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If your talking about milling the pistons, you won't have to, the KB190s require no milling (as long as the block hasn't been decked), they are designed for open chamber heads like the J 915s, you say you would like the highest compression on pump gas, then these are the ones you want IMO, the Quench dome is approx. .040".042" high, you run a .039" gasket, the dome goes right up in the open area of the head, you can run a straight edge right across the gasket & the domes are right there, the outer part of the piston sits around .018" below deck. I've run both (190s & 107s), i will never use the 107s again after useing the 190s, the design of the 190 is to achieve the best quench possible, so you can get above 10.1, & still run on pump premium, the better the quench, the higher compression you can run on the same octane without detination, i ran the 268 cam in 1 360 that had the 107s, the other had the XE284H & 190s, stock J heads, RPM air gap, 750dp, it was night & day, cylinder (cranking pressure) was around 180, timing was at 36* all in at 2200, 456 gears, 2800 stall, never pinged a lick on 89.