Car and Driver article on chassis dynos, clearly not the best way to measure HP.
#1
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Car and Driver article on chassis dynos, clearly not the best way to measure HP.
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
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
#3
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
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
#4
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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.
#5
Re: Car and Driver article on chassis dynos, clearly not the best way to measure HP.
Originally posted by GoRideSno
[BThis article certianly supports my belief that what really matters is timed acceleration with weight factored.[/B]
[BThis article certianly supports my belief that what really matters is timed acceleration with weight factored.[/B]
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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.
#7
Three Wheelin'
Re: Car and Driver article on chassis dynos, clearly not the best way to measure HP.
Originally posted by GoRideSno
I wonder how smart the LH Jetronic is?
I wonder how smart the LH Jetronic is?
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#8
Nordschleife Master
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.
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.
#10
Originally posted by 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.
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.
#11
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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
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
#12
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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
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
Originally posted by Sterling
you can also make instant gains by adjusting the altitude setting...
you can also make instant gains by adjusting the altitude setting...
#13
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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?
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?
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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...
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...