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Topic Review (Newest First)

  • 02-18-2008, 09:44 AM
    bennyb
    well, i'm gonna say right off the bat that I can't live with that.
  • 02-18-2008, 08:50 AM
    hotbo
    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
  • 02-18-2008, 08:27 AM
    Brendellajet
    Yeah, Im coming up with 8.0:1 or thereabouts now.
  • 02-18-2008, 08:24 AM
    bennyb
    I'm getting (depending on the site) anywhere from 7.5 to 8.5 to 1
    I wonder if Dan remembers.
  • 02-18-2008, 08:23 AM
    hotbo
    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.
  • 02-18-2008, 07:56 AM
    Brendellajet
    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...
  • 02-18-2008, 07:55 AM
    Brendellajet
    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.
  • 02-18-2008, 06:48 AM
    hotbo
    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
  • 02-18-2008, 12:21 AM
    396_Ways_To_Spit
    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.....
  • 02-18-2008, 12:16 AM
    396_Ways_To_Spit
    Thats a pretty wide range of cc's for the chambers. You want to get them all as close to each other as possible.
  • 02-17-2008, 08:58 PM
    Brendellajet
    Pistons are flat tops, Im thinking with that chamber compression is in the 8.5:1 range...
  • 02-17-2008, 08:22 PM
    Brendellajet

    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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