Dyno sheet questions

[matt dunn]

if you were clever enough as sat down with,

a calculator,
the dyno sheet,
the tyre dia,
the diff ratio,
the gear ratio the run was done it,

you should be able to work out the engine torque,
not allowing for roller slip, if any.

Sound like a job for redmist or fivebob.

Matt

[fivebob]

if you were clever enough as sat down with,

a calculator,
the dyno sheet,
the tyre dia,
the diff ratio,
the gear ratio the run was done it,

you should be able to work out the engine torque,
not allowing for roller slip, if any.

Sound like a job for redmist or fivebob.

Matt

Been there, done that. It takes way too long for something that could be done on any half decent dyno in a few seconds

[strx7]

something that could be done on any half decent dyno in a few seconds

EXACTLY

[Caveman]

power by definition is force exterted times a distance, or torque times an angular velocity. Easy to work out from the speed of the rotating tyre and the torque it is exerting on the rollers.

To translate the torque to the flywheel, you would need to take into account all frictional losses in bearings, gears, gear oil and slip from clutch, rollers, etc. OR use the ratio of engine RPM to wheel RPM (or angular velocity to be SI correct ) and multiply that by the torque to give your flywheel equivilent (this doesnt take into account slip, loss, etc)

In the end, the shape of the torque curve will be the same, and is the thing you should be anaylising. torque at the motor is a usless value as far as im concerned. Torque at the wheels is more important, and is good to plot in each gear. This allows you to find shift points, etc.

Example 7000RPM in 3rd may be producing less torque AT THE WHEELS than 5000RPM in 4th, or vise versa. Often torque drops off at the top end however because of mechanical advantage through the drivetrain its sometimes better to redline the lower gears but the shift earlier as you get around 4th, 5th gear.

Torque performance only overlay engine RPM, it is not used in calculating power, and shouldnt be used given the measure or torque is taken at the wheels, not the motor.

[Caveman]

strx7: Im sorry you were wrong from the beginning, you dont need 'TRUE' torque (whatever that means ) to work out power. If you think the only formula for power is 'torque * RPM / 5282' you are wrong.

Have a quick look at http://en.wikipedia.org/wiki/Torque
(I know wikipedia should not be used as technical reference, but this is a public discussion forum so I feel it is suffice)

Have a look where it says Relationship between torque, power and energy

[fivebob]

I think every here is talking at cross purposes

What is desirable is not the torque at the flywheel calculated using some mythical drivetrain losses, it's the torque at the wheels that is produced by the engine. i.e. without the effect of gear ratios from the torque multiplier (gearbox).

That way you can compare changes regardless of which gear the run was done in, and theorectically what dyno it was measured on (though that is very debateable)

[RomanV]

What is desirable is not the torque at the flywheel calculated using some mythical drivetrain losses, it's the torque at the wheels that is produced by the engine. i.e. without the effect of gear ratios from the torque multiplier (gearbox).

I understand what you're saying, but I dont see how it's practical to do this.
For example, lets say its a saturday morning Torque Performance dyno day you're going to.
If they use roller RPM and roller torque, you get an accurate KW reading, a torque curve, and perhaps some indication of what sort of RPM your engine is doing.
They can get you on and off the dyno fairly quickly.

If you want to have the 'engine' wheel torque scale down the side, you need to precisely know what RPM the engine is doing. Now this is fine when you've got one car in there, and are tuning it for a few hours.
But if you've got a whole crap load of different cars coming in, with distributors, coil packs, etc, it becomes time consuming to figure out how to access an accurate RPM reading for each car. Without access to this, an 'engine' wheel torque figure would be useless, which is why they dont put one on.

if you were clever enough as sat down with,

a calculator,
the dyno sheet,
the tyre dia,
the diff ratio,
the gear ratio the run was done it,

you should be able to work out the engine torque,
not allowing for roller slip, if any.

Sound like a job for redmist or fivebob.

Matt

It seems simpler to just make a new torque 'scale' down the side of the drawing. If you had an indication of the RPM, then you could use the KW figure and the RPM to work out what torque it's making at that point on the graph, and do this a few times to work out the new scale. But yeah, its a PITA to do I suppose.

[strx7]

all you need is a timing light type pick up and then an electrical divider type gizzmo to use weather that ignition signal is per cylinder, per revolution, 4 times per revolution, once every 4 revolutions or whatever else it may be.

[fivebob]

It would be very simple if they had an RPM pickup like most other dynos. That could be as simple as a clip on an HT lead, or in the case of COP on the trigger wire.

The other way is to measure the tyre circumference and know the gear ratios, but that would be a PITA.

[pc]

Or do a run at say 50Km/hr on the rollers in the gear that you intend to dyno in, and note down the reading on the tacho. Then punch in the tacho reading for 50Km/hour into the computer and it should be scaled fairly accurately for the run.
This doesn't allow for slippage or inaccurate tachos, but should give a fairly good indication as opposed to none.

[Caveman]

Or do a run at say 50Km/hr on the rollers in the gear that you intend to dyno in, and note down the reading on the tacho. Then punch in the tacho reading for 50Km/hour into the computer and it should be scaled fairly accurately for the run.
This doesn't allow for slippage or inaccurate tachos, but should give a fairly good indication as opposed to none.

They run at 2000rpm, according to the in car tach, and push a button which calibrates the RPM to the speed. It is hardly ever acurate hence the rpm is overlayed as a guide

[fivebob]

Because there is no direct connection between the rollers and the engine, anything other than an ignition pickup is essentially useless for gathering accurate info.

[mister2]

At the end of the day - why do you care? Wheel torque is proportional to engine torque - so all you're talking about is effectively changing the scale on the graph.

All you need is to work out your engine torque is your drive ratio (edit: sorry and wheel diameter etc) anyway, if that makes you happier.

But there's not a great deal of point in doing it to compare to different dyno's given the amount of variation between dyno's.

As far as picking up on changes then a wheel torque graph will show them equally well as engine torque.

Anyway, Dynapacks don't have this (and many other associated) problem

Cheers

Nick