Posted by Art H on August 24, 2003 at 22:39:23:
In Reply to: Re: Re: Re: Re: MW 2145 small vs. large valves? posted by he-man on August 23, 2003 at 23:55:59:
I guess I am just quibbling here. The fact that the pistons get faster when you make them fit looser indicates that their slowness is due to the tight fit rather than the large surface area. You aren't changing the area significantly when you loosen the fit. But the viscosity of your oil probably has a lot to do with it. A larger surface area will certainly result in more viscous drag on the piston. (That's not the same as friction.) So if you use big pistons with a very snug fit then you probably need an unusually thin oil.
My Nirschl pistons are similar to the MW "big valves", and they are the tightest-fitting pistons I have ever seen, but they seem to be very fast to me. Their speed seems limited mainly by their mass, rather than by friction or drag. My Mirafone 1271 pistons are faster not because they are looser and not because they are smaller, but rather because they are less massive.