the hustler effect. smaller A/R on bigger turbo = better spool.
08-20-2009, 02:24 AM
#22
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GT2860RS with 0.86 A/R
vs
GT2871 with 0.64 A/R
I'd need to see the full turbine maps. Basically look at the compressors, for say 3500 RPM and 7.5 psi, read out the RPM and efficiency. Calculate the shaft power and engine horsepower. Then, look at the turbine maps and determine if that exhaust flow at that horsepower can deliver that required shaft power at that shaft RPM. Whichever has more excess shaft power will spool quicker at 3500 RPM. Repeat this at 0, 5, 10 psi; at whatever psi there is no excess shaft power from the turbine, will be the max boost at that RPM.
vs
GT2871 with 0.64 A/R
I'd need to see the full turbine maps. Basically look at the compressors, for say 3500 RPM and 7.5 psi, read out the RPM and efficiency. Calculate the shaft power and engine horsepower. Then, look at the turbine maps and determine if that exhaust flow at that horsepower can deliver that required shaft power at that shaft RPM. Whichever has more excess shaft power will spool quicker at 3500 RPM. Repeat this at 0, 5, 10 psi; at whatever psi there is no excess shaft power from the turbine, will be the max boost at that RPM.
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08-20-2009, 02:29 AM
#23
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P.S. my gut feel is the 2871 with 0.64 would spool quicker, but a 2860 with 0.64 would be even quicker.
The reason for that is the small A/R would generate more shaft power at lower exhaust flow rates, even when comparing the 2 compressors (and thus at different shaft RPMs).
The reason for that is the small A/R would generate more shaft power at lower exhaust flow rates, even when comparing the 2 compressors (and thus at different shaft RPMs).
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08-20-2009, 10:07 AM
#24
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you can't really argue the point about MBT without actually putting the .64 on and tuning it because even though it might seem to preclude running near MBT, none of us has data to prove it. so lets assume we can cheat that portion by other means in choice 2.
All those turbos share the same hotside wheel. 53.8mm 76 trim. here's the garrett excuse for a map.
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08-20-2009, 10:26 AM
#25
I'm with Hustler on this one. I'm switching to a bigger A/R turbine because I almost exclusively track my car and I would rather have lower underhood temps and lower engine load than 400rpm earlier spool.
Bigger A/R = less restriction = less overall heat output by the turbine = lower underhood temps = happier track car..... at least that's what "Maximum Boost" taught me.
Bigger A/R = less restriction = less overall heat output by the turbine = lower underhood temps = happier track car..... at least that's what "Maximum Boost" taught me.
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08-20-2009, 10:49 AM
#26
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I'm with Hustler on this one. I'm switching to a bigger A/R turbine because I almost exclusively track my car and I would rather have lower underhood temps and lower engine load than 400rpm earlier spool.
Bigger A/R = less restriction = less overall heat output by the turbine = lower underhood temps = happier track car..... at least that's what "Maximum Boost" taught me.
Bigger A/R = less restriction = less overall heat output by the turbine = lower underhood temps = happier track car..... at least that's what "Maximum Boost" taught me.
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08-20-2009, 11:10 AM
#27
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Well, I'm new here, so I'm not going to jump in the fray...but I do have a question:
Where are the pre and post turbine pressure measurements? That is what dictates whether a turbine A/R is too "big" or too "small."
Turbine pressure ratios dictate spool. Not EGT's, although EGT's and mass air flow dictate how much energy there is to be extracted from the exhaust.
Where are the pre and post turbine pressure measurements? That is what dictates whether a turbine A/R is too "big" or too "small."
Turbine pressure ratios dictate spool. Not EGT's, although EGT's and mass air flow dictate how much energy there is to be extracted from the exhaust.
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08-20-2009, 11:26 AM
#28
I am running the .64 on my 2860 for my street/track car. I did that beacsue I am ultimately not looking to make 375 hp, just around 300-340. Even then, the car will be a handful on the track.
I don't feel that in the range that I will be running, with respect to power, that the heat will cause a significant enough difference to merit a larger A/R. If and when I push it further, then it may come into play more. At that point I will move up to an .86 2871, IF I need more than 325hp on the track for some retarted reason. These assumptions were made on my limited knowledge of how all of this crap works, so if my logic is wrong please call me out on it.
