in fact I have some more runs from Powerstation

March 04 - wheel power = 207, drag loss = 59bhp
November 04 - wheel power = 217, drag loss = 77bhp
November 05 - wheel power = 191, drag loss = 125bhp


However, I seem to recall that in November 05, I ran with tyres at about 32psi

go figure.....

The answer is due to peak power being at different rpms like I explained to Tricky. In October peak bhp was at 6400rpm and last weekend it was 6800rpm, so 400rpm difference. As rpms increase so do the transmission losses. As Rich said, if you wanted a higher wheel power he could run it in third gear (assuming it wouldn't slip) as lower gears produce less transmission losses.

Nigel,

Did they come out with a figure of 191+125 (316BHP) at the fly for that then?

If so by my calculations thats a 65% transmission loss, there is no way on this earth it could have been that bad! Even with the tyres at 5 psi I shouldn't expect those kind of losses.

I'm in the camp of Wheel BHP is the only one that matters, anything else is a mere estimate / calculation. The article Trappy posted also makes some good reading

Ben

P.s I'm at a Dyno on Saturday which will be bolted directly to my hubs, be interesting to see what transmission losses I have (As tyres are a big factor) I've already spoken to the guy, even he said it's best to go on Wheel (Or in my case hub power)

IRC Nigel made 305bhp with it run in 5th gear, so the transmission losses would be higher.

Anyway, for all those that are advocates of wheel horsepower, the Dastek dyno is by far the one to go for

ok this is not my words but none the less they are from a mapper and dyno operator using a Dastek after researching this is the one he chose for his own reasons

"Just read the rest of this thread, should have done that before posting the above LOL. My Dastek does produce very similar, if not, the same figures on different ramp rates. Even conducting an inertia run will give similar, if a little higher, figures to a loaded run. For what its worth, I recently ran a modified Audi S2 (4WD) in 3rd gear which is the recommended gear to use for 4WD's, and it made 290bhp, Ran the car up again in 4th, but used the next slowest ramp rate and it produced 291bhp. The boost profile was slightly different as more boost was seen at the same RPM than the 3rd gear run, but apart from that, the graphs looked the same. I have to say, I was pretty gob smacked when I saw the results."

He was gob smacked at how well the Dastek dyno managed to come out with almost identicle results despite what gear was used, Flea maybe you can explain to why the MAHA dyno despite being nearly twice as expensive as the Dastek cannot do that?

and its worth reading this as well, again its Dave from Puma race engine

"It's engine power that is affected by atmospheric conditions and this is the figure that must be corrected to DIN standards. If you make the assumption, which is of course false to start with, that adding 'coastdown' losses to actual wheel bhp gives you actual flywheel bhp then it can only be this final figure that merits correction. As coastdown losses bear no scientific relationship to true transmission losses occuring when the engine is powering the transmission the entire premise is flawed to start with but it's the closest a rolling road can come to 'guesstimating' flywheel bhp from wheel bhp. It's discussed in detail on my site.

I high lighted this in red as its basically what i have been trying to explain my self, hence why i say WBHP is more relevant

Ramp rate does indeed play a part in affecting wheel bhp as you say. Only steady state power figures with the engine held at a fixed rpm can be considered as true bhp measurements. Anything else is affected by inertia. However if the ramp rate is chosen wisely and the car is in a high gear the effects should be minimal and should be allowed for inside the dyno software to some extent. It also depends on whether the operator has input a reasonable figure for the vehicle's inertia. It may well be that it's these factors not being used properly that lead to a normally accurate system like the Dastek not working at all in the case I described previously.

Back in the day when all we had were ancient Clayton waterbrake rollers and Heenan and Froude waterbrake engine dynos none of this nonsense played any part. All you could take were steady state wheel figures and no one had thought of coastdown losses as a fudge back to flywheel power. Every roller or dyno read the same, assuming it has actually been calibrated, and everyone knew where they stood. Nowadays it's little more than a lottery how many bhp you get told your engine has. As big numbers help sell tuning products there is pressure to apply large coastdown losses and big correction factors to what might have otherwise been realistic wheel bhp numbers. The average punter is unfortunately too uninformed or too disinterested to question anything they get told. Bragging rights down at the pub are more important to them than science."


I want to make clear that i have nothing against Flea/powerstation/Perfect touch or for that matter a Maha dyno or a Dastek dyno

As i said right at the beginning i just think its best to work from WBHP, its much less likely to be calculated wrong or be massaged in anyway, not to mention that if these dyno's are calibrated then the WBHP should not be to different from any other dyno that has been calibrated.

