davepl

He's got it. But I'd never dyno without RPM. You can usually do "tape on a drive belt with an optical trigger" if you get into a weird car.

Motor turns drum. Computer watches drum. Drum accelerates. Computer measures how much. Derives torque. Multiply by RPM. Divide by 5252. All done.

I read the linked articles by "F=ma" is a little pedantic. I went to a good school, didn't just fall out of a tree.

The biggest thing I can think of that would affect results in a different gear would be the rotational mass of the wheels. But even then, the Mustang or Dynojet no doubt has some assumption about wheel mass (they get accelerated with the drum, so act like drum mass). And actually the higher the gear (faster the drum) the more difference that'd make.

But if someone can fill in the blank, I'd read it:

"Being in 1:1 final drive matters because _________________ and that's different in every gear"

rflow306

Yeah, optical pick-up by using reflective tape on the engine Harmonic balancer. We use to have to do that on the older diesels in order to get a torque reading. Fun times, lol.

Back to the 1:1 recommendation, I always thought it was more to do with automatic transmissions which due to the torque converter show less slippage when 1:1 with the engine.

Mordeth

You select the gear that provides the most repeatable, testable set of data. This is the gear that allows the pull to occur over a long enough period of time to gather meaningful data, limit wheelspin and place enough load on the engine that replicates/represents actual usage. Additionally, you have to factor in the cooling capacity of the dyno. Many dyno facilities have inadequate cooling systems, which produces inaccurate results at higher speeds/loads/temperatures. So a lower gear should be used if cooling is inadequate (which it very commonly is).

I suppose one could argue over which gear is the most mechanically efficient as well. But that varies from car to car and ultimately can be taken into account.

PRE-Z06

Does post 11 below satisfy your blank that needs filling?
https://www.thenakedscientists.com/f...?topic=42746.0

Raced Guy

Regardless of therioes, trying to accurately Dyno and tune even a stock zo6 in first gear on the Dyno would be entertaining to watch to say the least. There are many factors and resdons that others have stated but it is a tuning tool more than anything. Myself just like others typically use the gear that gives the most repeatable accurate back to back results without ringing it's neck every pull when tuning. For instance a 2014 mustang I just did made 388whp base and 414whp within about 3 HP every pull once tuning was dialed in. Made 2 final pulls in 4th cool down, 2 in fifth. The later pulls in 5th resulted right at 423whp and 421. Do I nesceallirly care about the 9whp no, you can sit there all day and play Dyno tricks for 2hp. I'm most concerned about what the data logs say before anything and using the Dyno to verify changes. On the motorcycles we can go from 30psi to 60psi in the tire and see 2/5whp gain. Is it right or wrong doesn't really matter I like repeating the same procedures to keep all my data and results the same so everything I do can be used as a point reference and be realtively accurate at transferring over to similar vehicles. At the end of the day it's just a reference tool not a precision measuring device within .0001 hp

0Anthony @ LGMotorsports

That really doesn't matter much as with most of the laptop programs (EFI/HP Tuners), you can control converter lockup in any gear if you need to. With the newer 6spd and 8spd autos and the car in paddle shift mode they will hold and should have the converter locked above 25 mph if I remember right (sorry don't have my laptop in front of me)?

You get those odd ball drag cars with 4000-5000 stall converters and no lock up at all...those are some really odd graphs to look at because you might only see 4500-7000 RPM on the graph as the converter just spikes and away you go.

davepl

I agree, unless you had a MASSIVE roller that was really heavy and took a long time to accelerate. Then it'd be OK, wouldn't it? What you want is for it to take time.

I should be clear here before someone busts me on it that I'm only talking about intertial drum chassis dynos. There could be Eddy current or water-brake roller dynos too that I'd have to think about (and it's too early) before I made any claims about those...

davepl

Reply #11 reads "Have any gears been produced that incorperate rollers into the teeth it would seem to be a way to reduce sliding friction."

So no... can you paste or link to me whatever you're referring to?

Higgs Boson

the tune tables we have access to show the converter to lock at WOT but if you log the TCC slip would you say it is locked?

0Anthony @ LGMotorsports

From what I have seen in the past on other cars, there is always some amount of slip with them. I don't know if I have ever seen RPM variance as 0 on them. I am assuming you have seen the same?

Higgs Boson

yes, definitely, to me it seemed like it was unlocked at wot though on the 8 speed but I haven't looked at it since maybe May or so of last year.

I just assumed we were missing a table or two that revealed it unlocks at wot and moved on.

It's something I have been meaning to go back and play with but haven't had time and thought about it at the same time yet.

juanvaldez

So did the airplane take off on the treadmill?

PRE-Z06

Sorry post 10, the one above it.

X25

Apologies for replying to an old thread..

In order to 'apply' force, you need to find force to push back on you. Try to punch a feather in the air as powerful as you can; do you think you can use all your strength on it? You've likely used much less than you actually can, it was mostly caused by your inefficient arm quickly extending itself, not even the feather. Now try to hit a sandbag instead. Can you use all your punching strength/power on it? If you're an average human, you probably can.

Moving on, think about a bicycle. How much power can you apply to it on first gear? It probably just feels like it's free turning. What about a taller gear: can you now use more of your leg muscle strength to push that pedal down? I bet you can.

In short, in order to create Force, and in turn Power and ultimately Work, you need a counter force. When you rev your LT4 engine at neutral to 6000 RPMs, do you think you're generating 650 HP at the moment? You're not; you're actually only generating enough to win against all the frictional and other parasitic losses, which is very little... until you dump that clutch and create the push-back from driveline. This is actually why flywheel weight is critical to launch; it stores a big portion of the kinetic energy of revving engine.

Going back to the original question, you need engine load to make more power. The taller gears will allow you to do more work per unit time, thus increasing the push-back force, and engine load. If there is no load on the engine, you cannot make power. Of course, there is only so much power to generate by the engine, so at some point, gains will be minimal, even if there is more push back (potentially) available.

I hope this helps : )