Driveshaft Decision. I'm torn. Advice from experienced?

[1986.5supra_kid]

Damn i retract my statement regarding the "right now" and "production cars" and "illegal speeds" comment. im surprised i haven't had a brick with a note attached thrown threw my front window too.
Also i assume the "NA grocery getter" was directed to me as well?

So i own a 3'' steel ds and it has held up to the abuse of "child molesting speeds" clutch kicking,wheel hop,gf shitty driving,and my inability to drive a car as you would see fit too. BUT the purpose of this was to give advice to suprarx7nut on ds options. I feel that the oem equipment is the better option and that he could cheaply replace a item of the same dimensions bearing and put the money toward other parts,Until the cars potential overcame the trust of the oem ds. $1000 is alot of money to spend this early for a ds especially since its a w58 transmission,350 max hp.. HAD he said r154 with 350hp max i would say yeah get yourself a DS because its unlikely for a owner of a r154 to say 350 is my max when you know your trans can take more and you have a growing platform. so say he gets a carbon fiber for a w58 or a special 2 peice made; the w58 is shorter,different spline count, so it cannot be used on a r154 if and when the w58 does not suite his need.

P.S If there was a post from suprarx7nut regarding a statement toward a trans swap to the r154 i fully retract my statement and Apologize to the members of this thread for falsifying information.

 

[3p141592654]

My annoyance with "power loss" is that it is actually energy storage, so no power is lost, you get it all back when you slow down, and at steady speeds it makes no difference. More importantly though, as IJ states, is that it just doesn't matter unless you need 100ths of a second in a competition. The rotating mass of flywheel, clutch, tranny assemblies, differential, half shafts, hubs, rotors and wheels is so overwhelmingly greater that the DS mass is an irrelevant consideration here. If you want to pinpoint the location of energy loss in your drivetrain, just follow the heat!

 

[te72]

And theirs is far less exposed than ours.

One would hope to enclose it on our cars to protect it as much as possible from debris.

My annoyance with "power loss" is that it is actually energy storage, so no power is lost, you get it all back when you slow down...

I get that the drivetrain stores energy, but how do you get it back when you slow down? Your wheels will still spin the driveshaft as you slow down (when not on the power), correct? If so, I'm curious in what form you're getting that energy back...

You do mention all the other parts that are more of a parasitic loss, but aside from the half shafts, everything you listed has a larger diameter (and therefore requires more energy to turn) than the driveshaft... am I on the right track at least?

 

[figgie]

You're talking PMoI, I doubt you could measure the difference as it would be within the +- error of most Dyno's.

I build/drive my cars in the real world and unless you can figure out a shoud to enclose the Carbon Shaft I wouldn't use one in a street car, Duane destroyed one a few years back.

He did

but that was an oversight and not FOD (foreign Object Damaged).

IE, a bolt was sticking out to far in the trans tunnel and gouged the CF. One hard launch. Insta-sweeper.

 

[figgie]

One would hope to enclose it on our cars to protect it as much as possible from debris.


I get that the drivetrain stores energy, but how do you get it back when you slow down? Your wheels will still spin the driveshaft as you slow down (when not on the power), correct? If so, I'm curious in what form you're getting that energy back...

You do mention all the other parts that are more of a parasitic loss, but aside from the half shafts, everything you listed has a larger diameter (and therefore requires more energy to turn) than the driveshaft... am I on the right track at least?

and that is what 3p is alluding to.

The WHEELS have LOTS more stored energy than the DS.
The flywheel & clutch combo has MORE stored energy than the DS does.

They take more energy to turn but they STORE more energy. They are in essense flywheels (teh clutch/Flywheel, wheels, Driveshaft). A better thought analogy is a gyroscope. It is fairly heavy on it's outter circumference. Spin it and it continues to spin until frictional loses make it zero. The energy does not just disappear because it goes away, otherwise the wheels would stop after "energy" removal. Same with clutch/Flywheel. Same with the gyroscope. Hell that is a very good example.

Look at the cars with lighweight flywheels.
Yes they accelerate quicker but then DECELERATE quicker also due to less energy storage.

If you have ever seen the videos of the F1 cars playing music (latest one is the Redbull f1 team playing stars spangled banner). That is due to a very very light flywheel clutch combo. No way to achieve those RPM changes with heavy FW/Clutch setup. Even at 15k RPM, if they cut power, that engine goes to zero almost immediately.

