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Dyno print, spot the errors.
Nickp - 24/6/16 at 10:01 PM

A car a mate's considering buying.
Dyno print seems to contain 'errors' (no reflection on the seller btw)
I spotted 3, any more?

Slimy38 - 24/6/16 at 10:25 PM

How does a torque vs horsepower graph have five crossing points?

femster87 - 24/6/16 at 10:47 PM

quote:
Originally posted by Slimy38
How does a torque vs horsepower graph have five crossing points?


On a different scale

jeffw - 25/6/16 at 05:58 AM

Put power is the calculated figure, it is a product of rpm and torque measurements. So if the torque and rpm don't dip how does the power?

[Edited on 25/6/16 by jeffw]

jelly head - 25/6/16 at 08:21 AM

quote:
Originally posted by jeffw
Put power is the calculated figure, it is a product of rpm and torque measurements. So if the torque and rpm don't dip how does the power?

[Edited on 25/6/16 by jeffw]


Yeah and because it's calculated shouldn't the two curves cross at 5252rpm?

MikeRJ - 25/6/16 at 11:24 AM

quote:
Originally posted by jelly head
quote:
Originally posted by jeffw
Put power is the calculated figure, it is a product of rpm and torque measurements. So if the torque and rpm don't dip how does the power?

[Edited on 25/6/16 by jeffw]


Yeah and because it's calculated shouldn't the two curves cross at 5252rpm?


Only if torque and HP are on the same scale, which they are not. Torque and HP have the same value at 5252RPM if you look closely (around 136 bhp / lbft)

phelpsa - 25/6/16 at 11:33 AM

quote:
Originally posted by jeffw
Put power is the calculated figure, it is a product of rpm and torque measurements. So if the torque and rpm don't dip how does the power?

[Edited on 25/6/16 by jeffw]


Torque is the calculated figure. Dynos measure power.

Slimy38 - 25/6/16 at 12:26 PM

quote:
Originally posted by femster87
quote:
Originally posted by Slimy38
How does a torque vs horsepower graph have five crossing points?


On a different scale


Nope, on any scale it should still only cross once. If the scales are different then they won't cross at 5252, but it should only ever cross once.

phelpsa - 25/6/16 at 12:34 PM

quote:
Originally posted by Slimy38
quote:
Originally posted by femster87
quote:
Originally posted by Slimy38
How does a torque vs horsepower graph have five crossing points?


On a different scale


Nope, on any scale it should still only cross once. If the scales are different then they won't cross at 5252, but it should only ever cross once.


The likelihood is that the 'smoothing' factor applied to each graph is different.

Nickp - 25/6/16 at 12:38 PM

quote:
Originally posted by femster87
quote:
Originally posted by Slimy38
How does a torque vs horsepower graph have five crossing points?


On a different scale


Never seen it done on different scales before, makes it look odd.

What about only 11bhp transmission loss? It's a Westfield with a type 9 and Sierra LSD.

And why would they run it at over 150mph on the rollers?? Every one I've ever been to have only used 3rd or 4th gear.

MikeRJ - 25/6/16 at 12:48 PM

quote:
Originally posted by phelpsa
quote:
Originally posted by jeffw
Put power is the calculated figure, it is a product of rpm and torque measurements. So if the torque and rpm don't dip how does the power?

[Edited on 25/6/16 by jeffw]


Torque is the calculated figure. Dynos measure power.


A chassis dyno measures torque at the wheels, either directly via a brake (water, eddy current etc.) or indirectly on an inertia dyno via the acceleration of the drum.

Torque at the engine is then calculated using transmission loss etc.

[Edited on 25/6/16 by MikeRJ]

phelpsa - 25/6/16 at 12:54 PM

quote:
Originally posted by MikeRJ
quote:
Originally posted by phelpsa
quote:
Originally posted by jeffw
Put power is the calculated figure, it is a product of rpm and torque measurements. So if the torque and rpm don't dip how does the power?

[Edited on 25/6/16 by jeffw]


Torque is the calculated figure. Dynos measure power.


A chassis dyno measures torque at the wheels, either directly via a brake (water, eddy current etc.) or indirectly on an inertia dyno via the acceleration of the drum.

Torque at the engine is then calculated using transmission loss etc.

[Edited on 25/6/16 by MikeRJ]


It measures energy at the brake, not torque. The torque is then found by dividing the energy per second (power) by the engine speed.

Nickp - 25/6/16 at 12:56 PM

Also, it's a std Vauxhall Red Top with ITBs, DTA ECU and an exhaust.
Peaking at over 7200rpm? Surely it'd peak lower than that and struggle to top 180bhp?

