Saff_cossie,

Thanks mate, and just fyi I'm not a bitch and I don't *think* pugo is either

It makes for an interesting read and we can all learn from it!

Cheers

Steven RW

 

Pugo,

The following is all based on my limited experience and about 20 chats with Alan over a period of 5 years. It would be better if he had the time to answer your question directly as there is no doubt I’m preaching about something I have little knowledge of and whatever knowledge that is, is gifted rather than earned! (dangerous!)

Example:

BMW M3 Evolution. Runs up in fourth gear and makes 268 at the wheels as I saw moments after my own Evo 6 ran up. If this car was to run up in 3rd gear the r/r would see around 275 at the wheels. Less RPM of the rollers meaning less transmitted loss. 2nd gear would see maybe 285 at the wheels again due to less rpm of the rollers and therefore less “transmitted loss which does not infer that the loss is in the transmission” The car still makes std flywheel bhp every time you run it up as we all know the engine itself is unaffected by which gear its in.

Alan has given his estimation on the “transmitted losses” based on the gear selected and roller speeds as in this quote “The 40 BHP mentioned is an approximate loss is based on the power consumption of two sets of 20” rollers at the speed of testing approx. 80mph” In the Evo’s they were talking about that would be 3rd gear.

If you go back to the m3 example: “The % alluded to is in there as well but is probably very small (1 to 3%) as a guess” which in my understanding is say that the “transmitted loss” would go up by between 1 to 3% by changing up into the next higher gear. In the m3 example my understanding is Alan would state around 53 bhp loss in 4th gear which is a 16.5% loss if the car is perfect and making its 321 flywheel bhp and in 3rd gear the transmitted loss is 46 bhp and thus 14.3% transmitted loss. This is the 1 to 3% loss from experience by changing up a gear.

So I think from what you are stating that indeed he would take into account the change in leverage as from experience a car running a higher gear produces less torque at the wheels and therefore a larger estimate would need to be added to the wheels figure to give the flywheel figure.

Re: the losses being 24% What he is saying is that the run down method is little use because it would show a constant loss regardless of which gear you are in and is not a relevant calculation as the gearbox drag is not the entirety of the “transmitted loss” and most of that is in the rollers themselves.

As for banging your box from 4th to 1st, surely this is because the force of compression maybe 5lb ft of braking per rpm and in 4th and 60 mph that would be less lb. ft per second braking than when you slap it into 1st and the engine is forced up to 10,000 rpm and would be producing 4 times the amount of braking due to many many more compression cycles per second along with other engine drag (crank through oil pan etc ) thus creating a major slowing effect on the car. I don’t see how that’s relevant?

Unfortunately I am at work at the moment and like I said I’m not mathematical theorist or scientist and the royal bank don’t pay me to try and work my head around all this so i need to get on!

Cheers

Steven RW

 

Whatever the correct answer is, this makes for some properly interesting reading fellas

 

you have misunderstood me..........you need to do this with the clutch disengaged i.e pedel down

right, your starting to see where i am coming from with your quote

so to get a true figure from a fourth gear run you would run the car in fourth gear and then using a simple formula arrive at your flywheel figure
now if you run your car in third gear you would obviously arrive at the same flywheel figure( we are both in agreement there), however to get a true at wheel figure we need to calculate back using another simple formula with the known transmitted (frictional transmission ) loses(and compensating for gear ratio differences)to give us a real at wheel figure as that has to be at 1:1 ratio through the gearbox !


so therefore the true at wheel figure should never change(if your calculations are right)

Pugo

 

Pugo,

I agree that to get the TRUE at the wheel figure you would need to take out some of the transmitted losses as losses in the rolling road should not effect the true at the wheels figure. The at the wheels figure quoted is the torque registered by the retarder, which is effected by rolling road losses and SOME transmission losses which from my understand are much lower than most people think. However I think we are stepping away from the use for a rolling road. It is not get an exact bhp figure, be that at the wheels because that is corrupted by rolling road losses that would require a calculation (or guesstimate) to correct or a flywheel figure which requires another calculation (or guestimate) to correct.

The best rolling road would be there to provide a consistent reproducible figure to allow measurement of modifications (or comparison of similar cars on the same day) rather than the worlds most accurate figure that we all get hung up on. It would require a good experienced operator who could utilise their experience to estimate the differences in transmitted losses when roller speeds are increased if a higher gear is required to be used (as is often the case if a car has had a substantial power hike due to grip issues and going beyond the recordable figure of the retarders) to ensure a consistent and reproducible figure to compare modifications with and to produce the most extreme conditions that could be experienced on the road “170 mph, 4 heavy mates, up a hill, into the wind” ie max throttle for a sustained period of time with no engine rev increase. ( I had my rst tested at max revs for several minutes whilst we tested the charge cooler system to see what point inlet temp the car would det at to ensure it was ready for Brunters )

At the end of the day experienced operator with a good rolling road can estimate the bhp of the car relatively accurately and that’s all we are asking for. (checking the sense in their rollers and estimation by using a powerful standard vehicle like an m5 or m3 which tend to make their factory power)

So to conclude. Alan measured 287 at the wheels on Euan’s car, and from 24 years experience decided that the transmitted losses on his rolling road at the roller speed and engine speed tested were circa 40bhp (if I recall Euan’s email as I type this off line).

