As a science experiment, I put my Elise SC on DRS' dyno to try to quantify the heat soak. My car has an exhaust and a DMC header that BOE shows to be worth a decent amount of power. How much? I have no real idea. My WAG is 10 hp on my car, but I have no dyno plots to prove it.
Anyway, with engine oil up to temperature, but a cold SC, the car pulled about 185 whp on his dyno on a very cool California day. We then ran the car for two minutes at which time my oil temperature was at 220 degrees. The car then did two pulls which returned around 175 whp, with the second pull about 2 whp lower (noise?). So approximately 10 hp drop from simulating about one lap's worth of heat build up. Typically, my oil temperatures are in the 240-250 degree range on track so I'm sure my car probably makes less than 170 whp after it's been on track for awhile.
2011 Lotus Elise SC Final Edition 15 of 15 - Ardent Red