Quote:
Originally Posted by BruceM
Thanks. Are your measured numbers to the crank directly from an engine dyno, or extrapolations from a wheel dyno? If the latter, what driveline loss do you apply to get to the numbers?
Is 93 commonly available where you are from in California? I had thought it was 91 down there....
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It is 91 at the pump out here. We mix gas to get 93 octane since that is what most of the country uses as premium gas. We use both our own engine dyno and our chassis (Dynapack) dyno to ascertain the crank numbers. While our engine dyno is mainly used for our race engines we do use it for street car testing as well. I will just copy and paste a previous response to the dyno question as it saves me some time. =)
The short answer to your question is we use both.
We do use a Dynapack chassis dyno and a DTS engine dyno for all of our testing. Like most OE's, we publish our crank numbers, not wheel horsepower numbers, simply to keep things as accurate as possible. Dinan tests multiple cars with multiple runs and averages them so no one chassis dyno test would be representative. When we compare our engine Dyno Data to our chassis dyno data we find that most if not all chassis dynos, including ours, overstates the lower RPM torque values. Our chassis dyno does not do a coast down for inertia and friction corrections. If we are using the chassis dyno once we have performed multiple Chassis dyno runs and averaged them we apply different correction factors to each RPM to correct for these inflated torque numbers. All this is done to ensure the most accurate reporting to our customers. We list both Stock and Dinan numbers using the same corrections to ensure the comparison is fair. If we are using the Engine Dyno the data is just averaged over multiple runs to get a fair average performance. With both the engine dyno and chassis dyno we ensure the room is as close to standard weather conditions as possible and all dyno runs are performed in the same weather window to ensure comparisons are fair. In most cases Dinan Dyno numbers will be lower than those you will get at low RPM because of the inaccuracy at low RPM previously mentioned. Also in most cases Dinan's numbers will be higher at hi RPM because of the work we do to ensure proper heat exchanging that we find almost no one else does.
A few years ago, we put together a really in-depth article on our dyno process and how even slight variables can affect the outcome of any test. http://dinancars.com/dinan-university/ - (Dynamometer Testing and The Modern BMW Engine)
It's a long article, but it gives you a really detailed looks at the process with a conclusion that has a good breakdown of what we covered. The most accurate thing we can say is that we've observed over 36 years of tuning, with most models we've tested, that the drivetrain loss is between 6.5 and 15 percent. It’s not as simple as a percentage however, as it varies on car, transmission, RPM, vehicle speed and a myriad of other variables.
The percentage listed in the last line is a bit off for the current generation of cars--- most of the modern RWD cars cap out at about a 13% drivetrain loss from what I have seen. On an AWD car that number is still in the 20% range however.