Home » AutoModified Website, Modified Cars

Dyno tuning FAQ

19 June 2012 3 Comments

We have put together a bit of a dyno frequently ask questions blog for those of you that aren’t too sure how a Dyno works.

Q: What should I do to prepare for a dyno test?
A: Make sure the tire pressure on the drive wheels is where you want it.
Make sure you have enough oil.
If there is a cover over the spark plug or coil wires, remove it.
Make sure you have good spark plugs and that are gapped correctly.  Dont trust pre gapped spark plugs.

Q:  How does the dyno work?
A: A dynamometer is a device that measures force and power.  There are lots of different kinds of dynamometers, including the kind that test springs and shocks, but we don’t care about them because I don’t have any.  I have an inertia-type chassis dynamometer.  It measures the force and power that the spinning wheels of an automobile produce.  It is not a “brake-type” dyno that measures the power that is actively absorbed by a water, oil, or eddy-current brake or by a generator.  An inertia-type chassis dyno consists of two great big heavy drums hooked up to a computer.  The wheels of an automobile spin the dyno drums, and the computer measures the speed.
Simple? If you remember the stuff you were supposed to learn in high school, it is. The computer calculates the acceleration of the dyno drums by continuous measurements of their speed and the time.  If the surface of the drums spin from a speed of zero to a speed of 10 feet per second in one second, then their surface acceleration is 10 feet per second per second, or 10 ft/s2.

Q: Can I drive my own car on the dyno?
A: NO.  Driving on a dyno is nothing like driving on the road, leave the dyno testing up to the professionals, there is a reason you are taking your vehicle to them in the 1st place.

Q: Does the dyno measure wheel Kw or engine KW?
A: The dyno measures wheel Kw. Torque is a slightly different story, however.  Since gearing has a direct bearing on torque and 1st gear would obviously generate a great deal more torque than 5th gear at the wheels, to return a useable number, the dyno actually gives you engine torque as measured at the wheels.  It does this by factoring the engine RPM into the equation and negating the effect of the different gears.  If this hurts you to think about it, then stop – just trust me.

Q: What is the difference between engine and wheel KW?
A: About 15 – 20% is the general rule of thumb.  Engine KW is always greater as some power is lost through the drivetrain on its way to the wheels.  Most believe that standard transmissions are closer to the 15% number and automatics are closer to the 20% number.  People will argue about this number forever, and frankly – you shouldn’t be concerned with it.  Once the engine is in your vehicle, you don’t care what the engine’s power is.  You only need to be concerned with the wheel KW, as that is the only one you can use now.  If you really need to know – most stock vehicles seem to be in the 20% range.  Higher KW cars have a lower loss, as it’s not possible to lose a great deal of power through the drivetrain without burning it up.  The higher KW cars usually have racing (lightweight) drivetrain components, so that will result in a lower loss also.


  • Lenka said:

    How often must i do a dyno tunning on my car


    Blair Reply:

    Lenka a dyno is only to really Map a car and get power readings from. It doesn’t really diagnose any problems.
    So you don’t actually need to dyno it unless you are looking for power gains


    Lenka Reply:

    Yes im looking for power gains therefore how often


Leave your response!

Add your comment below, or trackback from your own site. You can also subscribe to these comments via RSS.

Be nice. Keep it clean. Stay on topic. No spam.

This is a Gravatar-enabled weblog. To get your own globally-recognized-avatar, please register at Gravatar.