Southern Softies - Southways Automotive 14 Dec 2013 PICS

[LiamT4]

I haven't been on many different manufacturer dyno's. But the best examples I can think of, from my own car - was my T4 ran on a maha, and was 'x'whp (I can't remember the exact figures), and was 222bhp at the fly. 2 weeks later I ran on a Mustang dyno, the flywheel horse power was 221bhp, but the whp was much higher than the maha whp.

If you lined up the same car on ten different manufacturer dynos, I bet the BHP result would be more consistent than the WHP results. You can't compare whp results dyno to dyno, they vary so much.

Already rolling, a 300bhp Scooby will be as fast as a 300bhp V70 all day long, there'll be nothing in it. But your fwd V70 will be (for arguments sake) 270whp, and the 4wd Scooby will be 230whp. You reckon the Scooby will be slower? NO! WHP is something that Americans (and Smithy) are obsessed with! And it's wrong to think that it tells the true picture of a cars performance.

Just look at these results from today. Rob's car is 310bhp at the fly, and 300whp?? Come on. And Judge's T4 is 260whp(????), yet 259 at the fly!! I fully believe the flywheel results from today, they seem very sensible, and what you'd expect, but the whp is a perfect example that defunks the argument that whp is the most accurate reading in the real world. The whp results are only valid for the dyno that it is run on, and nothing else.

Its hard to go on the Scooby example because, as there are many variables (weight, gear ratios, aero ,etc) its hard to compare so look at it this way, If car A and car B are the same weight, have the same gearing and the exact same engine running at the same engine power, but car A is 4wd and car B is 2wd then, when on the move, car B Will be quicker because it loses less energy from the engine to the wheels and it is at the point where the energy is transferred from the car to the road that is actually moving the car forward, this is simple physics. (same goes for why a manual will be quicker than an auto counterpart). The more drive shafts, diffs, tyres, etc, the energy has to/through be transferred to, the more energy will be lost.

On the question of the numbers today, having now looked myself, then yes I also have questions, just look at the measured and corrected figures and I don't understand whats going on with the numbers, without actually being there I don't know what and why its being corrected, so yes I would agree its that it is odd.

On the maha thing, that dyno is the only one I have seen that gives wildly different whp to the others, but that doesn't mean I disagree with its bhp numbers (frankies car at the time did go like a 310bhp car). That dyno make obviously measures things differently, or uses its software in a different way. Although I do question why sometimes they will measure a car in a completely different gear than other dynos do, but that's not a dyno issue but an operator issue.

I'm sure you'd agree though, that if a dyno has some form of issue measuring the actual power a car is producing, then because the ONLY way it can measure the power is at the wheels, then not only will the whp be wrong, but so will the bhp.

[T5frankie]

Its hard to go on the Scooby example because, as there are many variables (weight, gear ratios, aero ,etc) its hard to compare so look at it this way, If car A and car B are the same weight, have the same gearing and the exact same engine running at the same engine power, but car A is 4wd and car B is 2wd then, when on the move, car B Will be quicker because it loses less energy from the engine to the wheels and it is at the point where the energy is transferred from the car to the road that is actually moving the car forward, this is simple physics. (same goes for why a manual will be quicker than an auto counterpart). The more drive shafts, diffs, tyres, etc, the energy has to be transferred to, the more energy will be lost.

On the question of the numbers today, having now looked myself, then yes I also have questions, just look at the measured and corrected figures and I don't understand whats going on with the numbers, without actually being there I don't know what and why its being corrected, so yes I would agree its that it is odd.

On the maha thing, that dyno is the only one I have seen that gives wildly different whp to the others, but that doesn't mean I disagree with its bhp numbers (frankies car at the time did go like a 310bhp car). That dyno make obviously measures things differently, or uses its software in a different way. Although I do question why sometimes they will measure a car in a completely different gear than other dynos do, but that's not a dyno issue but an operator issue.

I'm sure you'd agree though, that if a dyno has some form of issue measuring the actual power a car is producing, then because the ONLY way it can measure the power is at the wheels, then not only will the whp be wrong, but so will the bhp.

that maha dyno i got 298bhp and 199whp lol, at 18psi on an 18t

[LiamT4]

A few dynos I've seen give a measured and correct flywheel hp, the Maha does. It's the corrected hp result that counts. Sometimes it works the other way, and the corrected is higher than the measured IIRC.

But "corrected" results are also the easiest to manipulate.

[LiamT4]

that maha dyno i got 298bhp and 199whp lol, at 18psi on an 18t

I simply don't understand the way those dynos go about there calculations in measuring and calculating the numbers, but I don't disagree with your bhp results as, considering your 1/4mile times at the time, 300bhp seemed about right.

[S70T5Chris]

The point of most dynos is to obtain as accurate flywheel figure as possible. The power is measured at the wheels, but as each dyno is different on how it obtains that figure, it vary's from dyno to dyno. Whilst the flywheel hp generally stays consistent within reason, once the magic has happened.

Surely the fact that you admit the bhp figures on a maha are accurate enough, but the whp figures are wildly different, proves that whp figures in general are bogus. You can't possibly think the whp figures from today's runs are accurate?!

[S70T5Chris]

But "corrected" results are also the easiest to manipulate.

The fairies in the computer do that, not the monkey behind the wheel.

I think it was Greg who went to a dyno operator and specifically asked him to manipulate the dyno run to give the highest possible reading as a test. It didn't actually make that much difference iirc. But I can't remember the specifics.

[LiamT4]

The point of most dynos is to obtain as accurate flywheel figure as possible. The power is measured at the wheels, but as each dyno is different on how it obtains that figure, it vary's from dyno to dyno. Whilst the flywheel hp generally stays consistent within reason, once the magic has happened.

