Understand how elevation and air conditions affect your watercraft's power output — and get the right impeller pitch recommendation for your riding location.
At higher altitudes, the air is thinner — which means your engine makes less power and your WOT (wide-open throttle) RPM changes. If you ride at a lake or reservoir significantly higher than where your ski was tuned, you may be over-revving or under-performing without knowing it.
This calculator takes the conditions at both your tuning location and your riding location, and tells you:
This is where your ski was tuned — typically sea level or wherever your Maptuner tune was developed and your current WOT RPM was measured.
| Field | What to enter | Example |
|---|---|---|
| Elevation | The altitude of your baseline location above sea level. | 0 ft (sea level) |
| Air Temp | The air temperature at your baseline location on the day the tune was made. | 80 °F |
| Humidity % | Relative humidity. If unsure, 50–60% is a reasonable default for most riding days. | 60 % |
| Baro (sea-level) | Sea-level barometric pressure. Standard is 29.92 inHg. Check weather.gov for the actual reading on your baseline day if you have it. | 29.92 inHg |
This is where you'll actually be riding — a lake, reservoir, or body of water at a different elevation or in different conditions than your baseline.
| Field | What to enter | Example |
|---|---|---|
| Elevation | The altitude of the lake or riding area. Check the lake's Wikipedia page or a topographic map if unsure. | 3700 ft |
| Air Temp | Expected air temperature on your riding day. Hotter air = thinner air = more power loss. | 95 °F |
| Humidity % | Expected humidity at the riding location. Desert areas are often 10–30%; coastal or mountain areas higher. | 20 % |
| Baro (sea-level) | Leave at 29.92 inHg unless you have a specific forecast reading. This is the sea-level equivalent, not the station pressure at altitude. | 29.92 inHg |
Enter your ski's specs and your real on-water numbers from the baseline location.
| Field | What to enter | Example |
|---|---|---|
| Rated power (HP) | The rated horsepower of your tune — check your tune documentation or the RIVA Racing tune spec sheet. | 230 HP |
| Baseline WOT RPM | Your actual measured wide-open throttle RPM at the baseline location with your current impeller. This is NOT the spec RPM — it's what your ski actually did on the water. | 8000 RPM |
| Engine type | Select Supercharged, Naturally Aspirated, or Turbocharged. Most RIVA Racing tunes are for supercharged engines. | Supercharged |
Tell the calculator what impeller you're running and what RPM you want to achieve at the riding location.
| Field | What to enter | Example |
|---|---|---|
| Current pitch | Your impeller's pitch specification — the leading/trailing angle, written as two numbers separated by a slash. | 13/18 |
| RPM per 1° trailing edge | How many RPM change per degree of trailing edge adjustment. ~100 RPM/° is a good starting point for most RIVA impellers. Your impeller manufacturer may have a more precise figure. | 100 |
| Target WOT RPM | Two options: Leave it blank and the calculator will target your baseline RPM — the goal is to get back to the same RPM your ski made at home. Or enter a specific RPM if you have a different target in mind, for example if you want to run slightly higher or lower than your baseline for a particular reason. | Leave blank to recover baseline |
After filling in all fields, click Calculate. The results panel will show:
How much denser or thinner the air is at the riding location vs. baseline, and the estimated HP difference.
What RPM your ski will likely hit at the riding location with your current impeller — before any changes.
The suggested new trailing edge angle to bring RPM back to your target. The calculator shows the exact degree change needed.
Use the unit toggle at the top to switch between Imperial (ft / °F / inHg) and Metric (m / °C / hPa) at any time.
Try searching by the nearest city instead. Then manually enter the lake's elevation — a quick Google search for "[lake name] elevation" usually gives it.
Make sure your Baseline WOT RPM is your actual on-water measured RPM, not the spec RPM from a brochure. The spec and real numbers often differ.
Supercharged engines are less affected by altitude than naturally aspirated ones, but can still benefit from an impeller change for high-elevation riding. A full re-tune is generally not needed unless you're riding above 5,000 ft regularly.
The two numbers (e.g. 13/18) are the leading edge angle and trailing edge angle in degrees. Only the trailing edge is adjusted for RPM tuning — the calculator only changes that second number.