That was the original argument and I think we finally got there

Best Regards,

Steven RW

 

i have posted up my rolling road figures in another thread, they were taken on supposedly the most up to date rollers in the country. As for transmission losses they were measured at around 10 % maybe a little less.

 

Bud,

Define: "most up to date rollers in the country"

If you follow our discussion above, it is not transmission losses but transmitted losses due to how a rolling road works.

Cheers

Steven RW

 

apologies, i probably didn't read as closely as i should have

as for the rollers this was taken from the site;

New Dynojet Rolling Road Chassis Dyno!

Our new Dynojet Rolling Road Chassis Dyno is the most up to date chassis dyno in the UK and is capable of measuring 1000 bhp at the wheels at speeds up to 180 mph, so there won't be many road cars that will trouble it!

For the most advanced dyno testing available, look no further!


Features

* 1000 bhp Eddy Current Absorbtion Unit and Torque Cell
* Static load tests, step tests, sweep tests and wind drag simulation
* Measurement of Air Fuel Ratio using Wide Band Lambda sensor
* Measurement of multiple sensor readings simultenously, such as boost, EGT, IAT
* Plots Power, Torque, AFR and other sensor readings all on one chart
* Automatic Ambient Conditions module can correct to industry standard calculations
* Prints dyno charts and also saves them as JPG images, so charts can be emailed direct
* Full digital electronic control system


there is more info on the site but i doubt any1 will read it if i posted it so i kept it short

 

Bud,

Sounds like a good rolling road setup. Did it have some decent airflow around the front of the car?

Cheers

Steven RW

 

yes mate it had a huge industrial looking blower, not a big 'fan' you normally see but a proper large motor driven unit, needed two people to move it into postion .

also it was a 'single cell' roller which i'd not seen before

 

bud-weis

That on mmy old greens mate ?

 

yes matey it is

they are working wonders thanks

 

and that is the bit that concerns me

the frictional transmitted loss through a t5 and a viscous lsd differential @circa 6k are higher than 40bhp they are about 28% from all the graphs i have seen at 287-290bhp atw i would have expected 360+bhp and that ain't gonna happen on greens and a std 2wd fuel pump will be starting to to max out around 370bhp!

if memory serves my original argument with yourself was the fact that a TRUE atw or flywheel bhp figure cannot alter from roller to roller dependant on there size and i think i have explained clearly enough as to why

Pugo

 

Lol,

The fact your still looking at transmitted losses as transmission losses or comparing a 12 inch roller rolling road with the transmitted losses on a 20 inch rolling road without understanding there will be a difference shows we have not managed to get anywhere

Unless some of the other rolling roads u are talking about have 20 inch rollers?



Steven RW

 

you have to include transmission loses awithin the whole of the transmitted loses as they exist and we would not be able to accuratly estimate a flywheel figure or are you saying that they don't need to be included, i am wondering if thats why your rr operator is falling short in his flywheel estimates????
and you will agree that we have included the fact that the known mass (or rollers) we are accelerating can be different hence we account for it in the calculations to give us a true reading

 

The flywheel HP figure is the sum of the HP "@ the wheels" and the drag measured during coastdown. The Coastdown drag curve is exponential therefore the drag is NOT a fixed percentage. The wheels figure is meaningless without some form of drag measurement. All these factors affect the power @ the wheels. Tyre type/size/pressure/temperature, gear/diff ratio, gear oil viscosity and gear selected. The gear ratios and gear selected have the most dramatic affect because, simply put, the greater the speed the more the drag hence the lower the wheels HP figure.

The greater the speed the higher the drag figure and the lower the "@ the wheels" figure.

It should be noted that the drag figure measured on a rolling road is far greater than you would experience on the road as on the dyno the car sits on 8 small circumference rollers which deform the tyre. The drag measured is true, though you would have a lower drag and a higher "at the wheels" figure on the public highway.

I hope the explains some of the variations seen between different cars.

 

Fagin

here is a hypothetical question for you.....my rwd car makes a genuine 100bhp at the wheels and 125bhp at the flywheel @ 6k rpm(lets just say those figures are accurate)

now i visit 25 different rolling roads with my vehicle that are the top rolling roads in the country (just for stephen, AVA will be one of them )

would you expect more than a 2% difference of atw power for each rolling road if none of the parameters of the car/weather had changed and the car was always run in the same gear??

now what about accounting for different roller size?

 

fuck me are you lot still arguing over this shit?

 

no , we are discussing it

 

Ryan,

I second Pugo's comment. Discussion is not " arguing over this shit "

Steven RW

 

Pugo,

I suppose its more simple than that. Get the car on the rollers load it up, as they are not using the inertia based calculation, whatever resistance the retarder has to give to hold the car is the torque, calculate the bhp from this at the wheels. Then run it up again in another gear. See the difference in the figures, this difference must be attributed to a higher/lower gear and a higher/lower roller speed. Make a flyhweel estimate from there. You are measuring the entire transmitted loss from engine to final retarder figure from my understanding. This gets higher as the rpm of the rollers and gets higher.

