So allowing for transmission loss that is over 500bhp ATF.




Trout

[Edited by Trout - 9/1/2002 11:34:32 AM]

 

Firstly I am not a Rolling Road man, I have only dealt with engine dynos on a detailed level, I have in the past, only researched rolling road type dynos for product/marketing comparisons.

But, I know they use coast down testing as the basis of measuring transmission loss. Haveing attended a Rolling Road day for the first time saturday, I took a good look at what was going on.

The rolling road I visited is typical of a UK rolling road (Maha), it appears to have a large eddy current or friction brake in each corner using a huge vented cast iron disc which. Somewhere in the mix is also an inertia rotor to smooth out the load, and enable the cost down test.

So anyway, power run is done, operator takes it to the peakpower point then dips the clutch, and it will begin to slow. The software knows what the inertia load f the dyno is without a car, becase you can do the test without the car and measure the dyno's baseline inertia. As the wheels slow the dyno measures the rate of decay of the wheelspeed, since the dyno is now driving the whole drivetrain right up to and including the clutch plate, it will slow more quickly. As the wheels slow the software then compares the measured decay with the baseline, printing the loss as it goes. The difference between the baseline (no car) and measured (car under test) is caused by the transmission/wheel drag, and can be seperated out into torque and therefor power.

Most UK dyno plots will show the transmission loss as a seperate curve, and will be added to the corrected wheel HP curve to give the estimated flywheel power.

The theory is sound, and car manufacturers have been doing coast down testing for years, only on the road you have to add a curve for aero drag, and if you really want to be accurate, you can seperate the linear motion from the rotary motion and look at the equivalent mass of rotating parts due to inertia.

The problems can come from the assumptions made in the software one way or the other about bearing losses, and whether the baseline figure is calculated or measured.

Hope this answers a few questions.

Edited since andy's reply.

The no-load measurement is probably pretty good as is. The drive train losses are probably mostly vicsous, especially at higher speeds. What you gain in no load measurement you might lose in increased tyre deflection etc. I also wonder if they don't add a load multiplier into the software, that says multiply any initial losses by X% of the wheel torque.

Paul

[Edited by Pavlo - 9/2/2002 11:06:28 PM]

 

because I saw this thread coming months ahead of time, so I started to draught my reply back then.....

S'net glitch.

Edited to add the dates transposed 09/02 instead of 02/09

[Edited by Pavlo - 9/6/2002 9:32:13 AM]

 

I love my new LINK !

412 HP - - 345 ft lbs at the wheels on unleaded pump gas and 26 psi of boost yesterday on my competley stock STI VII jdm engine with upgraded turbo (Garret GT30); fmic and LINK ecu

Nothing like subaru power !

Some pictures - - - >

http://forums.i-club.com/forums/showthread.php?s=&threadid=235004

 

say's it all

 

Just been on i-club - they must have different size horses over there as the BHP they are quoting does not correspond to the 1/4 times they are quoting.

They are saying that a car with 242bhp PAW would be struggling to do a mid 13s with terminal over 100mph.....mine did it with around 190bhp PAW - measured in a UK way of course...

Trout

 

he still quotes 345 lbs/ft

 

Agree with yout there Trout
They must have a different way of measuring things out in the states as ive seen near standard uk cars do mid 13 sec 1/4's
I think they just cant drive properly over there and they put the steering wheel on the wrong side too

Tony

 

By way of Standard cars - do you mean STI's ??? My regular WRX did the 1/4 mile in 14.00 flat

My sti V7 does the 1.4 mile in about 13.3 stock

I have gone 12.085 with 350 wheel HP as rated here in the US

I will be going to the track soon to see how fast it goes with the new set up

By way of comparison - - the dyno I use - Dynojet - measures a stock 2002 WRX at 170 to 180 wheel hp and one with exhuast mods at 190 hp

 

I mean uk turbos which have 215bhp, ive seen one with just an exhaust do 13.32 1/4 mile but he was quite abusive to it to get that time so that was probably running 230-240ish bhp.

Tony
(ps remember that miles in the states are slighly less than our miles over here! so quoting 400m would be better than 1/4miles)

 

I think someones dyno's are messed up
are you talking about the standard New shape WRX's which have 215bhp?
If you check out our dyno section (power engineering one) and see Pete Croney's modded MY01 WRX you will see it pushes 244bhp of which 154bhp is on the road, so unless your cars are pushing 280ps in standard form you wont see 180-190bhp at the wheels

Tony

 

So you are saying that the 1/4 mile isnt a standard distance across the world? They may bulls**t their horsepower claims, but are they cheating the 1/4's now too?

 

-Alfriedesq
did you change your gear box and your trasmission ?
i think the standard one is not able to suffer a similar power...

 

Trout ... yeah, there is something really weird about it all. A few weeks ago Jerry/SAM had enough of it all as well on I-Club.

