Boost Chart

[Rotax_Kid]

I use this chart a fair bit when I ride between home base, here in Saskatchewan at an elevation of 1600'. Some places we go in the rockies we are up over 10,000'. When I first started playing with boost, I knew it had to increase, but could never figure out how much in the field. First few trips out, it always gave me a bit of a jittery feeling wondering if I'm over boosting or was I leave power on the table by underboosting.

To figure out what you need, it's pretty simple. If you know what pressure you are operating at and your elevation find the point on the curve. From there, follow the curve up or down to the elevation you want to operate at. Follow a line straight across to the Y axis and you'll find boost.

I use this for my own purposes and it's useful to me. This is by no means a bible and I can't take any responsibility for any damage that could occur in using this chart. The Excel file that populates the chart is also attached. Hopefully it can help someone out there.

 

[milehighassassin]

Where did you come up with this data?

Good info just curious the method.

Also remember that increasing boost pressure can sometime be counter-effective if you are heating the charge temp too much. Meaning if you are stressing the turbo to make x-amount of boost and overworking it, operating out of the efficiency range you might be ahead to dial down the boost and operate within the efficiency of the turbo.


Edit...

Also consider that atmosphere pressure changes with weather.

Also your chart seems to be off a little. Denver (5280) averages about 12.1 PSI or a barometer of about 24.63, your chart says about 11.4 PSI.


Here is a good reference chart for pressure and elevation:
http://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html

 

[Rotax_Kid]

Where did you come up with this data?

Good info just curious the method.

Also remember that increasing boost pressure can sometime be counter-effective if you are heating the charge temp too much. Meaning if you are stressing the turbo to make x-amount of boost and overworking it, operating out of the efficiency range you might be ahead to dial down the boost and operate within the efficiency of the turbo.


Edit...

Also consider that atmosphere pressure changes with weather.

Also your chart seems to be off a little. Denver (5280) averages about 12.1 PSI or a barometer of about 24.63, your chart says about 11.4 PSI.


Here is a good reference chart for pressure and elevation:
http://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html

I worked backwards from what MCX references. All we really want is the same absolute pressure at the manifold. I'm taking atmospheric pressure at various altitudes and adding the appropriate amount of additional turbo pressure to achieve the same absolute pressure no matter the altitude. Similar data was done over in the Yamaha fourm a few years ago and I though it was pretty handy. Figured it would be useful to make a chart, laminate and throw in my toolbox in the trailer.

You look to be correct on the atmospheric pressure. I'll find a few sources more sourves to verify and update. Looks like I made the incorrect assumption that it's linear as well. Appreciate the info!

Chart and Graph Updated with new Pressures

RK