the Duramax. (slightly rounded)

Displacement: (4.06/2)^2*3.14*3.90*16.387= 827cc
Head Gasket Space: (4.06/2)^2*3.14*0.042*16.387= 9cc
Deck Height Space: (4.06/2)^2*3.14*0.014*16.387= 3cc
Compressed Volume: 9+3+42+0= 54cc
Uncompressed Volume: 54+827= 881cc
Compression Ratio: 881/54= 16.3

The headgasket thickness and deck height are middle numbers for grade C thickness. The piston volume is a spec from Mahle for their aftermarket forged pistons which have a 16.5:1 ratio. I rounded enough numbers just to make things quicker and easier on the eyes. The LB7/LLY had a 17.5:1 compression ratio. Using the numbers above that puts the piston bowl volume at around 38cc. 827+50= 877cc. 877/50=17.5












I also don't get why they said the LML is just an updated LMM, but then they state drastic changes were made. The latter is true. I guess its what you get when you have an editor writing a story without personal knowledge and just going off what was told to them (pretty obvious throughout the article). Its also obvious the 15.8:1 was a typo because there was no mention of compression ratio changes anywhere and its wrong anyways.
 
JoshH

JoshH

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Actually, you would need to subtract piston protrusion volume, which is what I'm guessing you're calling deck height space, instead of adding it to compressed volume. You also need to add the volume added by the intake and exhaust valves. Intake valves are recessed a minimum of .6 mm and as much as 2.5 mm from the head surface, and exhaust valves are .9 to 2.0 mm. Also, the head gasket bore is slightly larger than the cylinder bore. I measured one I had sitting here, and it was 104.35 mm. I also measured the volume of an LBZ piston bowl to be right at 40 cc. I did a quick search for stock valve diameter, but I couldn't find it and don't know if off the top of my head. I used 30 mm for all the valves and found that all 4 would add at least 2.1 cc at the minimum depth and as much as 6.4 cc at 2.5 mm depth. My math shows an uncompressed volume of 52.2 cc needed for the 16.8:1 compression ratio, and using the numbers I have, the valves would need to add 5.7 cc to the compressed volume.
 
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