View Full Version : The LS7: How was it created?

01-09-2011, 09:47 AM
I understand the LS7 is a NA 7.0L engine that powers the Z06 Vette,but how do they actually go about boring a LSX block to 4.125. I know it has a 4.000 stroke also. Even with re-sleeving arent the cylinder walls paper thin? I have heard you can only bore an LS1 out to around .005 and the LS2 is a bit beefier at .030.(lol)Just curiousity but if anyone has knowledgable input I would like to get some education on how it was achieved.

01-09-2011, 02:48 PM
A big factor is that the Ls7 cylinder block assembly includes pressed-in cylinder sleeves and forged steel main bearing caps. Pressed-in cylinder sleeves are used to allow the large 104.8-mm bore while the six-bolt, doweled-in-place CNC-machined forged steel main caps offer the superior strength required at the LS7's power level. The smaller-displacement LS2 engine (101.6-mm bore x 92-mm stroke) has cast-in cylinder sleeves and powder metal main caps.

You can do some more reading here:
But that is the main idea. Its a lil different block than a stand. ls2 and with the use of coated and better parts like titanium rods, it is able to take the beating and not break easily.

01-10-2011, 09:58 AM
Simple. It is a different casting to the other LS blocks. It is purpose cast for the larger bores and has the right amount of wall thickness around the cylinders.

As Fbody notes, the liners are pressed in to accurately machined bores in the block. The regular blocks with the cast in liners can have the liner 1mm or so off centre in relation to the bore centerline. The LS7 liners a dead on and they also have different design bulkheads etc than the same LS blocks when they were introduced. Design features that were adapted into the LS3 etc blocks later.

01-19-2011, 12:54 PM
Ok, first off, the bore spacing of the LSx is the same as the GenI and GenII SBC which is 4.400". So, accomodating a 4.125" bore is not an issue.

The issue with the Ls1 and Ls2 and having a larger bore is the thickness of the cylinder liner in the block to start with. You have an aluminum block with a steel cylinder liner. The liners are cast iron which suffer some core shift during block casting.

Bottom line is the LS7 just has a sleeve which is larger in diameter than the Ls1/Ls2. it is also a bit longer to accomodate the longer stroke of the Ls7.

The dimension of a LS-2 block are @4.280 thickness of the outer part of the liner with an inner bore of 4.000 with a max tollerable over bore of .030 giving a GM min tolerable wall thickness of .125/3.125mm if the block has zero core shift. Since there is almost always core shift, that minimum wall thickness will vary and why bore is limited to .030.

You could in theory bore an Ls1/Ls2 block slighly larger if you sonic check all the bores and can verify the core shift on the liners in the block.

As an FYI with a re-sleeve using a dry sleeve (like a Darton) you can take a LSx block out to 4.185"

01-20-2011, 10:17 AM
Hardly any need to sonic check, they are very obvious when they are off centre. Very obvious. The eccentricity can be measured with a ruler. :)

01-20-2011, 12:19 PM
My point was with the core shift is that what you see at the top may not always be the same at the bottom of the cylinder. If you want to go more than the recommended overbore, a soinc check is the best way to verify it.