Nigel, with regard to your runs at powerstation

Unless the car has been modified in between sessions on the RR then something is really wrong

First of all we need to understand that BHP is a calculation between torque and RPM, your torque will tail off towards higher RPM for various reason, peak BHP is met at the point when your torque is dropping off at such a rate that despite the RPM increasing its actually producing less BHP

while your car would produce peak BHP at different RPM's from run to run i have never seen a difference as much as 400RPM

In fact my brothers old RS turbo had been on many rolling roads and despite getting slightly different WBHP figures (within 5%) the peak BHP always peaked with-in 200 RPM of any of the other runs on all the dyno's, i think i have 5 different print outs for that car


Let me make clear though that i do not run cars on dyno's on a daily basis, so it could be normal, you will need to talk to an experienced non biased dyno operator to confirm that

As for you losing 20 BHP from your october run and then your january run, it looks as though for some reason your engine was not holding the torque for as long on the lower power run and in turn your BHP peaked earlier, as it peaked at a lower RPM then it cannot produce the same BHP

So in short there must of been something effecting your cars performance that day or for some reason the dyno read it differently.

Thats how it looks to me at least

Trickymex - the 400rpm difference would easily be accounted for with the three boost leaks - two in the intercooler piping and one if the intake rubbers badly split

so - not really modification as such, but almost certainly the reason for the 30+ bhp gain and the increase in peak power revs

as for my question - it wasn't where my 30bhp came from - that's already sorted - its why the transmission losses were 20bhp higher on the later run

Tricky, you make me smile If you had read my previous posts you would know you have quoted Paul who I know very well, indeed it is his Dastek dyno that I use!

Two points:

1. He is referring to flywheel power, there was a 1bhp difference measured at the fly! That is how accurate they can be. A run with air con on or off can be measured at the fly.

2. Paul is an advocate of flywheel power measurements.

I have said all this before in this very thread, for some reason it's not being read?

Regarding Nigel's different runs, yes there are big changes in tuning levels over the years. However, first you need to understand the difference between transmission losses, gearing and rpms then it will be possible to read the results correctly.

As an example, last weekend I made 400bhp @ 6000rpm or 324whp @ 6000rpm. That constitutes a 16.75% transmission loss, acceptable to you? Lets have a look at some more rpm points:

5000rpm - 315bhp or 258whp (17.7%)
6000rpm - 400bhp or 324whp (16.75%)
6500rpm - 428bhp or 345whp (19.39%)
7000rpm - 449bhp or 355whp (20.9%)

So if the dyno had been stopped at 6000rpm I doubt we would be having this conversation? Only I made peak power at 7535rpm so the transmission losses continue to grow.

I reiterate my advice to people, of course everyone makes their own opinions, although if you read what I have said the actual data points to one conclusion. If the flywheel figures look right then they probably are, if they correlate better between dynos then that's the figure to use, if the dyno manufacturer says use flywheel for best practice then that's what we should do, if the dyno operator says use flywheel then that's what we should do. Afterall, who could know more about their own equipment?

Tricky, if you are interested then drop MAHA a line and see if they can give you some more technical information about how their dyno operates. The link I sent you does have the manual for download (in German) which lists a multitude of formulae that they use.

Here are the results i got from my dyno run at Track and Road.




Looking up to Flea's results, the losses seem about the same as mine at the same rpms and I can certainly see 24% losses at over 7,300rpms.

TurboJ, what do you make of Greenald at T'n'R? It's obvious you know him but you've never made a comment on the guy or his dyno...

Flea your missing my point, i am reading what your saying and i agree that trans losses do increase with rotational speed but your focusing to much on these figures and calculations

Your seem to be ignoring that all these dynos make there calculations from the WBHP, thats fact so any flywheel bhp figures are estimated and subject to calculations that can be argued

read this again

"It's engine power that is affected by atmospheric conditions and this is the figure that must be corrected to DIN standards. If you make the assumption, which is of course false to start with, that adding 'coastdown' losses to actual wheel bhp gives you actual flywheel bhp then it can only be this final figure that merits correction. As coastdown losses bear no scientific relationship to true transmission losses occuring when the engine is powering the transmission the entire premise is flawed to start with but it's the closest a rolling road can come to 'guesstimating' flywheel bhp from wheel bhp

The reason i say to stick to WBHP is simply because then we can all ignore these estimations

I will maintain that if you want accurate flywheel bhp figures then you need to put it on an engine dyno and as a rolling road can only measure WBHP accuratly then that is the only figure worth mentioning

The only problem i can see with the people that have used powerstations dyno and quoting WBHP is there dyno seems to read low on WBHP and high on trans losses, this is not just my opinion but of quite a few people in the know

Because you have used powerstations dyno most people with knowledge of them will take your figures with a pinch of salt, thats a shame

As flea has said people will make there own decisions on what way they look at this but its agreed amongst the experienced that WBHP is the only way you should be comparing and even then unfortunatly there will be discrepencies, but at least this way we are not relying on flawed calculations that are open to debate

Tricky I haven't missed your point, I dispute it based on professional opinion and data shown. Indeed, more than missing the point you have ignored much of what has been said so forgive if I am a little more direct and ask that you answer these questions specifically:

1. What do you say to these figures from Powerstation?

5000rpm - 315bhp or 258whp (17.7%)
6000rpm - 400bhp or 324whp (16.75%)
6500rpm - 428bhp or 345whp (19.39%)
7000rpm - 449bhp or 355whp (20.9%)

As Trappy has shown they are really quite similar?

