Quote:
Originally posted by turbolx:
Not to start a flame war here, but please don't throw out misinformation like this. We use chassis dynos to tune the whole car, not just the engine. (that's what engine dynos are for!) The primary purpose of any chassis dyno is to try to accurately simulate what's happening on the road or at the drag strip, which should include wind drag, especially with trap speeds in the 1/4 over 100mph.
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Ah, a Mustang Dyno owner.
Anyway, you're wrong. But that's okay. Hyping your product is cool. Dyno's were meant to do exactly what their name imply's. Measure horspower.
The weight of a vehicle can be completely offset with gears. If you change the gear ratio in your car, your weight information becomes completely distorted. There is something called a computer to adjust air/fuel ratio's if the tuner doesn't know what he's doing. Tune it on the ragged edge, you get what you asked for. As far as putting your Mustang Dyno up against a Dynojet car, both with 400hp measured, yeah, you're car is going to win. Know why? Cause your dyno is wrong. Take your car with 400hp (setup with your BS parameters) then send the guy to a Dynojet and voila, he's got more. 420, whatever. Why is it that so many people who tune their vehicles on a Dynojet experiance no problems with their cars? Cause you are floating hype. If a tuner knows what he's doing, your car will be setup right. As far as tuning, since the car isn't run in the same gear for tune purposes, the engine is placed under different load conditions (called gears). A 3rd gear run won't put as much load on an engine as a 4th gear run. It's called torque multiplication. If a car is properly tuned, the 3rd gear pull, and the 4th gear pull should appear almost exactly the same. Making up some make believe weight number (cause you really don't know, and the load on the engine is changed by gearing) for a car won't help you tune it.
Furthermore, a coefficient of drag is NOT a constant number at all velocities. Take a look at the Ferrari Testarossa. It has a god awful Cd of drag, at measured wind tunnel speeds. But, dispite that fact, it manages a very high top speed. That's because airflow changes and creates pressure zones where air builds up forming a barrier around the object. Take a look at your rear window and watch the changing patterns as your speed increases and decreases on a rainy/snowy day. That correlates to a direct change in drag coefficient.
All your engineering is partially right. Under 1 set of circumstances. Applying them to the real world is another thing altogether.