adjustment for driving at altitude

[laneranch]

Hi,

I may purchase a SWB car next month running Webbers. As i live at 6000 ft what adjustments, if any, can i make for driving at this altitude?
al

[RSTarga]

lean her out a bit and advance the timing a few degrees.

[edmayo]

The rough rule of thumb is 2% change per 1,000 ft. If the car ran 130 mains at sea level then a 12% change would indicate about a 115 main. I'd start with a 120 main though to be on the safe side. You may also need to reduce the idle jets one size. I'm sure you realize that no matter what you will lose around 15 to 20% of power compared to sea level

[Grady Clay]

laneranch, Al;

This is why so many of us “Mile-High” owners let our original engines ‘rest quietly’ while we played using larger displacement and higher CR engines.
My 2.0 has way less than half the miles of the chassis.
The chassis has had almost a dozen other engines over 44+ years.

What year is your ‘new’ 911? ’67?

You can build (or have built) an engine that is ’67 (normal) appearing yet is 2808 cc and as high CR as you can find high octane gas for.
That more than compensated for the altitude loss.

Expect another issue from our thin air and air-cooled engines: they run hotter than at sea level.
The ‘easy fix’ is to turn the engine fan faster.
Simply replacing the crankshaft pulley can increase the ratio from the existing 1.3:1 to about 1.5:1.
Additionally changing the fan hub can get the ratio to 1.82:1 using all stock Porsche parts.

Many add a front-fender oil cooler system but the fan change addresses the heart of the problem.

If you track your 911, brakes will become an issue. Vented rotors are a must.
The ‘67S brakes without the dust shields are usually adequate.

For track use, engine cooling becomes a non-issue.
You will find many of us using water spray into the fan:
http://forums.pelicanparts.com/porsc...-solution.html
The sub-$100 solution.

Bring your ‘new’ 911 to one of our PCA breakfast gatherings; I-25 & Colorado Blvd. in Denver.

Best,
Grady

[RSTarga]

at least you don't have to worry about octane. I had my 73 at 7200 ft in Mexico City and I would have to lean it out 3 clicks on the MFI. I think I had about 25% less power there too. At least I had less wind noise with my Targa.