So how do car companies give an accurate measure of the bhp? I know the differnce between bhp and wheel hp.

 

That's why SAE came out with the new SAE rated horsepower measurement. It's a very strict standard, in which a certain type of engine dyno must be used, and certified by SAE to be accurate, the conditions have to be within a very narrow set of parameters(certain temp, humidity, barro pressure etc) and the test has to be observed by an official SAE representative. It's basically a series of hoops that manufacturers have to go through in order to prove that their engine really does put out that amount of power. AND it has to be tested as a package in which it will be in the car, that means with a water pump, alternator, p/s etc etc. Everything that will be on the engine when it's sold. GM's LS7 was the first to recieve the SAE rated HP and when they tested it, the engine actually was rated 5hp higher than they initially rated it at, 505 instead of 500.

But ultimately yeah, dynos are just aides for tuning. The finality of performance is how the vehicle performs in it's given arena. Tune it for the best performance in what you want, mileage, 1/4 mile, oval....whatever it is, ultimately the goal is to get the car to perform it's best possible in that given citrcumstance. Dynos can help you get there, but they're not a be all and end all finality to tuning. They can often be utterly useless for most carbureted cars as well, since the dynamics of how a carburetor work invlove the actual real world driving of the vehicle. Often times a carb'd car may post power gains through dyno tuning, only to end up being slower, on account of it running under different loads on a dyno vs real life.

Too many people put too much stock in dynos, they want a certain numer on paper so they can say "I dyno'd at such and such." Like my sig says, who cares about the power, all I care about is the performance.

 

When I had my STI tuned, it was tuned on the dyno first. Then the tuner hooked up a laptop and rode shotgun to do a road tune. That was when he made his final adustments. He had me flying around some part of CT that I was completely unfamiliar with. He was like, "Hammer it! Hammer it" All the while he is tapping away on his laptop. It was pretty cool.

 

What formula do you use or what online calculator. I've found that the online calculators are all over the place when using trap speed. I dynoed 403rwhp and I trapped 117.6 twice in a row. My car with me should weigh 3730. That's 3480 curb weight + 100lb blower + my 150lbs.

 

unless your building nascar, formula, or prostock engines; dyno numbers really don't mean jack on a street/strip car. The best dyno is a racetrack. Hell i've seen times when we made a change on the dyno that didn't show power and took it to the race track and picked up et and mph....