View Full Version : Inflated Dyno figures
The figures cars were getting at the hubs at Thor yesterday seemed way too high to me. My '93 Auto RZ, standard apart from full De-cat, made 350.5 HP DIN
That can't be right can it? Maybe I could beleive that figure if it was the figure at the flywheel but not at the hubs surely?
I notice on the Dyno graph printouts that it states the figures are Flywheel figures but Pete definitely said it was the hub figure.
If you assume a 20% drivetrain loss that would mean my nearly stock car is making over 438 HP DIN at the flywheel. There's no way it's that powerful, it just isn't that quick.
There was two other Supras tested while I was there and they both made even more than mine.
Having a high figure to boast about down the pub is all vey well but I'd prefer an accurate one really.
Any thoughts?
hub figures have been seen to be higher than 'at the wheels' which is what most dynos provide. The usual 20% drivetrain loss doesnt apply with at the hub dynos, there were some discussions on here a while back where people had a rough stab at what the loses were but I cant remember it now.
It does also depend how much boost you were running, if you are at 1.3 bar or similar then its possible to be that high.
JB
Hi,
I thought the figures sounded about right. With all the mods on my car, I would expect to get 350bhp, It registered as 360bhp. Dont think that is unreasonable. These cars are 326bhp at the hubs as standard.
Paul.
Originally posted by Paul R
Hi,
I thought the figures sounded about right. With all the mods on my car, I would expect to get 350bhp, It registered as 360bhp. Dont think that is unreasonable. These cars are 326bhp at the hubs as standard.
Paul.
I think you will find they are 326bhp at the crank standard!
Originally posted by Branners
It does also depend how much boost you were running, if you are at 1.3 bar or similar then its possible to be that high. The 350.5 BHP run was at 1.17 Bar (manually restricted using by not using full throttle)
Pete wouldn't run it at full throttle/boost because of the scary A/FR
Originally posted by Darren
I think you will find they are 326bhp at the crank standard! Yeah that's my understanding too
Originally posted by Paul R
I thought the figures sounded about right. With all the mods on my car, I would expect to get 350bhp, It registered as 360bhp. Dont think that is unreasonable. What mods have you got Paul? You did tell me on the day but I can't remember now.
Also, any chance of you posting your dyno graphs so I can compare them with mine?.
Thanks
Really? hmm..I'm doubting the figures now as well then.
That means mine is making 432 at the flywheel (assuming 20% loss at wheels)
This does sound high!
Paul.
Originally posted by Jake
What mods have you got Paul? You did tell me on the day but I can't remember now.
Also, any chance of you posting your dyno graphs so I can compare them with mine?.
Thanks
I've got full de-cat, FMIC, induction kit, RSR exhaust, HKS bov. May have hybrids but we arent sure!
I was runing 1.13 bar to get 360bhp at the wheels.
Paul.
Jake I agree with what you are saying. Decatted Supras @ G Force were only making 380-390bhp at the crank as I remember.
Hub figures do seem to be very misleading and good for bragging rights only....:confused:
Originally posted by Paul R
That means mine is making 432 at the flywheel (assuming 20% loss at wheels)
This does sound high!
It's even higher than that! 450
20% of 450 is 90, right?
So, 450 minus 20% = 360
Originally posted by Jake
It's even higher than that! 450
20% of 450 is 90, right?
So, 450 minus 20% = 360
Yeah, but 360 + 20% = 432! lol.
Paul.
Originally posted by Paul R
Yeah, but 360 + 20% = 432! lol. but that's only a 16.66% LOSS from the flywheel figure.
Confusing isn't it? Tanhauser pulled me up for making the same mistake yesterday. :D
100 less 20% is 80, right?
But 80 plus 20% is 96, see? edit to make the example sums using 20% rather than 10%, seeing as that's the figure we're working with here
Anyone fancy ringing Pete Betts and asking him to explain the figures? He definately said that the figure was at the wheels, not at the crank. But, it does say at the flywheel on the dyno sheet!
Paul.
Originally posted by Jake
but that's only a 16.66% LOSS from the flywheel figure.
