scoooby slayer

iTrader: (4)

from a rr printout i have and a few others ive seen it seems to be about 17 % transmission losses rwd. im thinking that would be right to work it as a percentage as the harder you turn something the harder it is to turn it so will incure more losses of power to turn it. what do we think does that seem right ?

scoooby slayer

iTrader: (4)

noone gonna say im wrong then !

Rab

If this is about Euans car, I would bother trying to work it out. AVA don't even calculate it IIRC. For comparison, I saw Rainbird's old Saff there and it made 395@wheels.....

Euans is what, 505@wheels?? Rainbirds Saff was fucking fast too

SteveH

I remember one of Stus essays in Fast Ford, and he said the only way to measure loss is to engine dyno, then chassis dyno a car. I dont think there is a hard & fast rule to go by AFAIK.

Steve

scoooby slayer

iTrader: (4)

just a general thing im thinking about. generally seems around 17 % losses nomatter what bhp they are so must be a percentage rather than a fixed ammount.

scoooby slayer

iTrader: (4)

seen a mustang with 1000 bhp and 850 whp thats 17 % too !

155lee

iTrader: (10)

stu at msd mentioned this a few fast ford issues ago,cant remember how its calculated but he said some tuners blame transmission losses for low power readings when its not the case.

Rab

I agree that it's a percentage, not a fixed figure like 40bhp or whatever.

But that figure on your car might not be 17%, might be 23% or 15% if you follow. The only way to REALLY know it to get the engine out and put it on an engine dyno. Then run it on a rolling road. Some operators use the run down to calculate the losses, but have been known to cheat by clicking on the handbrake a few clicks to make the losses seem higher hence a higher flywheel power figure. Thats why AVA only deal in power at the wheels. Because thats what they measured.

rapidcossie

It all depends on who you speak to and who you listen too.

Losses are NOT are percentage but are fixed and depend on a vast number of factors.

Alot of people will argue with this by I can only go by what I beleive.

A simple way to prove that its not a percentage is....

Take that mustang for example the owner says it losses 250 bhp thru the transmission.

Convert this bhp into Kilowatts

1 hp is 0.7457 kw

so 250 hp is 186 Kw.

a good modern central heating boiler on full burn will rn a 30kw.

So imagine 6 and a bit central heating boilers on full chat heating up the transmission on that mustang.

The gear oil would cook instantly and the casing would glow cherry red in seconds and before long the whole thing would seize solid.

Se what I mean?

Rab

What...

KW = A unit of measurment for Power. You can't measure power.

RWD Pete

I remember stu's science on this subject he converted claimed losses into kw and the heat would melt components!!!

rapidcossie

Rab most modern car manufacturers give the engine outputs in Kw nowadays

Rab

Aye, but it's impossible to measure power.... You can infrer it from what you can measure....

I mean a standard cossie makes 204bhp. Now surely it puts less stress on transmission components than a 500bhp cossie using the same transmisson....

Rab

Even still mate, it's impossible to measure power, you can calculate it. Doesn't matter if it's KW or HP

rapidcossie

I cant find a conversion for braked horsepower to kilwatts

Rab

one HP = 0.746 kW, braked horse power is just HOW the unit of horse power was calculated. Brake Horse Power just means a brake was used to provide the load.

In diesel engines we have SHP (shaft horse power) IHP (indicated horse power) and plain old HP.

The rollers measure the Torque.

HP = Torque x RPM
------------
5252


Now, whatever unit you use for engine power, it's all calculated from torque. All comes from James Watt of Greenock working out how much weight a Horse could pull in 1 minute. He decided 1 HP was equal to 33,000 foot pounds of torque per minute.

So if an engine made 1 foot pound of torque it'd need to run at 5252 rpm to make 1 HP. Which is where that formula comes from.

This of course, has fuck all to do with transmission losses

SteveH

edited

Rab

LMAO at your reason for editing

scoooby slayer

iTrader: (4)

i just found an article about a guy who tested this on a motorbike and he saw 12 % losses then doubled power with nitrous and saw a 6 % loss so it would seem that whatever losses are standard they will stay the same no matter how much engine is tuned !

Rab

Ok, imagine your car makes 500bhp. But only 350 ATW cos of 150bhp losses..

Then your wastegate penny drops off, and you can't make boost. Your car now only makes 155bhp. Does this mean you only have 5bhp ATW?

Of course it doesn't....

C4llyT

For RWD add 10 and divide by 0.88.
17% is accepted figure, but goes off as power gets higher.

col cos1

iTrader: (5)

a bit off subject but i had my car on a supposed to be state of the art rolling road 100k dastek job at extreme in witburn

the sheet said 456bhp at engine,and 357bhp i think at wheels

i asked him how its calculated,he replies its not the rolling road /machine etc is taking a reading from the engine

whats that about?

and the fact it was only running 25 psi

and usually is 30 psi i thought the at wheels fig was accurate as it was 373 at wheels on ava a couple of months previous

Rab

I'd ignore the flywheel power tbh, as thats calculated from the power at the wheels and the drag. And as without that 5psi you made 16bhp less BHP at the wheels, which is a good result and shows your engine in good health. The flywheel figures are for pissing contests down the pub IMHO.

col cos1

iTrader: (5)

i thought that at the time rab,its making 417bhp@wheels at ava now so probably 550bhp at crank at extreme

Stu @ M Developments

iTrader: (12)

A few thousand words by me on it f you can stay awake lon enough...

