Postby Tom @ FFS » Sat Feb 17, 2007 11:58 pm
Kijima, Asking which clutch or radiator on a web forum is like asking which wine do you prefer at a wine tasting. ;-) You will get dozens of answers and, mostly, they will be right. In any case, I like the ACT stage 2. The stage one (HD) has a foot pressure like stock but grabs too close to the floor. The stage 2 (XT) grabs closer to the stock position but takes more foot pressure. I have had both and just prefer the XT. In stop and go traffic, it can be a real pain in the, err, leg.
I have had the PWR raidator and now have the Koyo 55mm. Hands down, the Koyo 55 is far superior in taking heat out of the engine. In round numbers, an internal combustion engine is around 25% efficient. That means that 25% of the energy stored in the fuel (BTUs) goes into making power. The other 75% goes into making heat which the radiator is required to remove. When you increase the power in the engine by 75%, you raise the heat induced by 75% as well. Personally, I think the stock radiator is marginal for stock Miatas in locations like Arizona where the summer temps range from 40-50C. The Koyo 55mm allows us to run the AC here in the summer and still beat on the car without having a heat issue. The PWR was way better than stock but not as efficient as the 55 Koyo.