GT350 vs. Z/28

[Norm Peterson]

Dismissing out of hand what you consider to be only amateur knowledge might really be a case of trying to fool yourself. I'll stay out of the crap that's been flying around (it's why I went MIA here for a bit). But I did get paid pretty good money to do various forms of structural analysis for most of my career, and I've got some idea how to relate that knowledge to vehicle dynamics. There's a Clemson.edu / SAE paper on improving chassis torsional stiffness that's useful for grasping the concept, if nothing else.

Anyway . . .

20 seconds in about 8 minutes is about a 4% improvement in average speed. That's an 8% increase in lateral acceleration assuming that that 4% is distributed evenly around the entire distance (V-squared/R). But that's an unreasonably low estimate, since forward acceleration isn't going to be grip limited in the upper gears and max straight-line braking deceleration is not heavily dependent on chassis torsional stiffness. So now you're asking people to believe that a cage is going to cause tire grip somewhere in excess of a 15% increase with no other changes and no attempt to optimize the no-cage tuning that would be your basis. You're trying to convince us that there is that much tire grip sensitivity to camber as a function only of chassis torsional stiffness.

Frankly, I just don't see enough chassis torsional deflection happening to support that kind of gain, unless you started with a wet-noodle for a chassis and truly questionable roll stiffness distribution (to exaggerate the amount of torsion carried to the stiff end and hence exaggerate the actual torsional deflection at one end relative to the other). Camber change due to load transfer and differential tire vertical deformation is a bigger effect, probably much bigger.

Bushings have already been mentioned, so why don't we carry that a step further. Let's say the bushings are 15000 lb/in and at the front struts there is 20" difference in the lateral link and strut top pickups. 1g @ 4000# x 50/50 weight distribution is 2000 lbs, so the lateral link bushing sees over 2000# load (I'm not going to do all the math). That would be >0.13" deflection, but since we know that OE suspension bushings aren't linear maybe it's closer to 0.08" (bear with me for my WAG here). 0.13"/20" → 0.4° if we assume zero lateral displacement at the strut top (which isn't quite true). Brackets deflect, too, so let's make that 0.6° total. Are we to believe that a fraction of that 0.6° from chassis deformation is worth 15%?

Feel free to fill in the gaps.


Maybe it's worth something unmeasurable in terms of driver confidence . . .


Norm

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[thePill]

It's impossible to tell what you are really gaining without the equipment you mentioned. I've never caged a car that didnt show decent gains after tire/suspension tuning on shorter tracks. It's just a completely different car after a simple roll bar is installed.

A good example would be a 6 point in a 3rd Gen. Yes, it's a wet noodle so gains were probably appear large.

 

[thePill]

It's impossible to tell what you are really gaining without the equipment you mentioned. I've never caged a car that didnt show decent gains after tire/suspension tuning on shorter tracks. It's just a completely different car after a simple roll bar is installed.

A good example would be a 6 point in a 3rd Gen. Yes, it's a wet noodle so gains probably appear large.

Also consider that percentage gains you talked about. If Nurburgring consist completely of turns, we could apply all gains there. However Norm, performance in corner entry/braking would see a considerable amount of improvement. Your mid corner gains would be great, your exit speed would be amplified due to speed increases mid-corner. All that contributes to a higher speed in straights... Also, high speed sweepers could have more/less gains than the carousel. Those, along with the cage construction are unknown to me. It is also unknown to everyone else... This point being, once the cage goes in, the platform has a greater potential that was previously not achievable.

Even considering the gains a restricted Boss 302R gets at Laguna Seca (2 mile track) vs. the 302LS. That's a 4 second differance at a 2 mile track...

A sloppy translation from a 2 mile track to a 14 mile track, using just 4 seconds, translates to a 28 second gap between the two. I know this is napkin math but as long as a limiting factor like top speed doesn't arise, the gap should be somewhat stable (day, driver, weather). Obviously, the Boss 302R is more than just a cage and tires but, you can begin to see what a 4 second gap translates elsewhere between a caged car and an non-cage application.

A lot depends on the cage construction, which Chevy has hidden. Until I see the car, given Chevy's past behavior at the track, I just can't use a caged car as a benchmark for performance.

To be honest, we haven't even considered the amount of force that is on a typical 5th Gen chassis at z28 speeds and G's.

Edit: I apologize for the recent content of the thread. I try and remain a reflexion of the posters attitude. I try to explain things as simply as I can, if people don't get it and decide to attack me personally, it's game on... Ensnaring these "faithful" is my hobby and I'm probably the best at it People let themselves get upset and they desperately try and defend a product they have little or no real knowledge about....

