Dyno Dynamics - Shoot out modes

[Mignon]

Stan Weiss said:

Dave,
Somewhat off topic. You seem to like to do mathematical modeling. Have you ever taking data logging from the OBDII port a long for the vehicle weight, gearing, tire size, and CDA and calculated wheel HP and Torque?

Stan

Not from an OBD port but from track test data yes. Thousands of times. It formed the basis of much of the work I did on transmission and tyre losses because wheel power is what actually accelerates a vehicle. If you can work out true wheel power from tested acceleration, mass,Cda and you also know the flywheel power then the losses can be deduced very accurately.

[Stan Weiss]

I really do not know how these rolling roads work. Anyone with knowledge want to share?

The one inertia engine dyno that I have an understanding of how it works, is a very high end, big dollar unit. Very simplified, it is nothing but a weight (which is adjusted based on engine being tested) and, very accurately measured RPM and elapsed time and software to calculate Torque and HP from these inputs.

Stan

[stevieturbo]

There are different designs...but I guess little different than an actual engine dyno. Just with a different interface to connect the test item to the equipment.

But there are various designs as to how any reactive force is applied ( and measured ) against the test item.

[stevesingo]

AW111 said:

stevesingo said:

Would wheel speed related losses also increase with a higher gear and therefore higher wheel speed?

They would, but I'd have to crunch some numbers to see how the tradeoff compares.
For "normal" cars (say sub 250 hp) I'd expect the speed effect to be more prominent, but the tiedown tension and consequent tyre deformation required for high horsepower / torque engines in too low a gear really hurts.

I run my 160 hp MR2 in the 70-150 kph range, but it's barely tied down at all, since it doesn't have the power to spin the wheels in any reasonable gear.

In which case, the algorithm for a 4cyl NA mid engine car must cover Honda Beat at 63hp to 200+hp. I'd be interested to see the math on that.

What tie down tension is it based on?

[AW111]

stevesingo said:

In which case, the algorithm for a 4cyl NA mid engine car must cover Honda Beat at 63hp to 200+hp. I'd be interested to see the math on that.

What tie down tension is it based on?

The loss calculation agorithm uses both speed and torque as inputs, so it will be different for a lower powered car.

Tiedown tension is basically common sense - enough to avoid wheelspin. The tiedown system has a leverage effect, so as the drive force increases so does the tyre-roller pressure.

We have experimented with measuring strap tension, hydraulic tiedowns, etc., but it's extra cost for little benefit.

[Mignon]

GregK2 said:

Thanks for the input so far, i'm about 30bhp disappointed, I ran the same dyno bone stock months before at 326BHP on Shoot 6F

I trust you've seen the other thread on the day of tests of the various shootout modes and found it interesting. Assuming your car is the 301 bhp version then 326 bhp in 6F mode would appear to be exactly the sort of over reading the software is programmed to generate. 8F would probably have given you 350 bhp.

[GregK2]

They all seem to perform better than quoted figures on various dyno graphs I have seen. Is the manufacturer figure based on the minimum grade fuel perhaps?

[Mignon]

GregK2 said:

They all seem to perform better than quoted figures on various dyno graphs I have seen. Is the manufacturer figure based on the minimum grade fuel perhaps?

No, it's just most rolling roads read high.

[GregK2]

Mignon said:

No, it's just most rolling roads read high.

I'm running the car again on the same dyno but in 6F in a few weeks time so will report back then. More interested in the difference in my figures than the actual numbers.

[Mignon]

The boost pressure curve on your engine must be interesting. I calculated it from the torque values.

[GregK2]

Mignon said:

The boost pressure curve on your engine must be interesting. I calculated it from the torque values.

Interesting in what way? Please elaborate i'm interested to hear.

[Mignon]

At low rpm it bangs straight up to over 1 bar then falls away to maybe 9 psi. If it stayed at 1 bar you'd have over 400 bhp. Presumably you have a boost gauge you can see this on?

[spitfire4v8]

GregK2 said:

They all seem to perform better than quoted figures on various dyno graphs I have seen. Is the manufacturer figure based on the minimum grade fuel perhaps?

What do BMW quote as the power output for a standard version of your car, and how does that compare to the power achieved in this graph for a standard car?

[GregK2]

301 bhp is the quoted figure from BMW.

[Mignon]

spitfire4v8 said:

What do BMW quote as the power output for a standard version of your car, and how does that compare to the power achieved in this graph for a standard car?

Seeing as we now know how much 6F over reads one presumes the standard car in that test really only had about 275 bhp.

[GregK2]

Mignon said:

The boost pressure curve on your engine must be interesting. I calculated it from the torque values.

I have a log I took myself if that helps?
https://datazap.me/u/gregk2/stage2?log=0&data=...

[Mignon]

GregK2 said:

I have a log I took myself if that helps?
https://datazap.me/u/gregk2/stage2?log=0&data=...

I don't think you were getting those boost levels at high rpm on the rollers. Maybe the ramp rate was too quick for it to spool up properly.

[spitfire4v8]

How big is the turbo that it can't spool up within many seconds of dyno run?

It's a funny old game.

Std car quoted at 301hp
dyno dynamics say 302 for a tested std car.
Mignon suggests 275hp is more realistic

there's a few conclusions all with their own merits staring us in the face

1 the std BMW really is around 300 hp and the dyno reports this with a close accuracy

or

2 BMW don't actually know how powerful their own engines are and made a number up (unlikely)

or

3 BMW are misleading their customers with their published figures, the car really is 275hp and the dyno just happens to give the BMW published number by fluke.

any other suggestions?


As an aside .. are there any motor manufacturers or engine tuners/builders who actually do publish accurate information ? You'd natually assume that BMW might publish accurate info, but I don't know. We'd all have thought VW would publish accurate emissions data but it seems you can't believe anything these days (allegedly)

It also begs the question why did the op's car run 326hp standard previously olso on a DD .. are people not doing the test properly? Or do BMW engines vary that much? (surely not) ..

grrrrr

Edited by spitfire4v8 on Thursday 15th November 13:14

[Mignon]

spitfire4v8 said:

Std car quoted at 301hp
dyno dynamics say 302 for a tested std car.
Mignon suggests 275hp is more realistic

Only on the basis of your tests of how much S6F seems to read above steady state. But who knows how that other dyno reads. I've seen Dasteks read differently and one that moved premises never read the same again after the move.

Looking at Rototest figures BMW seem to be accurate or even conservative in their power claims. They haven't tested the 135i but similar cars are certainly making the claimed numbers.

Edited by Mignon on Thursday 15th November 14:17

[PeterBurgess]

I think Dave is correct about BMW making more than claimed power, I think the same obtains to VAG. I believe in the past ( certainly in the 80s) tax was based on horsepower in Germany so it would seem the wheel power was quoted by the manufacturers or massaged. I am happy to be corrected if I am wrong about the tax based on bhp, twas many moons ago but explained why most cars wheel power seemed ok whereas VAG and BMW made at wheels what engine was quoted at.