'03 Drive train loss %

[Black Cobra]

What effect does having 3.55:1 vs 3.27:1 have on the torque measured at the rear wheels?

My quess it that the 3.55s show more torque on a Dyno and therefore more rwHP. So isn't this equivalent to a lower drive train loss percentage? I've seen dyno numbers for stock mustangs that show rwHP numbers that are 10-12% lower than advertised flywheel HP.

So I'm thinking that we should be using 10-12% when we are estimating flywheel horserpower from rwHP for the '03. I've seen one post where a guy said that the engines were dynoing from 415-420 HP. 420 Hp / .88 = 368 rwHP or 420 HP /.90 = 378rwHP.

415-420 HP LINK

 

[Rob03]

I might be wrong here and I'm sure someone will correct me if I am, but I don't think running a higher rear end gear will change the final torque number.

Cheers, :beer:
Robert

 

[StangD281]

I think you are right on that one Rob....

 

[Black Cobra]

I might be wrong here and I'm sure someone will correct me if I am, but I don't think running a higher rear end gear will change the final torque number.

That's the trivia question for the day. Can anyone go into a more detailed explanation on this?

Gears are like Levers right? Take a childs teater totter. Take two kids of equal weight. Have one child sit at one end and have another child stand at the fulcrum point. It will take a certain amount of torque to raise the child that is seated. Have the child walk towards the opposite end of the teeter totter. The child that is walking is exerting the same amount of force downward (his weight). As he walks his Lever is getting longer and eventually enough torque is created to lift the other child.

Anyone got dyno numbers before and after a gear change?

It sure seams like the torque would be greater for the 3.55s vs the 3.27s.

 

[Rob03]

Well to give a little more info...3.55:1 means the drive shaft turns 3.55 times to one revolution of the wheel. So how do you get more torque from more revolutions of the drive shaft? Again I'm no expert but a fulcrum and gears are very different things.

Cheers, :beer:
Robert

 

[jpetre]

I am not sure but I think that you will lose some ponies with steeper gears.

Someone got to know what the magic number is. Has anyone dynoed there 03 yet?

 

[wildosvt]

You have to consider the roll out for any gear-tire combo in order for the question to be solved.The 3.55 spins more yes we all know but it also makes it easier for the engine to push the vehicle forward.I dont see how it will take power away having a higher gear but I can see how it might add torque.

 

[jtfx6552]

Torque is the rotational equivilent of force, i.e. force around a shaft, 1 lb of force at the end of a foot long wrench is 1 ft*lb.

Horsepower is how fast you make torque, i.e Torque per second. 550 ft lbs/sec is 1 hp.

Now, if you ever looked at a dyno sheet, you will notice that it has a figure for rpm/mph, which the dyno calculates using a lead hooked to the engine. It "knows" how fast the rollers are going, and it "knows" how fast the engine is turning so it "knows" the effective ratio between the engine and the wheels.

When you change rear gear ratios, or the gear you are running the test in, this figure changes, and the torque at the rear wheels still gets correctly calculated to torque at engine speed, which is used to calculate the HP.

Now you say, why does the HP matter? Can't I just put higher numerical gears in and since the force put to the pavement will keep going up with higher ratios, the car will go faster and faster with each higher ratio? Well not neccessarily because the the engine will run out of RPM earlier in each gear. You then you have to switch to the next gear in the transmission. Lets say you went to a 20% higher numerical gear, and you used to be able to get to 50 MPH at redline in first, now you will only be able to get to 41.667 mph in first at redline, so from 41.667 to 50, you will now be in second gear and have less overall gear multiplication between the engine and transmission than when you were in first gear with the original rear gear. The same thing happens at the top of each gear.

There is more to the whole mess than this, I think there have been at least chapters, if not whole books on all the effects different ratios have on a car.

For the most part using higher numerical gears for a dyno test will result in lower HP numbers. the reason being, the higher the numeric ratio, the shorter time duration the pull, which means the rotating parts behind the engine got accelerated from the low point to the high point faster, which takes more HP, that HP then, is not transferred to the rollers to be measured. I think some programs attempt to measure the inertia of the driveline to attempt to account for this. Not sure about that though. This is one of the reasons that makes 4th gear the gear of choice for most chassis dyno tests, the other is that in t-5's and t-45s and t-56's in 4th, the input shaft is coupled directly to the output shaft and power is not being transmitted (and partially lost) through the gears.

