Full spool moved from 5250rpm to almost 6000rpm, and they were able to carry the power higher in the RPM range. Looking at the dyno graph you can see the larger A/R changed the shape of the power and torque curves. Switching to the larger 1.01 A/R turbine housing, Boersma picked up 50whp and 75ft/lbs of torque! There was a trade off in spool moving to the larger housing. Thankfully, turbine housing changes are simple and require no changes to manifold piping given you stay with the same inlet flange, so Boersma figured it was worth a shot to see how it all worked. The team decided to change to the 1.01 A/R turbine housing to increase horsepower as the competitor’s cars were making between 50 and 100whp more than they did. For a complete build breakdown on Chris’ Civic click this link. This housing also delivered good mid-range power and response for on track performance. 83 A/R housing which netted 600whp and 400ft/lbs of torque. Chris was using the GTX3076R Gen II turbo with a divided v-band. Garrett sponsored Time Attack racer Chris Boersma performed a similar test with his 1.9L Honda Civic. So, selecting the right size A/R for your turbine housing is very critical to reaching the optimum performance for your build. The engine produces exhaust air that flows through the turbine housing and propels the wheel assembly. This is very similar to how an engine and turbo work together. The straw’s larger air passage can flow more air and you are able to exhaust your breath easier without as much pressure (back pressure) in your cheeks. Now imagine the same example with a larger diameter straw. Finding a way to decrease engine backpressure helps promote flow from the cold side of the engine (intake) to the hot side (exhaust). In turbo talk we call that back pressure which can be really bad for an engine especially in the quest for higher horsepower. You may have also noticed pressure in your cheeks as you were not able to get the air through the straw fast enough. If you take a coffee straw and try to blow air through it, you quickly reach the flow limits for volume and velocity of the straws air passage. The smaller the A/R, the smaller the diameter of the straw, or air passage. Huh?Ī/R Simplified: As an example, think of A/R as a straw and you are trying to blow air through it. It is defined as the inlet (or, for compressor housings, the discharge) cross-sectional area divided by the radius from the turbo centerline to the centroid of that area. What is A/R?Ī/R stands for Area over Radius. Have you ever wondered what that A/R number means on a turbocharger? Why is there one on the compressor side and why is there one on the turbine side and what does it all mean? This write up is here to explain the difference an A/R makes on performance and show dyno graph overlay data for horsepower and torque to analyze how the changes affect engine response. Advanced Controls and System Optimization.48V Electric Compressor for Mild Hybrid Vehicles.