It's a big motor, but for all intensive purposes, the M120 is just the euro EFI 104.98 x2. I'd base my rev limit off of that number and drop it a little do keep crank movement in check (though pagani does spin a stroker version 8k with an alloy block) and turn it 7k, like jay said. You can always drop it if it runs out of breathe before then, I'm not sure if the cams on the 120 are as conservative as they are on the 104.

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1993 190E 2.6 Sportline