LML Piston protrusion/head gasket...

[M.A.M.]

Getting ready to start engine assembly as soon as it gets back from the shop. I have a couple questions concerning piston protrusion and quench.

The block was decked once already, and is bored .040 over. Split a piston in it a little over a year ago. Back then I put in Fingers pistons (17.5:1, .095 VR). Had the shop assemble the bottom end. I didn't check any protrusion when I got it back, just slapped on grade C gaskets, and ran with it.

The engine is out again because of pinhole leaks in one head. Replacing both heads with good used ones that were never milled yet.

Going with a SC 6480 cam this time around.

From what I've read, protrusion spec is around the .012 area. I do have new grade C gaskets ready to go on again, but I'm thinking I need to check protrusion and tighten my quench as much as possible.

Am I correct in thinking I don't need to worry about piston to valve clearance, with the reliefs I have? If I still need to check this clearance, is putty/play dough the way to measure? And what's the procedure as far as gaskets go in the process? Is the gasket trashed after you torque the head down on it to check the clearance?

How will the larger reliefs affect quench?

So in my mind, I need to check protrusion and then figure out what grade gasket I need to keep the quench tight? This will be the second time the block gets decked.




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[tsd_billy]

I have specs on over bore protrusion in my toolbox and ill post them here in a minute. Measure protrusion of the piston at tdc and add gasket thickness then subtract the valve height on the head from total measurement on head and that will tell you the clearance between valves and head at tdc


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[M.A.M.]

Thanks...


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[WolfLMM]

When you check valve clearance, just use your old gaskets. As long as they are the same compressed thickness.

 

[M.A.M.]

Old ones are grade C, so that should work...

Is overbore protrusion spec less than std bore?


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[M.A.M.]

Waid, how do you like the 200s you have in your truck? What pump are you running, or do you have duals?

 

[tsd_billy]

About to post up protrusion


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[tsd_billy]

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[M.A.M.]

Thanks again... so if I understand it right, if protrusion is anything over .0148, I'd need to jump to a grade D gasket?


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[tsd_billy]

If the block has been shaved and bored id get the over bore gasket.


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[M.A.M.]

I'll check with the shop for sure when I pick it up on how much it was decked. It is bored .040.


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[M.A.M.]

I used a std bore grade C when it went together last time. Just wondering since I have grade C laying here if they'll be fine to use, or not. From what I've heard, std bore gaskets have been used up to .040 over before with no problem...


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[WolfLMM]

I love the 200s, I like my fuel now. Chargers light off quick, sane pw, and sane timing. The only draw back is Can be smokey, def have to relearn how to drive to keep from smoking the block out. I’m running a 12mm S&S pump. Injectors are S&S as well.

 

[M.A.M.]

I'm trying to decide what fueling I wanna go with. Both Scott at SDP and Aaron from All In recommended 200s and a 14mm pump for what I'll be doing. I had originally planned on 100s, but I'm leaning toward 200s pretty heavily now, after talking with them. I can definitely see turbos lighting right now, lol!


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[malibu795]

Im, .007" out running B grade and .040 over

Don't want to be less than .025" quench unless you're really on top of your clearances.

Quench is distance between piston crown and cylinder head

Example
.010" protrution
.040" gaskets
Is .030" quench

 

[M.A.M.]

That's what I thot, Adam.

Still have a question about how the reliefs affect any or all of this?


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[malibu795]

Quench is technically all the dead air space that doesn't change in relationship to stroke length..

General it's referred to as distance between top of pistons and cylinder deck..usually less considered is better
Valve Reliefs/pockets affect flame travel... How much? IDK definetly some long threads about it though

 

[Fingers]

Very small distances between the metal surfaces in the chamber cause "quench". That is, they snuff out the combustion in that area by drawing off the heat in the air/fuel charge below the combustion threshold. This creates a dead charge. Minimizing the volume in the quench zones improves economy and reduces hazing.

In my limited experience, anything equal to or less than 0.050" will "quench", and 0.075" and larger seems to be OK.

A down side of the oval bowl design is that the generous edge radii, which greatly improve durability, allow more charge to force it's way into the "quench" zones during combustion.

 

[M.A.M.]

Good info there, thanks! That's why I hope to get the quench as tight as possible this time around. Hazing wasn't real bad first time around, either...

So that's where the haziness and lost fuel economy come from, right?

Tony from RidgeRunner has done great in clean tuning. I've been talking with Aaron/All In, really looking forward to try his tunes once I throw more fuel at it...


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[Fingers]

Maybe some, but it is mostly because the pistons run much cooler than stock. Keep in mind the available quench area on a piston with valve reliefs is very small..

The exposed area on the top of the oval piston has a significantly smaller area and thus absorb and impart less heat to/from the air charge. The result is you have to tune like the engine is not quite up to temp.

But like all things, there are other factors.