[GTS 5.7]

OK-so it measures torque,then calculates horsepower-we got that.....but the question still remains...is there a value entered into the computer that tells it what gear is in the car AND if the wrong value(say-3.08) was entered instead of the correct value(say-2.73) is the dyno chart right for the car.............and if not,which way is it off and by about how much?

A key word Kyle used-CALCULATE....gotta have values to calcluate with to get the end number,right?

[tripleblack]

A lot depends on what kind of dyno was being used. A Dynojet (or any other inertia type dyno) is not reliant on mathematical estimates of gearing or measurements of the "brake type" dynos that measure the amount of power absorbed by the water, oil or eddy current brake system.

Assuming it was an inertia type dyno, the dyno is measuring the work being produced by the wheels of the cars acting directly on the two large drums. The computer is detecting how fast the drums accelerate from a full stop.

This type of dyno uses the simple Force = Mass x Acceleration formula. It then renders a horsepower number based upon the old HP = RPM x Torque/5252 formula.

In reviewing this, there's not doubt that gearing plays a critical part in producing whatever comes out the rear tires (gears do multiply torque), but I don't see where the gearing would "fool" the dyno - the dyno simply detects how fast the drums rotate.

If the idea is to take the dyno results and create a facsimile of a quarter mile run or estimate what that power will produce in terms of elapsed times, then accurate gear numbers are CRITICAL for those computations.

But the dyno will tell you the power output regardless.

Now, a brake type dyno often utilizes a lot of variable math inputs to arrive at the result (its reading power in a more indirect fashion), but I still believe it would also not be fooled unless part of the data input included gearing (which again, might be the case if mph or even gas mileage estimates were being generated).

I've got a grok ache from all this, but I think this makes sense.

Some other handy formulas to use in this process:

Work = Force (or torque) x Distance

Power = Work / Time

Torque is a rotational force.

[GTS 5.7]

I quit...I'll wait til I get it all done and try (harder) to get back to them

[Kyle F]

Sorry guys, I am a mechanical engineer by degree...So, this is the stuff I live for. As for fooling the dyno... sure you can... adjust the parameters. All dynos have to correct for temp and pressure to get an accurate (Standard) reading. You know, SAE corrected TQ and HP.

A good dyno operator can get you an accurate number... a Great Dyno operator can get a car to produce any number he wants.

[GTS 5.7]

OK,OK..so I can't quit.Even if there is no variable to allow for gearing(and there is probably not,since the dyno measure at the wheel) then I still think the power that gets to the wheel would be more/qucker with a 3.73 than a 2.73.BUT when it peaks,it wouldn't matter what gears there were because all it's got is all it's got.Gearing,like has been pointed out only accelerates the process.

Posting that...key word accelerates..you guys that said no to the original question are right...the gears would accelerate through the RPM range quicker-not put more power to the wheel,and a dyno reading force(torque) would still have the same numbers to plug into the formula of
HP= RPM X torque / 5252
SO,no gears will not affect the end number,just how fast you get through the rpm range,right Kyle?
Forgive me,I'm just an old country boy and sometimes it takes me a while

[GTS 5.7]

now I'm done...

[downsideup09]

no... 3.73's is an actual bigger gear as in it has to spin more to get the wheels going just as fast one whole revolion more than 2.73's multiple this by several hundred RPM it adds up this creates more friction and more heat and more friction and more heat = more horsepower loss

[Kyle F]

Yes, but the 3.73 is still multiplying the available Torque more to the wheels at a given RPM... so you have more Torque which would equal more HP... but you would have a slightly larger drive line loss. So, when the variable is accounted for they are not accounting for the added drive line loss. Thus.. all things being equal and accounted for a Higher numerical gear will show less power and torque... but only if its calculate out to be a true 1:1 ratio. Like an Engine dyno.

[tripleblack]

The inertia dyno works on the Force = Mass x Acceleration formula. (So do the brake dynos, but more indirectly).

Force (torque) is created when the 2700 pound drums are rotated, and the computation would be F = 5400 x Acceleration (2 drums of course).

As the drums move from rest, the sensors measure the speed of the rotation, which plugs into the formula as "acceleration", ie, so many rotations per minute (rpm).

The dyno neither asks nor needs to be told what gears are in the car spinning the drums (or how much they are multiplying torque, or how much mechanical inefficiency is created by this gear set or that type of gear lube, etc.) It just reads what speed its sensors tell it the big round drums are spinning at, over what period of time.

Given this result, it can compute how much torque has been created (directly - it doesn't need to know anything more about the car) - and with other formulas tell you how much horsepower has been created.

NOW, to match the RPM's of the drums to the rpms being turned by the gear set in the car (which of course, due to mechanical losses, will never be the number of RPM's actually being turned by the crankshaft unless you're using an engine dyno, which is not what we've been discussing here), THAT is where the dyno would need to be told the correct numbers. This would distort the chart on one side (the rpm side), but would not create wrong top numbers, just wrong numbers at a given rpm.

The shape of the curves would also be distorted by this (as pointed out earlier).

You would know the maximum numbers generated during the run - but the chart would be useless for much else.

If they saved the run and you later went back and had them plug in the correct numbers, you should be able to get a good chart.

[Joes 5.0]

I just have to say this is an awsome post with lots of great info, and I cant really say anything that someone hasnt allready said, but ill say it anyways. The gearing in the differential, and tranny for that matter, do multiply the torque. 1st gear in a transimission is built for toque to get you off the line so it multiplies the torque, but 4th gear you allready have the momentem so you dont need the toque. So the rear end has the same affect of multiplying toque. I dont know how dynos compute HP and TQ but i beleive that your number will be off, and I think it could be a considerable amount... I'll call my local dyno shop on Monday and ask for sure, but your question is deffinetly a brain stimulator!!

