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Z torsional stiffness

Old 06-03-2003, 02:06 PM
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Z torsional stiffness

Just curious if anyone has measured the stiffness of a stock 240/260/280 and has data to share. I will be measuring Alan Walker's old car soon and wanted a baseline.

Alan's car ran in the NHA hilllclimb series and holds quite a few records. The car is pretty basic with the exception of having the motor moved back via GT rules provision. I'm planning on some mods to the cage to increase chassis stiffness but have never measured a stock car to see what the increases are.

My primary method for doing this is to get a baseline for my tube frame EMOD car. I'm trying to determine how stiff the car really needs to be (torsionally) to handle versus extra weight.

T
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Old 06-03-2003, 03:58 PM
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Tube80,
I haven't a clue what the difference is between the 240/ 280. I am not sure how you are going to use a tubbed car and cross the numbers over to your tube framed one. I would think that the differences in design would be hard to transfer over.

It would neat to figure out where the car would need to be braced to stiffen it up without adding weight in the wrong places. I have seen a lot of different cages in the Z race cars , and always wondered what they were doing. I know that safety and GCR's dictate some of the design.

BTW ... when you going to be up and running and are you going to make any of this years NHA events ?? I was just over at their site checking out the Knox Mountain photos .

Mike
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Old 06-03-2003, 07:32 PM
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Hi Mike,

I should be running in about two weeks with the unibody car. The tube car is a roller at this point and I don't think it will be running in anger before the end of the year, which is one reason I bought Alan's old car. This way I can at least get some good playing in this summer.

I won't be able to make Larison Rock because of a work commitment. NHA cancelled Cascade Lakes so that one is out too. I should be at Bogus Basin, Bible Creek (my backyard), and Hoopa, and I may venture to Black Otter but that jury is out on that one. I may go to nationals instead.

For the torsional test I'm just trying to determine the lowest number I can run. You can always make them stiffer but each tube adds weight etc. Alan's car has a lot of tubes and I'm trying to figure out if some of them really need to be there as I'd like to add a passenger seat.

I want to measure it for torsion, CG heght, RCs, etc. to have a baseline to compare against the tube car. One of the things I really want to understand better is what does a 2 inch reduction in CG heigth get you for lap time in an autocross. Or is it better to add a certain amount of ballast to balance a car, etc. I hear a lot of theoretical BS but I haven't seen anyone show me hard data for autox and hillclimbs. Or what is the right amount of ackerman to run ...

I have a basic datalogger that I can use to get the answers. I'm happy to share the results it's just going to take some time to get through all the tests. If you have something you are really interested in let me know. I can't promise anything but if it is interesting to me I'll give it a shot.

So far here's what I'm planning to do.

1. establish baseline (boring but needed)
2. CG height, balance, and polar moment
3. sprung weight and rotating weight
4. steering (caster, camber, KSA, pin lead, reduced scrub)
5. mulit-link front struts

wish me luck,

T
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Old 06-03-2003, 09:19 PM
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Tube80,
I discussed this once with a local Z racer. He is also really big into BMW's now. When the Z was originally built the computer design and most of the technology we have now wasn't available as you know. The set ups were through trail and error and the experience of the crews. If you look at the John Morton video thats on the web he was saying that the Z wasn't near as the developed as the Roadster was , yet is still won races . My freind tells me that BMW has done huge computer generated set ups on their race cars. He has looked at some of the factory cars and he said the cages and they use only bars that are necessary and even those have been lightened in some way.

I would really like to see what actually happens under load in a Z car. That would allow you to just spend time and money were its needed.

Are you on the D/E Mod Yahoo groups ? those guys toss around a bunch of suspension theory . Not sure if they can back it all up though.

I would really like to drop down and run Bogus some day . I was hoping this was the year I was going to be able to get more seat time.

Mike
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Old 06-05-2003, 09:04 AM
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Britt,
Here is the information page for Bible Creek. I will post the rest of the NHA Hillclimb Associations schedule as well.

http://www.wmclub.org/hillclimb.html
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Old 06-05-2003, 09:18 AM
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Originally posted by BrittB
Where is Bible Creek? I was talking to a guy name Marc Johnson who runs a white Rabbit out of Eugene and he was telling me about that run.
Also, are you doing any Auto-X this year? I here there's a run in Salem at the end of this month put on by the Willamate Motor Club. Might you be going?
Bible Creek is outside of Willamina about 40 minutes from Salem. You should see me at the next WMC event.

T
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