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I am in the precess of rebuilding my old 98 670 with fresh crank and top end. I have two rotory valves, one stock and the other came with a parts motor i bought, its also a 98 670. If I line the edges up on both RV's and put the pin wheel on top there is aproximatly 7 degrees more or 3.5 deg per side. the larger RV is in better shape. can anyone tell me what its from/aftermarket? How to time it and what will happen if i put it in? thanks!
 

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it very well could be a valve from a different engine. a very popular mod was to buy a 501 stock number rotary valve from a 1995 Mach I 670. It was a 169° duration rather than a 164° duration. this mod woke the motor up. The larger RV will be the one that is more toward stock, because the opening is smaller. the performance advantage comes from the open part of the valve, not the closed part.
 

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I believe that guys put the RV out of the 98 and 99 670 H.O in the older 670s as well. The 98 Mxz was the standard 670 while the 98 Summit X and the 99 Mxz Summit X had the 670 H.O. I know there is more information on this at dootalk.com and snowest.com that I have read.
 
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