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Discussion Starter · #1 ·
Hi All,
I'm hoping some one can help me with the compressor and turbine wheel sizes for a HE400WG with assembly number 3783070.

The information I've found so far is that it has a 13cm2 exhaust housing.

Appreciate any information.

Thanks!
 

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My information shows the turbine shaft as being a 76 mm inducer, 67 mm exducer, 12 blade. Unfortunately I don't have any compressor side info. It looks to essentially be an HX40 shaft but the turbine tip height is shorter so it wouldn't be a direct drop in. I would guess the compressor wheels would also be in the HX40 range as far as inducer size, probably in the 60-62 mm range. But that is just a guess.
 

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Holset lists that turbo with the HX40W series so it's a pretty safe bet the compressor is in that size range. It is spec'd to have a billet compressor wheel. It has a T3 exhaust flange and like you I read it has a 13cm2 turbine housing. That is very small for a turbo that is used on engines up to 15 liters. The Super HX40W only had a 16cm2 housing which is fairly small for that large a turbo. Original application is showing to be a Cummins ISLe 9.5 L. Might have some potential as a primary in a twin set for a 4bt. Might work as a single on a 6bt.
 

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Discussion Starter · #4 ·
My information shows the turbine shaft as being a 76 mm inducer, 67 mm exducer, 12 blade. Unfortunately I don't have any compressor side info. It looks to essentially be an HX40 shaft but the turbine tip height is shorter so it wouldn't be a direct drop in. I would guess the compressor wheels would also be in the HX40 range as far as inducer size, probably in the 60-62 mm range. But that is just a guess.
Thanks!
This is contradicting with some other information I've been told which has the compressor inducer 58mm and turbine exducer 60mm. Not sure on the confidence of this though as there wasn't any pictures.

Holset lists that turbo with the HX40W series so it's a pretty safe bet the compressor is in that size range. It is spec'd to have a billet compressor wheel. It has a T3 exhaust flange and like you I read it has a 13cm2 turbine housing. That is very small for a turbo that is used on engines up to 15 liters. The Super HX40W only had a 16cm2 housing which is fairly small for that large a turbo. Original application is showing to be a Cummins ISLe 9.5 L. Might have some potential as a primary in a twin set for a 4bt. Might work as a single on a 6bt.
Funny you should mention it's potential as a primary. I'm currently looking at this turbo to go with a 7cm2 HE200WG in an ISBe4.5
 

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Discussion Starter · #5 · (Edited)
So I've been able to find out some more information. What I've got is
7 blade compressor
Compressor inducer - 58mm
Compressor exducer - 85mm

Turbine exducer - 60mm
Turbine inducer - Guessing 70mm
Exhaust housing size - 13cm

I've guessed the turbine inducer size by looking at the common the other holsets around this size.

By the looks of it this HE400WG is a renamed HE351W and has a slightly larger compressor than a HX35W.

As char1355 guessed I am looking at using this as a primary for a compound set with a 7cm2 HE200WG in an ISBe 4.5. Digging through the threads I see HE221/HX35W set has had good results in 4bt.

Using dougal's rule of thumb of primary compressor inducer area should be about 1.5 times the secondary and primary turbine exducer area should be 2 time the secondary, a primary match for the HE200WG would have:
Turbine exducer 61.9mm (HE200WG - 43.8mm)
Compressor inducer 52mm (HE200WG - 42.5mm)
So it's in the ballpark

I'd be interested in the forum's view.

The reason I'm looking at compounds is that I'm looking to widen the torque curve and extend the usable rev range for towing and offroad in sand.
 

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So I've been able to find out some more information. What I've got is
7 blade compressor
Compressor inducer -
58mm

Compressor exducer - 85mm

Turbine exducer -
60mm
Turbine inducer - Guessing 70mm
Exhaust housing size - 13cm

I've guessed the turbine inducer size by looking at the common the other holsets around this size.

By the looks of it this HE400WG is a renamed HE351W and has a slightly larger compressor than a HX35W.

