GT500 top speed test.

[Tomster]

Pretty sure full boogie in a 4000lb + car on 31 degree banks will cause unpleasant things to happen with the CV's.

Ok, ill bite..... explain.

I know the answer. Id like to hear your impressions.

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[Epiphany]

I was going to ask the same thing. There are plenty of CV equipped cars that race around Daytona for hours on end...

 

[Jmeo]

Ok, ill bite..... explain.

I know the answer. Id like to hear your impressions.

I was going to ask the same thing. There are plenty of CV equipped cars that race around Daytona for hours on end...

How can a 4 ounce bird carry a 1 pound coconut?

 

[Epiphany]

...a typical European swallow weighs 5 ounces and must beat its wings 43 times per second in order to maintain airspeed velocity. This is given as evidence that the bird could not, in fact, carry a 1-pound coconut. At least not without a partner and a strand of creeper held beneath the dorsal guiding feather.

Firstly, the average European swallow is not actually 5 ounces. In fact, they weigh less than an ounce, which surely makes a difference in how much weight they are capable of carrying while on the wing, especially when it comes to the question of couriering coconuts.

Additionally, a European swallow need not flap its wings 43 times per second in order to maintain airspeed. It's more like 12, or fewer, depending on the species.

https://www.syfy.com/syfywire/monty-python-and-the-holy-grail-swallows-coconuts-rabbits-black-knight

 

[Jmeo]

https://www.syfy.com/syfywire/monty-python-and-the-holy-grail-swallows-coconuts-rabbits-black-knight

I knew you would know haha

 

[Idaho2018GTPremium]

Pretty underwhelming video. I don't recall any other sports car so capable with such a low speed limiter. The "can't use it at most tracks" argument doesn't hold because other high performance cars are capable of higher speeds that could also easily hit 181 mph on the same tracks and are not limited, and they all weigh less than the GT500.

It appears to be under-engineered for repeated and sustained 181 mph runs based on Tomster's experience at Daytona.

Which makes me wonder - and these are honest questions:
a) Would other high performance cars have the same issues with the CV joints at similar speeds for similar durations (i.e., a C7 Z06, Camaro ZL1, 911 Turbo S, McLaren 720S, Viper, Huracan Performante, Ferrari 488, etc.?);
b) Does the bank angle cause additional issues that may not be realized with more mild banks or flat ground (i.e., sustained high g causing lateral weight transfer, etc.)?
c) Would the CV joints have failed on a flat course at the same speeds and otherwise similar conditions?
d) What caused the failures of @Tomster's CV joints?

 

[Tomster]

Pretty underwhelming video. I don't recall any other sports car so capable with such a low speed limiter. The "can't use it at most tracks" argument doesn't hold because other high performance cars are capable of higher speeds that could also easily hit 181 mph on the same tracks and are not limited, and they all weigh less than the GT500.

It appears to be under-engineered for repeated and sustained 181 mph runs based on Tomster's experience at Daytona.

Which makes me wonder - and these are honest questions:
a) Would other high performance cars have the same issues with the CV joints at similar speeds for similar durations (i.e., a C7 Z06, Camaro ZL1, 911 Turbo S, McLaren 720S, Viper, Huracan Performante, Ferrari 488, etc.?);
b) Does the bank angle cause additional issues that may not be realized with more mild banks or flat ground (i.e., sustained high g causing lateral weight transfer, etc.)?
c) Would the CV joints have failed on a flat course at the same speeds and otherwise similar conditions?
d) What caused the failures of @Tomster's CV joints?

a) those cars don't weight 4000#
b) no
c) yes
d) waiting on wild horse's theory before I elaborate.

 

[WildHorse]

Ok, ill bite..... explain.

Weight, weight transfer, weight, alignment, weight. Did I mention weight ?

 

[Tomster]

Weight, weight transfer, weight, alignment, weight. Did I mention weight ?

Please elaborate with specifics. These are obvious generalities.

I'm not trying to bust balls, but see if you are thinking like I am.

 

[WildHorse]

Please elaborate with specifics.

Biggest thing with running a 30 degree back is alignment, most important being the camber. Full boogy combined with downforce and cornering weights will wreak havoc on the CV angles. I'd go so far as to run positive camber but now you have the problem in the flat sections and cornering. I really don't think there can be a happy medium with the weight of the GT500. Just my humble opinion.

