Mini Mania is once again offering Dyno testing at our Nevada City Adventure event scheduled to take place June 1, 2013. The Dyno can yield a lot of great information and this was no exception! Dyno testing is like a ‘great dream’! Lots of us talk about them but how many people can really live them! Proving our metal is often equated to ‘dreaming’ about demonstrating how good we are by how much horsepower we can buy for our steed of choice. “How big is your dream” is a great experience at the Nevada City Adventure!
We were fortunate to being able to test 15 various MINI/Minis during the 5+ hours. Those of us that dream of Horsepower have all read all the claims by the factory as to how their stock engine performs and most of us simply are never satisfied and ‘want more’; and ‘more’ has to have a starting point. But finding that reference point is a major part of the challenge. Industry standards are well defined but seldom understood. “BHP” was one of the terms/system first used to measure the performance of a motor. “BHP”, which stands for ‘brake horsepower’ is not really a measure of horsepower at all, it is a measure of torque as applied to a ‘band brake’ that is connected directly to the output of the engine. Basically it is done at the flywheel with NO ancillary (but necessary) equipment such as power steering pumps, water pumps, transmissions, etc. installed. It will typically be the highest number you will ever hear for your motor. “SAE HP” has become industry standard throughout the world in the last 30 or so years and will it took most of the practical ancillaries into account for it’s results, it still measures at the flywheel and thus eliminates the loses within any transmissions, etc. Obviously the cost to simply tweak or test you motor to directly relate to factory numbers will require a budget that is left only to the really big race teams.
So what is our choice to attempt to ‘live our dream’? Along comes a chassis dyno. This is a devise that measures horsepower at the wheels and as most is us will only ever use a motor on the road, why not test it in the most practical way. If the first thing we learned from this experience was the difference in terminology of “HP”, the next thing was an understanding of the different concept of engine verses chassis dyno, the final lesson so far is that not even all chassis dyno’s are created equal. It is common practice when testing on an engine dyno (SAE HP) to simulate driving conditions such as load, cooling, air flow, etc. When a chassis dyno of any type is used, many of these conditions need to be taken into consideration. Modern motors as found in our little MINI Coopers are extremely sophisticated with closed loop sensors that tell the on board computer everything it is experiencing in an attempt to keep performance within the operating range as designed by the engineers. This is a great opportunity for the factory to provide consistent performance over a very wide range of conditions or use that the motor may be subjected to but makes it almost impossible for us to really understand how we are ‘living our dream’. On board sensors can adjust fuel mixture, ignition timing, blower by-pass valves and even water flow on some of the most modern motors, all to keep things safe and dependable to the warranted life of the car.
There are two other major considerations when attempting to ‘measure our dream’ on a chassis dyno. As the factory number are ‘at the flywheel’ and our will be at the wheels- how do they relate? Well, this depends ho who you talk too and what is the objective of the test. Driving the running gear of the car, transmission, differential, wheels and tires has to be factored. The most common practice is to simply multiply the results of the chassis dyno by 15 to 20% to arrive at a ‘flywheel’ horsepower number. If you want to feel good about your numbers you use 20%, if you want to demonstrate only a modicum of improvement you use 15%- OHH! Did I tell you this was a dream machine and thus very subjective?
The second very major issue to be considered when using most chassis dynamometers is who much friction loss occurs as you secure the tires the very large rollers as used transmit the power to the equipment. While it is easy to control the subjective figure you use to convert form chassis to flywheel horsepower, it is not so easy to control the extreme variable that results from how the dyno operator secures your car to the rollers. When tied down too tight, you will lose horsepower due to excessive loads, when tied not tight enough, you lose horsepower due to wheel spin (even if you can’t see or hear it). Of all the variables we have talked about, this is at least one that we can control with the right choice of chassis dyno.
The dynamometer we used for our test day was simple, fast, easy, and computer controlled. It eliminated the variable of operator error by having the drive hubs of the MINI connected directly to the machines, thus by-passing tires and rollers. What a joy to use.
So what did we really learn about 5 hours and all these cars on the same dyno in almost the same conditions (it was a little warmer in the afternoon than it was in the morning). First and foremost it was a fun experience to watch all the people get so excited about hearing and seeing the runs, looking at the computer screen live as it was happening and generally just communicating.
Both those that had their Mini tested and those that were just there to watch leaned that indeed a chassis dyno is first and foremost a ‘tool’ and not some sort of ‘God-like’ mystery machine that can perform mericles on a motor. No car ‘gained’ horsepower because it’s run on the Dyno, BUT the ‘tool’ did allow owners and operators to find a unbelievable number of problems that robbed many owners of ‘living their dream’. Not only were most performance numbers within 10% of each other but every-time the number just didn’t look right, we found a problem. Everything from slipping supercharger belts, to 2 different pressure by-pass valves not functioning correctly, to poor gas octane selection, broken motor mounts (3 of the 11 BMW MINIs tested had broken mounts that the owner was not aware of), etc. were all found by this great “Tool”.
The ‘Tool’ was also used by one owner that wanted to have bragging rights for day’s fun by having the best HP numbers. The operator made a second power run on the dyno while the owner dumped a bottle of water on the inter-cooler and (surprise-surprise) he picked up another 5HP.
The cars tested ranged in years from 2002 to present, with as few miles as 20,000 to as many as 122,000. Every car had some level of upgrades, all had changed the supercharger pulley added a cold air intake and modified the exhaust. As all the results were within 10% of each other (even after the guy the dumped water on his inter-cooler) and thus we learned that almost all modifications produce incremental gains that simply allow us to ‘live our dream’.