As char1355 guessed I am looking at using this as a primary for a compound set with a 7cm2 HE200WG in an ISBe 4.5. Digging through the threads I see HE221/HX35W set has had good results in 4bt.

Using dougal's rule of thumb of primary compressor inducer area should be about 1.5 times the secondary and primary turbine exducer area should be 2 time the secondary, a primary match for the HE200WG would have:
Turbine exducer 61.9mm (HE200WG - 43.8mm)
Compressor inducer 52mm (HE200WG - 42.5mm)
So it's in the ballpark

I'd be interested in the forum's view.

The reason I'm looking at compounds is that I'm looking to widen the torque curve and extend the usable rev range for towing and offroad in sand.
Rough calculated numbers.
An 70/60mm HX35-12cm turbine has a CCF (corrected choke flow - basically turbine size) of 26 lb/min.
A 76/67mm turbine with 13cm housing would have a CCF of almost 27 lb/min. so pretty similar.

Basically I'd expect it to spool fast and be about the right size. Turbos off more modern engines run more boost and keep the engine leaner. So this all makes sense.

Compressor wise a 58mm inducer is good for around 60lb/min. HX40 compressor (83/58mm) I have listed as 66lb/min max.
 

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Discussion Starter · #7 ·
Rough calculated numbers.
An 70/60mm HX35-12cm turbine has a CCF (corrected choke flow - basically turbine size) of 26 lb/min.
A 76/67mm turbine with 13cm housing would have a CCF of almost 27 lb/min. so pretty similar.

Basically I'd expect it to spool fast and be about the right size. Turbos off more modern engines run more boost and keep the engine leaner. So this all makes sense.

Compressor wise a 58mm inducer is good for around 60lb/min. HX40 compressor (83/58mm) I have listed as 66lb/min max.
Thanks for chiming in Dougal.

If my calcs are correct that means the combo would be good for about 550hp with A/F of 18 and BSFC of 0.36. That's way more than I need and the drive line will take!

Would you be able to point me in the direction of where to get a better handle on the turbine sizeing? Advance engineering maths is ok for me.
 

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Thanks for chiming in Dougal.

If my calcs are correct that means the combo would be good for about 550hp with A/F of 18 and BSFC of 0.36. That's way more than I need and the drive line will take!

Would you be able to point me in the direction of where to get a better handle on the turbine sizeing? Advance engineering maths is ok for me.
Yes that's what the turbo can flow, having to compress it to fit through the engine is the hard part. You need about 90psi boost to do that on a 3.9L. I haven't done the turbo sizing for the 4.5L.
Is the HE200 an existing working single? Some of those turbos were intended to run very lean to reduce NOX, in which case they may be a restriction as a compound turbo, but you'll find out pretty quick.

Turbine sizing is geometry, thermo and hocus pocus.
For example the turbine flow is corrected back to reference inlet pressure and temperatures at 15C and 1 atmosphere. Which turbines never work at, but is what everyone uses.

My formula for corrected choke flow (which is what a turbine will level out is:
0.75(correction factor)0.36(kg/m^3referencedensity)*632(m/ssonicvelocityin)*entryarea(mm^2)/1e6*60/0.4536(unitconversion)(EGTdegC+273)/288kreference)^0.5

Entry area is inducer flow area*cos(radians(flowanglealpha4)
Inducer flow area is pi* the mean wheel diameter (inducer & exducer average)*tip width.
flow angle alpha 4 is the arctan of(2*pi(tip width/25.4/AR).
A/R is the stated A/R of the turbine housing in inches.

Basically turbine scroll sets up a vortex which sets the entrance speed and angle into the turbine wheel. Turbine wheel converts that to shaft torque.
The turbine maps have a ramp in and level out (in corrected flow) around PR of 2. Actual flow keeps climbing though.

As you can imagine. It took me years to get this far.
 

