Spoons solution to Twin Turbo Tims FAQ's
Posted: Thu Sep 27, 2001 5:21 am
Hey Tim, I can see from your questions you are ready to rumble, but first we have got to get you up to speed with this turbo stuff.
=======================================================================================================
i thought that if i replaced the smaller turbo and put in a larger one, i
would be able to change the exhaust to a much larger one then take out the
cats which would allow me to boost the car harder with less restrictions, in
doing this the turbo lag wouldn't be very much?
is it possible to get my standard ECU reprogramed to run my turbos at the
same time rather than sequential?
=======================================================================================================
The answer to both questions is yes. However, were you to ask if you could jump out of a plane without a parachute and fall just as fast as the other skydivers the answer would also be yes. But there is a reason for the chute and a reason for your turbos sizes and sequencing.
Almost all twin turbo automobiles use same size non-sequential turbochargers. It's easier and cheaper to engineer, build, and maintain a non-sequential system. The Subaru Legacy GT Sequential Twin Turbo System (opinion coming up) is superior to the turbo system on the WRX. It's better than the turbo systems on Mazda, Toyota, Nissan, and Honda if they had one. It's better than the system on Volvo, Saab, BMW, Mercedes, Rolls-Bently, Jaguar, Maserati, Ferrari, Lamborghini, Buick Grand National and on and on. Why is it better?
A turbocharger is kind of like a sophisticated fan or pinwheel. Instead of power from an electrical motor, the energy from the engine exhaust is used to spin or spool up the part of the fan called the turbine. The turbine is connected to another fan on a common axle shaft so that it spins too. The other fan is a compressor, and spins fast enough to pull air from the intake, squeeze it, and pump it into the engine under pressure. This pressurized air is what gives you more power when combined with a corresponding increase in fuel, up to the point where the increase in heat due to pressure causes the air to expand faster than the compressor can squeeze it, sometimes called compressor stall. A smaller compressor has to work harder to deliver the same boost and volume as a larger compressor, and will generally heat the air more for a given boost level, which is why some people go to a bigger compressor for more boost.
However, depending how much more you want, a bigger compressor may not be necessary. And some of the other ideas for power increase are good only up to a point too, with their own tradeoffs. A monster turbo and exhaust will generally benefit most in certain types of full race applications where you are running wide open from start to finish like circle track or drag racing where lag is not an issue. On the street you would probably quickly tire of a monster system that has so much turbo lag that normally aspirated three cylinder Yugos are blowing you off.
The downside to this upsizing is the greater mass takes longer to spool up and so, other things being equal, a bigger turbo will have greater lag. Which brings us back to why the Subaru sequential system is better than the one used on those megabuck supercars. And hey I don't know what they have, but all this is for arguments' sake.
The Sube system is better because Subaru engineers went to the extraordinary trouble to design an asymmetric system that gives you what you cannot get by almost by other means. At low engine speeds the exhaust from ALL cylinders is directed to the smaller turbine giving you lightning spool up and instant power. As engine speed and exhaust velocity increases, the smaller turbine brings the smaller compressor up to its' maximum efficiency speed, and the exhaust is redirected so that the larger turbine kicks in smoothly with the larger compressor ALONG WITH the smaller turbo, taking the engine to power levels it could not achieve with the smaller turbo alone, with a response which could not be delivered with the larger turbo. You have the best of both worlds you lucky son of a gun.
In what area are you dissatisfied? If you could be granted any wish to improve your system what would it be? Do you want quicker response? Do you want more power? There is an answer, you can have both, with only a slight disturbance to the system you currently have.
As explained above there is a point where the compressor just can't generate more pressure no matter how much faster the turbine spins it. However, almost all factory turbocharged systems install a pressure relief valve set to a value far below that critical compressor speed. This is because the boost pressure generated would in all probability, cause a condition which would catastrophically overstress the engine before the compressor stall speed is reached. You may have heard of the pressure relief valve referred to as a wastegate.
And now the part you have been waiting for.
It just so happens, that most factory wastegates are set to relieve at a value much lower than the compressor can actually deliver to preserve engine reliability. There are mechanical and electronic devices commonly known as boost controllers, which will allow you to override the factory wastegate factory setting by any value you choose. Some are set and forget, some will let you play with the setting right from the cockpit while on the fly. An increase of 50% in boost and power is usually easily achievable without any other changes to the engine systems. More if you like with appropriate adjustments to fuel delivery, and NOW your exhaust system, component strength if you go boost crazy, etc. Simple, fast, cheap, and by far more bang for the buck on a factory turbocharged car than anything you can bolt on or bolt off except maybe a Nitrous Oxide System (NOS) depending on how fancy a controller you get. But if you have your nitrous ! system charge switch armed and somebody pulls up in the next lane with a cell phone transmitting at the wrong frequency, your car will blow up.