Confusing isn't it? Tanhauser pulled me up for making the same mistake yesterday. :D
100 less 10% is 90, right?
But 90 plus 10% is 99, see?
Ok, I'm shit at maths! :D
Paul.
Originally posted by Paul R
He definately said that the figure was at the wheels you mean at the HUBS not the wheels
Originally posted by Jake
you mean at the HUBS not the wheels
Yeah, sorry, hubs.
I guess if it was at the wheels(rolling road) then there would be further loss??
Paul.
Theres also a post on here somewhere from Pete saying its at the hubs, but the paperwork does say flywheel as thats whats written in to the software so it cant be changed. So it is at the hubs.
Imports would be down on power compared to a UK spec, probably about 310bhp standard. They were built for low end torque and performance and so didnt need big power figures.
Somebody did bandy about that it was a 10% conversion figure for hubs to flywheel but that seems a little low to me.
JB
Patrick_Devlin
07-06-04, 08:16
We had the same discussion on the first RR day to Petes!! :) 10% loss is too low, but 20% is too high, I think we settled on something like 15-16%, but it wasnt just as simple as that :( We based that on some cars that were pretty standard that were there! It was confusing... my de-cat Jspec registered 367 at the hubs... :eek:
THOR figures in general seem a rather more optimistic than other dynos. But then it is good in a way, as it seems to be bringing our power figures more in line with the US.
At the end of the day, the use of a dyno is to check the health of the engine, fuelling etc rather than a genuine power gauge.
Originally posted by Jake
It's even higher than that! 450
20% of 450 is 90, right?
So, 450 minus 20% = 360
Jake, where are you getting the figure of 450 from ??? I dont understand.....
Paul said his car made 360rwhp, which he worked out to be 432bhp, you then said its higher, at 450bhp, by using the following:
20% of 450 is 90, right?
So, 450 minus 20% = 360
Mine was dynod at 357@hubs, so your saying that I cant work it out by saying 357+20%, because 80+20%=96. But I cant say my real figure is 460 (for instances) - 20%........... mmmmmm, I just figured this out, seems I sort of explained it to myself :D Becasuse you can take a real figure minus 20% and if its lower than the dyno, up the real figure, so mine would be:
446(bhp) minus 20% = 357@hubs...........
Do I get a gold star........ :D
EDITED TO SAY: Does anyone know which type/or one dyno that is realistic in power figure, or closest...????
Patrick_Devlin
07-06-04, 14:50
Cant be bothered to try and figure out the maths... its too hot in this office! :(
If we're trying to get figures as close to 'at the crank' as possbile, then short of getting the engine out, you want to try and remove any of the inacuracies of a dyno or RR as possible. An RR will give a certain amount of wheel slip, this would be unmeasurable in real terms, and as such only a 'fudge factor' could be applied to give a 'crank figure'. A hub dyno removes wheel slip and would therefore be slightly more accurate, although you would still have to apply a guestimate on the transmission losses, and even then each cars' transmission losses would differ.
Am I making sense or talking out of my arse! :blink:
You could go to 20 different RR & get 20 different figures and probably + or - 15%. It is down to calibration and they way it is measured. PTS in Luton, although they had an old dyno seemed pretty on the ball. G Force is supposed to be good too.
I am sure Pete's is excellent, assuming you always use it to check the sucess of the mods undertaken. Don't get too hung up on output, it's pub bragging rights. Just be pleased with the way the car drives and that it is fuelling nice and safe, with a reasonable looking curve. If you start chasing power figures you will get sucked into a whole different game and may end up with a car you hate driving.
Tannhauser
07-06-04, 16:49
Originally posted by Ashley Willis
Jake, where are you getting the figure of 450 from ??? I dont understand.....
Paul said his car made 360rwhp, which he worked out to be 432bhp, you then said its higher, at 450bhp, by using the following:
20% of 450 is 90, right?
