340 pistons

-
AdamR

AdamR

Big Member
Joined
Dec 31, 1969
Messages
17,343
Reaction score
560
Location
Bethel, CT
Anyone know who makes 340 pistons that can be set up at zero deck ?

The KB sit arouns .020" above the deck so they wont work with my closed chambered heads.
Or I can go for the KB107s for a 360 and use a mopar perf. 3.58" crank.
 
It is very easy to machine off .020" on your pistons, can be done in a lathe. Due to differences in deck heights etc, you may be searching for a long time.

I built (and race) a set of zero deck pistons in my 360 magnum. I used a set of nos 72-73 std bore 340 pistons, bored the 360 out .040 and zero decked them. I did have to machine valve reliefs, which was tricky and clearance the balancing pads too but it worked. got 11.4:1 comp ratio with a flat top.
 
TRW used to make a replacement 1968 340 piston that was almost a zero deck. In my motor (340) they sat between .009 and .011 above the decks and yeilded 9.4:1. They are forged though, but I ran them for 13 years and burned the rings off them twice without hurting the pistons. I've also had the KB units and personally I think they suck. Killed two sets in 3 years - burnt the top ring lands off. Detonation problems you say? - With the KB's I'd definitely agree, but I never actually noticed it with the TRW's. If you're looking for pistons for a 360 the KB's get pretty close - I don't remember if I ever actually measured the deck heights. If you're looking for 340 pistons to put in a 360, be careful - I think the pin heights are different in some cases from a 340 to a 360 due to the difference in stroke. Yes, the bores are close and the rods are geometrically the same, but the strokes are a little over a 1/4" apart - 3.31" for the 340 and 3.58" for the 360.
 
I was thinking of doing the 360 crank in my 340. It would use a .070" over 360 piston. But the 3.58 crank is the same price as the 4" crank so then I may aswell go that way. Or I could leave the 340 alone and build a 390 out of the 318 Magnum block I have. Choices, choices.
 
The Keith Black KB243 will sit about 0.019" down in the bore on unmachined block (compression height of 1.840"). The Sterling/Speed Pro 428P will sit about 0.030" down in the bore of an unmachined block (compression height of 1.829"). Both these pistons have an effective dome of -6cc because of the valve releifs.

Assuming 60cc for your magnum heads, 4.150 head gasket bore with a compressed height of 0.039 the compression ratio for the KB piston will be 9.9 and 9.7 for the Sterling Speed Pro
 
You could also just use Cometic head gasket and specify a custom thickness to get the exact quench you want. I'm pretty sure they can do .060" compressed thickness, maybe even higher.
 
I have those TRW replacement pistons (L2316 ?) in my '71 340 and they are a bit above deck. Sorry for the large Pic...

22.jpg


Michael
 
You must log in or register to reply here.
-

Back
Top