Anyone have stock or stock replacement 72-73 340 Pistons?

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dibbons

dibbons

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My 340 was originally built in 73, but the pistons have me baffled. They are .040 over and have four valve notches. I was reading that 72 and 72 pistons have a smaller compression height 1.740 versus the 68-71 which had 1.840. This would have lowered the compression ratio. But measuring the compression height of my pistons, I keep coming up with 1.840. Just wondering if anyone has a later 340 and has done any measuring on the pistons, and how many notches the factory pistons had for each model year. I assume with four notches, the piston pins must be offset to reduce piston slap. It seems my pistons might be the high compression version, which would be nice (they are not forged though). Please correct me if I'm wrong. Thank you.

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I know that Kanter Auto Products has both the low compression and the high compression pistons available and I believe they still even have the H.C. in forged if that helps.

Thanks
James
 
My deck measurements were all over the place:
#8 piston .010" above deck (sleeved)
#6 piston .012" above deck
#4 piston .005" above deck
#2 piston .005" above deck

#7 piston .004" above deck
#5 piston .002" above deck
#3 piston .008" below deck
#1 piston .008" below deck
 
I don't think those are stock factory pistons, especially at .040" over. They must be aftermarket...
 
dibbons said:
My deck measurements were all over the place:
#8 piston .010" above deck (sleeved)
#6 piston .012" above deck
#4 piston .005" above deck
#2 piston .005" above deck

#7 piston .004" above deck
#5 piston .002" above deck
#3 piston .008" below deck
#1 piston .008" below deck
Click to expand...

Is your block deck square and flat???
 
They look like sealed power 428p big valve reliefs and a compression distance of 1.829. Summit racing has them if you want to look at specs. Id guess with the big reliefs maybe around 9 to 1.
 
I believe they are sealed power. I think the pistons with four valve reliefs replaced those with two valve reliefs in some of the aftermarket products. I saw that as a note on the listing somewhere (can't remember right now which chart I was looking at.
 
dibbons said:
The block is now at the machine shop, they are going to resurface it and I will go from there.
Click to expand...
I would also have the rod center-to-center lengths closely checked. If the engine every went through a re-man process, the rod lengths can be poorly controlled.

BTW, the notch on the piston is a good sign that these have a pin offset. The 4 notches just means that they can be put in either bank, left or right.
 
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