I do a chassis dyno service as a part time job here in Oregon. The best fan I have had so far was actually made for fighting fires. They are called PPV fans. The thing just worked and kept the IAT temps in check. Its not like an 8hp, three phase fan, but for the circuits you normally find doing mobile dyno work it did OK. The problem was the fan did not look like anything the magazines show. I had customers insist that I needed to use the big fans they saw in the magazines over and over. It happened so often that one day I just got tired of the the discussion over and over with different "know it all" customers and I ordered the big one they see in the magazines. Now not a word about cooling. It sucks compared to the PPV fan, but the customers stay happy. I need another fan as the big one does so little, so will probably buy a few squirrel cage fans to go with the big one. My thinking is since the small fan and the big one are rated at the same cfm, the smaller fan directed more of it into the engine compartment while the big fan that most chassis dyno places sell has a lot of air going around the car.
This is the small Unifire PPV fan made out of Spokane WA. Its a much better fan for a mobile dyno. Funny story, when I upgraded I did not have the room or the budget to keep both so I sold the smaller fan. I advertised it for what it was, a fire fighting fan. No takers for 6 months even at a very low price. One day I changed the description to say it was a portable green house fan for pot growers and doubled the price. It sold within a day and the guy called me back wanting a lot more fans. Like I said the thing just put out the air for the size.
Here is the fan I have now. Its made in the USA by Patterson and you can buy the same fan through most chassis dyno suppliers, but I am not impressed. Customer don't give me a hard time any more though about a "tiny" fan.