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Piston above deck question

 
Old 02-27-2019, 03:04 PM
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Exclamation Piston above deck question

some background.....

2005 6.0 iron - bored to 4.060
stock LSA Crank
stock LSA Rods
+4cc dome wiseco pistons
Thinking of stock LSA/LS9 headgaskets .055 compressed
HEADS are 65cc
Cam - 227/231 .613/.617

piston is .026 above deck, and my question is should i run the ls9 gasket or go aftermarket and get something like .060 compressed?
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Old 02-27-2019, 03:32 PM
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If your compression ratio will come it at 12:1 or more, then go a with the .055" gasket.

Less compression won't require you going with quench that tight....and a .060" or .065" would be fine.

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Old 02-28-2019, 11:51 AM
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forgot to add i am running a LSA supercharger setup on it as well.
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Old 02-28-2019, 12:31 PM
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Originally Posted by Swayc09 View Post
forgot to add i am running a LSA supercharger setup on it as well.
Really?

What size combustion chamber are you planning on running?

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Old 02-28-2019, 05:31 PM
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Originally Posted by Swayc09 View Post
forgot to add i am running a LSA supercharger setup on it as well.
running pure methanol eh?
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Old 02-28-2019, 08:19 PM
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You are around 11.46:1 right now. You will need to re-think the supercharger, or the combination, with that kind of static compression ratio.
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Old 02-28-2019, 09:48 PM
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.026" above the deck sounds more like a 6.125" rod than a 6.098" rod.

Wiseco pistons for a stock crank/rod combo are usually pretty close to "0 deck".
Did you deck the block considerably?
Are the pistons part number PTS523A6? If so, they are a +4cc and you probably want more around a -9cc volume.

I agree, that's a lot higher compression than you should run in a supercharged application.


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Old 02-28-2019, 10:51 PM
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.029Ē piston to head clearance is too tight. It will be kissing the head until it fully warms up. Iíd go sixty gasket as .032Ē-.034Ē is about as tight as Iíve seen the NA guys push it and plenty of those combos show signs of contact with 72-7400 shift points
lastly boosted engines arenít as dependent on tight quench. Cylinder pressure is just plain high. Turbulence will be present
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Old 03-01-2019, 06:07 AM
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I took it as he meant to post .0026”, and figured compression from that. Where is OP to confirm?
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Old 03-01-2019, 10:56 AM
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Yeah I don't know how he would get .026 out of the hole with the parts he's using.
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Old 03-01-2019, 11:36 AM
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lol post went crazy. sorry i don't get notifications.

i race at 7k-8200 DA

i am not sure on head CC yet. i have 2 sets of heads.

car runs on e80 min content.

i am stock CTS V rod and Crank. order from GM directly, so i know they are not 6.125.
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Old 03-01-2019, 11:37 AM
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also i only rev to 6500
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Old 03-01-2019, 03:10 PM
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I think what people are saying is that you should re-measure the piston in the engine.

If in fact it is .026" above the deck, then you could have problems. The "quench distance" which is the clearance between the top of the piston and the deck surface of the head should be around .040" minimum for a street car.

That would mean you should run a .066" thick head gasket. That will also put the top ring pretty far up the bore and a little too close to the heat for my liking.

Is there a reason you are stuck on these pistons? They are going to put the compression way too high for a reliable street car. You might be able to get away with it on the track for short runs, but on the street, you'd have issue with that much compression and trying to keep detonation down.
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Old 03-01-2019, 03:12 PM
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Originally Posted by G Atsma View Post
Yeah I don't know how he would get .026 out of the hole with the parts he's using.
The only thing I can think of would be the deck was machined WAY too much at some point.
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Old 03-01-2019, 04:51 PM
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Originally Posted by ColeGTO View Post
I think what people are saying is that you should re-measure the piston in the engine.

If in fact it is .026" above the deck, then you could have problems. The "quench distance" which is the clearance between the top of the piston and the deck surface of the head should be around .040" minimum for a street car.

That would mean you should run a .066" thick head gasket. That will also put the top ring pretty far up the bore and a little too close to the heat for my liking.

Is there a reason you are stuck on these pistons? They are going to put the compression way too high for a reliable street car. You might be able to get away with it on the track for short runs, but on the street, you'd have issue with that much compression and trying to keep detonation down.
didnt see issue til we assemblies the bottom end. I donít mind running a .070 headgasket. Trying to get more compression as my density altitude kills us.

when I measured it was .016 and when I would push down on one side to see how much is rocks. We come up to .026. I believe I am measuring correct.
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Old 03-01-2019, 06:46 PM
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I think you'll find different opinions on how to measure piston rock.

Some take the measurement at the center of the piston and ignore the "rocking".

Some take the measurement at the edge and then rock the piston back and forth to find the low & high, then use the middle of the two. (.016 & .026 for example would be measured as .021).

I like to take the measurement at the center and calculate the head gasket thickness needed to get a quench distance of .040".

It still baffles me that a Wiseco piston would be sticking THAT far out of the hole.


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Old 03-01-2019, 08:06 PM
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Originally Posted by ColeGTO View Post
It still baffles me that a Wiseco piston would be sticking THAT far out of the hole.
Cole
I agree! I still think something is not right with that setup. That is a LONG way out of the hole!
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Old 03-01-2019, 08:11 PM
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Local machine shop that did the work, did another 6.0 With same piston and sticking out of block. They did deck my block because I had to sleeve one cylinder. But I doubt they took off that much. I want to say it was 10 thousandths. So .070 gasket and send it lol
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Old 03-01-2019, 08:30 PM
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Most stock outta the hole specs I've seen are about .003+/-. So the deck is milled .010? Piston should be .013 +/- outta the hole. If you were measuring the high side of rocking the piston, then that might be right. But if it is average of hi/lo, it's a bunch....
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Old 03-03-2019, 04:43 PM
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1 did notice they have a 1.335 CH and that is bigger than other i have seen from wiseco. typically finding 1.311. also my piston is 4.060, can i run a 4.060 bore diameter gasket or 4.100?

GM Gen III/IV Small Block V8 LS Series .070" MLS Cylinder Head Gasket, 4.100" Gasket Bore.
or
GM Gen III/IV Small Block V8 LS Series .070" MLS Cylinder Head Gasket, 4.060" Gasket Bore.
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