Not that I'm suggesting it, but I-5 in CA's San Joaquin is plenty straight and plenty flat...

 

Had my 76 with a 83 euro SSI motor to an indicated 150. i doubt it was that fast, 143 maybe with speedo error.

 

Is it the speedo or the way it's "geared"... tire diameter will play a role in real vs. perceived MPH (on the speedo) also.

You could use a GPS and just track top speed for a give "trip" but I've had my GPS say I was going 5MPH when stopped at a traffic light a few times, too. ;-)

 

I think an interesting test would be, use the same car, test top speed for
1: No tail
2: duck tail
3: Carrera tail
4: Turbo tail

and see what variances you come up with. I'm sure the results from drag would be an eye opener, I know a friend of mine with an E30 M3 had to change his EVO wing setting due to the horrible freeway mileage! I'm anxious to see what my car can do once its back together with an improved set of lungs and legs. I have had both a hopped up M5 (E39) and a 996TT over a 140mph on a surface street in socal, (with no side streets or traffic though, I pick and choose my play places) amazingly it doesnt take long with some more power and a change in the final drive (M5)!!

 

Rumour has it that the Carrara Tail actually reduces drag. The standard 911 rear is not so efficient from a drag standpoint. Who knows?

 

Here is a very informative thread on the aerodynamics topic.

https://rennlist.com/forums/showthre...ferrerid=18844

 

OK, apparently you all have replaced your speedometer, mine only goes to 85 and it's usually pegged there. Someone please point me to where I can get one that goes up to 140mph and how to install it!

 

Pelican has them. Maybe Vertex. I would look for a used one first. Actually I might have a used one - not sure if it is 85 mph or not.
E me if interested.
or try eBay
You just pull them out of the cluster and push them back in - very simple to R&R

 

Seth
I did change mine and I bought the entire dash cluster off of E- Bay. I know you wont believe it but
I paid 150 for every gauge and everyone works. As far as replacing very easy. My 81 just pulled out of the dash and I marked the wires and replaced.

 

My 2 cents. 4th gear tops out at around 125, I've hit 150 in 5th at about 5900 rpm. It's slow after 135, takes a lot of road. Thats with lowered set-up and whale tail with the chin spoiler. Handled like a champ over 140. No fear or sketchyness.