677CP exact dish volume?

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GASnBRASS
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Stroker Displacement: 4.1 / 250ci
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677CP exact dish volume?

Post by GASnBRASS »

I've been trying to find the "D" dish volume for the 677CP pistons, and everything I read contradicts itself. I see specs anywhere between 13 -17.5 cc, which makes a huge difference in my compression ratio calculations. Are the different dish volumes based on different piston diameters? I'm using 3.895" (.020 oversize). I've tried using a sheet of glass and a 20ml syringe to inject water underneath at an open corner, but capillary action is drawing water between the glass and piston and giving me a different volume each time.
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Cheromaniac
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Re: 677CP exact dish volume?

Post by Cheromaniac »

I measured mine at 17.5cc. At first I thought this was wrong. However I used the same method to measure the stock pistons and the result was 13.1cc.
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GASnBRASS
I think I'll order a "tab"
I think I'll order a "tab"
Posts: 40
Joined: June 23rd, 2017, 7:01 pm
Stroker Displacement: 4.1 / 250ci
Vehicle Year: 1998
Vehicle Make: Jeep
Vehicle Model: TJ

Re: 677CP exact dish volume?

Post by GASnBRASS »

Did some more measurements and the old piston dish is .108 deep, the new 677 dish is .125 deep. That's 15.7 % more volume, so if the stock dish was 13.5 cc that means the 677 dish should be around 15.62 give or take slight contour changes. I was able to measure the pistons today by tightly sealing the dish with packing tape and slowly inject water til all the air was gone, using a straight edge to make sure the tape wasn't bulging. I was able to inject 13.5cc in the old pistons and 15.5cc into the new pistons which confirms my earlier calculation. Maybe not the most precise method, but it was repeatable and fairly consistent over three pistons each. This piston set is US made NOS from 20 years ago, so I don't know if where they were made is a factor in dish volume. Thanks for your info.
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Cheromaniac
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Re: 677CP exact dish volume?

Post by Cheromaniac »

The 677AP could have the same 15.2cc dish as the H802CP/H825CP as the dish depth is 0.116" on all of them, and the manufacturer is the same.
I did sand down the dishes on my pistons to a smooth finish, but I didn't think I'd gain as much as 2.3cc in the process. It was a bit of a surprise.
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