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Discussion Starter · #9 ·
Yes that's what the turbo can flow, having to compress it to fit through the engine is the hard part. You need about 90psi boost to do that on a 3.9L. I haven't done the turbo sizing for the 4.5L.
Is the HE200 an existing working single? Some of those turbos were intended to run very lean to reduce NOX, in which case they may be a restriction as a compound turbo, but you'll find out pretty quick.

Turbine sizing is geometry, thermo and hocus pocus.
For example the turbine flow is corrected back to reference inlet pressure and temperatures at 15C and 1 atmosphere. Which turbines never work at, but is what everyone uses.

My formula for corrected choke flow (which is what a turbine will level out is:
0.75(correction factor)0.36(kg/m^3referencedensity)*632(m/ssonicvelocityin)*entryarea(mm^2)/1e6*60/0.4536(unitconversion)(EGTdegC+273)/288kreference)^0.5

Entry area is inducer flow area*cos(radians(flowanglealpha4)
Inducer flow area is pi* the mean wheel diameter (inducer & exducer average)*tip width.
flow angle alpha 4 is the arctan of(2*pi(tip width/25.4/AR).
A/R is the stated A/R of the turbine housing in inches.

Basically turbine scroll sets up a vortex which sets the entrance speed and angle into the turbine wheel. Turbine wheel converts that to shaft torque.
The turbine maps have a ramp in and level out (in corrected flow) around PR of 2. Actual flow keeps climbing though.

As you can imagine. It took me years to get this far.
My napkin calcs say about 45psig @ 3000rpm for the 4.5.

Yes the HE200 is the OEM single. From its dimensions it looks like its a renamed or newer version of the HE221. The engine is a Euro 3 spec so don't think it'll be too lean for NOX reduction and anyrate the ECU is being remaped by a number of people. I've heard of people claiming to have gotten 400hp out of this engine with a bigger single but no information on the safety of the tune they used to get it.

I too have the concern that it will be too restrictive as well and will be monitoring exhaust manifold pressure.

Thanks for sharing your formulas, I appreciate the time it takes. It took me long enough to get my spreadsheet setup and validated for the intake side. When I got to the exhaust side I hit a steep hill and while conceptually I understand what's going on on the exhaust side I still haven't got the maths right.
 

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As another option, adding an external wastegate to bypass the choke point of the small turbine housing of the secondary and feeding the dump into the hot pipe before the primary is another option. It complicates plumbing a little, but allows the quick response of the smaller turbo without sacrificing overall capability. Spacer plates for the turbine side of the secondary can be used to add a wastegate, or a person can purchase a manifold from Steed that has an integrated port for a gate.
 

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As another option, adding an external wastegate to bypass the choke point of the small turbine housing of the secondary and feeding the dump into the hot pipe before the primary is another option. It complicates plumbing a little, but allows the quick response of the smaller turbo without sacrificing overall capability. Spacer plates for the turbine side of the secondary can be used to add a wastegate, or a person can purchase a manifold from Steed that has an integrated port for a gate.
If a turbine is so small that you need to bypass it you might need a bypass on the compressor too. One of the members here was working on a mercedes diesel which was going to completely unload the small turbo and found a good bypass valve for the air-side. But I don't know if he ever got it running and working.
 

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If a turbine is so small that you need to bypass it you might need a bypass on the compressor too. One of the members here was working on a mercedes diesel which was going to completely unload the small turbo and found a good bypass valve for the air-side. But I don't know if he ever got it running and working.
In my experience with the 5.9 and 6.7 engines with twin setups the exhaust side is the choke point. Drive pressure almost always far exceeds boost pressure. Keeping drive pressure as close to 1:1 as possible yields the best results, and that's done by tuning the exhaust side with wastegates, larger turbines, larger turbine housings. If the compressor is excessively small it could certainly restrict airflow but this is not typically the main issue. I've seen plenty of successful twin setups on a 5.9 using a 56-62 mm compressor secondary with a 75-83 mm primary supporting 800+ RWHP. Size that down by a third (airflow) to approximate what a 4BT might need to hit that 500 HP mark. Going off my data, a 44-46 mm compressor secondary with a 58-66 mm primary shouldn't be too restrictive on the air side.
 

