Dyno in third gear? ( W58)

[stradlater]

Just recently realised that the clown that dynoed my car did it in third gear (according to the graph).

Woudl this give me a higher reading or a lower reading than is realistic?

[Snyper]

who knows... from my experience you can never trust a dyno for figures, only good for a tuning tool.... I have seen power runs done in 2nd, been to another w/shop and they use
3rd, and another one has used 4th....
have also seen a car on 2 different dyno shops in one day, and 23kw difference.
as for the gearing I think it just works the car a bit harder.... depends on how fast they can make their dyno go...

Brendon

[stradlater]

wasn't my experience, but thanks for the input

[Jorrs]

4th gear is usually what most places use to dyno car,
try put ya car on car and just do 2nd gear, is very high reading, not sure bout 3rd but yeh they should really use 4th gear, unless your 3rd went out to 200 kms ?

[kingmick]

4th gear is 1to1 or very close to it in most cases! you dyno a manual car in 4th!

[Tarkers]

like jorrs said, 4th gear is what should be used.

They would do it in 3rd if your car exceeds 200km in 4th, but the dyno would have to be calibrated to suit 3rd gear, as using 3rd gear will throw out the readings a bit(this will give you alot higher reading than you should have)

This is the way the dyno guy explained it to me, but others with more knowledge of dynos might like to back me up or correct me ?

[stradlater]

but if you dyno a manual car in 3rd or 2nd, do you get a higher or a lower reading?

I thought lower, cos if you went to OVER drive, (5th) THEN you would get a higher reading, becuase THEN it's 0.7:1 or something like that.

[stradlater]

I would go in excess of 200k's in 4th I think, if it was pushed.

[Tarkers]

it definately gives you a higher reading when dynod in lower gears

[Rodger]

Interesting,

I would have thought the gear choosen would be the one to give you the least drive train losses and since most 4th gears are 1:1, locking the input shaft to the output shaft, most dyno shops would choose this gear when doing a power run.

I also thought the idea was to run the car up first, under no load to calibrate the dyno to the revs the car showed thus allowing for different tyre/wheel size, diff ratios and gearbox ratios.

With that thought, I'd say apart from different drive train losses in each gear, the power reading should be the same.

I'd also like to think a good tuning shop should be using the dyno like driving on the road. Tuning the car for the whole range of loads and throttle positions, revs and speed.

Regards

Rodger

[WDE_BDY]

Torque at the wheels (which is a bullshit number anyway) will be different, however assuming they put in the correct gear ratio factor the horsepower should be pretty much correct. As long as they are consistent between runs though it won't really matter, same as two cars running the same setup but different diff ratios. As long as its adjusted for the results should be pretty much the same.

Callum

[stradlater]

yeah, but how they gonna know what the gear ratio is?

[Jorrs]

thats why they usually just run most cars in 4th gear, for consistency, as a car can be run in 2nd or so and put out much higher readings as in power to wheels, thats how dyno guys explained it ?

[Enchanter]

I might be wrong but Im seeing most of the replys pointing towards the dyno guy stuffing up.
Am I correct ?

[Nark]

Yep. Lower gears have higher torque multiplication.

4th is chosen for consistancy. Most 4th gears are 1:1, that's why it's chosen.

[Jorrs]

perhaps ? though maybe he had his reasons.

[rxbenny]

the power output is wank factor, a dyno is a tuning tool and you will get different power readings based on many variables.
Find a shop and get your car dynoed there consistantly to find out how much difference each mod does.

i am sure he had his reasons cos if he wanted to hide the 3rd gear fact would he have noted it on the dyno printout.

[Lench]

what about automatics?
there were a few soarers at the last dyno day i went to and they were all autos (im guessing 3 speed auto?)
so do they wind it up til it changed to 3rd? or do they take a reading from a standing start?

[Jorrs]

autos they run in 2nd gear. i believe

[LeeRoy]

A friend when he got his car dynoed at a dyno day asked the guy to do a power run in 4th then 3rd. He made 162kw in 4th and only a few % more in 3rd. The difference was so small as in around 5kw from memory.

- LeeRoy