So, 450 minus 20% = 360
Mine was dynod at 357@hubs, so your saying that I cant work it out by saying 357+20%, because 80+20%=96. But I cant say my real figure is 460 (for instances) - 20%........... mmmmmm, I just figured this out, seems I sort of explained it to myself :D Becasuse you can take a real figure minus 20% and if its lower than the dyno, up the real figure, so mine would be:
446(bhp) minus 20% = 357@hubs...........
Do I get a gold star........ :D
EDITED TO SAY: Does anyone know which type/or one dyno that is realistic in power figure, or closest...????
Just a word on the maths. You've got the right answer but by a convoluted process.
Working with your 20% loss figure, to work it backwards (i.e. going from hub to crank), multiply your rhhp figure by (100/80). In other words multiply by 1.25.
So in general, to go from rhhp to bhp, do this:
rhhp x 100/ (100 - estimated transmission loss)
E.g. If your car got 340 rhhp and your guesstimate is that losses are 15%, then:
340 x 100/ (100 - 15) = 400bhp
Cliff
This is how I work it out.
Working out Flywheel power
rhhp / 80% * 100% = flywheel bhp
340 rhhp / 80 ( after 20% transmission loss) *100 = 425bhp
working out rhhp
flywheel bhp / 100 * 80 (transmission loss) = rhhp
425 / 100 * 80 = 340 rhhp
This seems to be best way i found and gets the same results as cliff. The real question is what are the transmission losses, 20% or 15%
being 340rhhp can either be 400 bhp (15% transmission loss) or
425 (20% transmision loss) at the flywheels so there is quite a difference of 25bhp.
Now just think if a Supra is pushiing out 750 at the hubbs, their flywheel bhp will either be 938bhp (20% loss) or 882bhp (15% loss). A difference of 56bhp which is quite significant when you are trying to boast a 900+ bhp.
But saying that I would be happy with 750 at the hubs! hell i would like 400 at the hubs. Keep saving keep saving I THINK.
I remember the thread a while ago about hub vs. crank power. I seem to remember that, for manuals at least, the losses were worked out to be ~11%.
So for a hub output of 350bhp this would mean a crank output of 390 odd. Which sounds bang on the money to me, in my experience anyway.
In fact I believe this was the thread...
http://www.mkivsupra.net/vbb/showthread.php?s=&threadid=14480&perpage=15&pagenumber=1
I say stick to comparing hub figures, don't try to compare from one set of rollers to another, and if you're being really really picky only comparisons done on the same day/morning hold true meaning.
If I had to be conservative when someone asked me, I'd add 10 maybe 11% to the figure from the Thor Dyno...at most. This is in a manual, auto maybe slightly more.
Just make sure you stick with the same dyno after carrying out different mods and then at leat you've got a relative idea what you've achieved with all the £££ ploughed into the car. :)
why would transmission losses b a percentage?
2 cars, same drivetrain, different engine. car A has 100 hp, car B has 800 hp. assuming a 20% loss car A looses 20hp and car B looses 160 through the tranny. why would this b? the friction and rotating mass of the tranny, diff, drive shafts, axles would b the same, so should the losses.
also with a hub dyno u dont get the losses of a pair of wheels and tyres having to b spun.
Originally posted by eyefi
why would transmission losses b a percentage? This has been gone over before and I think we all realise that trans loses aren't a fixed percentage.
Originally posted by Jake
This has been gone over before and I think we all realise that trans loses aren't a fixed percentage.
Well volunteered for an addition to the technical FAQ Jake :D
-Ian
Originally posted by Jake
This has been gone over before and I think we all realise that trans loses aren't a fixed percentage.
u've lost me there, it doesnt look like it from this thread.
Originally posted by eyefi
u've lost me there, it doesnt look like it from this thread. True but it's common sense isn't it?
If for example a 320hp Supra loses say 20% through the drivetrain thats 64hp lost.
So it takes 64hp to transmit the power
But if the same car has a major powerboost to say 800hp but the drivetrain stayed the same it would still only take around 64hp to drive the mechanical parts between the engine and the hubs.
OK, it'd be a bit more than 64hp lost because of some other factors like heat or whatever but not all that much, relatively speaking.
