Are you supposed to do 150 mph on a dyno?

Re: requirements, I suppose there's something to the reduction in parasitic losses, but I think the constraints fall into two categories:

Data: The car needs to run at WOT from whatever minimum RPM is useful to the maximum RPM useful. I'm not sure whether there are issues related to A) data resolution if the sweep is too quick, or (and this feels goofy) whether you might actually see different conditions depending on how quickly the engine's revving (can the fuel pump keep up on a quick sweep but not a more sustained one? With more time at each speed, would you get a better look at points bounce or something?)

Functional constraints: A) The lower the gear the run is done in, the greater the forces at the contact patch at any given power level; traction is probably a limit on the drum for many vehicles. B) constraints of the brake mechanism; assuming it can handle the net power, does it have limits in terms of speed? (I imagine an eddy current brake is less effective below some drum speed) Or limits in terms of force? (so you'd have to run it faster/in a higher gear)

Given the traction limits of a metal drum, I suspect that the other gears being less strong than a direct gear isn't too much of a factor for the occasional pull. OTOH I don't drive a Veyron-class car that probably can't put WOT to the ground below fourth...

One thing to see in what there is of the slow mo- you could see the back of the car and the tires oscillating. Can't tell which caused the other to do that, but between the heat and that- the system "rang"- so the tires blew. Much like the Tacoma Narrows bridge.

I've only been on one dyno ever so I don't have much to bring to this but the gentleman running it did all pulls in second gear. He said that higher gear pulls would show a higher hp number but weren't really useful and risked carnage like this. I'm thinking I'll stick with that.

Ransom wrote: Data: The car needs to run at WOT from whatever minimum RPM is useful to the maximum RPM useful. I'm not sure whether there are issues related to A) data resolution if the sweep is too quick, or (and this feels goofy) whether you might actually see different conditions depending on how quickly the engine's revving (can the fuel pump keep up on a quick sweep but not a more sustained one? With more time at each speed, would you get a better look at points bounce or something?) Functional constraints: A) The lower the gear the run is done in, the greater the forces at the contact patch at any given power level; traction is probably a limit on the drum for many vehicles. B) constraints of the brake mechanism; assuming it can handle the net power, does it have limits in terms of speed? (I imagine an eddy current brake is less effective below some drum speed) Or limits in terms of force? (so you'd have to run it faster/in a higher gear)

If it's a turbo car then the rate at which the RPM increases has a significant effect on the output, because it takes time for the turbine wheel to accelerate. A dyno run in 3rd will show a lot later turbo spool than one in 5th, for example.

If you're tuning the car (as opposed to simply doing a baseline pull for bragging rights), then there are other advantages. A longer pull means more time spent in each individual cell, so you get more time to figure out what it's doing there and how to tune it better. Also, engines on dynos heat soak differently than engines on the street, a slower ramp means you get a better reading on how much timing can be run without pinging.

The best dyno for tuning is a load-holding dyno that bolts to the hub, like a DynaPack. It avoids all of the tire concerns as well. :)

The dyno in the video looks like a DynoJet, which is an inertial dyno. The motor spins the big, heavy drum up for the dyno run, then you put the car in neutral and use the dyno brake (apparently it's a brake drum designed for a train) to slow it down. These kinds of dynos store a LOT of energy. But yes, all of the dyno components have a maximum speed you can run them at (for DynoJets I think it's 200 mph drum speed)

As for the tire failure, I don't think the dyno was to blame. Taking the car up to 150 on the street would probably have made it fail too, and would likely have involved a lot more damage than this. You could argue the owner got off lucky.

pointofdeparture wrote: What kind of moron runs through a high gear like that on a dyno? What does that even prove? Isn't third sufficient?

We had a project that had to be run on the dyno in 2nd gear because 3rd gear (1:1) was pushing past 140mph and they didn't feel safe running 37" tires that fast.

Looking at the video again, I see it's a DynoCom, so ignore my comments re: DynoJets. :)

I have a feeling there was excessive heat buildup in the rollers and therefore the tires. Add the extra load of strapping it down and going 140mph = BOOM.

Looking at the wheels... it wouldn't surprise me to see "H" rated tires

^plus 10^
I can't count how many cars I've seen with built motors, essentially hot rodded with cheap all season tires.
Benefit of that is burn outs are easier.

I watched this week's episode of Jay Leno's show. He was at John Hennessey's shop in Texas, and they ran a Mustang on a dyno up to 190mph.

You want to dyno a car in a 1:1 gear, usually 4th on a 5-speed or 5th on a 6-speed. The 1:1 gear is generally straight through -- input and output shafts are locked together with no gearing taking place. This means it's the strongest gear and also typically has the least frictional losses.

Yep, and the two deeply ironic things about it are that A: no transverse trans works like that, which is probably half or more of all dyno pulls, and B: that still doesnt stop people from WILDLY inflating their made-up driveline loss numbers. Just imagine, if they ran in 3rd they'd have 35% loss instead of 25% loss!

In reply to Vigo:

I can think of a lot of transverse transmissions that are "straight through" in a given gear. Mind you, they are all automatics, but I can think of a lot of them!

wlkelley3 wrote: ^plus 10^ I can't count how many cars I've seen with built motors, essentially hot rodded with cheap all season tires. Benefit of that is burn outs are easier.

Ha, on the opposite end of the spectrum, I have W-rated UHP-AS on my stock civic

wlkelley3 wrote: ^plus 10^ I can't count how many cars I've seen with built motors, essentially hot rodded with cheap all season tires. Benefit of that is burn outs are cheaper.

Went to a dyno day Saturday. My 55 Chevy 2 door wagon hit 110MPH at the top of 3rd, which is 1:1 on a 700r4. It has a 406 with fuel injection, a mild roller cam, headers, etc and did 300hp/323TQ to the wheels, which is less than I expected.

We had a pretty mild c6 ZR1 there that did 744HP and I think 712tq.....that car was incredible. At the top of 4th he was close to 150mph on the dyno.

There was a Camaro ZL1 there that was also low 700s on the dyno and hit similar speeds.

I can think of a lot of transverse transmissions that are "straight through" in a given gear. Mind you, they are all automatics, but I can think of a lot of them!

Unlike some rwd manuals, there are precisely ZERO transverse transaxles where power goes from torque converter to CV axle without moving across gears or chains to a parallel shaft (usually twice). And, if you're willing to make exception for moving across gears to a parallel shaft, you're implicitly throwing out the supposed 'advantage' of drivetrain loss of a RWD manual in 1:1 gear. And the funny thing is, FWD cars have less drivetrain loss than RWDs, in spite of their incessantly shaft-hopping power flows.

Vigo wrote:

I can think of a lot of transverse transmissions that are "straight through" in a given gear. Mind you, they are all automatics, but I can think of a lot of them!

Unlike some rwd manuals, there are precisely ZERO transverse transaxles where power goes from torque converter to CV axle without moving across gears or chains to a parallel shaft (usually twice). And, if you're willing to make exception for moving across gears to a parallel shaft, you're implicitly throwing out the supposed 'advantage' of drivetrain loss of a RWD manual in 1:1 gear. And the funny thing is, FWD cars have less drivetrain loss than RWDs, in spite of their incessantly shaft-hopping power flows.

Huh? I don't think the question was about drivetrain losses and efficiency -- it was about what gear you dyno a car in, and the resulting top speed of the wheels.

And yes, it's the fact that you don't need to turn any right angles that makes transverse 2wd drivetrains more efficient than longitudinal ones. (AWD you have 2 right angles in either case)