Does anyone know if 1mm or 2mm oversized valves will hurt my performance on a 690 300ft. dirt and dune drag racer? This motor will has a 11.1 piston, stage 2 cam, HMF pipe, and one hell of a port job. I am considering the 727 kit.

 

Ok Thanks Air, but why would i do this setup? Why not 2mm in every valve?

 

I would not on a 690. I had the larger intake valve on my 1st 686. It was not worth the 100 bucks to me.

 

Would it be worth it with a 727 kit ( possibly in the future) or a 102mm bore with 13/1 piston ratio??? Which kit is the better way to go?

 

I would only go with 1mm oversize, just because with 1mm you can use the same seats. With 2mm over, you have to get new valve seats, which are like $30 a piece, I think. So if you did all 5 valves, that's a $150 savings

 

Thanks!!