DIY Turbo Selection
by Ryan Smith

So I found a great deal on a few turbo parts in the classifieds and started piecing a home made turbo kit together. I finally got to the point where I had to choose a turbo for my application which was a B18B1.

I started to do my research and I found that basically everything on the web was opinion based with little factual information to support their choice for a turbo. I kept searching and found programs such as Turbo Calculator but none of them were free. I was then recommended Corkey Bell’s Maximum Boost which included mathematical formulas to help in calculating pressure ratio and the corrected CFM of an engine.

I am a Mechanical Engineering student at the University of Wisconsin Platteville and using my background in mathematics I started throwing numbers into the equations and plotting points when I decided that I needed to come up with a simpler way. They were not the most difficult calculations but they defiantly took time and it was a challenge converting units and plugging variable into different equations. So I took the general formulas and created a table in Excel where you could input the variables and it would give you the pressure ratio and the corrected mass flow at multiple rpm ranges. This allows a person to choose a compressor based on their need rather than a guess and check method.

Using my program you input the displacement of your engine and the amount of boost you will be running. From these inputs the program uses Corkey Bell’s exact equations and gives you a precise Pressure Ratio (PR) and Corrected Mass Flow (CMF). These numbers can be directly compared to your compressor map to find the most efficient compressor for your application. The CMF number is the lb/min result for x axis and the PR is the y axis. After that go to this website:

http://64.225.76.178/catalog/compmaps/fig3.html

…and look at the different maps until you find one that gives you the highest efficiency (measured in percent) for whatever rpm points you are most interested in. If you look at the circles on the graph those are efficiency ranges and the further from the center circle you go the less efficient the turbo will be at that point.

I created this program to help DIYers to choose the right turbo the first time and to save time for people tying do the calculations manually.

Written and submitted by Ryan Smith Platteville, WI