69 GT3 Cup
09-06-2012, 01:51 PM
#33
Race Car
Cage Info
Hey Pete,
Amazing build.... Great attention to detail and incredible vision.
Interested in some more information on the analysis you did on the cage design. How much force was applied to the cage in this pic? Have you done an analysis on different door bars and how it changes torsional rigidity?
Amazing build.... Great attention to detail and incredible vision.
Interested in some more information on the analysis you did on the cage design. How much force was applied to the cage in this pic? Have you done an analysis on different door bars and how it changes torsional rigidity?
09-06-2012, 08:20 PM
#35
Rennlist Member
Thread Starter
Thanks very much guys. Hayden really gets the credit...
Not sure what the force was in that particular pic, but it wouldn't matter.
I did a few different cage and body models. The models got to be quite complex, so all of them took liberties such as solid instead of hollow tubes, etc so that the simulations could be run faster. The simulations that proved most useful included more of the body, but were harder to see what was going on. The point is I simply focused on improving relative torsional rigidity rather than trying to get absolute values, so the forces I was using would result in different deflections in the real world.
What it was very useful for was analysing different door bars, bar placement, and ways to attach the cage to the chassis. The door bar concept I used, stolen from the street GT1, proved almost as rigid as the X door beam for the weight as long as the fillet was large enough. Key to getting good results from either design was getting the attachment to the main hoop (orange arrow) fairly high, then supporting this junction back to the rest of the body (yellow arrow). Without that even the X design still allows lots of flex. Cage attachment to the A pillar it the other really critical area for overall torsional rigidity.
I did a few different cage and body models. The models got to be quite complex, so all of them took liberties such as solid instead of hollow tubes, etc so that the simulations could be run faster. The simulations that proved most useful included more of the body, but were harder to see what was going on. The point is I simply focused on improving relative torsional rigidity rather than trying to get absolute values, so the forces I was using would result in different deflections in the real world.
What it was very useful for was analysing different door bars, bar placement, and ways to attach the cage to the chassis. The door bar concept I used, stolen from the street GT1, proved almost as rigid as the X door beam for the weight as long as the fillet was large enough. Key to getting good results from either design was getting the attachment to the main hoop (orange arrow) fairly high, then supporting this junction back to the rest of the body (yellow arrow). Without that even the X design still allows lots of flex. Cage attachment to the A pillar it the other really critical area for overall torsional rigidity.
09-07-2012, 01:21 AM
#36
Addict
Rennlist Member
Rennlist Member
Love the build and the reliability of the Cup motor -light weight - that must be fun to drive on the track or a mountain road! Thanks for sharing with us.
09-07-2012, 02:53 PM
#37
Instructor
Wow, that is just a work of art.
Pete, I love not only the concept of getting a cup engine in an old 911 but also the engineering approach you have had (FEA etc.). Being an engineer myself I can see that planning and bringing the project to life may be as rewarding and actually driving it.
You know we are discussing in this other thread
https://rennlist.com/forums/993-foru...ake-sense.html
about if modifying a 993 could make it as fast as modern 911. Well, I bet your car is actually faster than the Cup car you got the engine from, right? (it is below 1000 kg!!).
I would be interested to know if your FEA gave you an approximate value of the chassis stiffness. I’ve seen your previous reply and fully understand that you had to make some simplifications in the calcs and that if mainly helped you to find out the best design among the different cage concepts but do you have any ball park figure of the overall absolute torsional stiffness that we can compare with, say, a modern 991? I mean, did you manage to run an analysis modelling both the cage and the body?
I would love to to something similar to a 993 one day.
Enjoy in good health.
Pete, I love not only the concept of getting a cup engine in an old 911 but also the engineering approach you have had (FEA etc.). Being an engineer myself I can see that planning and bringing the project to life may be as rewarding and actually driving it.
You know we are discussing in this other thread
https://rennlist.com/forums/993-foru...ake-sense.html
about if modifying a 993 could make it as fast as modern 911. Well, I bet your car is actually faster than the Cup car you got the engine from, right? (it is below 1000 kg!!).
I would be interested to know if your FEA gave you an approximate value of the chassis stiffness. I’ve seen your previous reply and fully understand that you had to make some simplifications in the calcs and that if mainly helped you to find out the best design among the different cage concepts but do you have any ball park figure of the overall absolute torsional stiffness that we can compare with, say, a modern 991? I mean, did you manage to run an analysis modelling both the cage and the body?
I would love to to something similar to a 993 one day.
Enjoy in good health.
09-07-2012, 03:01 PM
#38
Race Car
Pete, That is an awesome analysis. I have always wanted to do a full cage in my car but hat the thought of full door bars. Always wondered how effective the GT1 style would be. Thanks for the info.
