0-60 for a 914/6 with 3.2? Options

[Tdskip]

The numbers are secondary to the driving experience of course, but just curious if anyone’s ever benchmark to their conversion against a stopwatch?

[Superhawk996]

This thread really got me thinking about what the lower bound might be for a 914 1/4 mile time.

If anyone is interested I found a decent on-line 1/4 mile simulation tool that accounts for key variables like tire mu, engine inertia, wheel inertia, aero effects, rolling resistance, etc.

Most models I could find were overly simplistic just based on weight vs. HP which is not a resonable modeling simplification. I also tried to find more elaborate Vehicle Dynamics Matlab or Simulink models but came up empty handed and I didn't want to have to create my own from scratch - far too time consuming. The only one I could find didn't work with my older copy of Matlab.

This model also has a traction control assumed in it that assumes torque will be limited to only what the tire mu can support. It also has a clutch slip factor that you can play with.

http://www.nightrider.com/biketech/accel_sim.htm

This on-line tool appears to be built off a standard "bicycle model" which is commonly used in automotive for modeling of things like longitudinal accelerations related to brake controls. Ufortunately I can't see the source code but the input variables are correct for a simplied bicycle model and include the important Cd and rolling resistance terms. Aero drag and rolling resistnace become very important at 60 mph+ speeds. They key points to use the model is that you will have to double the wheel inertia and that the engine inertia is "lumped" so ideally you would need the inertia of the engine and the transmission. These can be estimated based on other academic work found here.

http://transportproblems.polsl.pl/pl/archi...2010t5z1_04.pdf

Key inputs from Peter Russek 914/4 guide
914 Wheelbase = 96.5 inches
1st gear = 3.09
2nd = 1.89
3rd = 1.26
4th = .93
5th = .71
6th ==NA for 914 but you can use .71 again
Final Driver (Rear axle ratio) = 4.429:1

Cross sectional Area - I assumed 20 square feet
914 width = 65 inches
914 height = apporox 43 inches
This gives 19.4 sq. ft. of frontal area and then some fluff for tire frontal area I neglected to include.

Cg height for a 914 with a flat six is reasonable around 14 inches give or take. I recommend doubling this and then look at the results again. Gives you an indication of how much additional weight transfer and time reduction comes from getting more traction on the rear from increased weight transfer as Cg height increases.

Suggested engine inertia from academic paper referenced above for 2.0L VW TDI. Surely isn't a boxer motor and is probably too heavy but it will help offset the transmission which I've neglected.
0.246 Kg*m^2 which converts to 0.18 slug*ft^2

Transmission inertia - I neglected it. The flywheel and crank are included in the engine and are where the bulk of the inertia will come from. Likewise, I neglected axles. Neglecting these would make the model "optimistic".

The wheel inertias and diameters are pretty close at default settings.
Typical wheel is apporox. 26" diameter
Don't forget to double the default inertia to account for the 4 wheels on a car that have to be spooled up instead of only two.

Static Coeffieicent of Friction for a all out race tire is 1.5 nominal

The rolling coefficient of friction will be low (again only two rolling elements and based on motorycle driveline) but you can double it or bump up if you want. Again leaving as-is is optimistic.

Go ahead and start with something Viper(ish) of 400 lb*ft of toruqe flat lined across the entire RPM band for simplicity.

Have fun with it, you'll get an idea of just how hard it would be to break into 11-12 seconds due to traction control / tire slip. Look at the acceleration. To get to a Telsa P100D time of 10.72 sec 1/4 mile, you'll need to get the max launch acceleration up to about 1.4G. Varying the torque, gearing, and Cg height will change max acceleration potential to one degree or another.

PS: Link to site that will help ease rotational inertia conversions between Kg*m^2 and Imperial Slugs*ft^2

https://online.unitconverterpro.com/convers...t=4&val=.66