422 replies to this topic

[powerss]

If my SM donor had torn outer CV joint boots and 300k miles with dirty grease but were never disassembled, aren't my shafts "compliant" by all interpretations? If I repack them and the dyno shows I have less rolling resistance than everyone else which translates to horsepower, shouldn't everyone else have the right to make their parts equal to the most worn out (fastest) junk out there?

I race Spec Miata because I want to compete in contests of driver skill. I hope we can take worn-out-ness of outer CV joints out of the equation by making this legal and known to the entire community to equalize the cars further after these guys get to keep their finishing positions.

When I started this 2 years ago, I thought I could read the rulebook and build a competitive car with the information there. Not so. Make it easier for guys like me who come along later.

There isn't much ground to DQ, and even less to award higher finishing positions to those not teched. Thank you NASA for bringing this to light... now let's get on with it

I can't understand your point at all. What is easier to understand for someone to understand than you can't modify parts?

If you open up modifications like this then you have opened up a huge rabbit hole.

In my opinion, if the part is modified from a OE or a Remanufactured part then the DQ must stand it doesn't matter if it is a performance advantage or not. The only way this is not illegal is that there are Remanufactured parts that come the same way off the shelf and unmolested by the competitor.

[TylerQuance]

Made equal to worn? would that be modified ?? Hmmmm.

J~

NASA already covered this in case you missed it.
https://nasaspeed.ne...championships/#

[Steve Scheifler]

SAE paper talks about it as well as describing the difference between inner and outer joints.

Synopsis:

1993-03-01
Efficiency of Constant Velocity Universal Joints 930906
Efficiency of Driveshafts have not been analyzed in great detail in the past due to their relatively high efficiency. However, it is possible to obtain about a 0.1 percent increase in fuel economy by decreasing driveshaft torque losses by about 20 percent, owing to the combination mode fuel calculation. In order to improve fuel economy it is necessary to increase the efficiency of the constant velocity universal joint (C.V.J.) used for driveshafts. Additionally, propeller shafts with improved heat characteristics are required. It is for these reasons that this project is conducted.

In this paper, the motion of two typical joint used for front-engine, front-drive passenger cars is analyzed geometrically and efficiency formulas are derived. One of the joints is a Rzeppa joint, used on the wheel side of the driveshaft and the other is a tripot joint, used on the differential side. These formulas are then verified by experiment.
It is found that about 70 percent of frictional induced losses in a Rzeppa joint are due to internal friction caused by contact of the inner and outer spherical surface with the cage. Similarly 70 percent of frictional induced losses in a tripot joint are caused by internal friction which is a result of contact between the balls and the grooves of the housing. Therefore, the motivation to improve fuel economy and heat characteristics can be seen.

[Johnny D]

NASA already covered this in case you missed it.
https://nasaspeed.ne...championships/#

 

Yup, missed it.

J~

[TylerQuance]

My point would be easier to illustrate with unmodified raggedy v. low miles joints in your hands so you could feel the difference. It is there.

EDIT: Removed the part about RH based on Steve's comment below. I was visualizing the joint in droop which is not correct.

[Johnny D]

Lots of pics in the summary link, right?

 

Some that were machined surfaces and were out of tolerance compared to OEM or remanufactured spec.

J~

[Steve Scheifler]

My point would be easier to illustrate with unmodified raggedy v. low miles joints in your hands so you could feel the difference. It is there. More -camber or higher RH = more angle in the joint and exacerbates the mechanical loss.

Actually, unless you are running really high already then higher = less angle. At typical SM height the shaft slopes upward from inboard out.

You can feel it but you are weak compared to a horse. Total loss is low, what you can hope to “gain” by loosening it up is a fraction of low. Not nothing and it all adds up, but not even on the list for most people to worry about.

Oh, and the SAE numbers are for a front-drive car where a joint is worked and bound a LOT more than ours are with no steering and very little suspension travel.

[Steve Scheifler]

Although it seems like a made-up spec/test, if the joints in question had only been loosened up to simulate an old one and the balls still could not pass through the cage opening, there would probably be no issue. But as with a lot of things getting a little too greedy ended up biting them in the ass.

[Johnny D]

I think if you could do 2:44.0xx you're good.

https://racehero.io/...1073744963#show

 

J~

[Tom Hampton]

Johnny. Either you know something and are being cryptic, or you don't and you are speculating.

Either way, I don't really think it's appropriate.

[Johnny D]

Sorry, Steve was saying if you could modify/cheat just enough you could pass....

I threw out a enough lap time.

What the disclaimer....names used in this story don't represent anyone in true life...

 

J~

[Steve Scheifler]

It would be interesting to set up a test to measure the energy required to rotate an axle with the joints at various angles. As noted above you can certainly feel how much tighter a new one is compared to an old one, requiring more effort which ultimately translates to less power at the wheels. But how much?

This isn’t like gears where the power literally transfers from one to the next through the moving/meshing contact surfaces, or even like wheel bearings where the balls or rollers are always spinning at a speed relative to the shaft. This is just an articulation joint, a more complex but more versatile upgrade from the old fashioned U-joint. It is very efficient, but what does that mean?

Well, if 1hp is the amount of work (energy) required to lift 550 pounds a distance of one foot in exactly one second, how much wiggling of that joint can you do with that same amount of work? Ah, but in the real world the joint is loaded with the power exiting the diff and twisting the shaft against the force/resistance of the tires on the pavement trying to propel the car. That load would probably be difficult to reproduce in a simple DIY test rig and I’m not confident in estimating how much it increases friction losses from the joint. Any constructive thoughts are welcome.

