Recently, there was an article in Racecar Engineering magazine about a 1964 Mini from New Zealand setting speed records in class I, 750 - 1000 cc engine displacement. Their fastest record was 166 mph which is pretty good with some body modifications and a blown engine, free fuel class. I was surprised how much modification they had to do for 166 mph. The engine has a highly modified block, the head from a BMW K bike, and a billet crank. They claim 370 hp on methanol. That is both impressive from what started out as an A series block amazing to me how much extra horsepower is needed to get the speed.
I guess I'm comparing from a project I was part of back in 1988/89. A bunch of guys at Subaru got together to go for the 1 liter production class which allows no body changes and a modified, but production based engine. Our little Justy was so square that it makes the Mini look like a streamliner. Even slammed, it must have had significantly more frontal area than the Mini. In production class, we were allowed to change internal engine parts and carbs, exhaust, etc. The engine head, and block had to remain production based. So our 1 liter, 3 cylinder engine had motorcycle carbs, titanium intake valves, porting, and high compression. Some mods were done on site at Bonneville, for example, a cowl induction air box was made of a Huggies diaper box and lots of duct tape.
The end result was an I class production record of 123 miles per hour that still stands today. Not bad for pushing an origami body with a little 3 cylinder engine.