If you use a 401 piston & rod w/ a 390 crank & block the piston will be down aprox. .055"+ in the bores. It will detonate w/ this much deck height (compression height is different for 390 & 401 pistons.) If you have 69 390 rods It will be even deeper. This is NOT the way to drop compression !!!!
I think the 2381 pistons are early 1971 401 by Speedpro/TRW, NOT A 100% sure till I see the book tho.
amxron
70 AMX NHRA E/S
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