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Introduction to Engine Tuning: Dyno numbers - Don't believe the hype

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Dyno numbers - Don't believe the hype


00:00 - Obviously, one of the most important parts of any dyno tuning session is the dyno sheet that displays your results.
00:07 What you see on this dyno printout is going to depend on what dyno you've used to tune your car, but the numbers can result in endless debate and it pays to have some understanding of what they all mean.
00:19 When you're looking at the performance specifications for any new vehicle, the rate of power and torque values are always going to be listed as flywheel values.
00:28 That is to say, these are the values that the engine would produce, theoretically, if we removed it from the car and tested it on an engine dyno.
00:37 Often, comparing results from the more popular chassis dyno to these flywheel power figures is a little tricky.
00:45 Remember from the last section, that a chassis dyno for example, measures the power being produced at the wheels.
00:52 Since there's going to be some amount of power lost through the gearbox and differential, the power recorded at the tyre contact patch is always going to be somewhat lower than the power the engine produces at the flywheel.
01:07 How much lower, though, is a question that will endlessly be debated on forums everywhere.
01:14 The difficulty is that the amount of power loss, or drivetrain loss, as I refer to it, will vary from one car to the next.
01:23 For example, a four-wheel drive will generally lose a little bit more power than a two-wheel drive, by virtue of the extra differentials.
01:32 An automatic transmission will also tend to show less power at the wheels than a manual transmission, since there's always some slip inherent in the operation of a torque converter.
01:44 So now we know that the power at the wheels will be somewhat less than the power the engine produces at the flywheel.
01:51 It's not too much of a stretch, then, to figure out that if we run a completely standard car on the dyno, that's rated at, let's say 400 horsepower by the factory, and we find that it produces 300 horsepower at the wheels, then we know we've lost 100 horsepower through the drivetrain, and can calculate the power loss as a percentage.
02:14 Some dynos even go as far as to offer a correction factor that can be applied to the power measured at the wheels in order to turn it into a flywheel power figure on this basis.
02:26 The problem with this logic is that there's no way of knowing, with complete certainty, how the power loss will vary if we modify the engine and increase the power level.
02:38 For example, when we take our engine that produced 300 wheel horsepower, and we heavily modify it to the point that it now produces 600 wheel horsepower, does that mean that the drivetrain loss has also been doubled? Or does the drivetrain loss remain constant at 100 horsepower? Or, perhaps, is it somewhere in between? Sadly, there's no definitive answer, and the way one car responds might differ slightly from another.
03:06 The only real way to get a true flywheel power rating is to run the engine on a calibrated engine dyno.
03:15 The reality of this situation, though, is that the actual numbers don't really matter too much.
03:21 If we're using the dyno how it's intended to be used, what we're really interested in is how much power we started with, and how much we finished with.
03:31 Of course, that's not going to be overly helpful for those wanting internet bragging rights, but that really isn't what the dyno is designed for.
03:40 It's just another tool that we, as tuners, use, and like any tool, we need to understand how it functions, and what limitations it offers.
03:50 We also need to understand that it's impossible to compare figures from different brands of dynos, or sometimes even the same dyno being operated by a different tuner.
04:02 It's much more important to have consistent and repeatable dyno figures, than it is to have a large number simply for bragging rights.

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