[tripleblack]

Emailed the operator at Bristol Dyno:

"Do you need to know the gears in a car to get a good dyno chart?"

"No. Not with the DynoJet."

http://www.bristoldyno.com/info/whatis.htm

He mentioned that some other types of dynos might need that information, but that the 2 types he used did not.

[Cyphear]

Sorry to bring this one back from the dead. I found this thread on a google search, but I had to sign up so you could get this question answered. We don't need any more uninformed ford guys than we already have! (don't take that personally, i'm mostly kidding and if you're in on this discussion, you're good!)

You guys are forgetting about the RPM pickup. By measuring the RPM of the engine and knowing what the roller speed, the dyno (software) knows exactly what the (gear) ratio is between the engine speed and the wheels speed.

I'd love to see the full set of formulas used by a dyno.

[tripleblack]

Sure, oldie but goodie.

Hit the links in my posts and you'll find out a lot about dyno opertions and the math involved.

You're correct, of course, by linking to the ignition system the dyno can be told what RPMs are being turned by the engine.

It also measures what is happening at the driven wheels, and the two are rendered into a chart.

Should there be a problem linking to the ignition system, the dyno can STILL determine the power output, but as a sequence of numbers rather than a graph showing the power curve. Without RPMs, it cannot show the progression that forms the curve.

Originally Posted by Cyphear

Sorry to bring this one back from the dead. I found this thread on a google search, but I had to sign up so you could get this question answered. We don't need any more uninformed ford guys than we already have! (don't take that personally, i'm mostly kidding and if you're in on this discussion, you're good!)

You guys are forgetting about the RPM pickup. By measuring the RPM of the engine and knowing what the roller speed, the dyno (software) knows exactly what the (gear) ratio is between the engine speed and the wheels speed.

I'd love to see the full set of formulas used by a dyno.

[l_o_t_s_r13]

ok so a lot of things were brought up in this thread but one things kept popping up in my head, everyone has said that gears multiply torque and blah blah blah you know the drill, but is it not true that when using a dyno it measure WHP which in turn gears COULD change the HP reading because different setups will put the power from the engine to the wheels differently some more efficiently some less efficiently, this being said gears COULD in fact change the hp that any given car can put down.... just like trans gears, or an intake (even tho that boosts the engine horsepower as well) but in theory anything that helps get the power to the wheels could in fact change your dyno reading... whether you want to call it "fooling" the dyno or not i don't care, point being the hp at the wheels could be changed by gears... by how much would depend on gears used and so on...

[tripleblack]

Of course, hence the difference between "horsepower at the flywheel or crankshaft" and "horsepower at the wheels".

We went through all this already on this thread.

Regardless of what method of transmitting power to the wheels, the dyno reads the results AT the wheels. It doesn't care what method (AOD with a torque converter, 4.10 gears, 3.27 gears, chain drive, rubber band, CVT, etc) is used in the drivetrain, it just measures what happens at the wheels, compares that result to how many RPMs the engine is turning, and voila.

Now, if someone is trying to discover how much power is lost between the flywheel and the rear wheels, the dyno can't tell you that. Manufacturers do the bulk of their testing on engine dynos, and they usually advertise using that higher number, vs the real world number which comes out at the wheels.

Gears CAN change everything, just as you say, and less efficient gear sets (poorer quality, for instance) will transform more power into heat and less into torque. A slipping clutch will do the same - a bad torque converter or worn clutch packs in an AOD - slippery TIRES that don't grip on the dynos rollers... Air pressure, humidity, timing, ad nauseum, can all affect engine performance, and anything that affects engine performance (or parasitic losses, another can of worms) can affect what happens in terms of power production.

But Dynos don't care about all this stuff. They just tell you what is happening at the wheels.

Engine diagnostic equipment which is sometimes used in association with a Dyno can be used to figure out fuel/air, spark advance, troubleshoot, etc.

Final drive ratio and gear ratios throughout the drivetrain affect power output (via efficiency if nothing else), as does the clamping force of a given clutch, the condition of the surface of the flywheel, the balance of the driveshaft, etc, etc.

The stronger the gear set, the taller the resulting power curve (and the shorter the amount of time the drivetrain requires to reach operating peaks). However, all other things being equal (efficiency, quality of install, all the other variables), no particular gear ratio (in and of itself) will generate better horsepower or torque readings than another UNLESS the ratios are so high as to affect the operation of the engine, or so low as to prevent the engine from achieving maximum volumetric efficiency (this last might occur - the other would be very difficult to pull off).

In the real world where gear ratios are sane and well-matched to the cars, neither problem is likely.

Its easy to get bogged down in the logic, while the dyno is busy cutting the gordian knot and reading it like it is. Its really just a very fancy gauge, designed to yield some numbers.

Sure, like any gauge it can be off - have a defect or need calibration - require adjustment to compensate for unusual variables like weather - or be mis-operated. Dynos are like all machines, no better than the human operator.

But what the chassis dyno (good or bad) is always limited to the reality as it comes off the wheels.

Originally Posted by l_o_t_s_r13

ok so a lot of things were brought up in this thread but one things kept popping up in my head, everyone has said that gears multiply torque and blah blah blah you know the drill, but is it not true that when using a dyno it measure WHP which in turn gears COULD change the HP reading because different setups will put the power from the engine to the wheels differently some more efficiently some less efficiently, this being said gears COULD in fact change the hp that any given car can put down.... just like trans gears, or an intake (even tho that boosts the engine horsepower as well) but in theory anything that helps get the power to the wheels could in fact change your dyno reading... whether you want to call it "fooling" the dyno or not i don't care, point being the hp at the wheels could be changed by gears... by how much would depend on gears used and so on...