Daniel-S

Can't remeber where i read it on hereBut summant about dynos where they measure it on the comedown of revs in third.Also summant with a close ration gearbox buggering that up

speedking

Link from here?

Use 4th?

Daniel-S

WTF that link has nowt to do with what i asked

wrc350

why 4th? does it matter if 5 or 6 speed?

Maz

iTrader: (34)

Peak power is normally achieved in fourth.

The Fixer

Nope, some Dynos calculate transmission lossess using the coastdown method, more accurate dynos like Dyno Dynamics dont use this method as its open to abuse, different tyres, oils, wheels etc can all influence the results. Cars on our Dyno Dynamics are run in third, power at the wheels is measured and the flywheel figure is calculated, this is based on the transmission type.

So your car never makes peak power in any other gear????

The engine doesnt know or care what gear it is in? It will develop peak power at a given rpm, dependent upon factors like the engines VE, boost, fueling and ignition.

Maz

iTrader: (34)

Fourth is a good gear for a power run as the wheels are less likley to spin on the rollers. Doing power runs in third???? Surely with very high outputs you would have problems with wheelspin!

The Fixer

No mate, Dyno Dynamics Dynos dont have wheelspin problems, we can measure upto 1500hp

Had plenty of big power power Evos with nasty T88 powerbands (600hp AFW) with no traction problems. Ford F150 lightening, 5.4L V8, Supercharged and modified, 600 lb's/ft of torque No wheelspin

Problem with 4th gear is wheel speed, some dynos cant handle the MPH that 4th generates on a powerful car.

Cheers

Gerry Gaffney

Hi Guys,

Normally you will find on Bosch, Sun/Maha, Hofmann dyno's the test will be conducted in 4th gear, on Dyno Dynamics & Dastek Dyno's the test will normaly be conducted in 3rd.

There seems to be a huge amount of conjecture & misinformation of the subject of rolling roads, one of the biggest being that the only figure that matters is that of 'Power at the wheels' (PAW) However I strongly disagree. There is greater error on making judgements/assumptions on a PAW only basis.

Allow me to explain, the PAW on a rolling road is NOT the same PAW as transmitted to the road. The reason for this is that the rolling road in itself requires power just to be able to turn over the rollers & retarder (this power comes (or more correctly is robbed) from the power available at the wheels) This power requirement goes up in an exponential fashion with speed. Therefore the greater the roller speed at which a power measurement is made the lower the power at the wheels will be (more below) Other factors that can & DO affect the PAW is the wheel alignment, the tyre pressure, the sidewall height, the amount of strapping effort, the size & finish of the rollers, & the roller seperation (to name but a few)

I will also make another bold statement the power lost through the gearbx due to power input is less than 1/2%, the rest of the losses between flywheel & rollers, is made up of heat & noise created by the tyres, gears splashing through the oil, parasitic drag of bearings & seals (both car & dyno) & the drag caused by boundary layer windage of the rollers & retarder and this is more or less speed dependant (actually follows a 'Stribeck Curve')

http://putfile.com/pic.php?pic=5/13612560575.jpg&s=f5

So the whole agurement that power is not being transmitted & the gears are meshing on the wrong side, at worst will only make the measurement 1/2% wrong, much less than if the g/box oil temp changes by 10C or the wheel alignment is out.

I have huge amounts of real-life data on chassis dynamometers from when I first got involved in them when I was part of a team designing one for our own purposes (I was an engine builder for Toyota on WRC & SuperTouring engines) So it's not just useless drivel from the internet & salesmans blurb )

Conrad that's quite a bold statement 'some Dynos calculate transmission lossess using the coastdown method, more accurate dynos like Dyno Dynamics dont use this method' if you are genuinely interested in getting results that are truly meaningful, you need to go & try a few things (I've already tried them on the DD machine to see if any of the fabulous stories that Mr. G. spouts were even remotely true ) First mount a thermocouple in the g/box, then warm the vehicle up, do a couple of runs to get a base figure. Next drive the car hard on the dyno (like you were live mapping) & get the g/box oil temp up by around 25C. Now do another few runs, what do you get? Secondly try doing the runs in different gears? Finaly tighten your ratchet straps 2 - 3 clicks (assuming you are using the over arm ratchet pull down arrangement) then let me know if you still stand by your statement that PAW + your 'derived loss' is the only reliable number. As for no slip on the DD machine, EVERY roller dyno has slip of a certain %, some of course less then others , if you want to test this, set your dyno to 30mph, select 1st gear, at 1/4 throttle set the rpm:mph ratio (take a true independant rpm) then with the dyno controlling to 30mph (which will be xxxx rpm) start to gradually open the throttle, watch how the mph & rpm on the dyno remain constant, but your independant rpm will increase. Slip is ALWAYS present on a roller dyno, as it is ALWAYS present on the road also! Some dyno's handle it slightly better due to larger rollers, & closer roller seperation, as well as using an idler roller shaft encoder (speed pick up) to work out the slip

I have included a few screengrabs from our own dyno, to show the usefullness of the coastdown test (when used correctly) and how limiting it can be to ONLY look at the wheel power.

1) A power test conducted in 3rd to 5th gear on our own Civic Type-R

http://putfile.com/pic.php?pic=5/13611493774.jpg&s=f5

2) Zoomed in on the PAW & flywheel power

http://putfile.com/pic.php?pic=5/13611512841.jpg&s=f5

3) Zoomed in on the transmission losses on test 1 above

http://putfile.com/pic.php?pic=5/13612125068.jpg&s=f5

4) A test showing the difference g/box (& diff) oil temp makes

http://putfile.com/pic.php?pic=5/13612141620.jpg&s=f5

5) A test showing the huge affect a wrongly fitted wheel bearing can make

http://putfile.com/pic.php?pic=5/13612213418.jpg&s=f5

No Doubt this will open up a huge can of worms, but for people who are genuinely interested in credible information, they need to look much further than the marketing

Cheers,

Gerry
http://www.dastek.co.uk