Tom is correct on the oil cooler. Air just blowing on metal is a much poorer method to remove heat, then using a liquid to transfer heat. I know, I have three older VWs and each one is bigger the 2000 cc. The first thing that we do when hopping them up is to add an external oil cooler. In fact on my daily driver VW (2110cc) not only do I have an external oil cooler, but it also has a fan on the cooler and I have ducting to it to bring in fresh air.
The thing about air cooled engines is that they get rid of most of their heat through the heads, not the cylinders. However, the manufactures have only designed the heads to remove the heat of a stock engine configuration. So if you are producing more heat (HP), or have less air flow, you have a problem. If you can cool down the oil, then use the cooler oil to transfer the heat from the head, you can get by the manufacturing limitations.
So you may want to examine both sides of the heating issue you will face. Stagnant air around the engine, and cooling the oil. I really don't think that a good quality cooler will put much drag on the oil pump. At least not in comparison the oil passages in the engine.
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2005 Hammerhead 150
170cc BBK, PnP Big valve Head, A12 Cam, Uni Filter, Custom Exhaust, 10G rollers, 1500 Contra Spring, 2000 Clutch Springs
Just added - 2007 Joyner 250 SV - Let the fun begin
4-Dirt Bikes, Baja Bug and enough toys to keep me in the garage and out of trouble.
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