What is the best year of the CR500 motor and why?

I have decided to put the CR500 motor in my 400EX frame. I already spent $2,000 on the suspension plus the pipe and everything else.

This bike will be the king of ths hill!!!

I am thinking maybe 1987, 88, or 89 motor???

Thanks...

I believe the last few years of CR500 were the most powerfull. 67 horsepower at the crank and 55 to the rear wheels with twenty more available through porting! Your in for alot of vibration though. That big single vibrates like a mofo!