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wagnerjw
05-25-2013, 05:04 PM
Anyone know how tall of a piston I can go on my stock 74' 318.. I'm trying to get a little more compression and I know I will need a piston with valve relief. Just not sure if a 1.80 or 1.90 would be ideal. I believe my stock piston height is 1.74. They sit way down in the block at TDC. I'm not milling the block or heads.
Thanks

Dart 360
05-26-2013, 07:28 AM
Check out Keith Black Hypereutectic Piston, KB176 + O/S, they are flat top with a taller deck height therefore increasing compression.

JVMopar
05-26-2013, 12:49 PM
My '85 318 has pistons 0.066" down in the hole. So in theory 1.80" would be 0.006" below deck. Your supposed to have 0.055" between the head and piston for steel rods. I think in a street engine you could run that tighter. Head gaskets typically have a thickness of 0.040" but are available in many different thicknesses. So 0.040" + 0.006" = 0.046" I'd be ok with that personally.

Check your valve to piston clearance, this is critical. Keep that around 0.100" by having the pistons notched or degree the cam to obtain the clearance.

wagnerjw
05-27-2013, 01:24 AM
Thanks JV. so if I understand what you're saying I should be ok with my stock heads?? I was thinking of possibly doing up a set of the 302 casting heads but not sure yet. My guy at the machine shop has been out. Don't know if the 302's would make a difference with the interference or not? I do have a set of X heads as well. Just trying to get a little more ummph out of my 318.

Dart 360
05-27-2013, 06:55 AM
The 302 heads will better than the earlier X or J heads. The KB pistons also have valve relief's on their top surface, best of both worlds especially if you are using the standard cam and normal head gasket. The 340 cam really wakes up the 318 and works great on a street cruiser, the lift is not very high and shouldn't affect the piston/valve clearance which should be .090" on the exhaust and .060" on the inlets. these are for NON racing motors.
Just a caution, check to see how big the piston hole in the head gasket is as now days they seem to make one size to fit all, that is it will be big enough for the 340's 4.040" bore size and you loose a little compression on a 318.

JVMopar
05-27-2013, 02:12 PM
There were open chamber head and closed chamber heads. The 302's are closed chamber. You won't have a problem as long as the pistons are zero decked. If they stick out of the hole your clearences will be getting awful tight.

wagnerjw
06-03-2013, 11:42 PM
There were open chamber head and closed chamber heads. The 302's are closed chamber. You won't have a problem as long as the pistons are zero decked. If they stick out of the hole your clearences will be getting awful tight.

Thanks for the help. I'm still a few weeks out from tearing into it, I'll let you all know how it goes.