Chip

iTrader: (3)

Christian mentioned in another thread that he felt that a large discrepency in BHP could be at least partially accounted for by running the car in a different gear between two runs?

Now to my mind, that is a nonsense if the rollers are any good, they know the gearing, and should calculate accordingly, changing the gearing of the car shouldnt make any difference to the results.

Thoughts?

Any dyno dynamics operators on here who can either correct Christian or educate me as to why this would be the case?


CheeRS

Christian and Beccy

iTrader: (14)

Chip,

I never said that I accounted a large amount of BHP loss to the fact that the car was run in two different gears, but when you bring other factors about different ways they are run into the mix too, it is possible. We never encourage comparing of 2 runs from different places, unless you can be ABSOLUTELY 100% sure they used the same procedures.

Thats all I have to say on the matter, I've had enough Dyno arguments to last me a lifetime. LOL.

GARETH T

if that was the case, you couldnt compare any figures from any car that had different gear/diff ratios

Chip

iTrader: (3)

Agreed.

dojj

iTrader: (3)

there was a diagram in fast ford the other month that explained where all the various things to look for on a power graph were located and what they all meant

so to compare the 2 you would need to make sure that everything else was the same, just run one car up in 3rd, check the resluts and then do the same car again in 4th and see how different it was to give you some sort of benchmark for comparison

when you have enough benchmarks for various cars and various gears all done within the same settings on the rollers i think you would be able to see where any descrepancies lie

but other than that, runs in the morning and afternoon on the same day can differ so perhaps the rollers as a setting up tool would be what is needed and an engine dyno with the right air temps would be the place to start worrying about absolutle horsepower figures

as for the different gears you asked about, surely it's going to be about transmission losses across the board in different gears?

Chip

iTrader: (3)

I dont want an argument, I just want to know if these rollers are accurate in different gears or not?

I accept there may be some tiny amount of variation if the transmission losses are slightly different in the two gears, but other than that, does gearing have any significant effect?

The way your comment was worded in the other thread, made it appear that running in a different gear could make a significant (ie not just 1 or 2 bhp from different tranny losses) difference.

AlexF

Nah they are just rubbish rollers...

Chip

iTrader: (3)

I dont own a set of dyno dynamics rollers to do back to back comparisons in different gears, hence why I am asking for this thread, Im perfectly capable of working it out if I had access to a set of rollers, so not looking for suggestions on how it could be worked out, anyone with half a brain can see that, I just want to know the actual results from someone who has tried it.

Chip

iTrader: (3)

I assume that is just some pointless trolling post, and you have nothing useful to really add?

If so, please go to the muppet room, where its more appropriate.

Pete frst

im thinking RR's are good for setting up a car,but as for bhp figures,i'll take that with a pinch of salt..........
unless some one can tell me better............

ECU Monitor Enthusiast

iTrader: (1)

Surely the whole point of any figures produced by any rolling road is to give a standardised result irrespective of the rolling road and car type.

Of course any figures given must be produced using recomended practices and procedures.

Having said all that, I dont think I have ever come across any 2 RR's that have ever read the same. LOL

AlexF

You asked if they are accurate - IME I answered

Based on the fact my Cooper S GP was unlikly to make 25% less power than std with 15k miles on the clock but did - So either the rollers, setup, opperator or MINI are flaky.

Alex

GARETH T

any tool is only as good as the person using it!

dojj

iTrader: (3)

it seems fairly obvious that no one has, so there is a story in the making for a fetures writer to come along and steal if you haven't already done so

i was there and i can say that his car did indeed make a fairly heft loss in power according to what it was SUPPOSED to be making, but, to be fair, not 25%, i think it was more like 25 bhp less or soemthing, but that may have been to do with the air not being as fast as it should have been over the scoop

Chip

iTrader: (3)

Im assuming best practice in my question.

Obivously if the temperature probe is in someone's cup of tea its going to be giving the wrong results.

Im talking about when used correctly.

Rod-Tarry

When mine goes on in a few weeks time I expect to see 800bhp not 1200bhp or 450bhp. Mark has proved that the DD he uses are very accurate, for mine the head Honcho has asked to be present so I think we can eliminate operator error. Im confused that if I run 17" & not 19" wheels that the RR would change its mind on my Power, im afraid I cant see that.

dojj

iTrader: (3)

to replicate resluts you would need to have it in one of them hermodafricly sealed chambers (the ones where you can control the temp of the air coming in and out) so that all the base figures matched

then you vary the ambient temps to see how they have affected the power figures, but you would still be hampered by things such as heat soak in the engine etc affecting things even by a small degree

i can't really see that being done on a small budget unless you are talking f1 style development of main stream mass produced manufacturing

dojj

iTrader: (3)

a perfect testing opportunity then rod

AlexF

It was more than 25bhp matey... LOL

sunny

iTrader: (1)

I have (not saying which ones).....the BHP figure was less than 2BHP out between them however the only diffierence was that one was running 1 bar of boost more! LOL

GARETH T

i never assume nothing chip lol

ECU Monitor Enthusiast

iTrader: (1)

Agreed.

