Question about T3 & T4 turbine housing A/R ratios.
12-23-2006, 10:04 AM
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Re: Question about T3 & T4 turbine housing A/R ratios. (b16sedan)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by TURBObyGARRETTdotCOM »</TD></TR><TR><TD CLASS="quote">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.
Conversely, using a larger A/R will lower exhaust gas velocity, and delay boost rise. The flow in a larger A/R housing enters the wheel in a more radial fashion, increasing the wheel's effective flow capacity, resulting in lower backpressure and better power at higher engine speeds.
When deciding between A/R options, be realistic with the intended vehicle use and use the A/R to bias the performance toward the desired powerband characteristic.
Here's a simplistic look at comparing turbine housing geometry with different applications. By comparing different turbine housing A/R, it is often possible to determine the intended use of the system.
Imagine two 3.5L engines both using GT30R turbochargers. 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.
What can we infer about the intended use and the turbocharger matching for each engine?
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. </TD></TR></TABLE>
Conversely, using a larger A/R will lower exhaust gas velocity, and delay boost rise. The flow in a larger A/R housing enters the wheel in a more radial fashion, increasing the wheel's effective flow capacity, resulting in lower backpressure and better power at higher engine speeds.
When deciding between A/R options, be realistic with the intended vehicle use and use the A/R to bias the performance toward the desired powerband characteristic.
Here's a simplistic look at comparing turbine housing geometry with different applications. By comparing different turbine housing A/R, it is often possible to determine the intended use of the system.
Imagine two 3.5L engines both using GT30R turbochargers. 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.
What can we infer about the intended use and the turbocharger matching for each engine?
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. </TD></TR></TABLE>
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12-23-2006, 11:29 AM
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Re: Question about T3 & T4 turbine housing A/R ratios. (b18sihatch)
I think the question he is asking is:
How does a bigger AR on a smaller turbine housing compare to a smaller AR on a larger turbo housing?
BUMP cuz I wanna know too.
How does a bigger AR on a smaller turbine housing compare to a smaller AR on a larger turbo housing?
BUMP cuz I wanna know too.
12-23-2006, 11:58 AM
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Re: Question about T3 & T4 turbine housing A/R ratios. (JDMs1eeper)
A/R (Area/Radius) describes a geometric characteristic of all compressor and turbine housings. Technically, 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 (see Figure 2.).
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 (see Figure 2.).
12-25-2006, 12:08 AM
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Re: Question about T3 & T4 turbine housing A/R ratios. (not2slo128)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by not2slo128 »</TD></TR><TR><TD CLASS="quote">I think the question he is asking is:
How does a bigger AR on a smaller turbine housing compare to a smaller AR on a larger turbo housing?
BUMP cuz I wanna know too.</TD></TR></TABLE>
That is correct.
Ex: T3 a/r .86 vs. a T4 a/r .84.
How does a bigger AR on a smaller turbine housing compare to a smaller AR on a larger turbo housing?
BUMP cuz I wanna know too.</TD></TR></TABLE>
That is correct.
Ex: T3 a/r .86 vs. a T4 a/r .84.
12-25-2006, 06:05 AM
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Re: Question about T3 & T4 turbine housing A/R ratios. (gawath)
A .63 a/r stage 5 (SC6152e) spools about 200rpm faster than a .58a/r T4 turbine w/ a t3 stage 5 wheel (PT6152e)
This was on a 2l 16v VW engine w/ mild cams, 8.5:1 compresion, and ported head. Everything else was the same but some tweaks to the tune.
This was on a 2l 16v VW engine w/ mild cams, 8.5:1 compresion, and ported head. Everything else was the same but some tweaks to the tune.
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