Surely the fact that you admit the bhp figures on a maha are accurate enough, but the whp figures are wildly different, proves that whp figures in general are bogus.

I've only noticed that on the maha dynos though.

You understand the point I was making about the power losses with 4wd and 2wd though? Also people should stop thinking about it in bhp, whp, etc and think about it in a purely physics term, i.e energy, and as the dyno measures the energy at the wheels, and as this is the only contact point for the dyno, then a mistake there will cause mistakes in the bhp.

[LiamT4]

The fairies in the computer do that, not the monkey behind the wheel.

I think it was Greg who went to a dyno operator and specifically asked him to manipulate the dyno run to give the highest possible reading as a test. It didn't actually make that much difference iirc. But I can't remember the specifics.

But the point there is, its very easy to "correct" ;-)

[T5frankie]

bhp figures have always been consistent for me, whp figures are all over the place

[LiamT4]

bhp figures have always been consistent for me, whp figures are all over the place

And when I used to go to vag, Datsun and the odd bmw event, all the figures where pretty consistent. But we can only go on our own experiences.

[smithy]

To be honest I don't give a fig because it's what it does on the road that counts period .as I will prove 140bhp can be pretty quick even a 140whp can be quick too lol.

[JUDGENINJA]

Wonder if you can get your old slips out where you expect the data to be the same and see if there is a reading for barametric pressure and temperature? MRP and I had a Dyno lesson 101 yesterday regarding the concern over different Dyno calibrations and it was conveyed that in fact there is nothing to calibrate on a Dyno rollers.

The reason for similar WHP vs Fly yesterday is purely down to the environmental conditions.... I'm not an arm chair Dyno expert to be able to comment on this, but looks like you lot are. I still haven't figure out who's right on this..

[smithy]

Wonder if you can get your old slips out where you expect the data to be the same and see if there is a reading for barametric pressure and temperature? MRP and I had a Dyno lesson 101 yesterday regarding the concern over different Dyno calibrations and it was conveyed that in fact there is nothing to calibrate on a Dyno rollers.

The reason for similar WHP vs Fly yesterday is purely down to the environmental conditions.... I'm not an arm chair Dyno expert to be able to comment on this, but looks like you lot are. I still haven't figure out who's right on this..

I'm not ether but I just luv to wind things up lol.the reason why I look at whp as being the geniune figuires is because it's the wheels that are in the dyno not the engine .i just look at basics always been the same lol.and that the crank figuire works on drag loss on the run down witch seem to be anything from 20bhp to 100bhp witch seems werid .also that hub dynos don't have drag loss and they only give figuires out in whp .i could be wrong on all of this but hey ho lol

[rikcougar]

Good day by the look of it, some good results

What have you done to yours Martin (other than taken the chavvy air filter off!)

[JUDGENINJA]

The measured WHP should vary the most due to barometric conditions?? A cold wet day at sea level should be the best time to measure a cars HP? Hot, dry and up a mountain should give the lowest?!

[smithy]

The measured WHP should vary the most due to barometric conditions?? A cold wet day at sea level should be the best time to measure a cars HP? Hot, dry and up a mountain should give the lowest?!

But wouldn't the crank do that too but it looks like I'm thick then and isn't that what correction is for .as said before I go on the same rollers every time to check afrs and boost etc .I'm only interested in going as fast as possible from 0 to 150 mph done .

[charlie-r]

Right basically what happens, the guy measured our BHP and WHP, but then corrected the figures using what's called and SAE conversion which would essentially give a result if the car was running in SAE conditions, I don't know what they are but for example 20degrees at sea level. What that dyno sheet says is because it was cold (between 8-11 degrees) our cars pulled more power that day, but it calculated at SAE standard we'd have pulled less.

Problem is SAE standard doesn't apply to turbocharged cars as the wastegate negates the affect if pressure change in the atmosphere too significantly. So really what was measured on the rollers before correction (283bhp 260whp for me) is the much more accurate result.

[jamesy12345]

I'm only interested in going as fast as possible from 0 to 150 mph done .

Gets my vote!

edit: the whp will vary depending on atmospheric conditions....but only in the same way it would on the road or track. The point of the correction is to account for this, and come with a 'standard' figure to use for comparison. Problem is, it can be manipulated. Mine is an auto so I couldn't give a fudge either (I don't want to see those 20-odd % losses )

[LiamT4]

Wonder if you can get your old slips out where you expect the data to be the same and see if there is a reading for barametric pressure and temperature? MRP and I had a Dyno lesson 101 yesterday regarding the concern over different Dyno calibrations and it was conveyed that in fact there is nothing to calibrate on a Dyno rollers.

The reason for similar WHP vs Fly yesterday is purely down to the environmental conditions.... I'm not an arm chair Dyno expert to be able to comment on this, but looks like you lot are. I still haven't figure out who's right on this..

Wayne, think of energy transference, the whp CANNOT be the same as the bhp because energy will be lost going from the engine to the wheels, whatever is true regarding whp and bhp, that is a simple fact of physics.

These debates are good because eventually, one day, one of us will come up with a definitive answer and we'll know for definite............hopefully.

[charlie-r]

If someone can find a standard conversion factor for turbo engines then we can have definite figures but I can't find one . Atmospheric pressure will just shift the turbo efficiency on the compressor map So it will make a difference but only minimal compared to the SAE conversion on our dyno printouts problem is different dyno shops will use different conversion, and some won't use any at all because they'll know not to on turbo cars. Every dyno SHOULD read the same BHP but WHP will vary slightly due to the dyno itself. The two shouldn't vary because of atmospheric conditions they should stay relative to each other, but they will change if your oil/water temps increase/decrease.