So a 800hp Supra would be losing a much lower PERCENTAGE of it's power through the drivetrain. If the percentage loss stayed the same that would mean that our imaginary 800hp car was losing 160hp through same drivetrain that only sapped 64hp before.
eyefi stop causing trouble :innocent:
*hiijack* How's your car doing? */hiijack* ;)
Originally posted by Jake
True but it's common sense isn't it?
maybe it is, but all ive ever seen banded around is a fixed percentage to convert hub or wheel to crank. i posed my original statement as a question because i had not seen this "common sense" idea discussed before, and though it seems logical to me i thought i may b missing something. ive now noticed that tbourner and dandan brought up this notion in the other thread listed by thorin (gaylord) and id agree that the dandan equation would b alot better conversion method.
Originally posted by Thorin
eyefi stop causing trouble :innocent:
*hiijack* How's your car doing? */hiijack* ;)
its very sort of in lots of bits, im really missing it now. :(
MONKEYmark
08-06-04, 22:56
Originally posted by eyefi
its very sort of in lots of bits, im really missing it now. :( i know how you feel lad. i have been real bored cant do anything. been messing on astra have doe a ice install (fitted ariel in correct place outside of car) fixed my parcel shelf topped it up with oil. it runs like a dream now and you can hardly hear engine. was thinking of becoming a DYNO queen like all the people in here :)
what next DYNO QUEENS + TRAILER QUEENS
there is so much confusion on dynos and some places dont know how to dyno the auto`s. use them to get your car tuned for running right. mcanny has been on quite a few dynos with different results. i like to see how well cars do in the 1/4 to get an idea of power. not ideal but the black dyno dont lie
i would be well happy running car in ttc mode as its mad. you always have in back of your mind whens it going to let go, so getting fueling checked is good to find any problems.
if you dont get the numbers you want you come away dissapointed. when you were happy before with the performance of your car.
Tannhauser
08-06-04, 22:57
Originally posted by Jake
True but it's common sense isn't it?
If for example a 320hp Supra loses say 20% through the drivetrain thats 64hp lost.
So it takes 64hp to transmit the power
But if the same car has a major powerboost to say 800hp but the drivetrain stayed the same it would still only take around 64hp to drive the mechanical parts between the engine and the hubs.
OK, it'd be a bit more than 64hp lost because of some other factors like heat or whatever but not all that much, relatively speaking.
So a 800hp Supra would be losing a much lower PERCENTAGE of it's power through the drivetrain. If the percentage loss stayed the same that would mean that our imaginary 800hp car was losing 160hp through same drivetrain that only sapped 64hp before.
OK, strictly amateur time now, but here goes....
Let's take one example of a transmission loss. Some of the horsepower is used to spin the flywheel, the function of which is (if I understand) only to keep the crankshaft spinning evenly to give a smooth idle.
It takes a certain amount of energy to accelerate the wheels from 0 to, say, 18 rps ( I reckon that's about 60mph - prepares to duck!). The 320bhp supe engine can supply this energy in, say, 5.3 seconds. It takes 238kJ of energy per second to accelerate the rear wheels this fast. To accelerate the wheels any faster needs more enrgy per second - more bhp.
In the 800bhp supra, it's supplying energy at the rate of 596kj per second. This is sufficient to accelerate the wheels to the same 18rps in, say, 3.5s.
BUT...just as it takes more energy to accelerate the back wheels faster, it also takes more energy to rotate the flywheel faster. In fact, because they are both just masses that need to be moved, the amount of energy, or power 'wasted' will rise at exactly the same rate.
Frictional forces within the system will also rise in proportion to the acceleration, which is a function of power..
There may be certain losses that don't depend on power, but I don't know what they might be. But intuitively it seems to me that some of the power loss must rise proportionately.
Where's Darren Blake when he's needed?
Cliff
Cliff someones fu**d with yer sig dude its all in Spanish !!!!
Dude:flame Dev
may wee rodney may wee !!!
Tannhauser
08-06-04, 23:08
A little googling turned up this from an engineering site:
http://www.engineersedge.com/wwwboard/posts/1847.html
Interesting.