 

[Epiphany]

Weight, weight transfer, weight, alignment, weight. Did I mention weight ?

Ok, you've mentioned weight specifically a few times now. Can you delineate as to why the internals of a known good CV joint would fail because of the weight given that the joint was designed for that specific application?

ON edit as you posted...

Full boogy combined with downforce and cornering weights will wreak havoc on the CV angles.

Yet the CV joint angles weren't close to being excessive. I've spoken to Tom in detail about the failure he suffered and I never heard him mention anything about the rear tires being driven up and into the wheelwell...



22 to 31 degrees is a heck of a lot of degrees of freedom without being excessive.

Typical inboard CV joints provide a plunge movement of about 50mm and a maximum articulation angle of about 22 to 31 degrees (depending on make and model).

https://www.autoserviceprofessional...ant-velocity-drive-joints-and-diagnostic-tips

 

[WildHorse]

Ok, you've mentioned weight specifically a few times now

Newton's second law primarily (Fnet=m•a) .
In layman's terms: heat, resistance, weight. And secondary things like angle, flex, etc. Anything you do to combat that will yield less stress on the part, in this case, the CV's. Could even be something as simple as the grease used breaking down very quickly.

 

[Sergeant Gearhead]

I am sure all of them top out at the 180-182 mark. By slower, do you mean how quickly they get there?

No. By slower, I meant a reduced top speed. I figure that the big wing on the CFTP will increase drag on the car, making it harder to go faster in a straight line at high speeds.

-SG

 

[Tomster]

Biggest thing with running a 30 degree back is alignment, most important being the camber. Full boogy combined with downforce and cornering weights will wreak havoc on the CV angles. I'd go so far as to run positive camber but now you have the problem in the flat sections and cornering. I really don't think there can be a happy medium with the weight of the GT500. Just my humble opinion.

Alignment is not a factor. I use a pyrometer to check tire temps after each run. The tire temps are a tell tale sign that there is an alignment issue. I have spoken to michelin engineers about the peculiarities of Daytona quite some time ago when I was running my R models there flat out. Yes, alignment is important, but tire pressures and staggering them for the induced weight distribution on the banks is important. The right rear does carry more weight induced by centrifugal forces, so you carry more tire pressure on the right rear, followed by the right front, and rhen by the inner two tires.

Anyway, none of that has to do with what happened here. This is an example of a particular course and being able to run it flat out. Yes, like you said, the car is heavy. The CVs are nothing but a mechanical transfer of energy. The engine is putting out a huge amount of hp and torque. The transmission transfers it to the differential. The differential transfers those forces to the half shafts via the CV joints. The CV joints consist of a race, a cage, and bearings that lie within the race to transfer the hp and torque to the wheels, which make the car go.....

It is my opinion that the CVs overheated from repeated accelleration of a 4000# car from maneuvering speeds on the inside course to maximum speeds as seen on the outside course all the way up to repeated hits on the speed limiter. 30 mins of this cycle heats the grease in the CV (which ford chose to not use high temp grease) to the poimt that the grease hit its drop point (where it changes from a grease to a liquid) and then stopped lubricating the CV joint components. The CV overheated due to lack of lubrication (it went bye bye after it turned to liquid) and the the joint overheated and tore itself apart. The situation was exaggerated by the cherry red exhaust pipes that sit right near the joint with no heat shielding.

So the video has a guy running up to the speed limiter and then backing off before running off the runway. If he were to keep doing that over the course of 30 mins (without cooling time) he or anyone else would probably melt the grease that lubricates the CVs...... and they would eventually fail.

Why this hasn't happened so much is twofold. First, there are not many tracks in the country like Daytona. Second, there are not many people who would drive their cars to reach this point.

 

[Epiphany]

Newton's second law primarily (Fnet=m•a) .
In layman's terms: heat, resistance, weight. And secondary things like angle, flex, etc. Anything you do to combat that will yield less stress on the part, in this case, the CV's. Could even be something as simple as the grease used breaking down very quickly.

Newton's Second Law had to do with force acting upon an object and the mass of the object with respect to the acceleration of said object. I'm not sure you are using the right example. You were talking about CV joint angles being excessive - they weren't. Grease breaking down, obviously relative to heat from a given velocity, well that is always a concern that the formulation used meets the needs of the joint.

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