JT

 

[Black Cobra]

An article on Dynojet's website had the following information.

PHYSICS LESSON

At the core of a Dynojet 248H is a pair of metal drums joined by a shaft and riding on antifriction bearings. The drums weigh about 2700 lbs. apiece, are four feet in diameter and have knurled surfaces to enhance traction. Because 5400 lbs. takes time to slow once the dyno run is complete; the drums have air brakes, similar to those on rail cars, operated via a button the dyno's hand-held controller.

A key principle of the Dynojet is: the drums' inertia acts as a sort of passive power absorption device. "Mass equivalent" is a term engineers and physicists use to quantify the difference in inertia of a mass in linear or, more properly, "translational" motion and one in rotating motion. The mass equivalent of a rotating drum is quite different than its mass for translational motion so the weight simulated by the drums when rotating is different than their actual weight.

During manufacturing, Dynojet Research figures the mass equivalent of each pair of drums to four places and bearing drag to five places.

Those proprietary figures are figured into the computation the dyno computer makes. If the mass equivalent of the drums is known and the rate at which a vehicle's drive wheels accelerate the drums is accurately measured; then the "thrust force," in pounds, at the rear wheels can be computed with a high degree of accuracy.

A combination of two laws of physics, force equals mass times acceleration and work equals force times distance, gives us this equation: W=m X a X d. "W" is the work (in pound-feet) the rear wheels are doing, "m" is mass equivalent (the drums), "a" is acceleration (increasing drive wheel speed) and "d" is distance (drum circumference). Once we have the work, we can find horsepower. One horsepower is 550 pounds-feet of work done in one second, so we divide the work number by the length of time measured, then divide the number we get from that by 550. To simplify: we get horsepower by multiplying the mass, acceleration and the distance, then dividing that product by time multiplied by 550. This can be expressed by: hp=(m X a X d) / (t X 550).

Torque can be figured by multiplying the horsepower by a constant, 5252, then dividing that product by the speed at which the thrust force was measured. Generally with rear wheel numbers, axle ratio is not considered in the torque computation. For comparison purposes, this makes more sense. The computer factors out the axle ratio by using engine speed data in the torque derivation.

In the real world, the measurements and computations are not quite that simple, but the complex methods Dynojet Research uses to apply these laws of physics and their mathematics to accurate measurement of rear wheel power is a proprietary secret.

I've always assumed that Dynos were reporting rwHP and rwTorque. Since the rear axle gear ratios are factored out then Chassis Dynos are actually attempting to report Flywheel HP and Flywheel torque less drivetrain loss as measured at the rear wheels? I'm still thinking 10-12% for drivetrain loss.

As for true rear wheel torque. How much torque would it take to lift say 2000 lbs sitting at the end of a 101.3" wrench?

 

[blown03cobra]

as for not wanting to read LONG ASS POSTS,,,, the car HAULS ASS,,,, I belive you LOOSE when you go TOO STEEP OF A GEAR, but man, does it feel good.... Its just like screwing too hot of a girl,,, it feels GREAT but it goes too fast :lol: sorry for being blunt and yall have a great one :beer: :beer: :beer:

 

[verbs]

Having 3.55 gears in the car will cause the car to dyno less than if say 3.27 gears were in the car.

I went from 3.42 gears in my car to 4.10 gears in my car and lost 10rwhp. I think it's because the car doesn't have to work as hard to make the rear wheels turn as much, so the dyno sees that as less hp somehow.....

Basically, being that the 03 Cobra and LS1 cars have the same tranny gears, an 03 Cobra with its 3.55 gears dynoing in 4th gear, will lose 2rwhp compared to if it had been dynoing with the 3.42 gears that the Fbody uses.

Not that that is a big deal, but put a stock 3.55 geared Cobra on the dyno, and then an other near stock Cobra on there with the only mod being 4.10 gears, the Cobra w/ 4.10 gears will dyno about 8rwhp less than the one with the 3.55 gears, but will win in a race by a few cars assuming you can get traction.