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#81 | |
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They do read power at the wheel. Do you think it's just coincidence that the rear wheel spins a roller on a dyno? |
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#82 | |
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From what I gather it doesn't matter what gear you are in...the engine will still put out the same power and the gearing just affects how this is translated into speed. |
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#83 |
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#84 | |
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Measured power runs either happen in top gear or one below. The reason this is done is because the lower gear ratios do not provide time to get correct/accurate measurements. They do not put out 1000nm in first. They have little or no resistance from the rear wheel because of the lower gearing. The only thing that changes drastically is the speed of the rear wheel. For example, if an engine puts out 100ft/lb of torque at 5000rpm it does so in every gear. Run that through a 5th/6th gear ratio of 1:1 and it will be crusing. Put it through a lower gear ratio and it will accelerate like hell. Its the same amount of torque, just being used differently through the gearbox. |
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#85 | |
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It is easier to do on pre-unit engines ( ie; older british bikes, Harleys etc ). Found this link to the Superflow engine dyno benches. Last edited by simonDyna; 05-08-09 at 06:17 PM. Reason: added link |
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#86 |
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F = ma
P = Fv Different gearing has no effect, except for possibly probably differing transmission losses.
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#87 | |
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Exactly. And the gearing residual/parasitic losses will come down to the number of touching parts/cogs or the weight of the drivers and driven cogs. And another thing to add to the overall equation is atmospheric pressure/humidity. Last edited by simonDyna; 05-08-09 at 07:44 PM. |
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#88 | |
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Weight of the cogs you're spinning though? Constant mesh box innit. And only a factor on an inertial dyno. Anyway, we are going around in circles. We know it's dynojet dynos that are full of s*** and there are a million ways to play with the power readout. Adjustment factors for crank power are one of my pet hates. It's nothing more than a guess. What's more it's a meaningless, misleading guess which is no use to man nor beast unless you just want to brag down the pub!
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#89 | |
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I agree crank torque/power is meaningless to a certain extent. But if you want to tune high performance engines, you need the crank output so you can see what the losses are at the back wheel and then look to minimise the losses. |
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#90 |
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High performance/ any performance. You would want to reduce these losses at any level of tune.
Anyway, you can't know these things by taking a flying guess based on the first percentage you read in the Sunday sport. If you are using an engine dyno, fair one. My point about guesswork "crank power" figures based on RW figures being utterly useless boswallox still stands. Hence the problem in this thread.
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