Has anyone used pistons made with offset pins in their Nailhead? Since custom pistons are the only choice on a performance rebuild, it seems like this would be a great option. Already spending a grand on custom pistons. It seems like having 4 lefts, and 4 rights, couldn't add too much more to the piston cost. Forged pistons need more clearance, and offsetting the pins reduces piston slap, and wear, on the rotating assembly by placing the rod angle not parallel with the bore when the piston is at TDC. Smoother running engine, with less friction. could only add to efficiency and longevity, it seems....... How much offset to use, and how much, exactly, that calculated offset, will add to the stroke, are formulas I have yet to locate.... It seems I have done all the math for my 401 rebuild. Now, this x factor has me thinking I might integrate this into the equation....... This is what I have come up with, so far: Bore - 4.197" Stroke - 3.69" - crank offset ground to use BBC rods. 2.20" rod journals. Rod length - 6.8" Gasket bore - 4.24" Gasket thickness - 0.016" Deck height - 10.00" Top ring down - 0.30" Head chamber volume - 125cc Piston dome volume - (-50cc) Deck to piston - 0.020" Compression height - 1.335" CID - 409 Static compression - 10.91:1 Cam - TA25 Dynamic compression - 8.02:1 w/cam installed straight up Dynamic compression - 8.29:1 w/cam installed advanced 4 degrees. Agree, disagree, or agree in part?
How do you know they are not already offset? It's been standard practice for decades to offset the pins in pretty much everything except all out race applications. It was done so Grampa didn't have to hear a few seconds of piston slap in the morning. IIRC, tests on super stocker Mopar showed maybe 10(?)hp at the hp peak... Why the high compression with such a tiny cam? Are there circumstances beyond the norm that would make that a reasonable idea, such as really high altitude or E85? What about the vehicle and operating conditions? There are more criteria to the vehicle regarding high compression and detonation than just the engine.
I'm no nailhead expert, but with what I know about other engines, you're going to want more bleed off from the camshaft, or as stated if you're at higher elevation or using E85 you'll be ok. Otherwise you're going to run into pre-ignition. By the way, a left and right piston are the same piston, if you take one from the left and put it on the right, it's exactly the same as you've turned it 180 degrees.
Your deck clearance will be fine, I'm guessing it just came out that way from selecting parts? FYI, tighter than .032" clearance is within the range of 'diminishing returns' regarding quench benefits, and Nails don't have much quench area. I think I've read here that there were tests shared on Nailhead's specifically to the effect of quench clearance, but like any...it more or less depends on chamber activity and how it's maintained from the port's influence. I'm curious if this in an expert tuning effort with well thought out planning? 'Can be done' vs 'recommended to an anon mystery person of unknown skills' are two very different things. Even if you can keep out of detonation, I see no earthly reason to run a cam that small in anything.
