Re: oil cooler
If you're serious get hold of Mickey Dunlap at Four Stroke Tech in NY State. He has a cool kit which hooks into the oil gallery on the right side cover and has a small oil cooler that won't get in the way.
I fitted one to a Warrior I had, it was pretty easy and worked well.
But I only got peace of mind, didn't notice any more power. The power came from an FMF muffler and Pro Design air filter system. With all the mods it felt like a 500.
But having said all that, the Big Bear oil cooler fits over the oil filter setup which is the same on most yammy 4strokes.
But boy would that be bulky.
Besides having a dry sump with the frame reservoir is similar to an oil cooler anyway.
I have a TTR 250 and just change the oil with good semi synthetic 10w-40 every 2 to 3 trail rides, depending on how hard and long the rides are.