 This is the KB Pistons domed and 421 gram piston. Not bad, huh? |
The pistons I am using are made by KB Performance Pistons. KB Pistons is most well known for manufacturing various models of what are known as Hypereutectic pistons and cast “claimer” pistons. However, when I went looking for an “off the shelf” forged domed piston for a 347 I was amazed to find very few manufacturers offering a domed piston. The majority of pistons for this application are flat tops. I imagine because so many 347’s end up in street cars. I want 13:1 compression, though, and a flat top isn’t going to get me there. In my search I came across the piston made by KB and it was the hands-down winner on all fronts. I honestly didn’t know that KB was getting into the higher end forged piston market. The pistons are part of their Premium Forged series and are a completely CNC finished part. The part number is KB739 and it weighs in at a scant 421 grams and comes with a standard 133 gram wrist pin.
 The KB Forged pistons weigh 421 grams. Good to go! |
 Each bob weight will be matched to exactly 1723 grams. |
The effective dome volume is -6.80 cc’s with a .150” tall dome and according to the chart on the very informative KB Pistons website this yields a 12.9:1 compression ratio with a 58 cc head chamber. BINGO! I will, of course, compute my exact compression ratio as time goes on but I expect to see at least 13:1. The ring grooves are cut for a 1/16” top and
second ring with a 3/16” oil. Probably the only thing I would like to see changed is the availability of a thinner 1.5mm ring or preferably a .043” top and second ring groove just to allow an even lower tension ring set to be used. But hey, this is a bracket engine and we will get plenty of power out of these pistons regardless! The quality of the machining is impressive, they only weigh 421 grams, and they have a dome! Sounds good to me!
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When weight matching the pistons I was very pleasantly surprised to find a variance of only 2 grams from the lightest to the heaviest piston and this makes life simple. I like that. A little material removal on the underside of the pistons that were heavy was done with a drill bit and a drill press, being careful to drill more positions without going too deep versus trying to drill less positions deeper. That way the piston will not get too thin. That is a bad thing to do!
