Boost pressure vs air flow vs power
06-10-2014, 08:29 PM
#81
Boost Czar
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If one turbo can stuff more air into a space during a given time period, lots of things being equal, which means more oxygen to burn, would not said turbo produce more power?
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06-10-2014, 08:32 PM
#82
-obviously its less restrictive, despite the same size on all 4 inlets and outlets on both turbos
-I said nothing at all about boost control, since both use the same
-I said nothing about lower air temps, because they weren't
-No idea what that has to do with anything, and the test I referred to wasn't even a gt2554, but a td04 right in the middle of its efficiency range.
WAT
in the crap
are you talking about?
*edit: I actually did the same test on a vf39 (roughly 2860 sized turbo) vs a 20g, and achieved similar results.
I'll dig up the plots
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06-10-2014, 08:36 PM
#83
As a matter of perspective on how much difference. Re the Subaru swap:
What would you say you would have to turn the boost on the VF39 down to in order to keep the max HP the same as stock? If from 10 to 8, then that would be one thing. If from 10 to 5, then another answer altogether.
If the first case, then we would say, "it takes 25% more boost on a small turbo for the same power". If the second case, we would say, "it takes 2X the boost on a small turbo for the same power"
Maybe on the next swap, you could try that, or you may already have the data.
Another correllary is that the situation sounds a bit like the net power from a supercharger. Some of the power stroke is negated by some of the exhaust stroke. Therefore, for the same net power (torque), the rods are more highly stressed with the smaller turbo (or restrictive exhaust) than with the larger.
What would you say you would have to turn the boost on the VF39 down to in order to keep the max HP the same as stock? If from 10 to 8, then that would be one thing. If from 10 to 5, then another answer altogether.
If the first case, then we would say, "it takes 25% more boost on a small turbo for the same power". If the second case, we would say, "it takes 2X the boost on a small turbo for the same power"
Maybe on the next swap, you could try that, or you may already have the data.
Another correllary is that the situation sounds a bit like the net power from a supercharger. Some of the power stroke is negated by some of the exhaust stroke. Therefore, for the same net power (torque), the rods are more highly stressed with the smaller turbo (or restrictive exhaust) than with the larger.
That is not the case.
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06-11-2014, 12:19 PM
#87
still have no idea what you're talking about, and I'm actually trying to follow you here
-obviously its less restrictive, despite the same size on all 4 inlets and outlets on both turbos
-I said nothing at all about boost control, since both use the same
-I said nothing about lower air temps, because they weren't
-No idea what that has to do with anything, and the test I referred to wasn't even a gt2554, but a td04 right in the middle of its efficiency range.
WAT
in the crap
are you talking about?
*edit: I actually did the same test on a vf39 (roughly 2860 sized turbo) vs a 20g, and achieved similar results.
I'll dig up the plots
-obviously its less restrictive, despite the same size on all 4 inlets and outlets on both turbos
-I said nothing at all about boost control, since both use the same
-I said nothing about lower air temps, because they weren't
-No idea what that has to do with anything, and the test I referred to wasn't even a gt2554, but a td04 right in the middle of its efficiency range.
WAT
in the crap
are you talking about?
*edit: I actually did the same test on a vf39 (roughly 2860 sized turbo) vs a 20g, and achieved similar results.
I'll dig up the plots
Reply
0
0
06-11-2014, 01:13 PM
#88
The best video of turbo destroying spool up surge you can find on the internet is an RB26 with a GT35R on it, I think they're doing terrible things to it with a mustang dyno though to make it make the sound. I've also heard of people pushing 16gs on 2.5 subarus across the surge line on cold days.
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06-11-2014, 01:22 PM
#91
I guess I should have said, go repeat that with two turbos that use the same exact hot side. Both turbos will behave nearly the same except for the small intake temp changes due to the differences in efficiencies and the behaviors at the left and right hand sides of the compressor map.
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06-11-2014, 01:30 PM
#92
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no advantage on the hotside, coupled with compressors that are nearly identical, so there's no efficiency advantage or shaft speed advantage.
one is simply better suited for higher pressure and lower flow (18g - steeper surge line) the other lower pressure and higher flow (20g - shallower surge line, capable of higher CFM output).
again, another Braineack post that suggests an actual understanding, so im sure everyone will ignore this.
Last edited by Braineack; 06-11-2014 at 01:40 PM.
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06-12-2014, 05:00 PM
#93
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Join Date: Jul 2005
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For a given engine you can map and thus predict power (or torque ) production based on 3 things:
- RPM
- MAP
- TIP (turbine inlet pressure, aka exhaust backpressure)
(ignoring temperatures)
bigger turbo -> less TIP -> moar powah
- RPM
- MAP
- TIP (turbine inlet pressure, aka exhaust backpressure)
(ignoring temperatures)
bigger turbo -> less TIP -> moar powah
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06-12-2014, 09:34 PM
#96
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Join Date: Jan 2011
Posts: 22
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Other than being slightly dated can someone tell me why we should be reading internet forums and self made experts on turbos instead of reading a book about it? Someone explain to me why this thread isnt laughable but maximum boost is
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06-12-2014, 09:42 PM
#97
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06-12-2014, 10:14 PM
#100
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