This is the first decision to make when choosing a turbo kit or the compressor for a DIY project. From reading thousands of posts on the subject the most common misunderstanding and mistake is basing this decision on what someones else wants, or wants to sell you, poser value, or just being able to generate a big dyno number.
So why not chose one big enough to put out huge hp when desired, like to impress your friend at the dyno, and then just turn it down for every day use. The reason is what is referred to in the business world as NO FREE LUNCH. Just like a cam change can increase peak hp you will likely find that low rpm hp has been lost in the process. The larger the turbo compressor the more efficient it will be at high boost but low rpm hp and spooling will suffer. While compressor designs have continually improved over the years the basic rules of this design decision have not. What most people really need is as much peak hp as can be used in their intended application and as much area under the hp/torque curve as possible. Don't trade off the area under the curve for more hp than you can practically use or if you do at least realize the consequences. You could end up with a product that lower hp bikes will motor away from on the low end and an uncontrollable pogo stick at the high end.
It has been proven time and again that a turbo Busa engine is capable of generating more peak dyno hp than could ever be controlled on the road or track and I doubt that the engines limit has even been reached yet. While these stratospheric hp numbers are a tribute to the designers, builders and tuners their real life use is limited to the 1/2 of 1 percent that live for the dyno shootouts.
So why not chose one big enough to put out huge hp when desired, like to impress your friend at the dyno, and then just turn it down for every day use. The reason is what is referred to in the business world as NO FREE LUNCH. Just like a cam change can increase peak hp you will likely find that low rpm hp has been lost in the process. The larger the turbo compressor the more efficient it will be at high boost but low rpm hp and spooling will suffer. While compressor designs have continually improved over the years the basic rules of this design decision have not. What most people really need is as much peak hp as can be used in their intended application and as much area under the hp/torque curve as possible. Don't trade off the area under the curve for more hp than you can practically use or if you do at least realize the consequences. You could end up with a product that lower hp bikes will motor away from on the low end and an uncontrollable pogo stick at the high end.
It has been proven time and again that a turbo Busa engine is capable of generating more peak dyno hp than could ever be controlled on the road or track and I doubt that the engines limit has even been reached yet. While these stratospheric hp numbers are a tribute to the designers, builders and tuners their real life use is limited to the 1/2 of 1 percent that live for the dyno shootouts.
