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Thread: 425 pistons from 2004

  1. #1
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    425 pistons from 2004

    I have read reports on the Internet about Egge pistons for the 425 engine not achieving 10.5 compression more like 8.5 compression. Can anyone here verify their experience about this subject? I am getting ready to assemble a 425 with new pistons I bought from Egge in 2004. They look like good quality pistons. I do not have any factory 425 pistons to compare with. I do have 401 pistons I could compare with?

  2. #2
    I have a set of Rebuilders Choice pistons and have just measured the dome and found it to be 38cc. It appeared the same as the OE. The dome height does not confirm the compression though as, although unlikely, the pin height could be different. I will try to have a closer look tomorrow.

    I expect that we will find the Egge, Rebuilders Choice and OE pistons will all be the same. On a visual inspection, the Rebuilders looked the same as the OE.


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  3. #3
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    Great Bob, I am going to try to get familiar with this pin height measurement. How do you measure the dome volume? It is going to take some major snow melting before I can get to my spare 401 pistons? I bought my pistons in 2004 so I am hoping my pistons are not effected by some of those undesirable later changes that were implemented. I been working with straight eight pistons and these 425 pistons are monsters compared to them.

  4. #4
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    For a quick comparison, hang the replacement and 401 piston on the same wrist pin. With a straight edge compare the dome height and the lower flat area.

  5. #5
    Correction: The OE dome is about 30cc, and so is the Rebuilders Choice. The dome is about 5/16" high and about 3.645" diameter at it widest. The pin measured about 1.4325" from the top of the pin to the top of the piston.


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  6. #6
    They are NOT designed for ANY spirited driving especially being they are cast. As far as I know there have NOT been any design changes forever. Compression will be way lower than stock. They were supposed to be 10.25 from the factory but in reality the BEST I have EVER measured was 9.75-1 & this was with the ORIGINAL piston in the hole at .040". On average they are in the hole .055" which lowers it even more. Then use the composite head gaskets on a 425 & you loose another .44-1. On a 401 it works out to be .77-1.


    Tom T.
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