DYNOmite vs. SLEDdyno
OK, some of you wanted us to pick the better dyno in our Product Evaluation of the Land & Sea DYNOmite engine dynamometer in the September issue of SnowTech. It's not that easy.
As many of you know, SnowTech uses both an engine dyno (Land & Sea DYNOmite) and a track dyno (DynoJet SLEDyno). Many shops can not afford two dynos, and they want to know which one is better; the engine dyno or the track dyno?
The two really are so different that it would be tough for us to only pick one. The DYNOmite does a better job of showing the differences from engine modifications, as it is going to show you the actual torque and horsepower being produced at the engine crankshaft. The SLEDyno, since it is showing you the track horsepower, it is more dependant on the transmission calibration, and can not give you as definite information as to engine changes.
We use the engine dyno for testing things like heads, pipes, reeds; engine mods. We use the track dyno for clutching and gearing changes. If you make any kind of change to the engine horsepower, you would like to first test it with the same clutching (if possible) to see if there is any change in power, and then make the appropriate clutching changes. But it gets pretty murky as to if any increase in track horsepower is from an engine change, or simply a transmission change.
Both dynos are very capable pieces of equipment, but the data from both can be skewed and misinterpreted; it is very easy to obtain false information, and it is very easy to make either say pretty much whatever you want. We'd have to say that it is easier to get bogus data from the SLEDyno than the DYNOmite, but you can make them both give you misleading data. Just because you see a dyno chart does not make it true; only the dyno operator knows if the data being presented is accurate or not. And sometimes, the dyno operator may believe his test procedure is fair, when in fact it is not. This is why we wanted to do it ourselves; whose numbers can you trust, really?
It takes a high level of discipline to be as fair and as accurate as possible in your test procedures, making sure the conditions and variables are being measured properly and with great accuracy. If you go into a test with a bias as to the conclusion, your data can be biased. Objectivity is critical.
Maybe the best single piece of information from either dyno is not really how much power something makes, but the spread; before and after. Numbers from one dyno to the next can vary quite a bit; but the spread should always be the same from dyno to dyno, assuming consistent variables (similar water temp, pipe temp, air temp or fuel consumption).
Some things to remember when looking at the dyno charts; engines tend to make more power with cold water temps, and less power as the engine gets hot. A "before" run with a hot engine and an "after" run with a cold engine can show some big power gains, but much of the spread can be from the difference in temperature, not any for-real power gain. The exact engine rpm that the most power is made at can also move around; a cold pipe peaks at a lower RPM than a hot pipe.
And of course there is fuel consumption; basically, jetting. A "before" run with the rich jetting can look very poor compared to an "after" run with the leaner jetting; so is the power gain from your modifications, or simply from the leaner jetting?
Most dyno runs are taken at wide-open throttle. The engine is swept through the rpm range with the throttle wide open, so the change that may enhance partial-throttle performance (like reeds) really don't show up on a dyno test; but in the field you could really notice a change in performance.
If we were absolutely forced to choose only one dyno, it would be the Land & Sea DYNOmite engine dyno. We believe it to be the more accurate and more technically sophisticated piece of equipment, with greater capabilities and upgrade ability. But it would be tough to live without either. Remember, we are magazine guys trying to seek more accurate information, instead of relying on what someone else tells us.
We say this despite the fact that we know of many shops that own one or the other dyno; some swear by each of them, and some swear at each of them. SnowTech has had acceptable success with both units, but only after extensive training, experience, and consultation. We've found it easier to "over-power" the track dyno, where we've pretty much haven't found the upper limit of the engine dyno (yet). Big displacement engines can spin the track dyno easily, and we suspect it should have more mass for testing at our elevation (1500 feet).