While I haven't had a stock 261 piston to verify, I have found in a Sealed Power parts book, that the replacement piston for a 261 has a compression hgt. of 2.046". So,doing the math, if we subtract -.200(Difference in rod length from 235/261 to GMC) from that we get 1.846" as our new comp.hgt. Looking through my TRW/sealed power book,I have found several part #'s that can be used with little additional mods(mostly making a bushing for the rod to match piston/wrist pin).I'll list them in order of increasing bore size, not knowing what the overbore limit is for a 261(stock is 3.750"),you'll have to determine how much to go bigger.
L2469F(3.8 Buick): 1.868" C/H, .940 pin, 3.800" Bore!
L2338F(283 Chevy): 1.810" C/H, .927 pin, 3.875" Bore!
L2463F(318 Chrysler): 1.840 C/H, .984 pin, 3.914" Bore!
any overbore or superceded piston # should also work as well!
Additional mods might also include machining lock grooves in pistons pin bores, since GMC rods are floating! Also decking block or flycutting pistons to arrive at your desired actual finish deck hgt. The above piston #'s are for Forged pistons....
Last edited by CNC-Dude; 11/28/08 04:41 PM.
