Ask the Right Question

What is the Right Question ?

Is an engine that produces 135 hp is better than an engine that produces 125 hp?..Well maybe it is and maybe it isn't. What is the definition of horsepower anyway? The common definition is HP = (Torque x RPM) / 5252. Everyone is so enamored of peak horsepower these days that they will trailer their hot rodded V-Twin from dyno contest to dyno contest searching for bragging rights as to who has the most peak horsepower.

We hate to burst their ego-filled bubble, but in the real world it's the rate of acceleration that wins races, not peak horsepower. Torque is the most important element of the equation and if you can't produce torque in the lower rpm ranges it will take forever to get to the upper rpm ranges where the dyno junkies worship the God of peak horsepower. Every time you grab the next gear your rpms fall and you have to climb that elusive mountain to get back to those so damn important peak power readings. The rate of acceleration from one point to the next is how we judge a vehicle's performance, not how much peak horsepower it makes. The right question isn't peak horsepower but is the search for maximum torque in the rpm band that produces the greatest transient acceleration.

The next time you need a definition of usable power take a look at all the diesels roaming the highways. They are out there for a good reason, they make a bunch of torque right now, not at the top of the rpm band. A typical diesel will crank out 90% of its torque by 2000rpm!

Chassis Dynos: Lies, Damn Lies, and Statistics

Put your bike on a chassis dyno and spin up a 900 to 1200 lb steel drum and pick up your dyno slip. This is a great method to impress your friends and to develop motors that you are designing to spin steel drums. How many people have called us that spent $10,000 on a "billet motor" that was slower than their stock motor when they did roll ons against their friends...Oh, the billet motor made a lot of peak power, and as long as you left it on the trailer you didn't have to worry about the pesky real world. The real world, however, is where we live and it's not a simplistic world like accelerating 900 lb steel drums. Racing stoplight to stoplight and passing semis at 70 mph or banging the next shift headed for the traps is where the rubber meets the road not where the rubber meets the steel drum. Chassis dynos are useless for development but a great way for people to gather and see who has the most peak horsepower.

As the people who sell them will tell you..."They are a great way to build traffic by organizing dyno contests!". If you ever pay close attention to the time these dyno runs take and compare the time between shifts you will quickly see you are simply accelerating a known mass and it does not correlate to the real world.

Conventional Engine Dynamometers

Water brake Dynos (many manufacturers) like Superflow are routinely used in performance engine development. You program these dynos to hold or stabilize your engine for "x" number of seconds in a series of ascending rpm steps to measure the torque at wide open throttle at each step. These steps are then plotted to generate the "Dyno Curve" for the engine. Usually, depending on the software and flow controls, transient accelerations are not measured, only the torque the engine will produce at specific points while being artificially held there so measurements can be made.

Without going to million dollar AC Transient Dynamometers these dynos are the best type of dyno for both brief and extended testing. Water cooling and high rpm capabilities make them the engine developer's choice.

When was the last time you were racing that holding a particular rpm had anything to do with winning? A race vehicle is always accelerating not sitting at some particular rpm and the vehicle with the most torque will always beat the motor that sacrifices torque for peak horsepower...This is why an engine with 135hp is not necessarily a better motor than one with 125hp.

Races are won, not on one factor, like peak power, but on a myriad of variables like traction, driveability, a wide torque curve etc....and if you don't believe this then why did Honda struggle so hard in Class C AMA racing against the archaic XR 750 Harley-Davidsons and finally had to take out horsepower in their search for traction and driveability. Honda won the Championship 1984-1987. It's all XR's now.

Multi-million dollar dyno cells are pretty much going to AC style water-cooled dynamometers. The accurately control the rpm and load at lightning speed and pump power back into the power grid.

Eddy Current Dynos

RB Racing uses Eddy-Current Dynos to do load testing. It's the cheapest form of accurate control of load and rpm but still has variables. These type of dynos can perform automated tests such as roll-on times from one rpm band to another, quarter mile et and mph as well as other tests since rpm and load is all under computer control. We have our Dynos set up to do engine direct as well as chassis-mounted testing. Companies like Superflow use Telma retarders.

Eddy Current brakes or retarders were originally developed to provide frictionless braking on trucks and industrial equipment. They have been adapted for dynamometer use in both air cooled and water-cooled (vastly more expensive) variations.

With Chassis mounted testing you still end up with all the variables of gearbox, tire pressures, etc. but it still is the best way to do in-chassis testing. All those variables such as brake heating, tire heating etc are still present. It does afford you computer control of engine rpm and load. This allows you to examine specific areas.

Companies like Dynojet use Frenelsa retarders in their eddy current dynamometers. Some companies re-badge Mustang Dynos as sell them under different names. There are some things that are pretty well defined, however, like roller diameter. Smaller rollers like 12" are only good up for brief tests into the low to mid 100mph range. You need to get up to about a 20" diameter roller for 200 mph brief accelerations.