Edited to say: to cut to the chase, look at the final paragraph on 'iskit4iam's post.
Dude, I also speak fluent West Bromwich/Black Country.
Originally posted by Tannhauser
OK, strictly amateur time now, but here goes....
same boat mate. no expert but up for the novice debate.
the flywheel is there to store energy (among other balance issues). apply power to spin it then remove the power source and the energy stored in the flywheel will keep it spinning. without a flywheel the engine would just drop to idle when u let off the throttle, making the car impossible at best to drive. so the fly would b parasitic when being made to spin faster but enhance torque when at a steady state.
the rest of the drivetrain is ultimately rotating mass to b moved and friction to overcome. so what we r interested in here is whether it takes the same amount of torque to overcome the resistance of turning this lot with a 100ft/lbs force as it does with 800ft/lb's.
acceleration is a measure from one state to another and i dont think it has an impact on this losses debate, just like the weight of the car doesnt. it does have a real world effect but not on a dyno measuring the twisting force of the engine.
does any of that make any sense?
Originally posted by Tannhauser
A little googling turned up this from an engineering site:
http://www.engineersedge.com/wwwboard/posts/1847.html
Interesting.
Edited to say: to cut to the chase, look at the final paragraph on 'iskit4iam's post.
Dude, I also speak fluent West Bromwich/Black Country.
hmmmm, interesting.
just for ref. here is the post from tannhauser's link
The answer is neither of your answers may be correct._ You_ have to look at what is causing the energy loss._ Part of the loss is due to moving the lubrication fluids around._ The energy to move the fluid is not a function of power through the system._ Part of the loss is due to frictional forces._ Frictional forces are proportional to the transmitted force, which is proportional to the transmitted power._ So friction forces will be a percentage of transmitted power and fluid movement forces will be fixed._ And there are lots of other factors making up your losses._
So, the 285HP motor may not lose 18% but is will certainly lose more than 38HP._ For the exact same drivetrain at the same rpm._ (experience tells me fixed losses are small compared to proportional losses so the practical answer is you lose 18%)
Tannhauser
09-06-04, 00:08
OK, I know how to convert between hp and torque, but TBH I get a lttle lost in the relationship between the two and that doesn't help in trying to get my head round this..
However, IMO, I think that acceleration is very relevant here. The drive train has a certain rotational mass, as you say. This is fixed and doesn't vary with the power of the car. But, force (torque) = mass x acceleration. Therefore, the faster the engine accelerates the drive train, the more torque it requires to do so.
Therefore more torque is wasted, in absolute terms, the faster the drivetrain is accelerated. A more powerful engine can accelerate the drivetrain faster than a less powerful one. Therefore loss in torque or loss in power both increase in proportion to maximum power output of the engine.
What do you reckon?
So to conclude the only way to find out what bhp your car is - is to measure it at the flywheel which is pretty unworkable. F*ck knows what actual bhp j-specs come out of Japan are. 280 is obviously not accurate.
My Thor dyno was 357 at the hubs. If I was to upgrade something (Hybrids or intercooler whatever) on the same day with the same ambient temps etc and it came out 420 then this would equal a good power enhancement. Pete always says that his measurements are at the hubs. Finding the true bhp seems to be a bit impossible. His machine is consistent so you can see, by using his kit, what difference a mod has made to your individual car.
The best thing is for a few totally stock cars to be measured and see what they average out at. Then we could calculate the transmission losses a bit more accuratley.
Having said that a totally stock J-Spec could be anything between 280 - 320 bhp so there is already a 40bhp discrepancy there!!!!!!!
The mystery continues :(
PS: at the pub I say my car is around 400 bhp or just over :) 357 rhhp + 15% = 410bhp :p
Originally posted by Tannhauser
What do you reckon?
im off to bed, see ya tomorrow :)
Originally posted by Justin
The best thing is for a few totally stock cars to be measured and see what they average out at. Then we could calculate the transmission losses a bit more accuratley.
Which is what we tried to do in the other thread that I linked and hence came up with the 11% figure.
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