howyhowy

So what gets hooked up to your car on a dyno? Is it just a data-logging computer and a wide-band O2 sensor? If this is the case why cant someone tune a car by attaching these devices and running it on a flat piece of road or a drag strip? Wouldn't you actually get better real-world measurements this way? I realize you will not get an accurate reading of RWHP, but I would think this would be the most accurate way to tune your car for max HP on the road.
-howy

cekim

The issue is to limit the influence/loss from driveline, you need to perform the dyno run in 4th gear (1:1 ratio)...

Depending on what you tuner is trying to do, they may hook up any number of sensors, but at a minimum it will be O2/Airfuel, RPM and the tires on the rollers (which use electrical current to push back on the car to measure its ability to "fight")

So, the kink comes in getting to 6200RPM in 4th gear - see various other threads on what that means in terms of speed, but the short version of it is "go directly to jail" on the street...

1/4 mile ETs are certainly the most "meaningful" measure of a car's power for most people (i.e. how fast can I go is all we really care about... )

The trouble with using data from the road is all the other variables (traffic, temp, driver etc...)

doodad

just run at 1/4 mile and caltulate your HP by using your mph and time!
1

CrazyAl

Some dynos will have various sensors like air/fuel mixture and so on, but the REAL KEY to a dyno is it's ability to directly measure torque at the rear wheel, and it's ability to track RPM. Any dyno will have at least those two sensors: An RPM sensor (Tach, basically) and a torque sensor.

There are different types, but they generally all have a large roller that gets turned by the rear wheels, and then a torque sensing mechanism that can measure how much force the tires actually are exerting. The Dyno measures a chart of torque vs. RPM and then back-calculates HP from the torque reading.


Measurements made "on the road" are nototiously inaccurate becasue there are many extra variables, such as air resistance (drag) that interfere with the data. Though, you can get "dyno information" from some hand-held tuners or other electornic devices that you keep inside your car. (Like the G-tech meter). Note that these are NOT very accurate.