04-09-2012, 10:19 AM
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#119 (permalink)
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The370Z.com Sponsor
Join Date: Feb 2010
Location: Edmonton, AB
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Quote:
Originally Posted by sinceday1
I'll try to elaborate to the extent of knowledge.... (puts flame suit on)
T3, T4, T6... refers to the compressor size. Bigger the number, bigger it is but there are different dimensions entirely. Usually to reduce the lag, T3/T4 hybrid uses T3 hotside and T4 compressor so there can be expansion of some power due to T4 compressor and T3 hotside reduces lag to certain extent. It ultimately becomes limitation of the turbo in some cases...at same turbo rpm, the amount of gas T3 hotside will push will be smaller than that of true T4 thereby becoming the limitation. A/R ratio also works to determine the spool speed. Bigger the A/R later the turbo spools but if compressor size is different, same A/R does not mean same spool speed. So the compressor size and AR numbers work in conjunction to determine the spool speed per se.
It's still all arbitrary nomenclature of the size..... no exact dimension is set up.. what really matters is CFM...
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No... 
It is much easier to link:
http://www.turbobygarrett.com/turbob...Tech%20101.pdf
http://www.turbobygarrett.com/turbob...Tech%20102.pdf
http://www.turbobygarrett.com/turbob...Tech%20103.pdf
To be more specific to the question:
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.
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