My car, having 200 Powerstation BHP at the wheels back then, driven by a rally driver (a good one), managed 12.9 secs a few times.

Estimated flywheel power was 295 BHP. With PACE FMIC, I might be lucky to see 305 BHP there now.

Same car would probably get 175 BHP on Aussie RR's ...

Mind you, it's not a UK thing, as our local 4WD RR gave me ... 3 BHP less than at PS.

It just all proves how sad these RR numbers really are.

Alfred, this was not meant to have a go at you at all ... it's just a fact that US RR's measure in a different way to European or Oz RR's. I'm sure yer car is pretty much a monster at the moment

We should all stop quoting PAW BTW... they do not compute.

Engine dyno's might be a bit more meaningful.

 

Steve, there is something like 70 or so yards difference between our imperial mile and the US mile (will have to look it up) and their hp against our bhp seems to be better so i dunno what subaru do to our cars to drop the power so thus they should use 400m as a run and not 1/4 mile times as we all know that there is no way in hell a standard wrx can do 14 sec dead on 1/4's (well they tested an MY98? at santa pod, v low fuel and grippy surface and got 13.9secs) now taking into consideration that there is a 130+kg disadvantage for a wrx..... work it out


Tony

 

As mentioned, PAW figures are irrelevant for comparison. Same car will get different PAW's depending on gear used or tyre pressure, etc.

However, they should have the same flywheel power once the drivetrain losses are calculated during the freewheel bit.

Richard

 

I think US "at the wheels" figures are horsepower as measured at the wheels and then run through a transmission loss formula and therefore are roughly equal to our flywheel bhp. As far as I can tell, anyway.

US miles and British miles are identical, a 1/4 mile is actually 402.336 metres.

If that 412hp figure is at the flywheel, it's still a monstrous output!

 

I seem to remember some dynos running in 2wd. Vishnu performance at one time were fitting something in the transfer box to lock the diff and they would take out the propshaft.

As a result they were only getting about 1/2 to 2/3 the transmission loss you would on a regular dyno.

Things may be different now. But a standard wrx losing only 40hp through the transmission is not what we see in the UK. Losses work out to about 85hp at peak revs in 4th gear for a uk geared car, and is pretty much dependant on road speed rather than power for a given model of car (all imprezas say).

Impressive figures nonetheless.

Paul

 

Agree the horses are different in the states/auz

Earlier in the year, I ran a 11.7 1/4 mile at 118mph and posted on i-club asking for guesstimates of the power (I had not yet been on a r/road) the estimates all came back at around 350 @ wheels 400+ flywheel................I wish !!

I later r/roaded and had 263 wheels, 349 flywheel.

horses for countrys

 

Andy,

11.7 is VERY IMPRESSIVE mate - keep up the good work.

I-Club is hilarious - the latest thing is that AWD does not have any more transmission loss than a 2WD.

I could be dumb - but that don't compute in my little head

Trout

 

Well, if you look at the gearbox and try spinning the shaft in a shaft you would know there's more.

There are a couple of people on I club I notice that keep to the facts, Spounangle or whatever he's called, has done a lot of testing, engine swaps etc. On the other hand some guy pulled a 13.7 on a stock WRX just by putting the vacuum tube to the actuator!!!!

Paul

 

In Australia, most stock MY00s get 89kw at the wheels, give or take 1 or 2 kw, which is 119hp ATW. They mark even harder than the UK ones.

Cheers,

Wrexy.

 

Not taking sides here or anything, but in the USA, when we say "at the wheel" it means just that. No formulas or calculations. A USA-spec WRX is rated at 227HP at the crank (engine dyno) and gets a wheel dyno number of ~170HP.

I think Dynojets and Dynapaks both get this number, and Dynapaks are made in New Zealand.

 

cico - I have had great results thus far with the STI RA 6psd box - no problems yet

 

What is the Octane rating of US fuel? I thought it was about 90 RON.

If they say Jap Imports here lose a fair chunk of bhp due to not running on 100 RON, how the hell do they get them to run on US fuel, and stiil get 227bhp, which is 12bhp more than they are booked at here?

I'm confused!

Rich

 

US fuel is specced as RON+MON/2

MON (motor octane number) related to higher load situations, soo is lower. Typically 89 for SUL.

So 93octane is more like 98-100 RON uk fuel.

Paul

 

It's got to be the dynos they're using. As Sam mentioned above they are using dynapack

There was an article in Autospeed some time back where they tested this but I can't recall the outcome...

 

Here's the article.

They do have a picture of an Impreza on the dyno but I don't think they actually quote the figures....shame

 

Most of the Aussie workshops use Dyno Dynamics, RRs, which don't give a flywheel hp reading at all.

Cheers,

Wrexy

 

Oh, it's in the link too. Posted same time as Mo. I clicked on the link and there it was, Dyno Dynamics.

Cheers,

Wrexy.