aluminum drive shaft - anyone?

[EAGLE5]

Originally Posted by cdrazic93

or, somehow they reverse trolled you so hard, you begin to question whether or not they understood you, but they wanted to argue with you in the first place.

Shhhh!

[Ultramaroon]

Originally Posted by cdrazic93

or, somehow they reverse trolled you so hard, you begin to question whether or not they understood you, but they wanted to argue with you in the first place.

Awww, damn dude. I just popped a fresh bowl of popcorn.

[EAGLE5]

Dude's name is "justatroll". Maybe it's just at roll?

[EAGLE5]

Anyway, when I see the name Alcoa, I always think cloaca. Anybody else do the same?

[Drakiv]

This is the funniest, largest troll thread i have read through in a while. Thanks for the entertainment guys.

[Votlon]

i mean, i learn something useful about dynos today, so its a little useful of a thread

[justatroll]

Originally Posted by Votlon

i mean, i learn something useful about dynos today, so its a little useful of a thread

Here's another one: an old school inertia dyno is very simple.
You have a really big heavy wheel.
You know the precise rotational inertia of this wheel.
You couple that to the car drive and do "max power pulls" and all you have to do is measure the time it takes to get that wheel from a stop to 'X rotations per second'.

Then you would know the energy per unit time to accelerate the wheel and you could derive the average torque and calculate average hp over the full pull.
(notice you are not measuring torque directly in this example)

In these types of tests, if you then remove a large amount of rotational inertia (lightened flywheel), then repeat the tests, you will show an increased calculation of horsepower.
That is because when you calculate the average torque based on the total energy expended in T seconds, the equation requires you to use a known value for total system inertia.
When you repeat the test with a lighter flywheel you will get a higher value for average horsepower because you do not include the new value for the total system inertia.
If you DO include the adjusted value for the total system inertia (lighter flywheel) then you WILL get the same value for average horsepower.

You would get the exact same effect if you used the same car to do two dyno pulls.
Once with brand new stock tires, and again with the same tires shaved down to minimum tread depth.
On an Inertia-only dyno you would definitely "measure more horsepower" on the second pull with the lighter tires, but would anyone try to argue that shaving the tires actually gave the car "more horsepower".

Newer load based dynos (Dynojet, dynapak) run preprogrammed load profiles that only allow the car's "full pull" to ramp at a certain rate.
These dynos DO measure the torque applied by the engine to the dyno (or from the dyno to the engine) directly (as opposed to the inertia-only style)
The test pull ramp rate is supposed to be chosen to do the pull as SLOWLY as possible to get the most accurate data over long duration (more realistic) pulls.
The requirement of the SAE engine testing requires the RPM & torque measurements to be stable to within 1% for 5 seconds before taking a 10 second data sample. You repeat this test at all target RPMs to make a HP curve.
Some pulls can take 10-20 minutes to get realistic head/exhaust temps.

Most people believe that a "dyno pull" is a race to see who can ramp the dyno faster. Not if you are trying to do it right...

[Drakiv]

I dont think anyone ever claimed any of those items give horsepower or increases horsepower....im actually pretty sure everyone said it frees up horsepower through reduced rotational mass. But continue please

[justatroll]

Originally Posted by Drakiv

I dont think anyone ever claimed any of those items give horsepower or increases horsepower....im actually pretty sure everyone said it frees up horsepower through reduced rotational mass. But continue please

You must have been sleeping under a rock.
There is NO shortage of people who claim that their lightweight pulley, or flywheel, or driveshaft increases horsepower and they will present their +/-3hp dyno charts to prove it.

[nikitopo]

Originally Posted by justatroll

I'm not arguing that it makes no difference on the track or even a drag race.
In fact it was calculated that replacing the DS with a magical one that weighs zero pounds made tens of milliseconds of difference in a ~15 second quarter mile.
I'm saying that you cannot measure a hp difference on a dyno by replacing rotating mass.

If you check the Porsche 911R car, it is focused on the lightweight idea. They took a Porsche 911 GT3 RS and tried to remove as more weight as possible. They removed rotational weight by using a lightweight single mass flywheel and non-rotational weight in other areas like sound-deadening material, A/C delete, etc. The result is a much more responsive and agile car designed for the road (not the track). It never meant to be a track car. Was the factory trying to fool their customers?


Btw. a few journalists had the chance to drive the car in Germany. They were just amazed on the result

[justatroll]

Originally Posted by nikitopo

If you check the Porsche 911R car, it is focused on the lightweight idea. They took a Porsche 911 GT3 RS and tried to remove as more weight as possible. They removed rotational weight by using a lightweight single mass flywheel and non-rotational weight in other areas like sound-deadening material, A/C delete, etc. The result is a much more responsive and agile car designed for the road (not the track). It never meant to be a track car. Was the factory trying to fool their customers?


Btw. a few journalists had the chance to drive the car in Germany. They were just amazed on the result

"Was the factory trying to fool their customers?"


