What gear to use on Dyno? And RS Power outputs

[911-32]

I am no expert but seem to recall that the best gear to use is the one closest to 1:1 - so usually 4th?

Conflicting opinion in the UK suggests top gear (5th/6th) for the following reasons (and I quote):

"There is no right way or wrong way really, as long as you compare eggs with eggs you will have meaningful results. The difficulty is in comparing the 993RS with the 964RS due to the different gearing, hence my comment above. You can test a car in any gear, but with powerful engines and only two tyres to use the most common method is to use the highest gear possible to minimise the torque at the tyre. When we ran up Vic's 993GT2 there is no conceivable way the car could have been tested in 5th gear instead of 6th, with 800Nm even in 6th the tyres were lighting up until I loaded the car with ballast (thanks Vic & Paul for volunteering!)

As for accuracy, in my experience, top gear (overdriven) tests seem to be more accurate, furthermore because the inertia gain is higher for any engine speed range test (eg 3000-7000rpm) the engine acceleration reduces making it easier to monitor the results (back to datalogging sample speed again). "

Does this make sense? Are there any pitfalls in using top gear?

This comment is in the context of some very high power claims for 964RS and 993RS engines with mapping and/or Motec changes, ie:

964RS live remap 290-300 flywheel, 265-270 wheels, 380-390Nm
964RS Motec 320-330 flywheel, 293-299 wheels, 395-410Nm
964RS Motec +1 340-350 flywheel, 309-317 wheels, 410-422Nm
all tested in 5th gear

993RS cup cams, RSR mag intake, as arrived 291 flywheel, 246 wheels
993RS cup cams, RSR mag intake, after live remap 348bhp flywheel, 290 wheels, 405Nm
993RS cup cams, Carbon RSR intake, after live remap 366 flywheel, 330 wheels, 424Nm
all tested in 6th gear

What do you think?


Richard

[Formerly Steve Wilkinson]

The person you got the advice from is quite correct in saying that a dyno number is not an absolute, only a comparison. i.e. is the number you got on the dyno today better or worse than the number you got before making, say, a tuning change? And at that, it assumes that you're using the same dyno for both tests with the same dyno operator at the same ambient temperature and humidity in the same location. Dynos are so fraught with variables that it's sort of like you or me hefting a bag of rocks and saying it weighs five pounds. that may or may not be the correct number, although it'll probably be close, but if you or I heft two bags of rocks and say this one is heavier than that one, we're virtually sure to be absolutely right.

Most dyno tests are done in top gear.

You can eliminate the slipping-tire factor (as well as variation due to tire growth at high speed) by using a dyno that bolts directly to the rear-wheel hubs (with the wheels removed). This is the type of dyno that some race teams use, because they're somewhat portable.

Stephan

[Bill Verburg]

As Steve mentioned and for the reasons Steve mentioned higher gears are used, but I need to add that as long as the dyno software knows all of the involved components and their effect the software is supposed to normalize the data.

A dyno measures torque and the software calculates hp from the measurements. Gearing and tires will affect torque, lower gears and smaller tires multiply this measurement condsiderably.

To avoid unnecessary manipulation of the data 1:1 is best, as is the DynoPac(bolts to the drive hubs so tires are removed from the data) type dyno that Steve referred to.

Different types of dynos measure subtly different torque effects so it is very difficult to compare #s from one type to another. They are not measuring exactly the same thing

In Europe Maha seems to be the most common type.
Michael Jarke has put together a nice page w/ info relevant to you questions.

[911-32]

This is a Bosch dyno - wheels on.

Thought you guys may like to see the claimed power numbers as well.

[PorscheGuy79]

40hp from a carbon intake...ive be looking at dyno tests on intakes for years and I have yet to see an intake that rivials a bolt on turbo. I have little knowlegde of these particular cars or the intake being used, I just know my gut says thats bizaar.

[911-32]

Carbon RSR intake nets 18hp flywheel over Mag RSR intake - not sure where 40 comes from.

Details of the shop doing this work is available here: http://www.9mracing.co.uk/

They are probably the most respected RS specialist in the UK.

[Porsche Doc]

We have a Dynojet here at our shop and we use 4 on all Porsches

[obrut]

hi richard, the most common approach down here is to choose the gear closest to 1:1 - and then argue wildly about the loss factor...

[911-32]

Nice call Ryan, I just find the hp claims hard to understand/believe so I was searching for clues.

I hear you know my good friend Hamish. Make sure you keep feeding him tastes of the Porsche bug while he is Porsche-less!