Compression
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Compression

  1. #1
    Senior Member Brendellajet's Avatar
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    Default Compression

    Can anybody tell me what approximate compression this generates?

    Head is a 336781 oval port casting which reportedly measure in the 113-120cc range for the combustion chamber.

    Piston is what appears to be a cast TRW L3027F. Piston is for a .030 overbore.

    Any ideas?

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  3. #2
    Senior Member Brendellajet's Avatar
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    Pistons are flat tops, Im thinking with that chamber compression is in the 8.5:1 range...

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    B.A.M aka "Black Azz Mike 396_Ways_To_Spit's Avatar
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    Thats a pretty wide range of cc's for the chambers. You want to get them all as close to each other as possible.

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  6. #4
    B.A.M aka "Black Azz Mike 396_Ways_To_Spit's Avatar
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    here ya go.....

    These pistons are not compatible with Gen V or Gen VI engines. Approximate compression ratios: 12.50:1 with 116.9cc, 12.21:1 with 119cc, and 11.58:1 with 124cc head


    I think you have the numbers mixed up. I cant seem to find the numbers that you posted.....

  7. #5
    Senior Member hotbo's Avatar
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    the 781s have a 118cc combustion chamber,you need to find the piston volume if they have domes and claculate the h.g. with the piston cc and h.g. volume,how far they are in the hole and you will get the correct compression,hope this helps

  8. #6
    Senior Member Brendellajet's Avatar
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    Quote Originally Posted by hotbo View Post
    the 781s have a 118cc combustion chamber,you need to find the piston volume if they have domes and claculate the h.g. with the piston cc and h.g. volume,how far they are in the hole and you will get the correct compression,hope this helps
    im not trying to get exact, just ballpark. Pistons are flat tops. Motor is about 80 miles away so its tuff to look at.

    all the part #s are correct.

  9. #7
    Senior Member Brendellajet's Avatar
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    Quote Originally Posted by 396_Ways_To_Spit View Post
    Thats a pretty wide range of cc's for the chambers. You want to get them all as close to each other as possible.
    Those are just the ranges I have found advertised.heads appear to be unmolested...

  10. #8
    Senior Member hotbo's Avatar
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    okay the 781s i have seen and tested all came up to 117-119cc range 3 sets.the flat tops either have 2 valve reliefs or one.depending how far in the hole,im gonna say 8.1.

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    Member bennyb's Avatar
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    I'm getting (depending on the site) anywhere from 7.5 to 8.5 to 1
    I wonder if Dan remembers.
    20'5 Advantage classic cruiser
    Go on get your ass outa here

  12. #10
    Senior Member Brendellajet's Avatar
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    Yeah, Im coming up with 8.0:1 or thereabouts now.

  13. #11
    Senior Member hotbo's Avatar
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    using my calculator im coming up with at zero deck 8.153.with a normal h.g.so if they are in the hole alot,mayb e 7.5-8.1

  14. #12
    Member bennyb's Avatar
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    well, i'm gonna say right off the bat that I can't live with that.
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