2. You quoted Paul albeit incorrectly. Why do choose to ignore his advise and that of the Dastek manufacturer that the flywheel power is what should be considered? MAHA also state the same?

I meet Greenald years back, top bloke (I aint see him since though) but I’ll be there with my mates Ford soon. My old Boss used to use his dyno all the time. He prefers a single roller for some reason??? and likes the fact Steve & Steve prints every detail on the printout. I was more interested in the two dyno cells and what was strapped to them at the time

I wasn't so sure about the dyno either at first, how does it compare to the other well known dynos (i.e. does it read high/low on bhp @wheels/@fly?

I thought he was a top bloke too, though he was a bit 'iffy' at first.

Judging by the website, they certainly have had a few monsters in there

I too love the printout, a full detail dyno plot, and 3 pages of numbers lol. Perfect for my excel version

Well I'm back from my session this morning, results here:

http://www.fiatcoupeclub.org/forum/ubbthreads.php?ubb=showflat&Number=767376#Post767376

Remember this is a hub dyno, and as such I have no tyre losses.

Ben

looks really good Benje, 193 WBHP is good considering how standard your car is

just to confirm that daves formula that i posted above seems to work quite well here as well

that is

193 WBHP + 10 BHP = 203 BHP / 0.9 = 225.5 estimated flywheel BHP, thats 2 BHP less then there own estimated flywheel figures

so its just above standard and as you have an aftermarket exhaust fitted that expected and seems right


Anyway your car looks as though its running pretty well, congrats

Tricky, it's not wheel horsepower, it's a hub dyno.

I know Flea the difference is not worth mentioning but its still measured in place of the wheels and its the power thats applied to the wheels, if you want to discuss potential losses from hub to tarmac then start another thread if you like

The tyres provide the greatest transmission loss.

...as I found out when I ran under-pressure - that's what gave me the 125bhp transmission loss

of course, the tyre losses are exaggerated on PowerStation's dyno [and all dual-roller dynos], as there are two contact patches per wheel (although the total contact patch isn't double the normal area, as the curve of the rollers shortens the contact patch considerably)

A hub dyno simply removes the tyres from the equation - in doing so, it potentially gives a less true reading than a rolling road, as the power reading you get on a hub dyno cannot possibly be recreated on the road - however, it does eliminate wheelspin - something that PowerStation's rollers aren't particularly good for - they are getting VERY smooth - when I ran the 355 there, they had to get two guys to sit on the back of the car for the run

Not to mention the more weight you put over the driving wheels the higher the rolling resistance becomes, then on top of that you will have abnormal tyre deformation, again adding to potential inacuracy's

This all effects how accurate a roller can measure the bhp

Thankfully most modern dyno's take all this into account and give pretty comparable results

I don't quite understand what you are getting at there Nigel, by less true reading? In theory a hub dyno should be more accurate than normal rolling road as it eliminates the tyres as a loss?!? (Which add such variables as Tyre Pressures, friction, rubber compounds etc etc )

OK fair enough, I think 227BHP is slightly optimistic, I'd have taken about 10% transmission losses for a hub dyno, which would have given me 192
*1.1 = 211BHP. In the grand scheme of things though, it doesnt matter, as I now have a baseline figure (193) so anything I do I can compare with what I had today (Assuming I go back to PJ Motorsports, which I will )Anything other than the 193BHP that was actually measured today in my opinion is an estimate!

I think your right, compare mods on the same dyno

I think Nigel means that a hub dyno does not take into account the relationship a tyre has with the tarmac, the way i look at it is a hub dyno replicates a perefect situation with regard to grip.

I also dont know how they take into account the inertia of the wheels, but they manage to do it with the inertia of the roller so its probably run of the mill stuff for a dyno designer

one thing i can comfirm though is the only hub dyno i have put any of my cars on provided almost identicle hub figures as WBHP figures on any other conventional dyno i had run that specific car on.

yes - what I meant was that without wheels fitted, the power reading cannot be replicated on the road, as its usually wise to refit the wheels before driving

However, it IS a more accurate measuring method, as it removes a variable

I understand, I'd had a little too much last night when I read it!