Hey guys,

Hope everyone is having a great new year

i have a couple questions or maybe just clarification about quench if you don't mind.

I'm rebuilding my 5.3 in my jet boat. What was going to be a "shit can the 5.3 and build a 408" situation went out the window when the gf showed up with one of those pee sticks.

So my 5.3 was in relatively good shape. Held decent compression on all 8 holes and ran well. But it's old. Had 200k plus miles on it when it went in the boat a year and a half ago. And that was 16 bottles of nitrous ago (150 shot).

Pulled it apart and it looks like a 200k Mike engine. Rod bearings look great, crank is decent, needs to be ground.

So since the little one is on the way, I can only afford a rebuild and nothing crazy like I had been planning.

I bought A set of speed pro hypereutectic Pistons for standard bore that also are flat tops. ( Replacement 4.8 pistons) I have not received them yet and my engine block is 6 hours away from me in Phoenix.

But I'm doing some math and getting ready to order the head gaskets. And if my math is decent (will be verified with the block next weekend) the pistons will end up around .010" in the hole with stock rods.
So my question is, which of the following sound like a good plan of action?

A. Have deck blocked .016" to bring piston .006 out of the hole then run around a .041 - .046 gasket to get quench to .035 - .040

B. Have deck blocked more and run a stock head gasket and aim for .035-.040 quench. I.e. - cut deck about .020

C. Keep deck where it is and run a .025 - .030 gasket to get the desired quench? (Piston will be in the hole)

D. Stop being an idiot and throw it together

Fwiw my stock 5.3 pistons were right at 0 deck with a compression height of 1.331.

​​​​thank you for any information you want to provide

Just to clarify:

Quench Distance = (Deck Height + Head Gasket crushed thickness) - ((Stroke/2) + Con Rod + Pin Height).

I understand that < .055 quench distance is the magic number to be under, with .037 (in a car) being the minimum.  Bore size, piston-to-wall clearance, and bearing clearances all factor in.  Also, you know my thoughts about jet boat water temps, which influence block expansion and therefore quench distance.  Too tight and the piston will rock in the bore at TDC and smack the head.

Do the new pistons have the same pin height as your old pistons?  Didn't sound like it, but I may have missed it.

Where will your compression ratio end up with those pistons?

I'm not an LS guy, but I heard some head gaskets have better success than others.

Joe,

I was hoping you would reply....

To touch on your questions.

The "higher perfromance factory" Ls's all come out of the hole at TDC. Seems to average around 6-7 thou from the factory

My stock truck pistons, are right at 0 deck.

These replacement pistons have a little less pin height.
Factory are 1.331 mine are 1.325, so this sets it lower in the bore to begin with.

I want my compression no lower than 10.5, my math says if i get the piston about .009-.010 out of the hole and stock gaskets im in the 10.78 range. Im fine with that, since i tend to run good fuel anyway

The compression i had before was in the 9.3 range. If i cut it like im thinking i will then my compression "should" be approx 10.78:1

Deck height - 9.240 (uncut)
Compressed head gasket - .051
Stroke - 3.622
Con rod - 6.098
Pin height of new slugs - 1.325
Pin height of old slugs - 1.331

Heres what ive been doing math wise... not quite as much

If piston is .010 out of the hole, i subtract from .051 and come up with .041


Im perfectly fine with it being out of the hole a bit.

On LS... I typically run the piston 10 out and a stk gasket... typically it runs approx .040.


Sent from my iPhone using SoCal Jet Boats

Thanks, So my thinking is along the right lines

To tight of a quench with a hyper piston and nitrous for my liking. Why wouldn't you put a forged piston in it if you plan on spraying it?
 

Has anyone gotten to the point of needing or benefiting from "chamber softening"?