 

[Poodles]

Lightweight flywheels WILL show on a dyno because they ramp up quicker. It's they way dynos function, but you're not really making more power.

 

[Orion ZyGarian]

One thing to note with the lighter drivetrain components, as figgie has said, is that you do decelerate much quicker as well. Getting a light flywheel has been one of the best mods I've done to my Miata, as it gets up and goes quicker, but I also pretty much only use the brakes to come to a complete stop because of how effective engine braking is. You dont get that too much with a nice heavy flywheel, but you also lose some smoothness and get some NVH with it. I recommend a flywheel thats a few lbs lighter than stock, but there seemed to be all sorts of people that were welding clutches to the aluminum ones. I'm assuming chromoly would be a better choice.

 

[figgie]

One thing to note with the lighter drivetrain components, as figgie has said, is that you do decelerate much quicker as well. Getting a light flywheel has been one of the best mods I've done to my Miata, as it gets up and goes quicker, but I also pretty much only use the brakes to come to a complete stop because of how effective engine braking is. You dont get that too much with a nice heavy flywheel, but you also lose some smoothness and get some NVH with it. I recommend a flywheel thats a few lbs lighter than stock, but there seemed to be all sorts of people that were welding clutches to the aluminum ones. I'm assuming chromoly would be a better choice.

i know the MKIV guys that ran the manual 6 speed chose to run a chrome moly clutch that weighed almost the same as OEM for drag as they weren't bogging as much due to stored energy with the heavier flywheel.

 

[suprarx7nut]

Lots of good discussion here. Keep it going!

My annoyance with "power loss" is that it is actually energy storage, so no power is lost, you get it all back when you slow down, and at steady speeds it makes no difference. More importantly though, as IJ states, is that it just doesn't matter unless you need 100ths of a second in a competition. The rotating mass of flywheel, clutch, tranny assemblies, differential, half shafts, hubs, rotors and wheels is so overwhelmingly greater that the DS mass is an irrelevant consideration here. If you want to pinpoint the location of energy loss in your drivetrain, just follow the heat!

When you slow down you sure do get the energy back... in the form of heat on your brakes. Is there another benefit to drivetrain inertia post-flywheel that I'm missing? I thought you'd want that to be as small as possible. Flywheel weight can help smooth take off and such, but I didn't think anything after that was desirable.

One would hope to enclose it on our cars to protect it as much as possible from debris.


I get that the drivetrain stores energy, but how do you get it back when you slow down? Your wheels will still spin the driveshaft as you slow down (when not on the power), correct? If so, I'm curious in what form you're getting that energy back...

You do mention all the other parts that are more of a parasitic loss, but aside from the half shafts, everything you listed has a larger diameter (and therefore requires more energy to turn) than the driveshaft... am I on the right track at least?

I think you're on the right track. Polar Moment of Inertia is a function of mass and radius. Radius is at least squared, cubed or to the 4th. My dynamics professor is facepalming somewhere... lol

He did

but that was an oversight and not FOD (foreign Object Damaged).

IE, a bolt was sticking out to far in the trans tunnel and gouged the CF. One hard launch. Insta-sweeper.

This is what I've seen with many carbon failures. A stray bolt, hanger, clutch dump # 50 on a modified track car, etc.. I cant find many street failures at all.

Lightweight flywheels WILL show on a dyno because they ramp up quicker. It's they way dynos function, but you're not really making more power.

I'd still argue you ARE making more power to the wheels. Any drivetrain loss that's minimized results in more power generated at the engine making it to the ground where you actually feel it.

Of course, this being said, the DS like everyone has mentioned is minimal compared to the 4 40-60# wheel/tires with diameters 5 times that of the driveshaft.

 

[3p141592654]

When you slow down you sure do get the energy back... in the form of heat on your brakes.

True, that is one scenario, but it also can be used to coast further or reduce the change in speed as the road slope varies and so on.... but my real point was that you're "chasing a will-o-wisp". There are so many other heavier and larger diameter things in the drivetrain to worry about than this; it's nothing more than a marketing gimmick. The brake rotors alone are good for 80lbs of large diameter rotating inertia, so better off getting some ceramic disks!

 

[JPsToyota]

I have a shaftmasters 1 piece aluminum. Perfect fit, and it's very light. I took it up to 120 with 4.30 gears, with no vibration or noise. If I was you, I'd go with the 1 piece 3.5" aluminum.

