New to me 73 duster 340

t2ae said

Thanks for that! Stock gears are 323. It was an original 318 car that had the 340 put in. The engine was rebuilt about two years ago and had speed pro pistons put in that were 10.5:1. I only had it backfire through the carb once today when I was messing with the timing. Other than that no backfires

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Pistons are rated for compression with a given CC combustion chamber. Just because a piston is rated at "10.5:1" means nothing, unless you have the combustion chamber size that the piston is rated at that compression for. Chambers could be anywhere from 65cc to 72cc. Possibly a little more. So unless this was blueprinted and MEASURED, it's unlikely you just "lucked up" and landed on 10.5.

Condolences on the loss of your grandfather.