Andy D - 25/6/16 at 05:49 PM

quote:
Originally posted by Nickp
Also, it's a std Vauxhall Red Top with ITBs, DTA ECU and an exhaust.
Peaking at over 7200rpm? Surely it'd peak lower than that and struggle to top 180bhp?


I reckon it peaked at about 6200rpm, 182bhp?.. the last little kick upwards is a glitch of some sort. I'm sure rolling road operators will know what caused it? Unloading the dyno early or something like that he guessed? ;-)

Phil_1471 - 25/6/16 at 06:27 PM

sarcastic comment retract to my own inaccuracies lol

[Edited on 25/6/16 by Phil_1471]

coyoteboy - 30/6/16 at 07:04 AM

quote:
Originally posted by phelpsa

It measures energy at the brake, not torque. The torque is then found by dividing the energy per second (power) by the engine speed.


Depends on the dyno in question. Plenty use an eddy brake and reaction arm to directly measure load. No idea about this specific one though. Measuring power out directly would by definition be harder and lies accurate.

Nickp - 30/6/16 at 07:28 AM

quote:
Originally posted by Andy D
quote:
Originally posted by Nickp
Also, it's a std Vauxhall Red Top with ITBs, DTA ECU and an exhaust.
Peaking at over 7200rpm? Surely it'd peak lower than that and struggle to top 180bhp?


I reckon it peaked at about 6200rpm, 182bhp?.. the last little kick upwards is a glitch of some sort. I'm sure rolling road operators will know what caused it? Unloading the dyno early or something like that he guessed? ;-)


Yeah, I'd agree. 182 @ 6200 would be about right for flywheel bhp.

MikeRJ - 30/6/16 at 07:46 AM

quote:
Originally posted by phelpsa
quote:
Originally posted by MikeRJ
quote:
Originally posted by phelpsa
quote:
Originally posted by jeffw
Put power is the calculated figure, it is a product of rpm and torque measurements. So if the torque and rpm don't dip how does the power?

[Edited on 25/6/16 by jeffw]


Torque is the calculated figure. Dynos measure power.


A chassis dyno measures torque at the wheels, either directly via a brake (water, eddy current etc.) or indirectly on an inertia dyno via the acceleration of the drum.

Torque at the engine is then calculated using transmission loss etc.

[Edited on 25/6/16 by MikeRJ]


It measures energy at the brake, not torque. The torque is then found by dividing the energy per second (power) by the engine speed.


No, it measures torque at the brake, typically using a load cell on a modern dyno.

[Edited on 30/6/16 by MikeRJ]

jeffw - 30/6/16 at 08:14 AM

Yes, torque is the measured figure not power in most dynos.

Power (HP) = (Torque (lb-ft) x RPM)/5250

phelpsa - 30/6/16 at 08:46 AM

quote:
Originally posted by MikeRJ
quote:
Originally posted by phelpsa
quote:
Originally posted by MikeRJ
quote:
Originally posted by phelpsa
quote:
Originally posted by jeffw
Put power is the calculated figure, it is a product of rpm and torque measurements. So if the torque and rpm don't dip how does the power?

[Edited on 25/6/16 by jeffw]


Torque is the calculated figure. Dynos measure power.


A chassis dyno measures torque at the wheels, either directly via a brake (water, eddy current etc.) or indirectly on an inertia dyno via the acceleration of the drum.

Torque at the engine is then calculated using transmission loss etc.

[Edited on 25/6/16 by MikeRJ]


It measures energy at the brake, not torque. The torque is then found by dividing the energy per second (power) by the engine speed.


No, it measures torque at the brake, typically using a load cell on a modern dyno.

[Edited on 30/6/16 by MikeRJ]


Whether it's sensing load at the end of a lever, hydraulic pressure or voltage, as well as speed at the brake, what the dyno is measuring is power. It has no idea how that power is being generated or transfered elsewhere in the system.

coyoteboy - 1/7/16 at 02:26 PM

quote:

Whether it's sensing load at the end of a lever, hydraulic pressure or voltage, as well as speed at the brake, what the dyno is measuring is power. It has no idea how that power is being generated or transfered elsewhere in the system.

There's a critical difference though, it's MEASURING torque and RPM. It's calculating power from that. If it measured voltage/current it would have an additional unknown (conversion in itself, losses in itself etc). If it measures torque at an arm and RPM it knows precisely the input power and it's really easy to do. I don't think anyone was arguing with the second half of your comment. My point was simply that your statement wasn't technically accurate from my experience with them. And this statement:

quote:
Torque is the calculated figure. Dynos measure power.


is wrong.

Dynos measure torque.