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In my experience with the 5.9 and 6.7 engines with twin setups the exhaust side is the choke point. Drive pressure almost always far exceeds boost pressure. Keeping drive pressure as close to 1:1 as possible yields the best results, and that's done by tuning the exhaust side with wastegates, larger turbines, larger turbine housings. If the compressor is excessively small it could certainly restrict airflow but this is not typically the main issue. I've seen plenty of successful twin setups on a 5.9 using a 56-62 mm compressor secondary with a 75-83 mm primary supporting 800+ RWHP. Size that down by a third (airflow) to approximate what a 4BT might need to hit that 500 HP mark. Going off my data, a 44-46 mm compressor secondary with a 58-66 mm primary shouldn't be too restrictive on the air side.
Drive pressure is set by turbine size (plus efficiency) and wastegating can't change that. Wastegating is just bypassing flow around a turbine that is too small for the current operating point.

For example if your turbine is working great at 2000rpm but needs to wastegate 10% of the flow at 2500 then your turbine is smaller than ideal for the 2500rpm operation. But the ideal turbine for 2500rpm operation doesn't give enough boost (or fast enough response) at 2000rpm so we have to compromise.

If you're building a dyno queen you run much bigger turbos to get peak efficiency at peak power rpm at your desired boost. Bingo. Excellent power numbers. But it becomes a smoke filled horror show if you attempt to drive it normally, tow or drive at altitude.
The turbo sizing I do is all for max driveability. So you can get a clean and safe tune that delivers the stated power. This means smaller turbos and higher boost than the max-power dyno queens.

With a 3.9 litre 4 banger we need more boost and better response for daily driving than a 6+ litre engine does in vehicles that aren't much different in size/weight.
 

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Drive pressure is set by turbine size (plus efficiency) and wastegating can't change that. Wastegating is just bypassing flow around a turbine that is too small for the current operating point.

For example if your turbine is working great at 2000rpm but needs to wastegate 10% of the flow at 2500 then your turbine is smaller than ideal for the 2500rpm operation. But the ideal turbine for 2500rpm operation doesn't give enough boost (or fast enough response) at 2000rpm so we have to compromise.

If you're building a dyno queen you run much bigger turbos to get peak efficiency at peak power rpm at your desired boost. Bingo. Excellent power numbers. But it becomes a smoke filled horror show if you attempt to drive it normally, tow or drive at altitude.
The turbo sizing I do is all for max driveability. So you can get a clean and safe tune that delivers the stated power. This means smaller turbos and higher boost than the max-power dyno queens.

With a 3.9 litre 4 banger we need more boost and better response for daily driving than a 6+ litre engine does in vehicles that aren't much different in size/weight.
I think you misunderstood what I was saying or didn't read it correctly. And yes, wastegates will relieve drive pressure, that is the whole point of a wastegate. Relieving and re-routing exhaust volume/pressure to not drive the compressor, control boost, and keep the compressor in the efficiency range longer.
So, to use your example, and this is how factory fixed geometry turbos are generally setup, to get the response at 2000 RPM a smaller than ideal turbine housing is used. The wastegate starts to open at a preset boost pressure to dump excess drive pressure around the turbine, so at 2500 RPM the engine isn't choked out and the turbo still operates efficiently. The wastegate just dumps the excess drive pressure into the downpipe, wasting that energy. Hence "wastegate". So yes, it is a compromise.
The point I was making is that wasted energy can be diverted around the secondary turbo into the hot pipe before the primary turbo, which will aid in driving the primary. This is not a technique I came up with, it is a pretty well established method on both aftermarket and factory turbo setups.
I also build trucks, for customers, around maximum driveability and towing. I don't build smokey trailer and dyno queens. I have been doing this for about 20 years and have seen and fixed a lot of bad turbo setups, on 4BT as well as larger engines. The same principles apply. I'm not really sure where you were going with your response, it has very little to do with what I was saying anyway.
 

