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High Elevation

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  • High Elevation

    I have a FFS kit on order. I live in Denver, and my car will spend 99% of the time at ~5000ft elevation and occasionally up higher to the mountains.

    Anyone have experience of running an FFS kit at these elevations and the effect on boost levels? Assuming it loses boost, is there anything that could be tweaked to retain the ~10psi boost level within the parameters of the kit (pulley size?) but still work on the 91 octane gas available in Colorado and not cause issues if the car ever went back closer to sea level?

  • #2
    I have an NA with the FFS supercharger and have driven it at high altitude without issue.
    96 Montego - FFS ColdSide, 97 Black & Tan, 90 White


    • #3
      Thanks bogey


      • #4
        I believe it will still indicate 10 PSI boost on the gauge if you run at 5000 feet. When you start, the gauge zeros itself at "ambient pressure". Boost is the number above "ambient". As the ambient pressure drops about 1 PSI per every 2000 feet, the 2.5 psi you lose at 5000 feet is already removed by the gauge. You will likely indicate 10 psi but you are actually only making power as you would at 7.5 psi at sea level. I have not physically checked this but I am pretty sure this is how it will work. If, for example, you started at sea level and drove to 5000 feet; then I believe it might indicate 7.5 psi as it zeroed itself at sea level.

        1990 with FFS Coldside. At least 260 WHP NON-INTERCOOLED


        • #5
          I partially agree...

          The internal pressure sensor on the FFS cards does zero out when you power on the car. This sets the fuel controllers to 0psi ambient. If you also have a mechanical boost gauge, you can see the discrepancy at altitude. It reads lower...

          However, as you climb the mixture will be leaner for a given rpm. As you descend it will get richer. I noticed this when I drive out west and make substantial altitude changes. If I am going to climb 8000 feet, it will tend to lean out. A reset will correct it but then you have rich when you drop altitude. This is not a big deal as there is enough adjustability to compensate. I would set the fuel add a little higher to prevent running too lean or if you ever hear knock.

          I have taken several firmware updates since I saw this behavior and I believe the fuel controller compensates better for altitude changes since version 1.0. I have 85000 miles on my FFS supercharger, nearly 170000 total miles on the engine. Couldn't be happier with the kit.
          96 Montego - FFS ColdSide, 97 Black & Tan, 90 White


          • #6
            Thanks Tom and Bogey.
            Based on the above, what are your thoughts on a different pulley size to try to make the equivalent of a 10psi-sea level power at 5000' where it will be most of the time? With the understanding that if the car goes below 5000' it would need switched back to the regular pulley size?


            • #7
              I run a larger pulley. I think it's 120mm. 2 sizes up from stock. Works fine at all altitudes.
              96 Montego - FFS ColdSide, 97 Black & Tan, 90 White