QUESTION ABOUT PISTONS

[CBODY67]

One of the more extreme stroker piston situation used to be with the Chevy small block 400 using 6" connecting rods. Where the piston pin was behind the piston rings. What really needed to happen was to fuse a 1" piece of metal onto the cyl block's deck surfaces to the piston pin could be in a more normal location. But that was not allowed by the particular race rules.

To me, kind of interesting how many of those situations were "fixed" in the taller-deck Chrysler B/RB engines. BTAIM

CBODY67

 

[70bigblockdodge]

I'll ask to see the math on a .125" in the hole piston with a 78-82cc 516 head making 9.2:1...

I've handled a few sets of heads, never cc'ed an uncut 516 that was actually very small.

I have a set of 516 castings on a 400 with the piston .130 in the hole, a .039 fel pro, and measured 73 CC's (very cut). I think it was mathed out at 8.43:1 and it is a detonation pig, I had to pull a little timing to run it on 89 gas with prices

 

[rd92west]

Its pretty easy to convert the 1.64 exhaust valves of a 516 into the 915's 1.70 valve.
It's not really required for a mellow street rebuild, but its noticable from 4500 to 5000 rpm.

 

[65CopCar]

I'll ask to see the math on a .125" in the hole piston with a 78-82cc 516 head making 9.2:1...

I've handled a few sets of heads, never cc'ed an uncut 516 that was actually very small.

You say that as if you don't believe me! LOL!

My records show that my 65 516 heads averaged 74.6 cc's (measured) so that is the number I used. I am pretty anal at measuring and keeping notes. At 74.6 cc my 65 383 came in at 8.35:1. At 78 cc it would be 8.13:1 and at 82 cc it would be 7.88:1. Supposed to be 9.2:1 so I say that the 74.6 cc makes sense. I found the 915 heads to be a higher cc than the 516 - my 67 were 80 cc and I shaved them 0.045" and got it to 71 cc. That is my experience. But that is why I say you really need to measure to know what you got.

I add 1 cc to the heads to adjust for the voids around the pistons - I have been told that is a good number to use. Wallace online calculator gives very similar number (Compression Ratio Calculator - Wallace Racing).

I copied this from my excel file so this is the best that I figured out how to post.

	inches
bore	4.32​
deck height TDC	0.125​
deck height BDC	3.875​
gasket thickness	0.02​
head reduction	0​
	cc	Head cc
head cc	75.6​	74.6​
piston	0.00​
gasket	4.94​
deck height TDC	30.0​
deck height BDC	930.7​
head reduction	0.0​
Compression	9.15​

	inches
bore	4.32
deck height TDC	0.125
deck height BDC	=3.75+B85
gasket thickness	0.02
head reduction	0
	cc	Head cc
head cc	=C91+1	74.6
piston	0
gasket	=((4.38/2*2.54)^2)*3.14159*($B$87*2.54)
deck height TDC	=(($B$84/2*2.54)^2)*3.14159*($B$85*2.54)
deck height BDC	=(($B$84/2*2.54)^2)*3.14159*($B$86*2.54)
head reduction	=(B88*2.54)*3.14159*(((4.505*2.54/2))^2)
Compression	=(B91+B92+B93+B95-B96)/(B91+B92+B93+B94-B96)

 

[furious70]

I've had 2 sets of 516's that were cut and still were only 76 and 78.

 

[Gerald Morris]

You say that as if you don't believe me! LOL!

My records show that my 65 516 heads averaged 74.6 cc's (measured) so that is the number I used. I am pretty anal at measuring and keeping notes. At 74.6 cc my 65 383 came in at 8.35:1. At 78 cc it would be 8.13:1 and at 82 cc it would be 7.88:1. Supposed to be 9.2:1 so I say that the 74.6 cc makes sense. I found the 915 heads to be a higher cc than the 516 - my 67 were 80 cc and I shaved them 0.045" and got it to 71 cc. That is my experience. But that is why I say you really need to measure to know what you got.

I add 1 cc to the heads to adjust for the voids around the pistons - I have been told that is a good number to use. Wallace online calculator gives very similar number (Compression Ratio Calculator - Wallace Racing).

