First off, excuse me if this has already been covered elsewhere. :smile:

The May '04 issue of Car and Driver has an article (pg 128) on using dynos to measure hp. Specifically goes into why, with so many car functions now being controlled by electronics, it is so hard to get reliable hp numbers on a dyno. ( And maybe why some cars appear to be running so rich?) In a nutshell, if the car isn't sensing the benifit of cooling airflow, the computer backs off the spark and turns up the richness, to head off over heating.

The article is written by Aaron Robinson, he interviewed Steve Dinan at Dinan's shop. Dinan demo'd the airflow effect on hp, using a Dinan M5 tuned to produce about 470 hp at the crank (about 415 whp)
So;
hood closed, no external fan, car squeaks out 334 whp, data logger records air-fuel at 9.5:1 near redline

hood open, small home depot fan blowing, now 371 whp

hood open, huge fan blowing (38,000 cfm) thru air duct right into radiator, 411.4 whp

Wow, big difference. And then there is the ambient air temp effect as well.

I know this is old news to some of you, but I figure there are at least a few people like me on the boards, that are new to the nuances of performance modifications and hp gains. Numbers may not lie, but it's important to consider the conditions under which the numbers were collected.

Moderators, I did consider putting this under Performance, but wanted it out where folks unfamiliar with performance mods would easily see it. Do what you think is best.

Shelly

Hi Shelly,

Thanks for the info. That is very interesting. I think i'll be forced to go buy a car and driver now to read the whole thing.

Thanks again