Now that we are well into the Electronic Fuel Injection (EFI) era with our Harley-Davidsons, it would be useful to discuss the most useful tuning tool available, the Dynamometer, or Dyno. Firstly, though, we need to understand the relationship between Force, Work, and Power, and for our purposes, Torque and Horsepower.

**Force**. In this case we are talking about something that is trying to rotate, so the force is known as Torque, and it is expressed in lbft. Let's say that we have a bolt that is already tight. If we put a one foot long spanner on it, and apply a one pound load to it, we have Torque of 1 lbft. Since it is already tight, it won't move, so our force has not produced any rotation, and therefore no distance has been travelled.

**Work**. Now let's consider another scenario. Our same bolt isn't tight, but the threads are a bit gummed up, which causes some resistance. We wish to turn it one full revolution, and our 1 ft long spanner requires 1 lb of force to do this. The end of our spanner has travelled the circumference of a circle that has a radius of 1 ft. The Distance travelled is twice the radius multiplied by pi, which is 6.283185 ft (remember this number).

Work = Force x Distance, and is expressed in ftlb. So using our 1 lbft of Torque, we have just done 6.283185 ftlb of work. This takes no account of the time spent in achieving this amount of work.

**Power**. Now we need to add time into the equation, as power is work done in a particular time period, but we should first look at how Power (or horsepower in this case), is defined. When James Watt was trying to sell his new refined steam engines, he needed a way of relating their power relative to the standard of the day, which was the strong Shire horse commonly used to drive machinery.

His tests showed that a horse could lift a 150lb load 220ft in 1 minute. So (150 x 220)/1 =33,000. This means that one horse can lift a 33,000 lb load, one foot, in one minute. Now we have Horsepower, and his engines could be related to the number of horses that they could replace. So a 5hp engine would do the work that 5 horses could do, and a 10hp engine could replace 10 horses. So not only was a standard created, but it could be calculated how big an engine was required to do a particular job.

So for our use, Horsepower is a way of describing how much power is needed to do a certain amount of work in a given time, and remember that we are dealing with something that rotates (i.e the crankshaft and the wheels). 33000/6.283185 =5252, which is the constant used in the formula for hp and tq.

**HP = (TQ x RPM)/5252**

**TQ = (HP x 5252)/RPM**

The machine used to take these measurements is the dynamometer, and they have been around in various forms for hundreds of years, long before the petrol and diesel engine was invented.

When manufacturers and high end race teams are developing and refining engines, they use an engine dyno. The engine sits in a cradle and the crankshaft is connected directly to the dyno. A measured resistance, or brake, is applied by the dyno, and the torque and horsepower (or rather, brake horsepower) can be accurately calculated.

In our world, though, it really isn't practical to remove the engine from the bike in order to measure the results of various experiments with air cleaners, exhausts, cams, headwork, etc. Neither is it practical to do this when tuning, either with carburetors and ignition systems, or with EFI.

We use a chassis dynamometer, or rolling road, and these have evolved considerably since the first motorcycle chassis dyno was introduced in the mid 1980s.So now we need to look at how a rolling road motorcycle dyno works.

With the cover plate removed, we can see that the drum is substantially supported in large bearings. At the bottom right of the picture a pickup can be seen. This senses the teeth on a ring gear as they go past, and sends this information to the dyno control box, so the software can calculate how fast the drum is rotating The roller has an inertia mass, which is measured and calibrated at the manufacturing stage. During an inertia run, the dyno software measures the rate of change of rotation of the drum (acceleration) and uses this to calculate the amount of horsepower required to do this. There will not be a torque reading given if the engine rpm is not known, as it needs to know engine rpm to calculate the torque. If there is no engine rpm signal, then the software typically defaults to road speed, which is why we sometimes see dyno graphs with no torque curve, and hp plotted against mph.

Powerglides - In The Press