Let’s look at it in a different way. If jerking 550 lbs one foot in one second is too boring as an illustration, you might like this one. An elite track cyclist riding a stationary bike attached to a generator. This guy has 30 inch thighs, sprinter power not long distance endurance. But that’s OK because we need him for only about a minute. The gimmick is to see if he can generate sufficient energy to brown a piece of toast for breakfast, so they plug a toaster into the generator output and cut him loose. In electrical terms 1hp = 746 watts. He appears to average something less than that but if we assume a generator conversion efficiency of about 95% he is generating right around 1hp and is totally spent in just a little over a minute. It’s all a bit silly but it really makes the point. As you watch think about the huge strength and effort required to produce 1hp and compare that to the effort required to articulate a joint through a few degrees, or to spin a wheel bearing. Real-world loads might increase the effort required but I don’t think this guy would even notice, and he’s barely one horse.

[Jamz14]

Steve the control arm example is not a good one as they still are out there used for sure and maybe new from Mazda.

 

However you bring up a good point, we are racing cars that are 12 to 20 years old and many parts are not available. Sounds like this is a good time to address how we go about dealing with it, but I suggest you don't do it in the tech shed. 

Half shafts are available from Mazda. I know this because it was looking like I had to buy one at the track that weekend and Mazda had an OEM in the parts trailer. I think what this is going to come down to is what constitutes aftermarket? If as a race shop I take a used shaft and reman it to my spec and then sell it to my customers does that constitute aftermarket reman? Not my question to answer but I think it is going to be the question asked.

[Jamz14]

I'm not saying they were worn, I'm saying they were made equal to worn. How common are the joints I described anyway? Not very, but plenty of folks have joints that are more worn but unmodified.

No they weren't. They were made better. However you feel about this situation lets at least be honest about it. These parts were intentionally modified to give advantage. Nothing wrong with that as long as there is nothing wrong with that. What I don't like is people bullshitting about what was done and why. Be honest about it and own it.

 

I don't really care which way the decision comes down. Cases to made on both sides. The good news is that either way we are going to end up with more clarity after this, and that is a good thing.

[Michael Novak]

Half shafts are available from Mazda. I know this because it was looking like I had to buy one at the track that weekend and Mazda had an OEM in the parts trailer. I think what this is going to come down to is what constitutes aftermarket? If as a race shop I take a used shaft and reman it to my spec and then sell it to my customers does that constitute aftermarket reman? Not my question to answer but I think it is going to be the question asked.

Reman only means redone-- It will fit and work in the same way and is built from mainly old parts. new parts (maybe of different sizes) will and can be added. Who does a reman is not in the rules.  Most of the Reman parts that are allowed by the rules are considered untechable or not worth teching---as these should be too.

[Tom Hampton]

Steve-

 

I think the point you made earlier regarding heat dissipation is more on point that the cyclist example above..or, at least more "tangible". 

 

As you said, 1hp = ~750 watts.  Which is about the heat produced by a hair drier on medium.  2hp = hair dryer on high or a heat-gun.  So, if the joints were absorbing that much power through friction, then the half-shafts should be hot coming off the track. Steel isn't a great conductor of heat, and the cage has no real, direct "conduction path" out of the joint.  So if 70% of the friction is in the cage interface, I would expect the joint to get pretty hot if a significant number of watts were being dissipated. 

 

I can't say that I've ever put my hands on a half-shaft immediately after coming off the track...but, it certainly isn't on my list of concerns about getting burned or even being "hot" to the touch.  Granted there are 4 joints, so if the total power loss was 1 hp, then each joint would be ~ 1/4hp...or 180watts or so.  That's still a lot of heat inside a rubber boot. Ever touched a 175 watt light-bulb?  Even after 60 seconds, and fully exposed to moving air, a 175 watt bulb will burn your fingertip.  I'm not sure those rubber boots would last for 5,10,15,20,30 years if they were exposed to that much heat (and heat-cycles). 

 

All that is to say, if it isn't hot then there isn't anything to "save". 

 

That's all moot, of course...because, a real performance advantage isn't necessary for something to be illegal. 

[Steve Scheifler]

All true Tom, and add to your description what would happen to the grease if a lot of energy was converted to heat.

Checking at the track isn’t great, too much tranfer from brakes and diff, too much airflow sucking it back out. Checking the outer joint on the dyno is better.

My point isn’t to lessen the offense but to provide a sense of what it’s worth and whether taking it off the tech list should drive everyone to the expense or effort of having it done. To which I should restate that whatever small amount of power the joints absorb, best case scenario this little trick saves only a fraction of that.

[Steve Scheifler]

Somebody call Myth Busters, this would be a great segment for the FWD F&F crowd.

[Johnny D]

But a 10th of a sec over a 3.4 mile track is way less than a hp, right?

 

J~

[TylerQuance]

Reman only means redone-- It will fit and work in the same way and is built from mainly old parts. new parts (maybe of different sizes) will and can be added. Who does a reman is not in the rules. Most of the Reman parts that are allowed by the rules are considered untechable or not worth teching---as these should be too.

Yes. What's to stop me from becoming a remanufacturer and machining my own bearing cages that don't drag? Or using the old one and machining and polishing the cage windows. Wait... that's what was done. If remanufactured parts are legal, why are we still talking about this?