Piston height for 340

[Dartcustom]

How far down in the cylinders should the pistons on a stock 72 340? how about the higher compression engines? Thanks

[Tarrbabe]

My calculations for the piston down in the bore is .018" for the 72 340. The block spec. is 9.60". Half the stroke of 3.31" is 1.655". Add that to the rod length of 6.123" and get 7.778". Add the piston height for the 72 340 piston of 1.74" and you get 9.518". Subtract the height of the block of 9.60" and size of the stroke, rod, and piston ht. of 9.518" and you get .018". Keep in mind that this only works for blocks that have been decked and straightened to the correct 9.60" deck height. If you get a different height, the block is not correct unless other parts have been changed to non-stock parts.

[Dartcustom]

Any idea on how much i can raise the compression by going to the thin head gasket????? Thanks

[345Dart]

I believe Tarrabe was a little off in the calcs. 9.60-9.518 leaves .082th down in the hole and probably gives you ±8.2CR with ±72cc heads, which is what 72 and later 340s and 360s had. The 68-71 340s had 1.840CH pistons with a .020 raised flat (dome) and is why you can not use closed chamber heads with these pistons.
Many piston manuf. make a 1.840 CHt piston, and with a .050 gasket and 65cc heads will give you a 9.7-9.9CR for prem. pump gas.
Go to www.kb-silvolite.com and play with the formulas to seek out what you want - and then how much you want to spen

[Tarrbabe]

Thanks for the correction 345DART.