I have a Shaftmasters 1 piece also, I spoke with them about what I wanted and sent them some info about my car and the driveshaft rotation speeds the car could possibly see as I thought they would need to make a 'custom' 3.5" shaft (or get my slipped 2-piece fixed by a high-quality shop near me, hadn't decided yet) to accommodate the high speeds the car hits.

They told me I would be perfectly fine with their regular 3" 1-piece AL shaft (they also gave me the rated critical speed of the shaft) and would not need them to build a 3.5" for me. 500ish-whp, 170ish-mph, driveshaft has been nothing but fantastic and so far I'm glad I went with the 1-piece AL. A chunk cheaper than a DSS also, they are getting a little pricey IMO.

edit - I see this thread has taken a technical turn, don't have time to read it all now!

 

[3p141592654]

The physics of driveshafts. The critical velocity is not just some number where all is good if you go slower than it.

First the definition, the critical velocity is the speed where for any small initial deflection, the centripetral force is equal to the elastic restoring force. That means the shaft effectively starts to whip out of control at that speed. But, as you approach that speed the effective rigidity of the shaft decreases, making it more prone to vibration.

You can see the shaft deflection versus speed in the plot below (and read about the derivation of that plot here http://www.roymech.co.uk/Useful_Tables/Drive/Shaft_Critical_Speed.html Notice that deflection is occurring well before the critical velocity, and that can lead to many problems.


The above applies to a perfectly balanced driveshaft. There is another parameter called the maximum unbalanced driveshaft velocity. This is the one to watch out for, because it is lower than the critical velocity, and any real world driveshaft will not be perfectly balanced. Therefore, engineering rules of thumb say you want to stay well away from the critical velocity, by as much as 25 to 50%.

Also, half critical velocity is a speed at which the shaft is very susceptible to vibration, so you need to make sure that speed is well out of the normal 50 to 80 mph range where vibration problems can be very troublesome.

Toyota knows all this, and chose a 2 piece as the solution for our cars with 150+mph capability.

 

[Orion ZyGarian]

The physics of driveshafts. The critical velocity is not just some number where all is good if you go slower than it.

First the definition, the critical velocity is the speed where for any small initial deflection, the centripetral force is equal to the elastic restoring force. That means the shaft effectively starts to whip out of control at that speed. But, as you approach that speed the effective rigidity of the shaft decreases, making it more prone to vibration.

You can see the shaft deflection versus speed in the plot below (and read about the derivation of that plot here http://www.roymech.co.uk/Useful_Tables/Drive/Shaft_Critical_Speed.html Notice that deflection is occurring well before the critical velocity, and that can lead to many problems.
View attachment 60519

The above applies to a perfectly balanced driveshaft. There is another parameter called the maximum unbalanced driveshaft velocity. This is the one to watch out for, because it is lower than the critical velocity, and any real world driveshaft will not be perfectly balanced. Therefore, engineering rules of thumb say you want to stay well away from the critical velocity, by as much as 25 to 50%.

Also, half critical velocity is a speed at which the shaft is very susceptible to vibration, so you need to make sure that speed is well out of the normal 50 to 80 mph range where vibration problems can be very troublesome.

Toyota knows all this, and chose a 2 piece as the solution for our cars with 150+mph capability.

Sounds pretty conclusive to me!

 

[SideWinderGX]

The physics of driveshafts. The critical velocity is not just some number where all is good if you go slower than it.

First the definition, the critical velocity is the speed where for any small initial deflection, the centripetral force is equal to the elastic restoring force. That means the shaft effectively starts to whip out of control at that speed. But, as you approach that speed the effective rigidity of the shaft decreases, making it more prone to vibration.

You can see the shaft deflection versus speed in the plot below (and read about the derivation of that plot here http://www.roymech.co.uk/Useful_Tables/Drive/Shaft_Critical_Speed.html Notice that deflection is occurring well before the critical velocity, and that can lead to many problems.
View attachment 60519

The above applies to a perfectly balanced driveshaft. There is another parameter called the maximum unbalanced driveshaft velocity. This is the one to watch out for, because it is lower than the critical velocity, and any real world driveshaft will not be perfectly balanced. Therefore, engineering rules of thumb say you want to stay well away from the critical velocity, by as much as 25 to 50%.

Also, half critical velocity is a speed at which the shaft is very susceptible to vibration, so you need to make sure that speed is well out of the normal 50 to 80 mph range where vibration problems can be very troublesome.

Toyota knows all this, and chose a 2 piece as the solution for our cars with 150+mph capability.

