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View Full Version : Big valves, where and why?


Chino886
12-20-2007, 07:04 AM
What are the pros and cons of going bigger valves?

Also, where (IN or EX side) and why?
400exrider707
12-20-2007, 07:09 AM
+1mm exhaust valves to help with top end over-rev.
Chino886
12-20-2007, 08:57 AM
Originally posted by 400exrider707
+1mm exhaust valves to help with top end over-rev.

So would the opposite be true? +1 mm IN for bottom end?
Scro
12-20-2007, 09:15 AM
When you say +1mm, is that the diameter of the valve?
mcleod
12-20-2007, 10:57 AM
don't forget to clay your engine when using larger diameter valves :)
400exrider707
12-20-2007, 12:25 PM
Originally posted by Chino886
So would the opposite be true? +1 mm IN for bottom end?

I would say NO, but I'm not positive. We should wait for Chad to chime in on this. I do know on most of his builds he chooses the +1mm exhaust for the top end over-rev. Obviously larger valves could allow the possibility for more air/fuel, but could also lower the velocity which is equally important. I'm not even sure how much more room there is to spare in the head for that machining. Also yes your motor should be clayed if this is done, and in a lot of cases the piston valve reliefs will have to be machined as well to accomodate the larger valves. I blieve the DRG piston is already made this way to accomodate the +1mm exhaust valves, but dont quote me.