Turbo discussion, does flow equal power?
Dec 23, 2011, 01:33 AM
#1
Turbo discussion, does flow equal power?
So here is a graph i threw together from the information i could get off www.turbobygarrett.com and www.full-race.com
The BW EFR turbo's are advertised as "X lb/min" turbo's, but those flow numbers are no where near the 60% efficiency numbers.
Both the EFR and Garrett compressor maps do not go past 60%.
Garrett states in their white papers that the choke point is 58% efficiency.
So we have made 520whp on a turbo (GT3076) that will flow about 52-53 lb/min @ 60% efficiency. This was on both a twin scroll housing (0.82 T3) and a single scroll housing (0.82 T3). The switch from 98RON pump gas to E85 didn't really have any effect on power, the compressor was already at it's limit.
"LeetEVO" made 640whp on the 7670. This is an advertised 64 lb/min turbo, that flows 59-60 lb/min @ 60% efficiency. Is this inline with what i'm trying to talk about?
Did it make that extra 40whp because it's a much larger exhaust wheel, resulting in lower exhaust manifold pressure?
As we all know, setups make power, not turbo's.
I'm seriously looking at running a 7064 on my 2.3+Mivec engine, hoping to max boost (25psi +) at 3400rpm. According to my graph, it should make slightly less power than the GT3076.
Once we test the 7670 on the Subaru we have here in the workshop, all will become clear. We will be testing versus the GTX3076 with a T3 TS 0.82 housing.
But until then, i like to ponder what the best setup is going to be
With all this in mind, how will the GTX3576 perform?
Will the larger exhaust wheel reduce the backpressure enough to make more power over the GT30?
Cheers, Mike
The BW EFR turbo's are advertised as "X lb/min" turbo's, but those flow numbers are no where near the 60% efficiency numbers.
Both the EFR and Garrett compressor maps do not go past 60%.
Garrett states in their white papers that the choke point is 58% efficiency.
So we have made 520whp on a turbo (GT3076) that will flow about 52-53 lb/min @ 60% efficiency. This was on both a twin scroll housing (0.82 T3) and a single scroll housing (0.82 T3). The switch from 98RON pump gas to E85 didn't really have any effect on power, the compressor was already at it's limit.
"LeetEVO" made 640whp on the 7670. This is an advertised 64 lb/min turbo, that flows 59-60 lb/min @ 60% efficiency. Is this inline with what i'm trying to talk about?
Did it make that extra 40whp because it's a much larger exhaust wheel, resulting in lower exhaust manifold pressure?
As we all know, setups make power, not turbo's.
I'm seriously looking at running a 7064 on my 2.3+Mivec engine, hoping to max boost (25psi +) at 3400rpm. According to my graph, it should make slightly less power than the GT3076.
Once we test the 7670 on the Subaru we have here in the workshop, all will become clear. We will be testing versus the GTX3076 with a T3 TS 0.82 housing.
But until then, i like to ponder what the best setup is going to be
With all this in mind, how will the GTX3576 perform?
Will the larger exhaust wheel reduce the backpressure enough to make more power over the GT30?
Cheers, Mike
Last edited by RSMike; Dec 23, 2011 at 01:41 AM.
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hokiruu (Dec 15, 2019)
Dec 23, 2011, 10:39 AM
#3
I think two good turbochargers to look at to give you some insight is the GT3582R and the GT3082R. You can get them with identical compressor sides and turbine housings, only difference being the turbine wheel.
Push them both to the ragged edge, and it seems the GT35 based turbo is still good for 50+ WHP over the GT30 setup. The difference can be even greater then this at lower boost pressures before the compressor limit starts to be an issue and engine VE is the governing parameter.
One thing to look at though, I believe BW corrects to a different standard atmosphere then Garrett. Corrected airflow seems to be the true story behind compressors and without correcting to the same standard inlet conditions, it would be like comparing two dynojet runs, one in SAE and the other in STD.
Beyond that, the 58% number you mentioned may just be a "functional limit" in that you really should never design a setup to drop below that but it may not be the end of making power. I wouldn't be surprised if people often push turbos past there. I would imagine though that it's a good guide line and it probably starts getting incredibly difficult to make power beyond there and reliability of the turbocharger probably starts to drop as well.
Brake specific air consumption will be impacted by the turbo match, which means one setup might only make 10 HP/lb-min and another setup might make 11 HP/lb-min. Even if two compressor have the same flow, one turbo might be able to make better use of that ariflow. Compression and engine setup obviously matter here too. Just because the turbo is ridding the choke flow line doesn't mean there isn't power to be made still. It’s just much more difficult and turbo match becomes more important as well since there has to be an energy balance between turbine and compressor. Too much compressor and not enough turbine will hurt you just as much as too little compressor as the turbine won’t be able to extract enough energy from the exhaust to drive the compressor without turbine back pressure skyrocketing and killing engine VE.
As far as not gaining power when switching to E85, that draws question about the state of tune. E85 for one should give you about a 5% increase in power just from energy content alone. Then on top of that, you can usually get a bit more power out of timing and fuel adjustments to better suit the E85. Then cooling benefits too can add additional gains. Gaining 10% on power over even good fuel isn't unheard of with the switch to E85. It's not 100% every time, but if the car fails to gain power over non-oxygenated gasoline when switching to ethanol, I'd look at the tune some more.
Push them both to the ragged edge, and it seems the GT35 based turbo is still good for 50+ WHP over the GT30 setup. The difference can be even greater then this at lower boost pressures before the compressor limit starts to be an issue and engine VE is the governing parameter.
One thing to look at though, I believe BW corrects to a different standard atmosphere then Garrett. Corrected airflow seems to be the true story behind compressors and without correcting to the same standard inlet conditions, it would be like comparing two dynojet runs, one in SAE and the other in STD.
Beyond that, the 58% number you mentioned may just be a "functional limit" in that you really should never design a setup to drop below that but it may not be the end of making power. I wouldn't be surprised if people often push turbos past there. I would imagine though that it's a good guide line and it probably starts getting incredibly difficult to make power beyond there and reliability of the turbocharger probably starts to drop as well.
Brake specific air consumption will be impacted by the turbo match, which means one setup might only make 10 HP/lb-min and another setup might make 11 HP/lb-min. Even if two compressor have the same flow, one turbo might be able to make better use of that ariflow. Compression and engine setup obviously matter here too. Just because the turbo is ridding the choke flow line doesn't mean there isn't power to be made still. It’s just much more difficult and turbo match becomes more important as well since there has to be an energy balance between turbine and compressor. Too much compressor and not enough turbine will hurt you just as much as too little compressor as the turbine won’t be able to extract enough energy from the exhaust to drive the compressor without turbine back pressure skyrocketing and killing engine VE.
As far as not gaining power when switching to E85, that draws question about the state of tune. E85 for one should give you about a 5% increase in power just from energy content alone. Then on top of that, you can usually get a bit more power out of timing and fuel adjustments to better suit the E85. Then cooling benefits too can add additional gains. Gaining 10% on power over even good fuel isn't unheard of with the switch to E85. It's not 100% every time, but if the car fails to gain power over non-oxygenated gasoline when switching to ethanol, I'd look at the tune some more.
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