GoRideSno

This is a link to a Car and Driver article about the measure of HP on a chassis dyno v/s actual real-world conditions.

I wonder how smart the LH Jetronic is?

This article certianly supports my belief that what really matters is timed acceleration with weight factored.

I'll still probably go to the dyno next week since I put an Autorotor and the big IC on my car tonight.

POC short track series tomorrow.



Andy K

slate blue

Go Andy, now to break 4 seconds!

2V4V

Andy,

I read that one too, but don't worry, LH is a stone axe compared to the versions of Motronic referenced in that article. Not bad for its age mind you, but definately does not have ANY of the functionalities that will bring a car 'down' on a chassis dyno - save for some temp stuff that goes without saying.

As a sidebar, if anybody is getting dyno'd at a shop that does not have a 36"+jumbodeluxe fan that creates a BIG wind on the front of your car - leave. Go find a real shop that has a fan and a clue.

Good luck on the speed quest...

Greg

mspiegle

Good find. And not all dynos are even the same, different manufacturers compute things a little differently... providing even more VARIABLES. If the dyno machine could compensate for the size of the cooling fan used - but i'd imagine that to be next to impossible. Wow... MORE VARIABLES.

SteveM928

Yes, just factor in weight, temperature, humidity, barometric pressure, altitude, wind, staging technique, tire traction, track surface condition, driver skill, gearing, track's timing method, launch technique, front tire size, rear tire size, weight distribution, aerodynamic drag, ...

mspiegle

Almost 1/2 of those reasons still apply to chassis dyno, and if not, there are other factors (some in that article, some not) that will further discredit the chassis dyno.

Lagavulin

It's not; it's probably the same computer Fred Flintstone has in his car. The only 'smart detuning' it's capable of is through the knock-sensor circuitry. Other than that, you have nothing to worry about with regards to the Bosch LH2.3 stealing/hiding horsepower.

GlenL

I thought the article was a typical puff piece for an advertiser. "Look at how complex this is. It must be worth Big, Big money!" Made me wonder if the author really understood the subject matter.

Chassis dynos are really good at making comparisons between runs on a single vehicle. Using the same dyno on consecutive runs will show the effects of tuning changes. But, only in the operating condition of the dyno which models acceleration of a typical car's weight but not increasing wind resistance.

Then there's the issue of fudge factors. Different brands of dynos give different numbers. I believe that Mustangs are lower than Dynojets.

If you want to test, say, cooling capacity at 150mph, forget a chassis dyno. No good for fuel economy either.

Brent 89-GT

Glen has it right. Use a chassis dyno to benchmark your car and your mods. Comparisons for bench racing do not work.

SteveM928

Weight doesn't matter on the dyno. Temperature, humidity, and barometric pressure are continually measured and corrected for by a dyno. Altitude is part of the initial dyno installation and is corrected for. Traction generally isnt a factor on a dyno until you start to usually get to around 1,000 rwhp. Driver skill plays no part in dyno readings. Even if "almost half of those reasons" did still apply to the dyno, it would make it FAR more consistent and repeatable than drag strip results, and a much more viable method for making comparsons between different cars in different locations and on different days.

mark kibort

dyno jet is real life (or as close as possible) it factors out inertial losses and other variables as the rate of accleration is fairly slow. (ie 6-8 secs for a run) over that period of time, you only see rolling and trans. losses.

the fan thing is important for the higher end motronic cars, while as was said, its not a big deal for the LJjet. my dyno rus on different dynos have all been pretty repeatable and close to the same HP with no changes. (and adjusted for different day conditions) brake dynos build up more heat and will allow fans to make more of a factor.

mk

mark kibort

but, that should be compensated by the SAE conversion.

if you want to cheat, you can cheat any number of ways.

if the dyno run has actual and SAE numbers, you can tell a lot and its very accurate/repeatable.

mk

Tony

heres a way to cheat.
On a dynojet I ran in 2nd gear and got 270ish ftlbs....then ran in 3rd and got 303 ftlbs..

So whats the standard for an AUTO? 2nd grear pull or 3rd?

I assume 2nd gear as those are the numbers mine seems to compare to most often?

ViribusUnits

Did you use the correct gearing ratio when figureing your real numbers?

If not, your just fooling yourself anyways.

John..

As I have said all along, the dynojet does not duplicate real world load conditions. The corrections factors can change the readings. What matters is where rubber meets the road and how the car drives and feels with the modifications. It is really about performance to the road, not to the rollers. I know for a fact that the Callaway can put more power to the road than is depicted on the dynojet, considering boost levels there and ambient cooling air to the front mount intercooler. A squirrel cage fan can't duplicate the CFM of air available to my A/A intercooler at 80+MPH and that is a fact.

I'm considering running the new twin turbo on a load dyno and skipping the dynojet. It would allow for a better tune and heavier loads on the engine, more like the real world. I don't really care about the end numbers, it is all about real world performance, not a 10 second inertia dyno pull.

Yes, I am still building the car...