Alan Herod

A number of us were discussing the top speed of a 911 - specifically 74 through 89 body. https://rennlist.com/forums/showthread.php?t=393305

My speedometer is fairly accurate now, due in a large part to taller then standard rear tires (255/40-17). At VIR the car will pull strongly out of Oak Tree and will pull away from a 996 until about 120, 6000 in fourth. It will continue to pull strongly to 6800, shifting into fifth produces little that could be considered acceleration. Fifth gear equivalent rpm is about 5500. Shifting at lower rpm results in lower speed, suggesting that fifth gear is too high.

Looking for means to raise this limit. Unfortunately I would also like to reduce lift or increase downforce. The car feels too light above 125. (not a normal SC, 95 993 engine and other mods)

smlporsche

Don't know mutch about your model 911 but one thing that works for the 944 series is to change the flag mirrors to the later 968 aero mirrors. Supposedly good for a couple MPH at top end. Some people actually remove the side mirrors all together and install smaller mirrors on their roll cage just inside the A pillar.

I also put a chin spoiler on my car and lowered it and this helped the lightness I was feeling at the top end.

racer

1) Gearing.. Need to re-gear to match the 3.6 HP and TQ curves Maybe even a 996 G50 6speed? Sounds like your 915 is stock.

2) You don't mention what spoilers (if any) you are running. Only way to reduce lift is to increase drag. Front splitter? 930 rear spoiler? 993RS rear spoiler? Does it feel light front and rear or only at one end?

Realize that the Cd of an 80s 911 is about .40 A 996 is about .33 That is a huge advantage at speed for the 996. Plus, 996 has different gearing to match that motor.

Alan Herod

Eddie -- I thought the flag mirrors might be a problem, thanks for the tip. Unfortunately, mirrors on the cage might interfere with the fixed part of the window and would interfere with emergency egress with Hahns and helmet.

Racer, thanks I know that gearing would help, it is a stock Euro 5-speed; but, I think the cost of a G-50 transplant is not something I want to contemplate. - running Carrera tail and chin. It is very light both ends at speed.

I had the spindles raised to lower the car.

What about the following -
993 windshield?
aftermarket front bumper cover
splitter
headlight covers

Can we get down-force without big drag penalty?

Sean F

rain gutter delete

Mark in Baltimore

Alan,

What about the RUF A-pillar inserts?

P/N: R64 500 599 00

38D

I'd be surprised if lowering the drag marginally vai small changes would make any difference at any track other than Daytona.

Mark in Baltimore

Then, why won't PCA allow me to put the RUF inserts on my car? I hereby promise that I won't ever run at Daytona with them on.

chancecasey

^^^^^

Well, it sounds like at VIR you are saying you are aero limited to 5th gear at 5500 RPM, is that correct?

You know if you reduce lift you will **necessarily increase the drag, making your 5th hit a wall even sooner than 5500 RPM.

If you are happy with your gearbox otherwise, just lower 5th gear a tad.

If you have stock ratios, a complete re-gear would work even better and produce better results in terms of final top speed for the dollar. There's only so much you can do to reduce existing aero drag, and has a much smaller effect than custom ratios.

You probably already know most of the aero drag tricks, though, like shaved rain gutters, lay the a-pillars and windshield back, smooth plastic wall on entire bottom of car, laid back headlights, flush windshield, smaller less "flat" frontal shaped mirrors, etc. Basically get rid of frontal harsh edges and flatness facing direction of travel - thought there are exceptions to that generalization.

RickBetterley

Hi Mark
I have not heard about these Ruf inserts. What can you tell me about their advantages?
Thanks

Larry Herman

Isn't that called a 996?

sleder

Alan, on your rear wing add racers tape over the last 3 to 4 vents it will add downforce in the rear and the splitter will assist greatly up front. gearing is an expensive adjustment but one that will put smiles on for years to come... Happy Holidays!

sjanes

If you are getting light at speed with the factory spoilers, maybe you don't have enough rake in the car? My car is very stable at 120mph (and was before I added the aftermarket spoilers). I have a 964 windshield and aero mirrors and there was no noticeable difference in top speed at the track.

I agree with the gearing changes mentioned. I have a lower 3-4-5, and it really helps.

Alan Herod

great information!!

transmission rework is a target; although as I understand it, the work required to put in a G-50 six speed is both technically challenging and very expensive.

aero-wise - CD numbers on 964 and 993?

chancecasey

You don't need a 6-speed. There are plenty of option for both the 5 speed G50 and even more for the 915. Four well-planned ratios will make an earth-shattering difference over stock 5-speed.