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I think you misunderstood what I was saying or didn't read it correctly. And yes, wastegates will relieve drive pressure, that is the whole point of a wastegate. Relieving and re-routing exhaust volume/pressure to not drive the compressor, control boost, and keep the compressor in the efficiency range longer.
So, to use your example, and this is how factory fixed geometry turbos are generally setup, to get the response at 2000 RPM a smaller than ideal turbine housing is used. The wastegate starts to open at a preset boost pressure to dump excess drive pressure around the turbine, so at 2500 RPM the engine isn't choked out and the turbo still operates efficiently. The wastegate just dumps the excess drive pressure into the downpipe, wasting that energy. Hence "wastegate". So yes, it is a compromise.
The point I was making is that wasted energy can be diverted around the secondary turbo into the hot pipe before the primary turbo, which will aid in driving the primary. This is not a technique I came up with, it is a pretty well established method on both aftermarket and factory turbo setups.
I also build trucks, for customers, around maximum driveability and towing. I don't build smokey trailer and dyno queens. I have been doing this for about 20 years and have seen and fixed a lot of bad turbo setups, on 4BT as well as larger engines. The same principles apply. I'm not really sure where you were going with your response, it has very little to do with what I was saying anyway.
I'm not misunderstanding. I think you're not getting the limitations and risks I'm considering.

Wastegates don't dump pressure. They divert flow and the pressures set themselves depending on how much resistance there is to the flow. There's no point where an engine is choked out. Engines are constantly working with different intake and exhaust pressures. I size compounds to work together at defined ratios. Sizing compounds to work at different ratios gives a totally different result in driveability, power, smoke and reliability.

In a compound setup the pressures compound through each stage. If you want to run it more like a sequential and bypass the turbine side of the small turbo then you also have to bypass the compressor side of the small turbo. Because a compressor not compressing becomes a significant flow restriction that screws everything up.
If you want to run it like a sequential your turbo sizing is totally different to a compounding arrangement and the switchover point can get really ugly. See the subaru "valley of death" below.

Product Rectangle Slope Font Line



If you want to run the majority of compression on the big turbo and only a little on the small turbo then you risk overheat and failure of the small turbo compressor. This is the main reason I don't recommend that approach. Sure you can get nice dyno numbers for a few seconds but past those few seconds you risk sending the small compressor blades into your engine as the compressor wheel loses strength and fails due to the elevated temperatures.
 

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I'm not misunderstanding. I think you're not getting the limitations and risks I'm considering.

Wastegates don't dump pressure. They divert flow and the pressures set themselves depending on how much resistance there is to the flow. There's no point where an engine is choked out. Engines are constantly working with different intake and exhaust pressures. I size compounds to work together at defined ratios. Sizing compounds to work at different ratios gives a totally different result in driveability, power, smoke and reliability.

In a compound setup the pressures compound through each stage. If you want to run it more like a sequential and bypass the turbine side of the small turbo then you also have to bypass the compressor side of the small turbo. Because a compressor not compressing becomes a significant flow restriction that screws everything up.
If you want to run it like a sequential your turbo sizing is totally different to a compounding arrangement and the switchover point can get really ugly. See the subaru "valley of death" below.

View attachment 133722


If you want to run the majority of compression on the big turbo and only a little on the small turbo then you risk overheat and failure of the small turbo compressor. This is the main reason I don't recommend that approach. Sure you can get nice dyno numbers for a few seconds but past those few seconds you risk sending the small compressor blades into your engine as the compressor wheel loses strength and fails due to the elevated temperatures.
Ok, I see what you are saying about flow vs pressure. The common nomenclature used is "drive pressure", which to most of us encompasses exhaust flow and pressure. Because what we measure is the drive pressure. So opening a gate dumps flow/volume, which in turn drops pressure. So thanks for splitting those hairs for me. From my real world experience, I have seen plenty of engines get "choked" by too small of turbines restricting flow from the engine at higher RPM causing a drop off in performance. I'm not saying you are wrong, I am saying gating around the secondary turbo has been proven to work. I am not wanting to drive the primary with the majority of the compression. What I would be looking to do is monitor drive pressure in the exhaust manifold and tune accordingly. Here's an example of what I am saying:

"Truck #1- 1996 Dodge Ram, minor fueling upgrades, 57mm/71mm ATS compound turbos with a single internal wastegate, street truck.
We had the pleasure of tuning this truck on the dyno with pressure monitors everywhere, so we can report on how much power it made under various configurations. Before we hit the dyno, we ran it on the street where it only made 57psi with its limited fueling. That seemed low so we pinched off the wastegate line, effectively closing it. Boost hit 65psi, but the truck didn’t feel any faster.
The dyno would tell the story. After our first run, the truck made 400rwhp at 65psi, but with a whopping 99psi of backpressure (or drive pressure) which was far and away from the magical 1:1 boost to drive pressure that most folks aim for. Opening the wastegate saw a drop in boost of 8psi to 57psi, but drive pressure was a mild 64psi, and the truck actually picked up in power to 432rwhp! In this case, wastegating netted an increase in power even at a lower boost level, due to an increase in engine efficiency."

I'm quite certain your calculations are correct and using them to size turbos works. But so does known procedures based on experience, and even well planned out and pressure ratio matched turbo setups require tuning and are directly impacted by individual performance requirements. So in a controlled environment where the variables are controlled to fit within the parameters of the calculations, I'm sure they are great. But if it was mine, I would still tune the setup to the engine in the vehicle in which it will be used, so all the variables are applied and I can find the best performance compromise. That's how I do it, and so far it's worked well for me.
 

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Ok, I see what you are saying about flow vs pressure. The common nomenclature used is "drive pressure", which to most of us encompasses exhaust flow and pressure. Because what we measure is the drive pressure. So opening a gate dumps flow/volume, which in turn drops pressure. So thanks for splitting those hairs for me. From my real world experience, I have seen plenty of engines get "choked" by too small of turbines restricting flow from the engine at higher RPM causing a drop off in performance. I'm not saying you are wrong, I am saying gating around the secondary turbo has been proven to work. I am not wanting to drive the primary with the majority of the compression. What I would be looking to do is monitor drive pressure in the exhaust manifold and tune accordingly. Here's an example of what I am saying:

"Truck #1- 1996 Dodge Ram, minor fueling upgrades, 57mm/71mm ATS compound turbos with a single internal wastegate, street truck.
We had the pleasure of tuning this truck on the dyno with pressure monitors everywhere, so we can report on how much power it made under various configurations. Before we hit the dyno, we ran it on the street where it only made 57psi with its limited fueling. That seemed low so we pinched off the wastegate line, effectively closing it. Boost hit 65psi, but the truck didn’t feel any faster.
The dyno would tell the story. After our first run, the truck made 400rwhp at 65psi, but with a whopping 99psi of backpressure (or drive pressure) which was far and away from the magical 1:1 boost to drive pressure that most folks aim for. Opening the wastegate saw a drop in boost of 8psi to 57psi, but drive pressure was a mild 64psi, and the truck actually picked up in power to 432rwhp! In this case, wastegating netted an increase in power even at a lower boost level, due to an increase in engine efficiency."

I'm quite certain your calculations are correct and using them to size turbos works. But so does known procedures based on experience, and even well planned out and pressure ratio matched turbo setups require tuning and are directly impacted by individual performance requirements. So in a controlled environment where the variables are controlled to fit within the parameters of the calculations, I'm sure they are great. But if it was mine, I would still tune the setup to the engine in the vehicle in which it will be used, so all the variables are applied and I can find the best performance compromise. That's how I do it, and so far it's worked well for me.
In your example you have blocked off the wastegate line and then released it. I have never told people to block off wastegate lines. It's a terrible thing to do.

