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why would one be going through the gears during a dyno run?
It appears the guy with his foot on the pedal was not the owner. I wonder if that was not deliberate.
Looking at the slowmo when the 'driver' lifts off, there seems to be a harmonic "wave" devolop and go around the tire just before it lets go
It appears the guy with his foot on the pedal was not the owner. I wonder if that was not deliberate.
Looking at the slowmo when the 'driver' lifts off, there seems to be a harmonic "wave" devolop and go around the tire just before it lets go
deniscCaretaker of 8MA1244 '70 Euro Mangusta DRIVE THEM, THEY WERE MEANT TO BE DRIVEN, IF YOU WANT TO LOOK AT ONE, BUY A POSTER!
In the above case the tire blew. A few years back similar situation but the dyno blew, new car to the owner. There are several views.
https://m.youtube.com/watch?v=zfNq8uPIQ1k
https://m.youtube.com/watch?v=zfNq8uPIQ1k
quote:Originally posted by JFB #05177:
why would one be going through the gears during a dyno run?
I assume that with a chassis dynamometer, you'd want to be in a 1:1 gear in the transmission, and that this would be an upper gear.
To get there, you'd need to upshift.
Yup. I just found this: "Drivetrain losses vary according to gear selection (testing should usually be performed in the transmission's 1:1 gear to minimize this factor)"
http://www.hotrod.com/how-to/a...-chassis-dyno-guide/
Looked like they were doing a Top MPH run, not a HP run. They said it was over 150MPH when he backed off the throttle and the tire blew.
Jeff
Jeff
Originally posted by JFB #05177:
why would one be going through the gears during a dyno run?
To read correctly, a chassis dyno must be at 1:1 input to output through the tranny. A ZF trnsaxle does not HAVE a 1:1 relationship between input & output. The operator may have been searching around for the closest approximation- which in a ZF is 3rd gear at 1.04:1.
Running at other than 1:1 gives different power readings. I once asked the Mallory dyno operator to verify this on Judy's Z-28, using 3rd and then 4th gear (auto tranny) only a minute apart. Sure enough, all the horsepower numbers were different in the two gears. In newer dynos, there may be a software factor to tune this effect out, but there's a LOT of older dynos around....
Of course, using any dyno as it is meant to be used- as a comparative tool in tuning- the actual numbers don't matter. What's important is the % varience from one run to another while changing something in the engine.
why would one be going through the gears during a dyno run?
To read correctly, a chassis dyno must be at 1:1 input to output through the tranny. A ZF trnsaxle does not HAVE a 1:1 relationship between input & output. The operator may have been searching around for the closest approximation- which in a ZF is 3rd gear at 1.04:1.
Running at other than 1:1 gives different power readings. I once asked the Mallory dyno operator to verify this on Judy's Z-28, using 3rd and then 4th gear (auto tranny) only a minute apart. Sure enough, all the horsepower numbers were different in the two gears. In newer dynos, there may be a software factor to tune this effect out, but there's a LOT of older dynos around....
Of course, using any dyno as it is meant to be used- as a comparative tool in tuning- the actual numbers don't matter. What's important is the % varience from one run to another while changing something in the engine.
My understanding is that "1:1" gears in many transmissions are "straight through" (i.e. the power path does not not go through any gears.
From Wikipedia: https://en.wikipedia.org/wiki/...ansmission#Internals
"In a rear-wheel-drive transmission, the input and output shaft lie along the same line, and may in fact be combined into a single shaft within the transmission. This single shaft is called a mainshaft. The input and output ends of this combined shaft rotate independently, at different speeds, which is possible because one piece slides into a hollow bore in the other piece, where it is supported by a bearing. Sometimes the term mainshaft refers to just the input shaft or just the output shaft, rather than the entire assembly.
In many transmissions the input and output components of the mainshaft can be locked together to create a 1:1 gear ratio, causing the power flow to bypass the countershaft. The mainshaft then behaves like a single, solid shaft: a situation referred to as direct drive."
A few % of the transmitted power is lost every time it goes through a set of gears.
The ZF has no straight through path and thus is always going through at least 1 pair of gears and thus is loosing a few percent of power compared to a "1:1" gear box.
From Wikipedia: https://en.wikipedia.org/wiki/...ansmission#Internals
"In a rear-wheel-drive transmission, the input and output shaft lie along the same line, and may in fact be combined into a single shaft within the transmission. This single shaft is called a mainshaft. The input and output ends of this combined shaft rotate independently, at different speeds, which is possible because one piece slides into a hollow bore in the other piece, where it is supported by a bearing. Sometimes the term mainshaft refers to just the input shaft or just the output shaft, rather than the entire assembly.
In many transmissions the input and output components of the mainshaft can be locked together to create a 1:1 gear ratio, causing the power flow to bypass the countershaft. The mainshaft then behaves like a single, solid shaft: a situation referred to as direct drive."
A few % of the transmitted power is lost every time it goes through a set of gears.
The ZF has no straight through path and thus is always going through at least 1 pair of gears and thus is loosing a few percent of power compared to a "1:1" gear box.
All engines are connected to the tires via a gear reduction, even in a 1:1 transmission situation, due to the ring & pinion. Tires never turn the same speed as the engine. In a performance car the "final" ratio is usually between 3:1 to 4:1, even in overdrive.
A chassis dyno is far more honest than an engine dyno in terms of determining a vehicle's ultimate performance because it relates to you what the car is capable of putting to the ground, via the drive train and tires (track testing at the hands of a skilled driver is even better). But, thanks to the aftermarket, the motoring world is dyno crazy.
Which do you think is better, a 400 horsepower engine connected to the road via Pirelli P Zero tires, or a 600 horsepower engine connected to the road via BF Goodrich TA radials?
A chassis dyno is far more honest than an engine dyno in terms of determining a vehicle's ultimate performance because it relates to you what the car is capable of putting to the ground, via the drive train and tires (track testing at the hands of a skilled driver is even better). But, thanks to the aftermarket, the motoring world is dyno crazy.
Which do you think is better, a 400 horsepower engine connected to the road via Pirelli P Zero tires, or a 600 horsepower engine connected to the road via BF Goodrich TA radials?
That was ugly, when we put my stang on the dyno I say inside we had to get to 5th gear, with the speed limiter off we crossed 150 also glad my tires held. So it is not unusual.
Trying to do a speed run on a dyno is a really bad idea (obviously) and in my opinion utterly pointless. A round roller cannot begin to simulate driving on a road and often the cars will be strapped so that there is more downward force for traction. This in itself increases the loading on the tire. The round roller causes more tire deflection which causes more heat. Our dyno actually had a safety that would only allow 120 mph. If that was exceeded the dyno would apply the brake and you would have to come to a complete stop before it would allow another run. Even at those Speeds I have personally witnessed a tire failure. This was on an extreme HP drag bike with softer tire compound. There was still rubber embedded in the ceiling tiles when we tore out the cell. Moral of the story is only run a gear high enough to maintain traction and keep the run length to a reasonable amount of time as well as allowing cooling time between runs.
While all of that is valid, I think it also depends greatly on the dyno itself. A friend of mine had one installed, back when they were developing and racing his SSZ Stradale's, that reportedly handles 1000hp and 200mph. Even the rollers on it are much larger than those in most dynos. (I've never seen it in action though.)
But I don't doubt the danger. His is in it's own sturdy compartment, separate from the rest of the shop spaces.
But I don't doubt the danger. His is in it's own sturdy compartment, separate from the rest of the shop spaces.