Rules for 2013 - Crank power vs Dyno

[WillM]

Here's another useful equation:

Dave's post + Chris' post + Nick's post = reason I love this place!

Hope you feel better soon Chris!

NickParlands...<chuckle>

[brucesallen]

Earlier Dan B wrote that a dyno does not measure wheel torque as you described earlier. This engineer replied to say that their machine does measure wheel torque. (which you have been denying from what I can understand) I'm sure something's getting lost in people's concept of wheel torque.

Dynapack requires the removal of the wheels and therefore maybe measures "hub torque?" Not sure.

Our dyno isn't a friction dyno either it's an eddy current retarder, magnetic.

The result of this arguing is that there is effectively no way to agree on measuring power to create rules. It's pretty clear that no one will agree.

Alex,
Dan and I understand that the chassis dyno measures the wheel torque. What we are saying as is the dynapack rep, is that the torque on your printouts is calculated crankshaft torque according to: Wheel torque X wheel rpm / engine rpm. Wheel rpm / Engine rpm is in the range of .33 to .25 with the trans in 1:1 gear. It is the diff gear ratio.

[WillM]

My observation.

If we are not requiring dyno plots, then this entire discussion is academic.

Likewise, if we are not requiring dyno plots, perhaps we should use a different metric than power to weight.

[dtlemoine]

If we are not requiring dyno plots, then this entire discussion is academic.

Likewise, if we are not requiring dyno plots, perhaps we should use a different metric than power to weight.

I think something that needs to be explored and tested a bit further is the use of a GPS datalogger & corresponding PC analysis software to estimate horsepower.

The following forum post has a calculation that can convert the values from the data logger into estimated wheel HP: http://www.racelogic.co.uk/Forum/archiv ... t-935.html

The AIM Solo is a logger that a whole host of folks in this club use, is relatively inexpensive ($400) and comes with software that allows the calculation in the link above to be automatically overlaid every 1/10th of a second. Find a nice flat straightaway at each track, and you have an easy way to estimate horsepower. Maybe a few members who have recent dyno plots could help us confirm the level of accuracy?

If the rule change proposal passes this year (and I hope it does, the NickParlands have put in an unbelievable amount of effort and thought into making it "work") maybe the club could consider purchasing 1 or 2 AIM solos that could be placed in a competitors car for a few laps to help them estimate their HP if they don't know it, or could be used in case of a protest.

[Chrispy]

As I see it there are 3 basic ways of trying to classify power potential that I've seen kicked around in our existing classing systems and systems used by other clubs.

1. Cylinder count - Currently used for our SP/P classes
2. Displacement - Some FIA/BTCC/WTCC
3. Power to Weight - Our own ST/SS classes, NASA, CASC, under consideration by BMW CCA.

Option 1 seems simple enough, but the power variance within a class has the potential to be huge. You can have a 120hp Miata against a 200+hp car of the same weight. Advantage, easy to enforce with a quick check under the hood (unless they are hiding an extra engine in the trunk).

Option 2 only seems to be used in racing organisations that have high budgets, and even then they usually end up having to add additional restrictions such as max HP/torque, air intake restrictor plates etc. A theoretical 5.0L+ class could have engine power ranging from 190 to 500+hp. It is also difficult to enforce, since many base engines have similar block dimensions with a large range of displacements. Over-bore/stroke can also increase displacement by up to 20% without any visual cues.

Option 3 seems the most logical, progressive approach provided you have enough class granularity such that the per class ratio range doesn't generate hugely disparate lap times. Data logging seems like it might be viable low cost way of verifying or even generating the required information. I have the software mentioned by Dave but had no idea this feature existed (not mentioned in the manual) so I will try it out.

[dradernh]

Maybe a few members who have recent dyno plots could help us confirm the level of accuracy?

I have recent plots showing a range of HP from 284 on a Dyno Dynamics at Dent Sport Garage in Norwood to 308 on a Dynojet 224X at ICS in Stamford. Do you think one or all would be needed to provide data points useful in confirming the accuracy of this approach?

[WillM]

SCCA uses displacement in national and regional classes. STO, STU, SPO, SPU.

Companies that make GPS loggers like to tout their ability to measure 'horsepower', but the functionality, accuracy, and usability leave a lot to be desired.

