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....

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.

 

 

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.

 

 

100 less 10% is 90, right?

But 90 plus 10% is 99, see?

 

Ok, I'm shit at maths!

 

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

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...

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 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........

 

EDITED TO SAY: Does anyone know which type/or one dyno that is realistic in power figure, or closest...????

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!

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.

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 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........

 

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.