Rollers are round and you race on a flat road surface.

When you get into serious high speed testing and the tire-roller contact surface area needs to be accurately modeled, rollers about 10 feet in diameter are called for. Like most things, the science and engineering was done a long time ago, now the compromises are the norm.

Real World Testing, The Old Way

We spent thousands of hours measuring rates of acceleration trying to develop carburetion in the 1980's endlessly recording 40 to 60 and 60 to 80 mph times as well as quarter mile e.t. and mph readings. If we couldn't get three tenths to half a second improvement in these "roll-on" tests and six tenths and six mph gains in the quarter mile we wouldn't sell the carb and pipe packages we were developing. We took stock engined 750's and put them in the tens and took stock 1100's and put them in the nines with no internal engine work.

When the Harley-Davidson Evo motors came out in 1985 we took a dead stock 4 speed California spec big twin and with only a RB Racing 2-1 and a 38mm carb we developed ran a 12.90 @ 104.37 quarter mile. We didn't use any dynos because we found the early chassis dynos like the Patraco and even the early Superflow SF-900 series to be useless for carburetion development...Our only recourse was to instrument the bikes and ride them to measure the transient accelerations to see if we were making progress. If you spend 2500 hours doing this, sooner or later you stumble on workable solutions and formulate approaches to tuning...like recording all the temperatures, barometric pressures, relative humidity readings and changes in altitude. It was an expensive and stupid way to insure we always had three to sixth tenths of a second advantage when we went hunting whether it was on the street or at the track.

It was also a process that had a lot of variables that were difficult to sort out like rider technique and road conditions and gradients. It was also dangerous because you were instrumented to high heaven and taking your eyes off the road made life interesting. Then there were the cops who took a dim view of 120 mph passes past Donut shops while trying to get exhaust gas readings with a tube stuffed up the exhaust.

What are you measuring?

Take an inertial dyno that everyone is searching for bragging rights on. Take the oil out of your transmission. Put on the lightest rear wheel than you can. Put on a chain and can the belt drive. Regear the mother. Shave the rear tire. Put on a set of 20" stepped drag pipes. Shave the flywheels. You win. Do you really?

ORCA Transient Engine Dynamometers

Eliminate the variables. No tires. No gearboxes. Just the engine.

These days we use personal computers that are more powerful than what was used to be called "Super Computers" to develop things like fuel curves, ignition curves, piston shapes, port configurations and the like. Running from the cops might be a lot more exciting but the cops have lost their sense of humor and they tend to be a bit rough on you and your motorcycle...handcuffs for you and chains wrapped around the bike to tow it away. Then there are the lawyers!

To develop the ORCA big twins we use a sophisticated engine dyno that we have developed to accurately measure transient accelerations in minute fractions of time in order to optimize the engine's torque where in counts, in the mid range not just at peak rpms. We can plot the engine's torque during lightning fast transitions without having to artificially hold the engine in a series of rpm steps. Your motor's transient acclerations in the real world do not look like series of steps but are in fact a continuous curve that we can minutely quantify.

ORCA transient dynos work by creating a load that accurately reflects the real world load in terms of the mass your motor really has to accelerate and not some fixed 900 pound drum like you find on chassis inertial dynos. We set the transient loads to mimic exactly what your engine would see if it was going down the quarter mile for some peak rpm or simply for a typical roll-on from 2500 to 4000 rpm. By evaluating the piston, combustion chamber and port shapes not to mention the fuel, timing and camshafts we can direct our research to get the highest rate of acceleration for the intended application. An ORCA Transient engine dynamometer is exactly that...i.e. an engine dynamometer. ORCA Dynos measure directly from the engine to the dyno and not through any transmission, final drives or tires. This is the only way we can eliminate the variables that contaminate chassis dyno results.

Show Me the Torque!

Harley V-Twins will destroy most any dynamometer if you attempt to directly couple the motor to the brake assembly. By making the ORCA dyno bulletproof we can test both normally aspirated and turbo ORCAS and have repeatable results time after time without tearing up or overheating the absorption units. This is the only way to develop an motor and it is the method we used to develop ORCAS for touring, racing, and the other real world applications that we all face. There simply is no other way to do the research so it correlates to the real world. You should realize by now our research is not dedicated to the mindless pursuit of accelerating your motorcycle's rear tire on 900 to 1200 pound steel drums. We don't have a lot of time to fool ourselves with the clock ticking away quicker everyday. You have to keep it clear in your mind that it's where the rubber meets the road that we ride, not strapped down to some stupid inertial dyno with tie downs like some dominatrix trying to melt down most of Milwaukee. Oh, the metal will scream, but it won't give you the truth.