Engine coolant temperatures, along with the transmission and rear end fluid temperatures should also be maintained, as heating or cooling the fluids will affect horsepower and torque readings. Obviously, we can’t control the weather, and the dyno will compensate for changes in the weather automatically, but you should always attempt to make changes while the weather is normalized. A run at 6:30 in the morning with no humidity and cool temperatures, compared to one after heat soaking the engine, the dyno cell, and the drivetrain done at high-noon with high humidity and 20-degree higher temperatures will not be very accurate for measuring small changes.
Real World Applications:
Ok, so we know how a dyno works and we understand that we must be consistent, but how can we use one of these tools in a meaningful way? Let’s look at a couple of real world scenarios:
Timing, timing, timing
Your car runs great at the track, and your starting to push into the front of the pack. The guys up front always snap off of the corners, while you’re thinking your car might be a little lazy coming into the power band. And, try as you might, it’s hard to get your foot any further through the floor. You’ve heard people talk about the effects of ignition timing advance and its affect on power but you really can’t afford to take each heat race and qualifying run with plus or minus half a degree of timing. On a chassis dyno however, you can quickly change timing in seconds, and you can record the entire rpm range and the affect the timing change made. With 28 degrees of total timing, you may make peak torque of 500 lb-ft at 4,700 rpm. A quick bump to 30 degrees total, and you gained 10 lb-ft and brought peak torque down a bit to 4,600 rpm. If some is good, more must be better, right? Add 32 and, uh oh, peak torque has dropped off and you’ve picked up a little pre-detonation, which caused erratic power output above 5,000 rpm. Now, in just three runs, you’ve found the best timing for maximum performance and the testing is backed by actually hard data.
"You’ve heard people talk about the effects of ignition timing advance and its affect on power but you really can’t afford to take each heat race and qualifying run with plus or minus half a degree of timing."
Carbs for breakfast
A bigger carb is always better for power, everyone knows that, right? No, you know better than that, but maybe a small change in flow could really help your particular combination. Now, are we going to go to the track with six different carbs and test them all? What about traffic, or the track surface changing throughout the night? Again, load that racecar up to the chassis dyno, stabilize all of your variables (tire pressure, straps, temps, and so on) and let’s change out some fuel leakers. Run one, record the data, remove it, and drop another carb in its place. Oh look, the smaller carb actually made much more power under the curve, while the big fancy one actually dropped power by 25 rwhp across the top of the curve. The big guy may have “felt” better, but here again, we have actual data to prove otherwise.
Remember when we said that the chassis dyno measures everything in the drivetrain, not just the engine? Well, that really means that everything can be measured for power gains or losses, including all of the hard parts between the engine and rear tires, and even some accessories we wouldn’t normally consider. Running an alternator? Ever wonder if a looser belt may free up a pony or two? Or, maybe that heavy clutch really is soaking up some power, what would a lighter one do? How about the actual gear oil in the rearend? Think you could go to a lighter weight oil and pick up some power in the process?
Testing, Testing, 1, 2, 3…
Are you starting to see just how much information you can gather with a tool like this? The big NASCAR teams have been doing it for years, and now you can get in on the action for less than it costs to tow your rig to some races. How about those low-impedance plug wires you keep hearing about? The list goes on and on and the only way to know what really works on your exact combination is to try it out and see for yourself. So, head on down to your local dyno shop and start making pulls. You’ll find what works, you’ll find what doesn’t, and you may even find some new tricks you’d never even thought of. At the end of the day, you’ll be more prepared come race day and you will have quality data, which can be the difference between guessing as to why you lost or climbing atop your car and holding up that big track trophy.
At the end of the day, you’ll be more prepared come race day and you will have quality data, which can be the difference between guessing as to why you lost or climbing atop your car and holding up that big track trophy.