The Relationship between Torque & Horsepower - Technical Articles

Powerglides - Harley-Davidson Superflow Cycledyn - How It Works - Technical Articles

How the Superflow Cycledyn works.

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.

This is the Powerglides Superflow Cycledyn. At the rear of the dyno is a roller that is rotated by the rear wheel. At the front is the wheel clamp that holds the bike in position.

This is the Powerglides Superflow Cycledyn. At the rear of the dyno is a roller that is rotated by the rear wheel. At the front is the wheel clamp that holds the bike in position.

The wheel clamp is pneumatically operated

The wheel clamp is pneumatically operated, and is attached to a carriage that is moved backwards and forwards by an electric motor. This is so that bikes of different wheelbases can be correctly mounted with the rear wheel axle directly above the dyno roller axle. With the extended carriage that is fitted here, anything from a Buell to a drag bike or chopper, can be accomodated.

The large grill at the front is for incoming air, essential for engine cooling, and reducing heat buildup in the dyno room. This is achieved using a massive 10hp fan, and has a wind speed of 80mph. The two ducts either side of the carriage are for additional engine cooling, and are supplied by two blowers inside the dyno driven by the roller.

This is the roller, or drum, at the rear of the dyno, and is driven by the bikes rear wheel..

This is the Powerglides Superflow Cycledyn. At the rear of the dyno is a roller that is rotated by the rear wheel. At the front is the wheel clamp that holds the bike in position.

This is the roller, or drum, at the rear of the dyno, and is driven by the bike's rear wheel..

The mph is known from the circumference and speed of the drum. Engine rpm is typically taken from the spark plug HT lead using an inductive pickup, but it can also be taken from the low tension side of the coil, the rev counter input, or anywhere that gets a pulse relating to engine rpm. If we were to maintain a constant speed on the dyno, the drum will be rotating, but since it isn't accelerating, the software cannot calculate the power required to turn the drum and there will be no power reading. This is the basis of the early chassis dynos, which are known as Inertia dynos. The dyno graphs that we frequently see, are generated using this information, and are created by putting the bike in gear, and accelerating using wide open throttle (WOT).

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.

The drum on the Superflow also drives these two blowers, which supply additional cooling air that is proportional to road speed. They are driven by a toothed belt similar to the rear belt that Harley-davidson use.
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The drum on the Superflow also drives these two blowers, which supply additional cooling air that is proportional to road speed. They are driven by a toothed belt similar to the rear belt that Harley-davidson use.

Eddy Current Brake.

Eddy Current Brake. This ups the game, and is used to control the drum, and therefore the engine. It is attached to the end of the drum spindle and has a rotor (driven by the drum) that rotates inside a coil.

A magnetic field is created that is controlled by the dyno software, and can be programmed to hold the engine at any particular road speed or rpm, as well as a percentage load applied in order to work the engine harder. This is absolutely essential when tuning EFI, as we need to hold the engine at different rpm levels whilst opening the throttle in order to take readings for the benefit of calculating optimum values for the "cells" in some of the tables that we need to evaluate.

The Volumetric Efficiency, and ignition timing being a good example. This device also allows Step Testing, where the brake is programmed to hold at a particular rpm level for a time, and then allow acceleration to a higher rpm, hold, and accelerate again to the next level. This is a useful way to see what is happening at smaller throttle openings, as acceleration power readings can be taken between the Step points. This eddy current brake can absorb 500hp (yeah, I wish).

Load Cell. This is a strain gauge connected between the Eddy Current brake housing and it's chassis, and ups the game further.

Load Cell. This is a strain gauge connected between the Eddy Current brake housing and it's chassis, and ups the game further.

As a load is applied to the brake, the strain gauge directly measures the load. This way, we can get a very accurate torque and horsepower reading at a steady state.

Since this does not rely on the drum accelerating to calculate horsepower, the engine can be held at a constant rpm, and different loads applied. Simultaneously reading the live data logs in the Direct Link tuning software that we use, (which can tell us rpm, throttle position, engine temperature, Manifold Absolute Pressure, etc), and having the relevant tuning tables open, is seriously useful when measuring the effects of air fuel ratio and ignition timing changes.

This is one of the XR1200 race bikes mounted on the dyno.

This is one of the XR1200 race bikes mounted on the dyno.

this is a 113

This is a 113" Supercharged Electraglide.

Whilst this is an 883R Sportster, there is a common misconception that only race bikes and high horsepower engines benefit from dyno tuning.

Whilst this is an 883R Sportster, there is a common misconception that only race bikes and high horsepower engines benefit from dyno tuning.

In reality, all Harley-Davidsons can noticeably benefit from being correctly set up, particularly the EFI bikes, especially after even relatively minor modifications have taken place.

So, here is what a dyno graph from a WOT inertia run tells us.

So, here is what a dyno graph from a WOT inertia run tells us. This is from a 2005 88” EFI Roadking with one of the Powerglides stage 1 conversions.

Because of the formula used to calculate torque and horsepower, notice how the two curves cross at 5252 rpm. The shape of the torque curve tells us a lot about the way that the engine produces it's power. This is typical air cooled H-D, and at low rpm both torque and horsepower are high compared to a Japanese multi cylinder engine. However, Harleys run out of air at higher rpm, and both fall off.

A multi cylinder engine that revs to 10,000rpm effectively does a smaller amount of work, but does it a lot quicker.

This graph shows how the dyno can be used to test a simple performance upgrade, in this case the value of an air cleaner change and retuning to accommodate this.

This graph shows how the dyno can be used to test a simple performance upgrade, in this case the value of an air cleaner change and retuning to accommodate this.

The red curves are a completely stock 2012 96" Dyna Fatbob, and the black curves are with the standard exhaust, with the flap programmed to remain open, and a Screamin Eagle Heavy Breather fitted. Using the dyno to measure these changes is the only way to accurately quantify what works and what doesn't.

This shows how the dyno can be used to tune a carbureted Harley-Davidson.

This shows how the dyno can be used to tune a carbureted Harley-Davidson.

This bike is a 2000 Sportster Sport with an 88" big bore kit, ported heads, cams, Supertrapp, Dyna 2000i ignition, and a Mikuni HSR42. Although the engine was very competently built, the tune was a mile off. By systematically experimenting with the number of discs on the Supertrapp, the effect of a better air cleaner, jetting, and ignition timing adjustments (both to overall timing as well as the advance curve), a massive improvement was achieved.

Not only was peak power increased by 20%, but power was increased by 36% in the mid range. Considering the parts and labour costs involved, when building an engine of this type, the costs involved in the dyno tuning process are excellent value.

This is a 2009 Dyna Fatbob CVO 110.

This is a 2009 Dyna Fatbob CVO 110.

Engine was completely stock, whilst the stock exhaust had a few small holes drilled in each muffler, and a Screamin' Eagle Heavy Breather had been fitted. The owner had been told that because of the narrow band oxygen sensors fitted as standard on these later bikes, and the sophistication of these closed loop engine management systems, that the relatively minor changes would not require tuning.

This is a common misconception and an absolute nonsense. The bike under performed and ran excessively hot. There were no parts changed when it came in, it was only tuned correctly. In additional technical articles, we will go into greater depth with how the dyno can be used to control the engine whilst tuning, how we take air fuel ratio measurements, and a more exhaustive explanation of tuning EFI. Whilst these WOT graphs can be used to illustrate one use of the dyno, it is only a fraction of what needs to be done when tuning. As we shall see, it's not just about the peak numbers.

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