I have a Race Technology data logger. Unlike most in the industry, R-T is among the few which manufacture tools for OEM supplier. The point being that their products are very robust.

That said, the logger's ability to estimate power depends on careful setup and calibration. You could never just plug it in and go.

The Analysis software must be configured with at least the following information:

1. Precise accelerometer offsets.
2. coefficient of drag (aero) or Cda
3. rolling resistance
4. Weight of car
5. rolling circumference of tires
6. gear ratios & final drive

The first two are required to remove drag from the equation, and small changes to these numbers create huge differences in the outcome. In other words, having accurate information is mandatory.

To determine the actual coefficient of friction and rolling resistance, a series of tests can be run, and their data fed into the Analysis system to determine. These are called 'coast down' tests. An ideal coast down test would be to accelerate to 100 MPH, and allow the car to decelerate on its own to 20 MPH. The test needs to be run on the same strip of pavement and in both directions to account for elevation changes and wind speed and pattern. Running in all 4 ways would be better.

I am a big fan of data and have invested an incredible amount of time into learning how to decipher data and put it to practical use. Though I have done coast down tests and spent an inordinate amount of time to on setup, after years and years, I have yet to extract any meaningful power measurement from the tools I have.

There are already many factors involved when trying to accurately measure power on a dyno, and in IMHO, the variables grow exponentially when trying to do the same on a road course and relying on accelerometer and GPS data.

It is not practical in the least. You would easily spend an entire event, all day long, both days, and still not get one car done accurately.

[dtlemoine]

Maybe a few members who have recent dyno plots could help us confirm the level of accuracy?

I have recent plots showing a range of HP from 284 on a Dyno Dynamics at Dent Sport Garage in Norwood to 308 on a Dynojet 224X at ICS in Stamford. Do you think one or all would be needed to provide data points useful in confirming the accuracy of this approach?

Hey Doug - in addition to your dyno plots, do you have a datalogger that is capable of measuring longitudinal G's? I can send you steps to build the equation over the data to see if the numbers add up.

If we assume the multipliers that CASC uses to be accurate (found on page 36: http://www.casc.on.ca/sites/default/fil ... es_net.pdf) the DSG dyno gives you 356.8 at the wheels, and ICS gives 360.2. Those numbers are very close (less than 1%) and I think could go a long way in helping us "equalize" results from different dynos.

If we could take it a step further to compare to the data logger's results, we might have a good first data point to help the cause.

[brucesallen]

And, since we use both horsepower and torque to classify cars, engine crankshaft torque can be easily derived from the Data Logger horsepower knowing engine RPM. BTW: at 5250 rpm, torque = hp in any car. If your car makes peak hp at 10,500 then torque is half of peak hp. My old rotary Greased Shadow bridge ported '89 RX7 made that rpm--- but it was past the hp peak of 9,000.

[Chrispy]

Will, everything you said is complete true in order to get a highly accurate measurement and your car probably has the most data acquisition features of anyone in the club. For a estimate only however you can ignore things such as rolling resistance, aero drag (just sample at lower speed). We're not trying to put things into orbit here, just get numbers that are within a reasonable range. The results I've been calculating so far are with a 15% margin of dyno results. So far just an experiment.

[austaz]

I've been running some HP analysis using the AIM system for my log files.

Based on trying to get around 10% accuracy :
Calibration of longitudal acceleration is critical + it seems a true accelaromter is needed, the gps one gives less accurate results.
cd factor and frontal surface area did not make that much difference to my results using data logs that ran up to 115mph.
weight makes a difference but small changes (50lbs each way) didn't do too much.
A run on the straight is ideal but the system returned good data for my logs using the entire track (mosport, NHMS, summit point).
If you want torque numbers you need a RPM input which can be hard to get, my system used a sensor on the ignition, the new Solo units use a ECU connection but that doesn't work for older ECU's or these strange old cars with distributors ...

From the data I saw this could never be a tuning tool, but could work to get +/-5-10% numbers but more testing is needed around calibration to make sure, and we need to decide if this is accurate enough.

[brucesallen]

with data logger, if it displays hp while driving, one could note the peak hp rpm on tach. Oh, wait, peak torque is probably lower rpm.

If you are plotting manually you could manually create an RPM curve and then a torque curve. Not too handy.

[dradernh]

Hey Doug - in addition to your dyno plots, do you have a datalogger that is capable of measuring longitudinal G's? I can send you steps to build the equation over the data to see if the numbers add up.

