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Old 07-24-2020, 05:52 PM   #46
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Join Date: May 2010
Location: Long Island, NY
Posts: 1,040
Default Re: Let's build a drag race 8BA engine

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Originally Posted by tubman View Post
"GOSFAST" uses 52% and you use 55% and agree with him? Looks like "flatheadmurre" is right again.
Not exactly, on 98% of our builds we use the conventional 50% bobweight formula, the others (all track-only) get anywhere from 52% thru 56%. We have dynoed literally "thousands" of motors (over a 40 year span) and refer back to the dyno sheets for the best results, including the bobweight numbers!

Thanks, Gary in N.Y.

P.S. Being a Flathead is definitely not going to be running at 7000/8000 RPM on the build were talking here I would use the 52% number! I would definitely also do something (like our girdle) to help keep it all together, at least on that "weak" center main area of the block (see the photo below)! I would also add, if Ford didn't "hang" the 2 large center counterweights on each side of the center main on the later units they would never have been able to keep that main brg from disintegrating. The Chevy race cranks have this same setup! Without those counterweights on 4.750" stroke Chev the mains will never survive, been there, tried it!
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File Type: jpg Flathead Ford Center Main Ribbing.JPG (85.9 KB, 71 views)
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