UUronL

Yes, I would have thought this would have been implicit when I made my statements. Thanks for helping clarify it for the others. All the conditions have to be the same as well - basic sound testing methodology.


You need to simulate the cooling effects of the wind that a car driving down a road would benefit from. Car and Driver reported on this several months ago - it can make an enormous difference. Without a very high powered fan blowing on the engine, a dyno test will be radically lower than it should be due to artificially high engine temperatures. Normal driving will always provide similar cooling benefits and hence more horsepower.


http://www.caranddriver.com/features/8020/...dyno-lying.html



In the article, it cites a set of tests done on Dinan's dyno:


2003 Tweaked M5 ~470 claimed hp at the crank (415 expected at the wheels)

With the hood closed and no air blowing on the engine - 334 hp


The computer indicated that as the engine approached redline, the ECU enriched the fuel-air mixture to 9.5:1 due to the rise in temperature. The computer expects 159mph of cooling wind blasting at peak hp. It's getting nothing, and it -knows-.


With the hood open and a $7000 fan running that pumps 38,000 cubic feet per minute of air at the radiator at 70mph, the dyno reported 411.4 hp. That was with an ambient temp of 81 degrees. Dinan claimed another 5hp would be reported if he tested at 70 degrees ambient temp.