If we assume the multipliers that CASC uses to be accurate (found on page 36: http://www.casc.on.ca/sites/default/fil ... es_net.pdf) the DSG dyno gives you 356.8 at the wheels, and ICS gives 360.2. Those numbers are very close (less than 1%) and I think could go a long way in helping us "equalize" results from different dynos.

If we could take it a step further to compare to the data logger's results, we might have a good first data point to help the cause.

I do, so send away. In the meantime, I'll read the relevant portions of the CASC document.

[Flame Suit = ON]

We're into this minutiae because requiring a dyno plot isn't part of the program. Maybe it should be. I mean, Will's points should be eye-opening if you're not familiar with this stuff. So, for example:

1 - Require a dyno plot where necessary (for everyone? only for certain classes? (note: I don't have the proposed ruleset in my head, except as it relates to the Super classes, so I'm not sure where all this notion would best be applied)),
2 - Make it the same dyno in all cases (i.e., everyone has to use the same dyno at the same shop, ideally run by the same operator; failing that, fall back to something like the NASA model*), and
3 - Don't forget to ask for a volume discount!

If this seems like a great idea (lol), I suggest Dent Sport Garage, if only because you're likely to have so much fun getting your car in there when you arrive with it in/on a trailer for the first time. Seriously, DSG is fairly central for most of us and, with employees already associated with the club, they may be willing to reduce their normal fees due to the number of cars. Also, I've been persuaded by other members' comments that Matt is a very capable tuner/operator. I certainly had that impression during my test session on the Dyno Dynamics unit in September.

* ...dynamometer tests must be conducted on a Dynojet Model 248 or 224 for front and rear wheel drive vehicles, and on a Dynojet, Mustang, Dyno Dynamics, or Dynapack for AWD cars, in a
commercial facility that offers dynamometer testing as part of their business and is open to the public. All (AWD) Dyno test results using a Mustang or Dyno Dynamics dynamometer will have 10% added to the maximum horsepower reading to obtain the number that will be used to calculate the “Adjusted” Weight/Power ratio (Mustang/Dyno Dynamics Dyno awhp x 1.1 = Maximum awhp for wt/hp calculation).

[WillM]

So, assuming that dyno plots are not mandatory, and using technology to create an approximation of 'power' is acceptable, given an agreed-upon range of error (10%, 15%?).

Is there a 10-15% acceptable range of error when stating a vehicle's weight?

If not, why the double-standard?

[dradernh]

If we assume the multipliers that CASC uses to be accurate (found on page 36: http://www.casc.on.ca/sites/default/fil ... es_net.pdf) the DSG dyno gives you 356.8 at the wheels, and ICS gives 360.2. Those numbers are very close (less than 1%) and I think could go a long way in helping us "equalize" results from different dynos.

I looked over the CASC calculation & came up with the following using four of my car's dyno sessions.

First, the text describing CASC's conversion calculation:

CASC Wheel-to-Crank HP Conversions

Instructions: To convert wheel horsepower to crank horsepower (which is then
substituted into the classification spreadsheet in order to determine your
vehicleʼs new Starting PI), divide your peak or maximum wheel horsepower
value as measured on the dyno by the value below that matches the dyno
type used and the drivetrain configuration of your vehicle.

Drivetrain
Dyno type FWD RWD AWD

DynoJet (inertia dyno) 0.865 0.855 0.845
Mustang (eddy current dyno) 0.840 0.830 0.820
DynaPack (hub dyno) 0.870 0.865 0.860
Dyno Dynamics 0.769 0.769 0.769

----------

Example: D. Rader's RWD E36 M3

DynoJet 224X 308 HP / 0.855 = 360 HP I never took this pull seriously
DynoJet 224X 295 HP / 0.855 = 345 HP This is a good pull taken at ISC
DynaPack 285 HP / 0.865 = 329 HP Pull performed prior to adding headers & CAI, and prior to the other three pulls, which I consider to have added a maximum of 10 RWHP
Dyno Dynamics 284 HP / 0.769 = 369 HP Recent pull at DSG

If you add 10 HP to the DynaPack's RWHP (my estimate for the increase in RWHP due to the added headers & CAI), the three good pulls come in within 8% of one another after applying CASC's conversion factor.