I was going to let the rest of the posts in this thread go, but I can't bite my tongue any more.

Toyota didn't choose a two piece because it is superior to a one piece, they did it because that's what they've always done prior to that. There is no reason to introduce a one piece driveshaft to a car that isn't going to be racing on a track where every horsepower counts.

Yes, critical speed is when the shaft starts to whip or jump-rope so to speak, but your claim that 'rules of thumb' say to stay 25 to 50% away from that rule effectively half the top speed of our cars in 4th to somewhere around 75 mph. Heck, you should go ahead and tell most sanctioned racing bodies (that REQUIRE one piece driveshafts because they have less points of failure) that they are doing it wrong going up near 200 mph with one piecers.

I wrote up a response to whoever quoted my post but I was at a job-site waiting on a start up guy to do his freaking job, come to find out it would let me browse the forum but not post...the calculator I was using was here: http://www.supramania.com/forums/showthread.php?58272-Driveshaft-Critical-Speed-A-Calculator/page2

Not sure if the links work any more but I have the Excel sheet saved in a folder on my desktop because I thought it was useful. And yes, 'factor of safety' is a great rule of thumb

I'd change my vote to a 3.5" shaft if you are really worried about rigidity, but again, you'll be fine.

edit: Ah yeah, someone brought up balancing. That's baloney. We can put a vehicle on mars but some people think we can't balance a 40" aluminum shaft? Sure.

 

[te72]

What causes imbalance? Is it impurities in the materials used, where a uniform weight is difficult (or nearly impossible) to attain? I'm just curious here, I always thought that a driveshaft could be balanced for certain speeds. Or is it one of those things where problems become more pronounced at higher speeds?

It was mentioned that there are speeds to avoid. I've heard this of engine speeds as well, certain rpms on some engines are prone to damaging the engine. Lower or higher is fine, but it is bad to stick at those speeds that could damage the engine over time. The same is true of driveshafts then?

 

[suprarx7nut]

Ordered the 2 piece aluminum. Lead time of about a month. Hope to have results by mid October.

 

[IJ.]

Ordered the 2 piece aluminum. Lead time of about a month. Hope to have results by mid October.

<golf clap> well done

 

[tlo86]

<golf clap> well done

now i just need to do it with a cheap support bearing ;p

 

[SideWinderGX]

What causes imbalance? Is it impurities in the materials used, where a uniform weight is difficult (or nearly impossible) to attain? I'm just curious here, I always thought that a driveshaft could be balanced for certain speeds. Or is it one of those things where problems become more pronounced at higher speeds?

It was mentioned that there are speeds to avoid. I've heard this of engine speeds as well, certain rpms on some engines are prone to damaging the engine. Lower or higher is fine, but it is bad to stick at those speeds that could damage the engine over time. The same is true of driveshafts then?

You're exactly right with your guess, the material and dimensions are not perfect throughout the entire length of the tube and therefore the true center of mass is not at the center of the shaft. As an MET student I was kind of pissed to learn that you can't just make a circular hole and call it a true circle...as a high school student I never thought down to the nitty gritty of it. At some point there will be inconsistencies, impurities and irregularities and how critical you rank these are what determines the quality of the part.

http://www.wimp.com/cuttingsteel/
Around 0:40 and 2:15 you can see some humps in the surface of the part as a result of the cutting tool removing material, taking less material off would lessen this but eventually you get to a point where you're barely brushing over the material to smooth out the surface for these stupid irregularities.

Resonant frequencies exist in everything, easiest example is a swing or a pendulum. You push at the apex of the swing, you add to the energy of the swing...you push at a bad time and most of the time you detract from the energy of the swing. Same deal with a driveshaft: there's a sweet spot which depends on (I'll just go to the equation) modulus of elasticity, length and diameter where the frequency is most pronounced. Does this mean failure WILL occur? Absolutely not, but the shaft will resonate more...might mean it will wobble itself into the tunnel or the loop, might mean that any pronounced wobble plus the power output of the car will overcome how strong the shaft is, there's a few options.

The stock dampener should take care of any resonance the engine has throughout its rpm band, but again you are right for both engines and driveshafts.

 

[suprarx7nut]

now i just need to do it with a cheap support bearing ;p

I struck a good deal, so the price in the poll isn't real accurate. My pricing put it at just more than a new bearing and u joints. The choice was easy then.

Plus, I'll never worry about the rear section twist and I'll remove a few lbs of rotating mass.

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