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Expert 5K+
Posts: 9666
    
Location: So. Cal | Can anyone figure out what these pistons fit? I picked them up at the fling today. They are part number 1617776. I am hoping they are 331 hemi pistons, but I would like to figure out the compression ratio somehow too. Thanks for any help. |
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Expert 5K+
Posts: 6500
Location: Newark, Texas (Fort Worth) | I couldn't find a match to your number. Please check it. Mean while here is something to read:
http://www.jalopyjournal.com/forum/threads/hemi-tech-index.118764/ Lots of links. Don't scrimp on Pistons! |
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Expert
Posts: 2289
Location: Eastern Iowa | Probably a casting number.
Is the number on the inside of the skirt cast into the piston itself
or are the numbers on a box or wrapper of sorts?
One would almost have to do a side by side comparison w/a known piston to be sure.
I'm in the same boat, a few NOS pistons w/no ID
Oh well, there is always the scrap bucket! |
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Expert 5K+
Posts: 9666
Location: So. Cal | The number is cast on the inside and stamped into the top of the piston. There is some paper with it, but it doesn't give any info on the application. Here is the paper. Pretty interesting. I never knew they made them elliptically shaped.
 (331 Hemi Piston Instructions.jpg)
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 331 Hemi Piston Instructions.jpg (197KB - 155 downloads)
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Elite Veteran
Posts: 888
Location: Peoples Republic of Oregon | Have you measured the diameter?
'Stamped into the top' is not usual for Mopar number locations and Mopar numbers are cast into place.
The '16' casting number says 1956 so the 331 Hemi is out. It is not the 354 Hemi cast number.
Does it have valve notches?
Are they straight across from each other?
Edited by wayfarer 2017-04-09 2:31 PM
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Expert
Posts: 1740
Location: Alaska | The reasoning behind the "cam ground" pistons was that when they reached normal operating temperature, they would be round and fit tighter in the bore. Not sure if pistons are still made that way. |
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Expert 5K+
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Location: So. Cal | The diameter at the bottom of the skirts is 3.852 which sortof matches the description of them being .04" oversize 331 pistons. But shouldn't there be more clearance than that - or do they take that into account with the bore size? There is an OS stamped after the part number indicating an oversize too. I assumed that the 161***** number was small enough that it could have been a 1955 part number. Is that wrong? I am thinking that it could be 1955 hemi pistons or 1956 poly pistons. What do the poly pistons look like?
 (331 Piston.jpg)
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331 Piston.jpg (163KB - 154 downloads)
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Veteran
Posts: 145
| That bore size does indicate a .040 oversize 331. You might check the compression distance. They might be for a truck / industrial application. |
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Expert 5K+
Posts: 8947
Location: WHEELING,WV.>>>HOME OF WWVA | all of the parts books i looked in so far doesn't show but i have one more to look in tomorrow or today i guess --------------------------------------------------------later |
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Expert
Posts: 1740
Location: Alaska | With the valve notches directly across from each other they look like hemi pistons. The notches in poly pistons are offset, not directly across. |
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Expert
Posts: 1740
Location: Alaska | I looked in my Hollander for 55 331 pistons (standard) and these were the numbers, part #1603331, casting # 1617772. Clearly the cast #s are different from part#s but very close to what you have so I would assume you have O.S. for the 331. |
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Expert 5K+
Posts: 9666
Location: So. Cal | If they sold a 1617774 that was .02" oversize and mine at .04" oversize, that would make a lot of sense. I'll assume that's what my casting number means.
How much boost would you think a cast piston can take? I have little interest in running 8.5:1 compression unless I can run a little boost with it. |
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Expert
Posts: 1740
Location: Alaska | I remember reading an article in one of the hot rod type mags. some time ago where they took a basically stock "junk yard" engine and added NOX to it, increasing the added power to see how much cast pistons would take. IIRC the engine held up to a 150HP hit without coming apart but did have some internal problems. Not sure how that computes to boost. |
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Expert
Posts: 3033
Location: N.W. Fla. | Powerflite - 2017-04-10 12:00 PM
I have little interest in running 8.5:1 compression unless I can run a little boost with it. From what some have posted elsewhere the advertised C/R on hemi can be optimistic by quite a bit. Truck hemis are adv. at only 7.5. You'd be better off getting aftermarket forgings of a known C/R, especially if you are thinking of boost. Talk to "wayfarer". |
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Piston Part No.