 

[Jim968]

^^^^^^^^^^

This may be an interesting discussion from an academic standpoint, but it almost certainly has nothing to do with the Z/28’s Ring lap time. The video proves that the silver Ring car did NOT have a full roll cage. Furthermore if you Google “Z/28 Nurburgring Pictures” all you get are pictures of a silver car with no cage and NO roll bar either.

Instead of trying to prove that a roll cage accounts for a ridiculous amount of the Z/28’s Ring performance perhaps you’d be better off trying to prove that the Z/28 Ring car had any kind of cage in the first place.

 

[thePill]

You mad?

...the Camaro's Ring times were caged AND, they went as far as stopping the stop watch before the finish line.

...and yes, multiple technical degrees DO indicate intelligence. The Federal Governement makes sure of this.

 

[Sabre]

It's too difficult to try and explain these things to people that have do not have an education in this area. It's more frustrating than anything... That's why I stick to the entertainment aspect.

Oh........if only.......

 

[Jim968]

You mad?

...the Camaro's Ring times were caged

Prove it.

 

[jimmythepage666]

Lol check out right above the helmet to the right.
Hahaha hahaha!

 

[on d bit]

The video proves that the silver Ring car did NOT have a full roll cage. Furthermore if you Google “Z/28 Nurburgring Pictures” all you get are pictures of a silver car with no cage and NO roll bar either.

What pics? Where in the video does it show behind the seats?

Z28 was caged as well as the zl1 and the gt500 and every other test car hitting those numbers.

I disagree that the cage makes that much of a difference. The added rigidity is only used in certain corners and would surprised if the overall time difference was more than 2 sec even with a track as long as the ring. 2 sec is eternity in racing.

 

[Jim968]

Lol check out right above the helmet to the right.
Hahaha hahaha!

That's not the car that set the time.

 

[Jim968]

Z28 was caged

I can't find any evidence of that. If you can, please share it.

 

[jimmythepage666]

I can't find any evidence of that. If you can, please share it.

Please find some evidence of it not being caged...
So the camo car was caged, then they came back with a different z28 without the cage? Why?

 

[thePill]

What pics? Where in the video does it show behind the seats?

Z28 was caged as well as the zl1 and the gt500 and every other test car hitting those numbers.

I disagree that the cage makes that much of a difference. The added rigidity is only used in certain corners and would surprised if the overall time difference was more than 2 sec even with a track as long as the ring. 2 sec is eternity in racing.

There is no sound way to apply additional lap time to a vehicle that has an upgraded structure. Once tubing is installed, the vehicle is no longer OEM. Even if it ran a 7:50 and ran a caged 7:48, the chassis still needed additional support to break that performance plateau. Most of the club members there that run 8-9 minute tourist laps (that's really fast for TD), usually made it possible by installing additional structural support. This allowed them to fully optimize the tires and suspension.

As we seen earlier, MT took a measly 6psi from the tires that showed a 1 second gain on a 2.3 mile track. Now, try to imagine the gains that would yield once the structural rigidity is increased by 50, 100 even up to 300%. The gains are incalculable... I say that 7:37 would likely be closer to a 7:50 once all the race equipment was removed. I can easily see 13 seconds gained on a 14 mile track over a non-caged z28. The 6psi trick could have yielded a 7 second increase alone...

Once the vehicle takes on equipment to make this possible, the "Official" lap time seems a little less official. Most of the anger displayed on this thread D is from those who just witnessed their belief system collapse.

 

[on d bit]

I can't find any evidence of that. If you can, please share it.

Show me the pic/vid it wasn't

As we seen earlier, MT took a measly 6psi from the tires that showed a 1 second gain on a 2.3 mile track. Now, try to imagine the gains that would yield once the structural rigidity is increased by 50, 100 even up to 300%. The gains are incalculable... I say that 7:37 would likely be closer to a 7:50 once all the race equipment was removed. I can easily see 13 seconds gained on a 14 mile track over a non-caged z28. The 6psi trick could have yielded a 7 second increase alone...

I can't believe you're comparing tires to roll cages. You're better than that. No doubt they do help when the chasis is beyond its normal compromise which would be what 10-15 times on the ring allowing the car to gain tenths of a sec each time.

 

[on d bit]

Please find some evidence of it not being caged...
So the camo car was caged, then they came back with a different z28 without the cage? Why?

If they test and tune with the cage they will run for best time with a cage. As Pill states they would need to retune for best run without.

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