Looking for 911 Technical Specs for College Assignment
 

Hi everyone,

I'm currently studying Vehicle Dynamics at University, I have to do an assignment analyzing the design of a car, and I thought I would do it on my 1967 911 but I'm having some difficulty finding some of the specs so I thought this would be the best place to post.

I have to find the center of mass of the vehicle with regards to the wheelbase and also the height. Anyone know these figures, google has failed me thus far. I have a few books at home I was going to have a look through but I thought someone on here might have it on hand.

If it is easier, I am happy to calculate the specs for a later model 911 instead if someone has the specs for that.

thanks
Drew

This is a great board but the true experts on all things early cars is the Early S Registry: General Info

Post there and you will get a ton of info. Good luck on the project

I asked this question for similar reasons- weight transfer, sway bars, roll couple distribution, roll centers, etc. but no one had any actual measurements. Every car is different, for one, and the other reason is that you would need to lock the suspension and have a tilting table resting on 4 corner balance scales to find the x-y-z location.

Finding the longitudinal location is pretty easy with some corner balance scales and a reasonably level floor. Just look at the front/rear weight distribution. You could do the same for side to side.

For a very lightened car, 20 inches high is a good place to start. Maybe 24 for a stock car.
Longitudinally, a lightened car's weight distribution would be maybe 36/64 to the rear, with a stock car 40/60 to the rear.

For your 1967 911, assuming stock, no sunroof, I would go 22in high, 40/60 weight distribution longitudinally, and maybe go ahead with 60% on the driver side with you in it.

The accuracy matters- ie you are trying to model the actual behavior of the car, then confirm with actual laptimes, slalom, skidpad things, or are you just wanting something close for a theoretical excercise.

Thanks for the replies guys.

According the book Porsche 911 Story the weight distribution was approx. 41.5/58.5 for the SWB and 43/57 for the LWB models so I'm going to work with those numbers, but the height I can't find anywhere so I might have to go with your suggestion of 22in. I will try and have a look around for a more accurate number. It seems this is a difficult value to find but I assume someone has a value as its pretty important if you want to do these vehicle handling calculations.

The calcs are for an assignment and as such is theoretical but I have to justify any estimations as far as the initial dimensions etc are concerned.

I want to get it as close as possible to the real thing though, it would be nice to know exactly whats going on with the handling of the car. Not only is it interesting because I love the car but the characteristics of the car are really unique so I think it will make for an interesting assignment too.

Thanks for all the input guys!

I also like studying vehicle dynamics in my spare time- reading mostly. I wish we had a vehicle dynamics concentration here at my school. I am just doing Mechanical Engineering. It is all quite interesting to me, though.

Most guys, racers included, just go with what other respected racers have said to work, and they like whatever takes time off a lap. They do not do so much theory- the only guys who find that interesting are us engineers. :)

Most guys know that the lower the center of mass the better, so they take out sunroofs and such. Other than that, there is not much they can do to tune the cg height or re-distribute weight unless they use ballast for a race class. They just remove weight where they can- then add it back in in the form of tubes/roll cages.

So, the vehicle dynamics stuff does not apply much in absolute/simulation/modeling terms here- that is more for pro racing GT, LMP, open wheelers.

The basics of roll couple distribution, and spring/mass/damper systems apply, and the concept of roll centers is good to know when thinking about raising spindles and working with bump steer, but the 911 suspension is rather antiquated, so the Colin Chapman principle applies of just keep it from moving.

I don't think the height of the C of G has ever been published. It's been discussed here many times before, so about all I think you'll find for it is an educated guess.

JR

yes, there are at least 2-3 other threads on it

why not do what the pros do -- estimate several values, plug them in to your mathematical model - write that up in the methods section

then in the results, present a graph of how the output variables change based on changes in the ht. of the Cg parameter

point out that it is a sensitivity analysis (or part of one) and not a full blown global stability analysis of an analytic model - use those terms are key words to search up some additional reading & include it in the Literature cited part of your paper - also talk to your instructor about your plans

http://forums.pelicanparts.com/porsche-autocross-track-racing/597864-911-cg-height.html


I believe there is some stuff a ways in in this thread where Grady Clay talks about an adjustable CG height 911 research car with a 1 foot cube of lead on a sliding vertical track.
http://forums.pelicanparts.com/porsche-911-technical-forum/582110-best-handling-lightness-vs-distribution-vs.html

Note: the oil tank moving forward should shift the CG about 0.6 inches, not 6 since the CG can only move a proportion of the distance the oil tank moved equal to the proportion of the total weight that the oil tank + oil weighs.
http://forums.pelicanparts.com/porsche-911-technical-forum/326860-where-center-gravity.html