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400 small block piston choice

7325 Views 6 Replies 6 Participants Last post by  rich1978
I have a 3951511 stock bore 2 bolt 400 that has stock dish pistons,crank and rods. I want to build this for a nice street manners motor . I would like to change the pistons to Speed Pro hypereutectics H615cp which have a comp. hgt. of 1.425 and change the rods to 5.7 . The block has not been decked; so I'm assuming I have 9.025 deck height.I want to see if I'm calculating this right so bear with me.
Stock stroke:3.75 /2 = 1.875
Comp.hgt of piston: 1.425
Rod length: 5.7
Total: 9

Should leave me .025 in the hole right?
Piston's have a .135 dish w/4valve reliefs. Will run cast iron Darts w/64 cc chambers.
Any experts out there let me know if I'm correct . Thank's in advance for your help. Don
1 - 2 of 7 Posts
Don, what you really need here is a CC value for the pistons, if you want to calculate compression ratio -- You've got the rest of the info you need, ASSUMING you're right about the deck height. Everyone will tell you to measure to be sure, but you're probably pretty close there. That said, the pistons you list are on this page:

And it says 10.0:1 with a 64cc head and 9.0:1 with a 76cc head. Not sure what they are using for deck height, but that gives you a ballpark number. In CC terms, you're comparable to a 20cc dish or so, the 18cc pistons I have (for a 400) are rated at 10.2:1 w/64cc heads and my new 22cc dish are rated at 9.8:1 with 64cc chambers.
John, you should be able to get the exact measurements from Dart as to what pistons they use, what the finished deck height is, etc. They can probably tell you what CR you'll have with a given CC chamber head and compressed gasket thickness...
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