The tru about dyno's:
http://www.motorsport-developments.co.uk/stus.html

Rab

That must shift a bit Col The only downside for you is your at that 'tipping' point where just a few more mods for stupid power, but they're all fooking expensive

Next time I'm at a meet I'll be badgering you for a passenger run!


Stu, will go have a read. Was it the same one as in fast ford?

SillyFezzaMk1

iTrader: (1)

reading the dyno article and it says about TUV aproval


Dan

Stu @ M Developments

iTrader: (12)

Ever day i awaited someone to spot that and make a topic, but nobody did!

SillyFezzaMk1

iTrader: (1)

That would have been a killer reply to the original thread!!!!!!!!!!!!!!!!!!!!
On a more serious note, what would you think fly bhp would be on a 2wd escos with 400bhp atw.

Just mulling over the idea of getting my engine dynod before it goes in the car....then same again after to see the exact transmission losses....

My aim is 400atw so would like to know a realistic fly target

Cheers
Dan

col cos1

iTrader: (5)

get yourself to crail on sun mate

Rab

Unfortunately I'm in Kent at the moment learning about the legislation on Refidgerant gases, which I'm sure you'll agree is thrilling

Stuck here till the 3rd of october

scoooby slayer

iTrader: (4)

i see what ur saying mate but the article i found makes out trans losses wouldnt reach 150 hp in the first place. still dont add up though i mean about 40 bhp trans losses on a standard 2wd cos well an old chevette only had 45 or something bhp and they cant be 5 hp atf !

scoooby slayer

iTrader: (4)

thanks mate just downloading adobe so i can read it. is there a rough guide you know as an average to work wheel to fly?

Charlie Chalk

iTrader: (1)

Cool, will have a read in a bit..

Rab

The thing is it's totally different for every car. And different for the load you input into the transmission components. The more load you put the bearings under, the more heat they generate hence more loss.

I work on ships, I'm an engineering officer. On our shafting and gearboxes we have a net loss, it's called 'slip'. It's a combination if heat losses through the gearboxes, shafting, stern tube and propellor cavitation. Now, this loss varies depending on how much load we are using at the time. Hence why we have a most economical engine load. Our plant for instance has the least 'slip' at 72% rated load. Which equates to 14 knots service speed. If we run below that at say 50% load, our slip increases (this is not due to shafting, or gearboxes but the propellor design). If we go to say 90% our slip increases dramatically and we have to increase cooling to the gearboxes and shafting. Our speed has only increase by 20rpm on the shafts, or 80rpm in the engine, but the extra load has dramatically reduced our efficiency.

Now take your Cossie or Mustang. At 4,000 rpm in your cossie, you're making peak torque as you're now on full boost. There is more load, but less speed on your transmission than at say 6,500rpm where you're making full power. But some people will continue to claim it's a set loss of 40bhp or whatever. Is it losing the same 40bhp at 4,000rpm as it is at 6,500?? There just isn't any way to accurately measure transmission losses in a car measuring them using a rolling road, so in my opinion people should stop guessing......

I can measure the slip in my ships plant, but thats using some compicated equations and alot of design information provided by the shipyard who built it, the type of fuel being bured, and exact measurment of the fuel used per 24 hour period etc etc The list of variables is huge.

To do the same in a car would be so time consuming you could easily take the engine out and dyno it in 1/10th of the time you'd need to measure everything.

People who measure power at the wheels, hubs etc are the only ones not guessing in my humble engineering opinion...

And stand by to be flamed

scoooby slayer

iTrader: (4)

i agree it cant be a fixed figure imo must loose more the harder its worked. i guess my 17 % guesstimate will have to do ! seems close from various rwd ive seen so far.

Rab

Mate, you don't need a guesstimate. Your new purchase makes 505bhp @ wheels. My mate had a very very fast Supra that did 10's and had 575hp @ wheels.... It was an Auto so more losses, but still, thats the territory it's in. Anything over 400 @ wheels is just stupid and death inducing if you ask me

scoooby slayer

iTrader: (4)

if i get a motorsport diff id hope shed be in the 11s. just found interesting read about new nissan gtr, nissan themselves say a 10 % loss due to the superior design of drivetrain components. nissan themselves even talking in percentages !

Rab

Well, Nissan can measure their losses because they have the specs of the components, oil and have done masses of datalogging and testing. Joe Bloggs and his Sun rolling road can't do that

Just enjoy the car, it'll be fast enough to make you not think about all this ruddy maths

Chip

iTrader: (3)

Removing your engine from the car and placing it on a dyno cell, where it has a different exhaust, and different airflow characteristics etc to on a rolling road, will make a difference to the power output so that doesnt work either by the way im afraid mate