#81  
Old 02-26-2021, 10:55 PM
Doug Doug is offline
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May be wrong place to ask but since it's about cc's: How did the 421 SD engines bump up the compression when they went from405 to 410HP rating?

  #82  
Old 02-26-2021, 11:27 PM
tom s tom s is offline
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12 to 1 CR.Small dome.Tom

  #83  
Old 03-03-2021, 07:46 AM
SD455DJ SD455DJ is offline
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Quote:
Originally Posted by steve25 View Post
Thanks much for the added CC info on the 12s and 16s!
We Whistler'd the RAIII in the '70 Formula 400 whose engine is still 100% factory original with 47,000 miles, and never been apart, except for a new timing chain/gears/cover and fuel pump. It measured 10.0 SCR cold (60 degrees) and 10.5 SCR warm (150 degrees). A compression test yielded 175 psi average (170-180). It has the original 068 cam & lifters, jamb nuts on the rockers, etc. down to the factory jetting and beefy advance springs in the distributor.

These readings sure give credence to the #12 heads 68 cc chamber sizes from the factory and we have no good reason to not believe them on the RA engines.

Dennis
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Last edited by SD455DJ; 03-03-2021 at 07:52 AM.
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