Compression Ratio Questions (trex,317s)
09-27-2009, 01:53 PM
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Compression Ratio Questions (trex,317s) Im changing the setup around a little on my car and have a few questions. I'm running a T-Rex with a forged 347 bottom end with mahle -4cc valve relief pistons, im also running stock GM MLS head gaskets, I have a set of 317's that are being ported and i would like to have them milled. From what i have read the 317's are 72cc heads, i would like to bump them down to 64cc or even lower if possible. With the trex would it be possible to get them down to 60 or even 58cc without running into any PTV clearences?
09-27-2009, 04:22 PM
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For starters I would not mill more than .040 on stock castings. For a couple of reasons: To avoid intake allignement and sealing issues and in order not to shroud the valves.
.040 o 317s is about 6.7cc
71cc - 6.7 cc= 64.3 cc
so yes, 64cc would be the limit i would mill.
Now as far as PTV clearance, only way to truly answer you Q is to measure.
IMO, I would sell the 317s and get a set of 243s or 799 castings. Much better base and you'll reach proper chamber size without having to mill to infinity.
you are about 10.2:1 compression with 64cc heads so too low IMO for a cam in the T-Rex size.
With 59cc heads and .041 gasket you'll be around 11.1:1 SCR
.040 o 317s is about 6.7cc
71cc - 6.7 cc= 64.3 cc
so yes, 64cc would be the limit i would mill.
Now as far as PTV clearance, only way to truly answer you Q is to measure.
IMO, I would sell the 317s and get a set of 243s or 799 castings. Much better base and you'll reach proper chamber size without having to mill to infinity.
you are about 10.2:1 compression with 64cc heads so too low IMO for a cam in the T-Rex size.
With 59cc heads and .041 gasket you'll be around 11.1:1 SCR