I do worry that I am not in posession of the full facts as I don’t know 1% of what Alan does when it comes to rolling roads. Its like playing patients with half a deck of cards. Sooner or later its going to come to a point you cant go on.

You say that Alan maybe falling short on his flywheel estimates. Why then if you bring a higher powered N/A BMW onto the rollers does it put out a wheel horsepower, Alan adds an estimate of an uplift to make the flyhweel bhp and its very close to the stated figure by BMW?

AVA for YEARS never even gave an estimate of flywheel bhp as its purely useful for pub talk. Aslong as the car has a bigger area under the graph that before the modifications and the test environment has stayed the same then the rollers have done their job. Exact BHP is never important IMO.

Plus there is nothing better than stating 165 at the wheels and about 185 flywheel and beating someone who claims 300 at the fly as done on behalf of my old car.

Cheers

Steven RW

 

Pugo,

Power at the Wheels is dependant on ALL the factors that I have stated above (and as correctly stated, including roller size).

ALL things being equal, then you would have to assume that there should be very little variance in RR to RR in an ideal world (again if ALL variances/conditions were equal)..... but we are talking a fair number of variances here though.

I mention variances over and over again, as there are so many contributory factors to this.

 

http://www.pumaracing.co.uk/power3.htm

http://www.pumaracing.co.uk/trans.htm

http://www.pumaracing.co.uk/coastdwn.htm

http://www.pumaracing.co.uk/setup01.htm

 

many thanks for responding
pugo

Rainman
i think if you read back, me and stephen have covered 95% of what you have just posted

but thanks anyway

stephen

one thing we both agree on 100% is that a dyno is handy as a comparisson tool i.e to see if we have made the car better

i cannot and will not discuss alan @ AVA for the simple fact is, i have never met him, had work done by him, nor know personally anybody that has and think it would be totally unjust to him and others if i go either way about him in an assumption especially considering the 50-50-90 rule(if you have a 50:50 chance of getting something right, there is a 90% chance you will get it wrong)

I have enjoyed this discussion, i think we are going to have to agree to differ on this as we are starting to go round in circles on this and before it gets to the nit picky stage we should stop
Many thanks

Pugo

 

Pugo,
I thought the bit about coastdown losses and flywheel calculations etc, seemed to confirm what RW was trying to say?

 

So with MY rolling road figures, which i believe from what the operator told me about the rollers, and from what i have read on there site ( link a few posts up )

the @the wheels power was 331bhp

now i have in the past heard people make assumptions about losses and if a car makes XXX @the wheels then it makes XXX @ the flywheel

IF i were to go with the general consensus, then my estimated flywheel figure would be WAY beyond what a stg3 cossie would make

however going by what the SINGLE CELL roller ( dunno what difference it makes, but theoretically means losses will be less as the wheels have less friction on 1 roller than on conventional rollers ) calculated as my flywheel figures then i beleive it to be spot on

360bhp

this figure seems high i guess but i don't doubt it one bit

i guess my point is i believe this particular roller to be fairly accurate

and if any1 wants me to organise a Pf roller day i'd be more than glad to

 

Pugo,

Couldn't agree more. Its been a class discussion on a subject that really gets the brain thinking. Its always a pleasure to chat with Alan due to his theoretical knowledge of building a rolling road and with his partner George programming and building the computers that run the rolling road ontop of both of their 24 years of experience using them and always challenging the accepted rules/thoughts out there.

It would have been a bonus if he could have joined in the discussion due to me having only some very basic (and probably incorrect/incomplete) gifted knowledge on the subject we are limited on going any further.

Many thanks

Steven RW

PS if you are ever in Scotland and want to chat about rolling roads and the rest, maybe we could pop over to AVA during their lunchtime with some pies n beans and have a chat with Alan, should he so agree.

 

Steven,
i may just take you up on that offer, as when my 3door is back on its toes(post restoration) i am going to take my son and tour every RSOC meet in the country, i am sure there is one near yourself and look forward to meeting up for a brew and a pie, doing it at AVA and getting to brainstorm for a few hours would just be a bonus

once again many thanks

Pugo

 

Pugo,

Sounds like a good trip! If you PM me closer to the time I'll be sure to reply and try and arrange a meet.

All the best

Steven

 

good discussion fellas

 

one of the best threads on here!

what makes it so could is that the usual suspects didnt come on and turn it into an arguement!

 

Indeed a very interesting read, but biggest note is the fact it didn't become a slagging match, something this board lives on unfortunately. Well done RW and Pugo

 

Up

 

Cheers James.

Respecting each others inteligence and treating people as you would in the real world *should* be par for the course. Strange how it isn't!

PS I had my eye on an M3 for a while. Very tidy cars. They didn't feel raw enough for me, that was my only complaint. Perhaps, too effective. If I replaced the exhaust with a 2 foot gutter pipe it might have given me the thril l I was after lol!

Do you miss the wheelsping and banging your RST used to make ( if it was like mine ) I DO!

RW