Head Gasket Compressed Thickness

[1972RedNeck]

I am finally going back together with the engine out of my '93. Had the block milled .010 (took .006 to get it flat, no wonder I couldn't hold a head gasket). Stock pistons.

Anyways, my piston protrusion is now .035 to .037.

What is the compressed thickness of a standard thickness Mahle headgasket? I have read everything from .057, .063 to .067.

If it is .067 I am good right? The truck will never spin over about 3K so even .063 would be fine, wouldn't it?

If it is .057, will I be alright? I would love to have the resulting compression (19:1) but is .020 enough clearance? I have read that D-maxes are in the .020 to .025 range...

If you roughly add .003 for rod bearing clearance, .003 for main clearance, .001 for wrist pin clearance, and maybe .005(?) for piston rock, we are down to .008 ish minimum piston to head clearance...

So I guess the main question is what is the compressed gasket thickness and will I be alright at whatever that thickness is?

[Rich dzl]

Run a .020 over gasket .

[1972RedNeck]

Originally Posted by Rich dzl

Run a .020 over gasket .

Why? With a VE pump, top end fueling is laughable. Low end fueling is decent, and more compression helps with power on the low end. This is a daily driver that will never see more than 300 to 350 HP and 3K RPM and low end torque and fuel economy are number one and number two priorities.

At most, I would run a .010 over head gasket as I decked the block .010. This would put everything back to stock specs and clearances would be A ok.

If I can get away with it, the standard thickness gasket will give me better low end torque and better fuel economy.

Back to the question, what is the Mahle gasket compressed thickness and what is the minimum piston to head clearance that I can get away with on a low RPM daily driver?

[Rich dzl]

What’s your valve face depth ? Are they all the same ? Valve depths are the main variables , why extra clearance is nice

[bigstacks95]

Piston protrusion of 0.037 seems like a lot. Last one I measured was 0.057 compressed. That leaves only 0.020 of piston to head clearance. Just seems tight to me. I think I'd run a 0.010 at the minimum.

[j.fondler]

Unless I fudged my numbers somewhere, you’re still looking at ~20:1 with a .010 gasket����

[DISTURBED]

Cummins spec is .023 piston protrusion and a minimum of .035 piston to valve clearance. You need at least a .010 over gasket and probably a .020 depending on the rpm range. I can measure a stock gasket when I get to the shop

[9724VF350]

If it was me, I would be after the extra compression also and go for the .057 gasket. That's tight, but I'd be willing to take a risk on it.

[1972RedNeck]

Originally Posted by j.fondler

Unless I fudged my numbers somewhere, you’re still looking at ~20:1 with a .010 gasket����

What do you figure for a piston bowl volume? I was too lazy to measure mine so I just worked backwards from stock specs (assuming it was actually 17.5:1 stock) and got 47 cc (I have read that they are either 41, 44, or 47 cc) and worked forward from there with my specs to get almost 19.5:1 with a .057 head gasket.

If the bowl is only 41cc, I should be pushing almost 21.5:1 with the .057 head gasket.

[1972RedNeck]

Originally Posted by 9724VF350

If it was me, I would be after the extra compression also and go for the .057 gasket. That's tight, but I'd be willing to take a risk on it.

So I bolted it up since I had the gasket and figured I might as well see what it compresses to. Currently sitting right at .060. I could see it settling in to .057 after a hot retorque.

I did have the head milled and the lowest valve face depth is right at .045 on an exhaust valve. I am running a Hamilton 178/208 cam and their calculator said I should be good with piston to valve clearance. I presume their calculator is accurate?

I really hope it runs this way. I asked myself the famous question last night:

"Do you feel lucky, punk?"

And I decided that I do indeed feel lucky. We will see what happens. If it works, I will take luck over skill any day.



Just out of curiosity, can anyone confirm that D-Maxes only run .020 to .025 piston to head clearance?

[1972RedNeck]

Originally Posted by DISTURBED

Cummins spec is .023 piston protrusion and a minimum of .035 piston to valve clearance. You need at least a .010 over gasket and probably a .020 depending on the rpm range. I can measure a stock gasket when I get to the shop

My Cummins book say max is .028 and stock it would have been .025 to .027 which would have been right in the range.

I am hoping that this higher compression and the mild cam will lead to improved mileage and greatly improved low end torque. We shall see.

[bracker8040]

Originally Posted by 1972RedNeck

Just out of curiosity, can anyone confirm that D-Maxes only run .020 to .025 piston to head clearance?

I can’t confirm or deny this, but I can tell you that on a 6.0 Powerstroke maximum piston protrusion spec is 0.034”, and the head gasket is 0.053” thick.

That’s 0.019” of piston to head clearance.

[Smokem]

Originally Posted by 1972RedNeck

What do you figure for a piston bowl volume? If the bowl is only 41cc, I should be pushing almost 21.5:1 with the .057 head gasket.

44.2cc's

[1972RedNeck]

Originally Posted by Smokem

44.2cc's

Nice. Right at 20:1 then.

[Smokem]

If you are using the same piston, and the chamber volume did not drastically change, only increasing piston protrusion 0.010" would net ~ 17.6:1

[1972RedNeck]

Originally Posted by Smokem

If you are using the same piston, and the chamber volume did not drastically change, only increasing piston protrusion 0.010" would net ~ 17.6:1

I didn't think protrusion would change a whole lot, but according to online calculators, I am sitting a little over 20:1. I have a little less volume in the head than stock because my valve face depth is a little shallow.

I have used the RSR Compression ratio calculator for years building gas engines and it has never been out of whack before.

[DISTURBED]

Originally Posted by 1972RedNeck

I didn't think protrusion would change a whole lot, but according to online calculators, I am sitting a little over 20:1. I have a little less volume in the head than stock because my valve face depth is a little shallow.

I have used the RSR Compression ratio calculator for years building gas engines and it has never been out of whack before.

So you poured the head? How many CC's did you come up with because its not much.

[1972RedNeck]

So I ran the compression ratio on 5 calculators.

2 said 20.18:1

1 said 22.5:1

2 said 19.78:1


Here's what I have.

Piston volume = 44cc

Combustion chamber volume = 3cc (probably closer to 2)

Stroke = 4.72"

Bore = 4.02"

Deck height = -.037"

Gasket thickness = .057"

What compression ratio number should I believe?

[1972RedNeck]

Originally Posted by DISTURBED

So you poured the head? How many CC's did you come up with because its not much.

I did the math based on .045" valve face depth. I came up with 2.xxxx cc so I just used 3cc since a few are a couple thousandths deeper and there is some area around the edge of the valve.

[DISTURBED]

Originally Posted by 1972RedNeck

So I ran the compression ratio on 5 calculators.

2 said 20.18:1

1 said 22.5:1

2 said 19.78:1


Here's what I have.

Piston volume = 44cc

Combustion chamber volume = 3cc (probably closer to 2)

Stroke = 4.72"

Bore = 4.02"

Deck height = -.037"

Gasket thickness = .057"

What compression ratio number should I believe?

Set all parameters back to stock and see which one comes up with close to 17:1. I just used your numbers and came up with 16.5:1. I had a really good calculator that was spot on for diesels and now i cant find it. After playing with a bunch of calculators none of them are even remotely close on stock cummins specs. They are all off by 2-3 CR