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I'm installing a 383 into my 1981 soon, I know the 383 has a 400 crank but I'm not sure what flexplate to get. What I need to know is 153 or 168 tooth, internal or external balanced and any recommendations on which maker would be helpful. I'm using a mini-starter that will work with either tooth size if that matters. Looking in the Jeg's catalog they have stamped ones from B&M, TCI, and Jeg's($60-75). CSI at $$179 looks solid and says it weighs 3 more pounds than stock...also a JW at 4 pounds heavier for $176.
If your 383 has a 400 crank you will have to find out from whoever built it if it was internally or externally balaced. If it is externaly balanced like a stock 400 crank is then you will need a externaly balanced flywheel and harmonic balancer. Externaly balanced harmonic balancers are easily to tell as they have a cutout in the outer ring rather than being completely round like a 350 balancer is. As far as 153 or 168 it doesn't matter which one as long as you have a starter to match and it has the correct bolt pattern for your convertor. Unless you have a high stall speed convertor you really don't need the high dollar flexplate.
I always go internally balanced and 168 tooth SFI rated. You want to run the lightest flex or flywheel and the smallest torque converter you can for your stall speed. right now i have a 3500 stall 9.5 inch