I copied this from my excel file so this is the best that I figured out how to post.

	inches
bore	4.32
deck height TDC	0.125
deck height BDC	=3.75+B85
gasket thickness	0.02
head reduction	0
	cc	Head cc
head cc	=C91+1	74.6
piston	0
gasket	=((4.38/2*2.54)^2)*3.14159*($B$87*2.54)
deck height TDC	=(($B$84/2*2.54)^2)*3.14159*($B$85*2.54)
deck height BDC	=(($B$84/2*2.54)^2)*3.14159*($B$86*2.54)
head reduction	=(B88*2.54)*3.14159*(((4.505*2.54/2))^2)
Compression	=(B91+B92+B93+B95-B96)/(B91+B92+B93+B94-B96)

VERY gratifying rigor! Nothing like actually summing up the figures.

 

[kmccabe56]

Hi everyone,

I have a 1966 issue 440 for which I will require replacement pistons. I am going to sleeve the block back to original bore. I will be using reconditioned 516 heads as they are what came on the engine originally.

I have a chance to buy a set of used original factory 440 pistons out of a 1973 440. All in good shape (I trust the seller, he's a member here and a personal friend).

View attachment 530384 View attachment 530385

The question is about the compression ratio - the original compression ratio of the 66 440 was 10.5:1, and if I recall correctly, the pistons sat just a tad in the hole. I need to know if the 73 440 pistons will be the same compression ratio, and if they'll be suitable to retain the original compression ratio.

Thanks in advance!

Ross

Won't the FSM tell you those dimensions? If not, they might be in the MVMA spec books. If you can't find anything let me know and I'll have a look. You might also want to measure pin-bore to dome height between your pistons and the one's you're considering. That will be a different way of determining the same thing. Mildly related: You might also want to have the machine shop doing the heads check the combustion chamber volume. Chrysler was notorious for being sloppy on that. If they got the surface flat and smooth, that was good enough.

 

[Gerald Morris]

Ross

Won't the FSM tell you those dimensions? If not, they might be in the MVMA spec books. If you can't find anything let me know and I'll have a look. You might also want to measure pin-bore to dome height between your pistons and the one's you're considering. That will be a different way of determining the same thing. Mildly related: You might also want to have the machine shop doing the heads check the combustion chamber volume. Chrysler was notorious for being sloppy on that. If they got the surface flat and smooth, that was good enough.

One can always resort to empirical data. Fill the bore with oil at TDC, then invert the head and fill a chamber. Measure the precise volume of oil used for each, add these, and that gives you the combustion volume. Then, you can 2.125^2*pi*3.75 for the volume of the stroke, add that to Vcombustion, then divide this sum by Vcombustion, and get a working ratio. One will need to probably convert the volume of oil to cubic inches from millilitres if using common volumetric devices, but that's not difficult.

 

[rd92west]

Ross

Won't the FSM tell you those dimensions? If not, they might be in the MVMA spec books. If you can't find anything let me know and I'll have a look. You might also want to measure pin-bore to dome height between your pistons and the one's you're considering. That will be a different way of determining the same thing. Mildly related: You might also want to have the machine shop doing the heads check the combustion chamber volume. Chrysler was notorious for being sloppy on that. If they got the surface flat and smooth, that was good enough.

Measuring pin to piston is a good way to get idea of how far down the piston would be in the cylinder. Best is if you have a intact original piston to compare.

This last winter I had a 383 bored .030 over. I installed a set of speed pro flat top pistons. I never had the block deck resurfaced. After installing the rods and pistons I checked one piston and it was right around. 035 below the deck.
I used a .039 felpro head gasket and 516 heads.
So far I have only ran it on my test stand. I'm happy to report that I havnt had a and piston to valve connection, mind you it hasn't be revved over 2500 rpm.
Any pinging will be found when the engine is installed and under load.
I'm prepared to address any issues should any arise.

Dont do anything on my recommendation , it would be a ***** to have to tear your engine apart after its painted and installed to address excess compression.

If I was betting I would say your used pistons, with 516 heads and a .039 head gasket would be just fine. Something tells me that you could get away with a .020 ish head gasket,
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