0352Marine

Ok so I’ve been told two different things both of which have been building LS engines a few years longer than I have so here goes. One of my friends that is very experienced in LS engines tells me that if a LS block has to be decked (I.E. .004” or more difference) to forget it and find a different block. The pistons already stick out the hole .006” and if deck it say .020” now the piston is out .026” and that’s why when making serious horsepower above 600 that this may cause some problems. Then again I just got back from the machine shop who says that it’s fine and he decks them all the time and that his truck has been done to .020”. So is it okay to deck a performance built LS? I’m leaning towards the first and just find a different block. Thoughts? Please state why and any evidence you have to back up your reason. Thanks

Jays_SSZ28

iTrader: (2)

Why would you have to go more than .001?

.004 or more is not usual, unless there's something weird with it.

68Formula

Have to leave a minimum for couple reasons, piston to valve clearance, and quench (piston to head clearance).

PTV is pretty straight forward, depends on cam duration and event timing as much as it does valve lift.

For the quench, things grow and stretch with engine speed and temperature. Things like piston speed, rod material and design, piston material, rpm, rod bolt strength, etc. all come into play. On a <400hp stock LS bottom end engine, that's not going to see more than 6000rpm, .038" as is usually safe. Start going up from there you need to check everything twice, use better components, and ensure everything on the block and head are square. With tolerances, not every piston/rod/crankshaft combo will stack up exactly the same when you're talking thousandths of an inch.

Do you really need to take off .020" just to clean it up? Seems like a lot.

Darth_V8r

iTrader: (4)

I sleeved my current block. Had to deck to 9.224. Expecting 800+ fwhp. When you order pistons you can order a custom compression height. And like said above, you typically only need to cut a couple thou to clean it up. If you are decking 020 for compression, take it off the heads. Or use domed pissed ons

JakeFusion

iTrader: (7)

First, if you're building up the block, you need to have your rods and crank and pistons to see what your actual deck height is. Then you can determine how much you can take off without running into issues.

If you don't have those things, you can order them to get what you want... 9.240" or less. My rotating assembly was designed for 9.235", and I decked the block to 9.235" for a "Zero deck." I'll still measure upon assembly to see if any additional decking is needed. But it'll probably be fine one way or the other and the gasket thickness can make up for anything .005" the wrong way.

If you need to square your deck height or machine it for a better gasket seal, then those are things worth doing, and you won't have to take off much.

RonSSNova

iTrader: (3)

I noticed on my L33 that the Wiseco Pistons,Manley 6.125 rods, and Molnar stock crank that the pistons were 0 deck.

When it was stock they were +.007”

So yes, you need the parts in hand as a reference.

You only need to remove enough to get the deck square with the main line, and the same both sides. Would be way less than .020”

SLP IROC-Z

iTrader: (14)

Straight edge the block. Whats the gm spec for flatness?

Know It All

Your machine shop is correct, and what your friend said is basically half true. It usually doesn't take much more than .005" to clean up the deck surface of an LS block, which won't cause any problems with a stock MLS head gasket and a stock rotating assembly. If you have to cut more than that, you can use a thicker aftermarket head gasket so that you don't have to little clearance between the head and pistons (aka quench)

When you go to aftermarket internals, you may end up needing to cut .020' or more depending on the stroke, rod length, piston compression height, and head gasket thickness. You or your machine shop will be able to determine how much need to come off to get the ideal quench.