Has anybody actually worked on one of these things? How does a dyno know how much HP/TQ are at the wheels, does it resist the tires, does it make a difference in which gear a vehicle is in?

Can any one explain this in easy-to moderate reading? or give a good link...

What can a guy expect when you take a vehicle in for a test? How much does it cost? How long does it take?

Thanks!

 

There you go.

 

I'm sure Mustang or DynoJet has a explanation page, but here's the quickest/easiest explanation I can make:

They hook your car to the dyno which is a big drum that weighs a good bit.

They measure how fast you can accelerate the drum.

Since they know your cars RPMs, the weight of the drum and the speed of the drum over time, they can compute the amount of work done and the amount of instantanious torque produced. With car RPM and torque, you can compute HP.

A "typical" dyno run is three pulls seperated by 10-15 minutes each plus about 15-30 minutes setup breakdown, so expect it to take an hour or so.

Cost is very variable based on the dyno and shop you are using, but it should be between $30-$100.

One thing to expect: Your truck will be going 100+mph inside a building. It will be LOUD. bring noise gear or borrow some from the shop; otherwise, you'll be walking around with your hands on your ears all day.

Coldie

 

Coldie pretty much summed it up with how an inertia dyno (dynojet) works. A hydraulic or water-brake dyno (Mustang eddy-current) works just like an engine dyno which measures brake-horspower, using a strain gauge to measure torque.

 

Are you guys saying that there aren't any gerbils running around in there?

 

If any of you use nitrous, avoid a brake dyno. Nitous doesn't like to be held back as the pressures build quickly in the combustion chamber. Your better option is an inertia dyno.

 

Eddy/Current is perfectly safe for nitrous. The only case where your argument would be valid is if the dyno is set up wrong for the weight of the vehicle.

Coldie

 

I have seen and heard of people using brake dynos with success, but I also have over 20 years of experience backing me up that have seen a lot of failures using them on a nitrous set-up if the load is not adjusted correctly. This is the same effect as going up hill in a high gear and bogging the motor. Problem is the massive pressures from nitrous will break something when in the same situation as you aren't expelling the gases fast enough. Just words of advice, take it or leave it.

 

Awesome explanation!

Now, what's brake horsepower? Is that the same as BHP - frequently seen in motor trend/car+driver vehicle reviews?

Sorry to sound stupid, I've never heard anyone outside of a magazine mention it before!

 

One last question on this subject!

When the vehicle begins the dyno - do you just go wide open throttle, pedal to the metal; for the entire run?

 

 

You are correct, BHP is brake HP. The way an engine dyno works, is the engine is run against an absorber (brake) and the torque is measured via a strain gauge (a glorified fish scale, no kidding).