I think you need to go back and read my work again. I size turbochargers to work correctly without butchery like that.
 

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In your example you have blocked off the wastegate line and then released it. I have never told people to block off wastegate lines. It's a terrible thing to do.

I think you need to go back and read my work again. I size turbochargers to work correctly without butchery like that.
Wow. You just refuse to see what I am saying. It's not my example, its from a magazine article. And obviously blocking the wastegate line is not the answer. The example simply illustrates how a restrictive turbine will create excessively high drive pressure, and how wastegating can reduce the pressure, increasing efficiency and power without sacrificing driveability. With real world results. But I guess these well known facts are mute to you. Clearly your way is the only way you will see it. That's fine, we will just have to agree to disagree.
 

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Wow. You just refuse to see what I am saying. It's not my example, its from a magazine article. And obviously blocking the wastegate line is not the answer. The example simply illustrates how a restrictive turbine will create excessively high drive pressure, and how wastegating can reduce the pressure, increasing efficiency and power without sacrificing driveability. With real world results. But I guess these well known facts are mute to you. Clearly your way is the only way you will see it. That's fine, we will just have to agree to disagree.
Why did you provide a jacked up article from a magazine when you say you have all these real world examples? It doesn't relate to any of my examples and it makes it look like you don't understand how turbines work.
Wastegated turbines are sized to work with the wastegated flow. You can't just pinch off the wastegate line and expect it to work well. Doing that creates a huge mismatch between compressor and turbine.

You haven't been able to show what your solutions are. If you want to run bigger turbines to drop drive pressure then you'll also drop boost, lose response and lose low to mid-range torque. Ending up with a dyno queen that has terrible drivability. Turbo sizing is a trade-off. You cannot have everything.
 

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Why did you provide a jacked up article from a magazine when you say you have all these real world examples? It doesn't relate to any of my examples and it makes it look like you don't understand how turbines work.
Wastegated turbines are sized to work with the wastegated flow. You can't just pinch off the wastegate line and expect it to work well. Doing that creates a huge mismatch between compressor and turbine.

You haven't been able to show what your solutions are. If you want to run bigger turbines to drop drive pressure then you'll also drop boost, lose response and lose low to mid-range torque. Ending up with a dyno queen that has terrible drivability. Turbo sizing is a trade-off. You cannot have everything.
Look, I was simply showing an example of how wastegating can reduce drive pressure and increase efficiency of a turbo setup. My original comment was a simple alternate solution to an issue brought up by the OP concerning the secondary turbo he was considering using in his twin setup. For some reason you took offense to my ALTERNATE SOLUTION.
I wasn't arguing that you were wrong. I wasn't talking about completely bypassing the secondary turbo. Just using a wastegate to divert some of the exhaust energy around the turbine to prevent an excessive amount of restriction. Routing the "wasted" exhaust energy into the intermediate pipe helps to recover that energy rather than dumping it to the atmosphere. The primary still operates at around 2.5-2.8:1 pressure ratio, and the secondary around 2:1, generally resulting in measured total boost of about 65 PSI. I use the wastegate to help fine tune the drive pressure and get the boost/drive pressure ratio as close to 1:1 as possible without significant performance loss.
In a perfect world spending thousands of dollars on different turbos to presicely match the application would be ideal, I agree. I don't usually have the luxury of custom designing a turbo setup to perfectly match the engine. By the time I see them the turbos are already there, but for multiple reasons the system is not performing as it should or is expected to. So I diagnose the problems and come up with solutions to not have to completely re-invent the wheel to come up with compromise that is acceptable to the customer. On some occasions I can make recommendations and help my customers decide on what compromises they are willing to make with a kit design. There is too many variables beyond the turbos themselves to list out examples. What I do know is I have a very good track record and reputation of improving the overall drivability and usability of theses setups.
Clearly you have what I assume is an engineering back ground based on your methodology. Good for you. I am not going to have a continuing pissing match with you over this.
 
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