09-07-2012, 06:11 PM
#39
Rennlist Member
Thread Starter
I would be interested to know if your FEA gave you an approximate value of the chassis stiffness. I’ve seen your previous reply and fully understand that you had to make some simplifications in the calcs and that if mainly helped you to find out the best design among the different cage concepts but do you have any ball park figure of the overall absolute torsional stiffness that we can compare with, say, a modern 991?
'88 911 7000 nm/deg (measurement by burgermeister)
964 11500 nm/deg (993 was 20% stiffer)
993 13900 nm/deg (996 was 45% stiffer)
996 20120 nm/deg (Excellence was Expected p.1381)
997 33000 nm/deg
991 40000 nm/deg (porsche used 20% torsionally stiffer as a design target, has claimed "up to 25% stiffer")
So even at 20- 25,000 nm/degree, while 3-4x the original, is still probably only somewhere between a 996 and 997 in terms of absolute stiffness. Now I'd argue that stiffness to weight is the more important number, and on that count my car weighs nearly 1/3 less than the newer street cars. On that basis it's perhaps better than a 997. All bets are off as soon as you cage the newer cars, however- they get much, much stiffer themselves.
09-07-2012, 06:34 PM
#40
Rennlist Member
In certain places and on certain courses yes, in others no. I have better power to weight, obviously, but the cup does almost everything else better at the moment. The cup has better aero (even when I have my aero package on, which includes a cup wing), much better corner entry with my current rear suspension setup, etc. I'd have to take tires, etc into account, but I'd say I'm currently slower. However I'm not finished...
Best estimate, we guess the car is in the 20-25,000 N/deg range. This is much stiffer than the car was to begin with, but not as stiff as a modern 991 or even 997. My estimates of the different models stiffness:
'88 911 7000 nm/deg (measurement by burgermeister)
964 11500 nm/deg (993 was 20% stiffer)
993 13900 nm/deg (996 was 45% stiffer)
996 20120 nm/deg (Excellence was Expected p.1381)
997 33000 nm/deg
991 40000 nm/deg (porsche used 20% torsionally stiffer as a design target, has claimed "up to 25% stiffer")
So even at 20- 25,000 nm/degree, while 3-4x the original, is still probably only somewhere between a 996 and 997 in terms of absolute stiffness. Now I'd argue that stiffness to weight is the more important number, and on that count my car weighs nearly 1/3 less than the newer street cars. On that basis it's perhaps better than a 997. All bets are off as soon as you cage the newer cars, however- they get much, much stiffer themselves.
Best estimate, we guess the car is in the 20-25,000 N/deg range. This is much stiffer than the car was to begin with, but not as stiff as a modern 991 or even 997. My estimates of the different models stiffness:
'88 911 7000 nm/deg (measurement by burgermeister)
964 11500 nm/deg (993 was 20% stiffer)
993 13900 nm/deg (996 was 45% stiffer)
996 20120 nm/deg (Excellence was Expected p.1381)
997 33000 nm/deg
991 40000 nm/deg (porsche used 20% torsionally stiffer as a design target, has claimed "up to 25% stiffer")
So even at 20- 25,000 nm/degree, while 3-4x the original, is still probably only somewhere between a 996 and 997 in terms of absolute stiffness. Now I'd argue that stiffness to weight is the more important number, and on that count my car weighs nearly 1/3 less than the newer street cars. On that basis it's perhaps better than a 997. All bets are off as soon as you cage the newer cars, however- they get much, much stiffer themselves.
Power/weight alone is a very basic measure, and becomes especially meaningless at high speeds.
09-08-2012, 06:04 AM
#41
Instructor
Great stuff Pete, thanks so much.
Amazing how the chassis stiffness has increased with each 911 generation, I guess mainly due to the introduction and development of FEA. No surprise then that modern cars are so much easier to drive and quicker than older ones (together with the suspension geometry improvements you pointed out in the other thread).
I look forward to follow your improvements
All the best.
Amazing how the chassis stiffness has increased with each 911 generation, I guess mainly due to the introduction and development of FEA. No surprise then that modern cars are so much easier to drive and quicker than older ones (together with the suspension geometry improvements you pointed out in the other thread).
I look forward to follow your improvements
All the best.
09-08-2012, 01:50 PM
#42
Rennlist Member
It is interesting on how simply body stiffness can be achieved. A significant percentage of the 993's 20% increase compared to the 964 was achieved by gluing in and stressing the glass rather than having it mounted floating in rubber.
05-06-2013, 04:38 PM
#45
Race Car
Any other simple/hidden measure Snr Cup?