As long as the engine RPM is measured correctly by what ever method

Chip

iTrader: (3)

Dojj, please shutup, seriously we ALL know that its never going to be a perfect test, im just talking to within a couple of %, which is then close enough to be useful, and given that it has two temperature probes and a barometric pressure sensor, it has enough info to do that IMHO.

So I just want to know, from someone who has tried it, does running the car up in 3rd or 4th gear make any significant difference to the resultant flywheel figures quoted as IMHO it shouldnt do.

foreigneRS

being in a different gear will of course produce a different power ATW as the transmission losses will be different. if one run is 4t hgear which is straight through, and another in a gear which is not, then the difference could be greater than the difference between 2 cars with differently geared 4th gears (or whichever gear is straight through)

but the gearing is only one factor of power loss, another significant one being the tyre to roller interface which obviously changes significantly with gearing.

i suspect that it all can have a significant effect on the value of power measured ATW, that is why DD have a spec. to follow to enable 'comparison' between their equipment at various sites.

the primary function of a rolling road is to compare runs on the same equipment, not necessarily over different sites with different operators and methods of use. manufacturers correlate their data over their various sites by using the same test piece on them running a prescribed test procedure. there are still errors though, as there will be in any experimentation. those of you expecting the same reading at better than about +/- 10% clearly have no idea how the various error factors in an experiment can stack up. just because the torque cell may be accurate within 1% does not mean that the measured result will be.

Chip

iTrader: (3)

Well then you can never make any comparison EVER as there is no set of circumstances for ANY test I can think of that doesnt make an assumption, even if that assumption is merely that your method of calibrating your tools is correct.

If talking about the accuracy of a tool, its fair to assume correct operation of that tool, otherwise its the operator you are judging not the tool, and Im not interested in operator variations as I am already well aware that they are NOT the same, so dont need to ask about it.

If people could just post if they have something useful to add, it would be great.

Seems to be something in the water today!

Chip

iTrader: (3)

I know all this already, I merely want to know how much difference it makes on a set of dyno dynamics rollers if you run a car up in 3rd or 4th.
There will be a difference in the ATW wheel figures based on the different transmission losses, but given that it aims to project a flywheel figure, it shouldnt do so if it cant account for the fact the losses are different.
And im convinced that unless you have a completely fucked cog, its only ever going to be a small variation between adjacent gears anyway.

GARETH T

ya your a patronizing cunt today! lol

AlexF

He's only playing

ECU Monitor Enthusiast

iTrader: (1)

Kev83

Interesting thread. There are so many different factors that would need to be accounted for when going from rolling road to rolling road. But, at the typical power levels that joe blogs has on the street, i cant see a couple of degree's of ambient temprature making a whole lot difference to the eventually BHP result.

IMO, rolling road figures can be manipulated by the operator anyhow, and as somebody mentioned, they really do mean diddly squat other than maybe pub talk or a riugh guide to what level of tune your car is at. How the car drives on the road is what should really matter, or how it performs on track/strip.

Just my 10p's worth

dojj

iTrader: (3)

if no one has done this, and it doesn't look like it either, would you be talking about rwd or 4wd of fwd chip as they all see to have varying amounts of transmission losses depending on who you talk to

so is there a bigger difference between these than just a different car with different gear spacings?

D700 OMB

iTrader: (1)

a little, what are the thoughts on these hub dyno's that PJ & others use?

Cheers

GARETH T

as the load cells would be very repeatable, im sure the errors are down to how the rollers are being used!

dojj

iTrader: (3)

but no ones done it

sbd16v

chip this is simple

when we next go to jkm we will book for an hour and do 2 runs in 4th then 2 in 3rd and see if there is any difference

Chip

iTrader: (3)

Rob, agreed, its like fucking pulling teeth on here to get info out of any of the tuners sometimes

scoooby slayer

iTrader: (4)

from what im lead to believe from where i had my car r/r ideal gear is 1.1 so it isnt geared up or down from that.
and to test a r/rs accuracy is simple imo just put a new car on it completeley standard but at least run in, and hp reading should be same as manufacturers reading if its accurate.
thats what i did anyway and a new fiesta st150 with 7k miles on made 151 hp atf 4th gear, so was near enough.

foreigneRS

not everybody else who reads or 'contributes' to the thread does

you're right. they shouldn't aim to project a flywheel figure, they should stick to quoting what is actually measured and how it has been measured. but again, you know that already.

scoooby slayer

iTrader: (4)

gears could make a difference on big turbo cars as turbo may not quite make full boost in a lower gear as engine load is less.

ECU Monitor Enthusiast

iTrader: (1)

Perhaps you should have added "FAO TUNERS ONLY" to the thread title.

This is a public forum in case you didnt realise..LOL