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. RE: calculating plenum size on 2.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. Look up "Helmholtz" in google for some formulas. If you blow into a beer bottle you can get a low frequency droning sound which has a wavelength far longer than the size of the bottle. This is not the same as tuned runner length which relies on the speed of sound. The volume of air in the runner, combined with the springiness of the air in the plenum causes the air in the runner to bounce like a spring. Its a bit like the tuned port in your loudspeaker box. The runner VOLUME, that is length x area, can combine with the air volume in the plenum to create Helmholtz resonance at a particular (usually low) frequency. Plenum volume is a third variable that may (sometimes) be used to create an additional low speed tuning hump in the torque curve. This can introduce tuning peaks and hollows into the torque curve, but the effect is not as strong as diameter. This will be the strongest tuning variable and will effect the torque peak. The first is runner cross sectional flow area. When tuning the induction on an n/a engine there are three tuning variables. In practice you will always be limited by the available space and layout. However, if you are planning on individual throttle bodies in each runner, it is going to have crisper throttle response with even a humongous plenum. A smaller plenum might be better in that regard. If you only have a single throttle body at the plenum entry, a large plenum is not going to help with throttle response or lag. ![]() A symmetrical plenum is going to be better than an end fed plenum as far as air distribution goes, all other factors remaining equal. If it does it can starve those cylinders of air, and they will run rich, while others further from the plenum entry will have excess air and run lean. There are many factors to consider, there is not really any perfectly "correct" size.įirst each runner must have enough volume to draw from so each cylinder is not going to rob the next, so bigger is better in that regard.Īlso the plenum entry must not flow at high velocity directly across the face of some particular runners.
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