I don't feel that in the range that I will be running, with respect to power, that the heat will cause a significant enough difference to merit a larger A/R. If and when I push it further, then it may come into play more. At that point I will move up to an .86 2871, IF I need more than 325hp on the track for some retarted reason. These assumptions were made on my limited knowledge of how all of this crap works, so if my logic is wrong please call me out on it.
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08-20-2009, 05:52 PM
#29
I'm with Hustler on this one. I'm switching to a bigger A/R turbine because I almost exclusively track my car and I would rather have lower underhood temps and lower engine load than 400rpm earlier spool.
Bigger A/R = less restriction = less overall heat output by the turbine = lower underhood temps = happier track car..... at least that's what "Maximum Boost" taught me.
Bigger A/R = less restriction = less overall heat output by the turbine = lower underhood temps = happier track car..... at least that's what "Maximum Boost" taught me.
TurboByGarrett.com - Turbo Tech102
Originally Posted by Garrett Turbo Tech 102
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.
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.
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08-21-2009, 05:02 PM
#30
I may have fallen victim to my own idiocity. With my smaller .64 ar I am not hitting a brick wall for power. It may be the turbo or may not, but i have a feeling it is just because I thought I was doing the right thing for response, but it punished me severely in overall power. I should have gone with a .86 2871 to begin with.
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08-21-2009, 05:35 PM
#32
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I may have fallen victim to my own idiocity. With my smaller .64 ar I am not hitting a brick wall for power. It may be the turbo or may not, but i have a feeling it is just because I thought I was doing the right thing for response, but it punished me severely in overall power. I should have gone with a .86 2871 to begin with.
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08-21-2009, 05:50 PM
#33
I may have fallen victim to my own idiocity. With my smaller .64 ar I am not hitting a brick wall for power. It may be the turbo or may not, but i have a feeling it is just because I thought I was doing the right thing for response, but it punished me severely in overall power. I should have gone with a .86 2871 to begin with.
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08-21-2009, 06:52 PM
#35
These are really good threads, just the right amount of discussion vs. friendly ****-talking.
This thread, and about 1/2 dozen more like it have cemented my choice of the .64 Disco as the turbo of choice for a 300whp street-car.
What I really want is a few more people to start exploring the 300whp range on stock 99-00 motors and gather datapoints. So far, there are only a few guys who do it.
S4, exhintake, adj cam-gears, Adaptronic, 3" exhaust... I CAN'T WAIT FOR CRUISE TO BE OVER!!!
This thread, and about 1/2 dozen more like it have cemented my choice of the .64 Disco as the turbo of choice for a 300whp street-car.
What I really want is a few more people to start exploring the 300whp range on stock 99-00 motors and gather datapoints. So far, there are only a few guys who do it.
S4, exhintake, adj cam-gears, Adaptronic, 3" exhaust... I CAN'T WAIT FOR CRUISE TO BE OVER!!!
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08-21-2009, 11:03 PM
#38
Sorry, I need to clean up that last sentence. I really didn't read through it before I posted. What I was saying is that I thought the trade off for ultimate power for quicker response would be better than what it was. I am now feeling the punishment for not doing my homework and assuming my logic is flawless.
This turbo would really be great for a daily car.
This turbo would really be great for a daily car.
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08-22-2009, 09:35 AM
#39
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Sorry, I need to clean up that last sentence. I really didn't read through it before I posted. What I was saying is that I thought the trade off for ultimate power for quicker response would be better than what it was. I am now feeling the punishment for not doing my homework and assuming my logic is flawless.
This turbo would really be great for a daily car.
This turbo would really be great for a daily car.
What are your pre and post turbine pressure measurements? What are your compressor efficiencies? What is your pre-turbo pressure to manifold pressure ratio? What data are you using to make your assumptions?
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08-22-2009, 01:30 PM
#40
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Sorry, I need to clean up that last sentence. I really didn't read through it before I posted. What I was saying is that I thought the trade off for ultimate power for quicker response would be better than what it was. I am now feeling the punishment for not doing my homework and assuming my logic is flawless.
This turbo would really be great for a daily car.
This turbo would really be great for a daily car.
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