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I know squat about tuning, as I've started before. But I DO know dynos, both chassis and engine. Let me assure you that Scott's basic assertion is correct - there's a huge difference between an inertial dyno (older DynoJet, for example) and a dyno with a PAU. It's not that the inertial dynos are useless, just that they are very limited, and especially for full range tuning. All they really can do is measure the rate at which the subject car can accelerate a fixed inertia weight, which limits their use only to WOT operation. Is track tuning necessary? Of course. As others have said, there are small tweaks that can only be made when the vehicle is under motion and subject to the physics of a body in motion.
A note on engine dynos. Even a basic Superflow hydrokenetic (water brake) can provide extensive useful data. However, given a choice, I'd take a flux-vectored AC or DC dyno, which can provide a full range of simulation, including motoring of the engine (picture the car coasting down a hill). These later types of dynos are, unfortunately, very pricey. The down side of engine dynos is that they can't provide ANY info on the assembled vehicle - just the way it is. A chassis dyno can at least fill in a few of those blanks on your spread sheet.
The usefulness of either chassis or engine dynos is largely determined by the accompanying instrumentation. The more the better. AFR (Lambda) for each cylinder is doable. Data logging of temps all over the engine and cell is necessary. And when was the last time the equipment was calibrated? Lots of shops don't even own the equipment to calibrate their load cells. At the EPA lab, we spent about 1/4 of our time calibrating and documenting.
Folks who don't know dyno testing often do go shopping for the highest number, which is, of course, just plain silly. That's like me saying I have a bigger 9/16 wrench than you have. The point is not the size of the tool, but what you can do with the resultant effort. (That wasn't meant to sound sexy, but it kinda does.....)
For more info, see my dyno article on the September 2000 issue of Hot Rod.
Later
Dan
I know squat about tuning, as I've started before. But I DO know dynos, both chassis and engine. Let me assure you that Scott's basic assertion is correct - there's a huge difference between an inertial dyno (older DynoJet, for example) and a dyno with a PAU. It's not that the inertial dynos are useless, just that they are very limited, and especially for full range tuning. All they really can do is measure the rate at which the subject car can accelerate a fixed inertia weight, which limits their use only to WOT operation. Is track tuning necessary? Of course. As others have said, there are small tweaks that can only be made when the vehicle is under motion and subject to the physics of a body in motion.
A note on engine dynos. Even a basic Superflow hydrokenetic (water brake) can provide extensive useful data. However, given a choice, I'd take a flux-vectored AC or DC dyno, which can provide a full range of simulation, including motoring of the engine (picture the car coasting down a hill). These later types of dynos are, unfortunately, very pricey. The down side of engine dynos is that they can't provide ANY info on the assembled vehicle - just the way it is. A chassis dyno can at least fill in a few of those blanks on your spread sheet.
The usefulness of either chassis or engine dynos is largely determined by the accompanying instrumentation. The more the better. AFR (Lambda) for each cylinder is doable. Data logging of temps all over the engine and cell is necessary. And when was the last time the equipment was calibrated? Lots of shops don't even own the equipment to calibrate their load cells. At the EPA lab, we spent about 1/4 of our time calibrating and documenting.
Folks who don't know dyno testing often do go shopping for the highest number, which is, of course, just plain silly. That's like me saying I have a bigger 9/16 wrench than you have. The point is not the size of the tool, but what you can do with the resultant effort. (That wasn't meant to sound sexy, but it kinda does.....)
For more info, see my dyno article on the September 2000 issue of Hot Rod.
Later
Dan
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