Rapid Bike altitude compensation fix

I've seen a lot of posts from folks running RB3's that were having problems with altitude compensation. I was running an RB3 on my MCX turbo kit and never had an issue. I sold my MCX and bought a sled with Powderlites kit. Now I understand what everyone was complaining about.

I could tune it in my field (200 ft elevation) and get it running perfect and then as I went up in altitude it would get leaner the higher I went. I then tuned it at altitude (5000 ft elevation) and then it would be pig rich as I came down in altitude.

The difference between the MCX and the Powderlites kit is the way the barometric pressure ties in. The Powderlites kit left the sensor untouched. The MCX kit originally did the same but MCX kicked out a tech update that said to install a barb fitting on the side of the intercooler and then route a hose from the barb to the baro sensor.

After making this discovery, I put the fitting in and attached the hose to the baro sensor just like I did for my MCX. I did the tuning in my field and then I rode at elevation. It ran perfect all day regardless of altitude.

I think what was happening is the RB3 was adding fuel based on boost as it should, but its a percentage add to whatever the sleds duty cycle is running at. Since the baro sensor was only reading the ambient air pressure and not the pressure the motor was seeing, it wasn't compensating correctly. It would pull fuel as altitude increased.

The fix costs about $5-$10. You can get the threaded 10-32 barbed fitting and hose from Clippard.

This is an awesome post.I never thought of this fix till just now after reading this.It makes perfect sense.This will work with RB3,Powercommander and others like it.
Dave

do you have a picture of this done would like to see exactly what you are talking about thanks

I don't have a pic. It's really as simple as I said. Get a 10-32 thread barbed fitting for a 1/8" hose. You can install it in the charge tube going into the intercooler (Don't plumb it into the vacuum side of the throttle body's like the BOV hose). I pulled mine apart so I could capture the shavings from the drill and tap process. You then run a hose from the fitting to the baro sensor. The baro sensor is just forward of the battery on the left side of the sled (Apex, not sure about nytro). The baro sensor has a nipple pointing straight down that accepts a 1/8" hose. You need to have a little extra hose so any condensation will settle in the hose and not get into the sensor. Probably wouldn't hurt to pull the hose once in a while to drain any moisture out of it.

I would expect that any sled that is tuned for higher elevations will need to re-adjust the map as this will fatten it up quite a bit. If you are tuned closer to sea-level, your map should be just fine as you go up in elevation.

This will only add fuel, no need to worry about it running too lean.