Turbocharger Basics:
Compressor/Turbine Wheel Trim:
Trim is a term to express the relationship between the inducer* and exducer* of both turbine and compressor wheels. More accurately, it is an area ratio. The inducer diameter is defined as the diameter where the air enters the wheel, whereas the exducer diameter is defined as the diameter where the air exits the wheel.
1. Engine #1 has a T3T4E 40trim with an A/R of 0.63
2. Engine #2 has a T3T4E 60trim with an A/R of 0.63
Engine#1 - This engine is using a smaller compressor wheel thus biased more towards low-end torque and optimal boost response. The results of a smaller compressor wheel are generally less top end power compared to the larger compressor wheel. This type of engine performance is sometimes desirable for street applications where the low speed boost response and transient conditions are more important than top end power.
Engine #2 - This engine is using a larger compressor wheel and is biased towards peak horsepower, while sacrificing transient response and torque at very low engine speeds. The results of a larger compressor wheel are generally more top end power compared to the smaller compressor wheel. The performance of Engine #2 is more desirable for racing applications than Engine #1 where the engine will be operating at high engine speeds most of the time.
Compressor housing/Turbine housing A/R:
Compressor A/R - Compressor performance is comparatively insensitive to changes in A/R. Larger A/R housings are sometimes used to optimize performance of low boost applications, and smaller A/R are used for high boost applications. However, this influence of A/R on compressor performance is relatively minor.
Turbine A/R - Turbine performance is greatly affected by changing the A/R of the housing, as it is used to adjust the flow capacity of the turbine. Using a smaller A/R will increase the exhaust gas velocity into the turbine wheel. This provides increased turbine power at lower engine speeds, resulting in a quicker boost rise. However, a small A/R also causes the flow to enter the wheel more tangentially, which reduces the ultimate flow capacity of the turbine wheel. This will tend to increase exhaust backpressure and hence reduce the engine's ability to "breathe" effectively at high RPM, adversely affecting peak engine power.
Example:
Imagine two engines both using the same turbocharger . The only difference between the two engines is a different turbine housing A/R; otherwise the two engines are identical:
1. Engine #1 has turbine housing with an A/R of 0.63
2. Engine #2 has a turbine housing with an A/R of 1.06.
Engine#1 - This engine is using a smaller A/R turbine housing (0.63) thus biased more towards low-end torque and optimal boost response. Many would describe this as being more "fun" to drive on the street, as normal daily driving habits tend to favor transient response. However, at higher engine speeds, this smaller A/R housing will result in high backpressure, which can result in a loss of top end power. This type of engine performance is desirable for street applications where the low speed boost response and transient conditions are more important than top end power.
Engine #2 - This engine is using a larger A/R turbine housing (1.06) and is biased towards peak horsepower, while sacrificing transient response and torque at very low engine speeds. The larger A/R turbine housing will continue to minimize backpressure at high rpm, to the benefit of engine peak power. On the other hand, this will also raise the engine speed at which the turbo can provide boost, increasing time to boost. The performance of Engine #2 is more desirable for racing applications than Engine #1 where the engine will be operating at high engine speeds most of the time.
Garrett Turbocharger Specs:
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