To deck or not to deck?
Thread Starter
Teching In
Joined: Feb 2019
Posts: 43
Likes: 2
From: Yukon Oklahoma
To deck or not to deck? 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
TECH Resident
Joined: Jun 2011
Posts: 936
Likes: 472
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.
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.
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
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.
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.
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”
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”
Trending Topics
On The Tree
Joined: Mar 2015
Posts: 154
Likes: 12
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
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.
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