No. I NEVER said that replacing rotating assembly parts with lighter ones would not make a difference.
I HAVE said two things:
1 - IF you want to lighten an otherwise street car then reducing weight in the drivetrain is FAR more expensive than reducing weight anywhere ELSE in the system and the return on investment is the LOWEST as far as weight reduction per unit dollar goes.
IF you are building a car from the ground up, by all means reduce weight wherever you can. But if I see someone with a full interior and a spare tire with a LW crank pulley and a CF driveshaft, I will not take them seriously.
and
2 - You do NOT get "more horsepower" by reducing rotating mass

[nikitopo]

Originally Posted by justatroll

But if I see someone with a full interior and a spare tire with a LW crank pulley and a CF driveshaft, I will not take them seriously.

Maybe you have in mind the interiors of some very old cars. Our cars have a very well thought interior and you don't gain too much. I was checking once to change the car's seats and the weight gains were very minimal. Even if I choose the very best materials, like Carbon-Kevlar fiber material the gain couldn't justify the very high cost. It was a gain of about 25 pounds for both seats. Besides, a car with a stripped down interior is not anymore a street car. So, we are trying to have the best of the worlds and still keep it a street car.

[justatroll]

Originally Posted by nikitopo

Maybe you have in mind the interiors of some very old cars. Our cars have a very well thought interior and you don't gain too much. I was checking once to change the car's seats and the weight gains were very minimal. Even if I choose the very best materials, like Carbon-Kevlar fiber material the gain couldn't justify the very high cost. It was a gain of about 25 pounds for both seats. Besides, a car with a stripped down interior is not anymore a street car. So, we are trying to have the best of the worlds and still keep it a street car.

I'll post a separate explanation just so you can hear from someone other than me:
Rotating Mass, Available Horsepower, and Acceleration

http://www.w8ji.com/rotating_mass_acceleration.htm

"Drive Shaft Example

Now let's think about a drive shaft. The driveshaft is a fairly thin hollow tube. Nearly all drive shaft weight is at the outside, since it is (of course) hollow. The shaft also turns at the same RPM no matter what the driveshaft diameter, because the RPM is set by the rear end ratio, tire diameter, and vehicle speed. If we make a driveshaft lighter and keep everything else the same, the vehicle acceleration change is often insignificant.

Why would it be insignificant in most cases?

In the first place, the drive shaft is small in diameter. With a small diameter, less energy is stored for a given weight. In the second place, a driveshaft is really not that heavy. A steel Mustang driveshaft weighs somewhere around 30 pounds, so we just can't take that much weight out.

Also, the driveshaft spins up gradually and smoothly over a long period of time. It accelerates fastest at slowest speeds, and that is when it needs the least energy to spin up. Because it has a long time to spin up, is a small diameter, and because it does not weigh much, the driveshaft does not remove very much horsepower at any instant of time. Despite what we are told, a change in driveshaft weight has, at best, a very small effect on acceleration. Likely any change is immeasurable in a street/strip car.

Now a lighter shaft certainly can help in a very light vehicle. It can also help in a road race car (as will a light crank and flywheel), because road racing requires instantly changing from acceleration to deceleration.

A light driveshaft won't change anything significant or measureable in a 3000-pound 11-second car, except how fast dollars leave your wallet!"

But that guy is also an electrical engineer (like me) so what does HE know?



EDIT - I'll add this guy's summary, he sounds like an intelligent person and the numbers he uses for his examples are close to our cars:

"I would never bother changing from steel to an aluminum driveshaft in my car, because my car takes 11 seconds to go 1/4 mile. The car weighs 3000 pounds, and this means I might save 20 pounds of weight and 1/2 horsepower lost to spinning that weight over the length of the track. $400 is not a good investment at all for 1/2 horsepower over the length of the track, or the extra 1/2 horsepower applied for 11 seconds I have to extract at the end and convert back to heat with my brakes.

I don't really have to worry about how fast things spin up at this point. I don't care if the crank is 12 pounds lighter out of 50 pounds. I don't care if the driveshaft is 15 pounds lighter out of 30 pounds! Right now that $400 to $1000 would go a lot further if it made 20 more engine horsepower, or removed 60 pounds of static weight. When I start running out of easy power, then I will spend money making expensive things lighter. The big problem right now is traction, so right now I want to smooth the power out. The last thing I need is to make the car more critical for launch RPM by using a lighter flywheel or shock the tires more by using a lighter driveshaft. The first major weight reduction will be the front K members, because that would remove weight from the front and effectively add a larger percentage of weight to the rear wheels! The last weight reduction for my car will be an aluminum flywheel or driveshaft."

[nikitopo]

I also have an electrical engineering background and what I've seen is that car physics is very different and many times counterintuitive. Removing weight from rotational mass is more important, than removing the same weight from other areas. Our engines don't generate much torque(*), so we have to rely on RPMs to get power. This means that we have a lot of RPM changes and the moment of inertia of the rotational mass plays an important role. Some people say that the weight of the car negates such small variations, but they ignore the fact that this weight sits on wheels.

By the way, the weight of the driveshaft seems to be one factor. Another important factor seems to be its rigidity. STi developed a driveshaft kit that has same weight, but it is stiffer. They are saying that it twists less and the power delivery on the wheels is much better and the car feels more linear. A few people tried it and said that it makes a real difference even on daily driven situations. I believe it is another example of how small changes can make a noticeable difference. Additionally, it looks that we have to take care about weight reduction because we might lose in other important areas like the stiffness of the part. So, we need a good balance between both.


(*) The maximum engine torque of 205 Nm is a joke and can be generated even with hands using a wrench.