Almost any automotive aftermarket performance business will either sell boost controllers or have a contact for you. They can range from simple vacuum solenoids or check valves that are so inexpensive you would consider the price negligible, on up to electronic fuzzy logic computers for several hundred. If you want more info let me know and I will send you my boost controller file, but info is everywhere.
Just don't go goofing up your turbo systems' sequencing and sizing unnecessarily, and don't jump without a parachute.
Larry Witherspoon
Torrance (Los Angeles)
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=======================================================================================================
i thought that if i replaced the smaller turbo and put in a larger one, i
would be able to change the exhaust to a much larger one then take out the
cats which would allow me to boost the car harder with less restrictions, in
doing this the turbo lag wouldn't be very much?
is it possible to get my standard ECU reprogramed to run my turbos at the
same time rather than sequential?
=======================================================================================================
The answer to both questions is yes. However, were you to ask if you could jump out of a plane without a parachute and fall just as fast as the other skydivers the answer would also be yes. But there is a reason for the chute and a reason for your turbos sizes and sequencing.
Almost all twin turbo automobiles use same size non-sequential turbochargers. It's easier and cheaper to engineer, build, and maintain a non-sequential system. The Subaru Legacy GT Sequential Twin Turbo System (opinion coming up) is superior to the turbo system on the WRX. It's better than the turbo systems on Mazda, Toyota, Nissan, and Honda if they had one. It's better than the system on Volvo, Saab, BMW, Mercedes, Rolls-Bently, Jaguar, Maserati, Ferrari, Lamborghini, Buick Grand National and on and on. Why is it better?
A turbocharger is kind of like a sophisticated fan or pinwheel. Instead of power from an electrical motor, the energy from the engine exhaust is used to spin or spool up the part of the fan called the turbine. The turbine is connected to another fan on a common axle shaft so that it spins too. The other fan is a compressor, and spins fast enough to pull air from the intake, squeeze it, and pump it into the engine under pressure. This pressurized air is what gives you more power when combined with a corresponding increase in fuel, up to the point where the increase in heat due to pressure causes the air to expand faster than the compressor can squeeze it, sometimes called compressor stall. A smaller compressor has to work harder to deliver the same boost and volume as a larger compressor, and will generally heat the air more for a given boost level, which is why some people go to a bigger compressor for more boost.
However, depending how much more you want, a bigger compressor may not be necessary. And some of the other ideas for power increase are good only up to a point too, with their own tradeoffs. A monster turbo and exhaust will generally benefit most in certain types of full race applications where you are running wide open from start to finish like circle track or drag racing where lag is not an issue. On the street you would probably quickly tire of a monster system that has so much turbo lag that normally aspirated three cylinder Yugos are blowing you off.
The downside to this upsizing is the greater mass takes longer to spool up and so, other things being equal, a bigger turbo will have greater lag. Which brings us back to why the Subaru sequential system is better than the one used on those megabuck supercars. And hey I don't know what they have, but all this is for arguments' sake.
The Sube system is better because Subaru engineers went to the extraordinary trouble to design an asymmetric system that gives you what you cannot get by almost by other means. At low engine speeds the exhaust from ALL cylinders is directed to the smaller turbine giving you lightning spool up and instant power. As engine speed and exhaust velocity increases, the smaller turbine brings the smaller compressor up to its' maximum efficiency speed, and the exhaust is redirected so that the larger turbine kicks in smoothly with the larger compressor ALONG WITH the smaller turbo, taking the engine to power levels it could not achieve with the smaller turbo alone, with a response which could not be delivered with the larger turbo. You have the best of both worlds you lucky son of a gun.
In what area are you dissatisfied? If you could be granted any wish to improve your system what would it be? Do you want quicker response? Do you want more power? There is an answer, you can have both, with only a slight disturbance to the system you currently have.
As explained above there is a point where the compressor just can't generate more pressure no matter how much faster the turbine spins it. However, almost all factory turbocharged systems install a pressure relief valve set to a value far below that critical compressor speed. This is because the boost pressure generated would in all probability, cause a condition which would catastrophically overstress the engine before the compressor stall speed is reached. You may have heard of the pressure relief valve referred to as a wastegate.
And now the part you have been waiting for.
It just so happens, that most factory wastegates are set to relieve at a value much lower than the compressor can actually deliver to preserve engine reliability. There are mechanical and electronic devices commonly known as boost controllers, which will allow you to override the factory wastegate factory setting by any value you choose. Some are set and forget, some will let you play with the setting right from the cockpit while on the fly. An increase of 50% in boost and power is usually easily achievable without any other changes to the engine systems. More if you like with appropriate adjustments to fuel delivery, and NOW your exhaust system, component strength if you go boost crazy, etc. Simple, fast, cheap, and by far more bang for the buck on a factory turbocharged car than anything you can bolt on or bolt off except maybe a Nitrous Oxide System (NOS) depending on how fancy a controller you get. But if you have your nitrous ! system charge switch armed and somebody pulls up in the next lane with a cell phone transmitting at the wrong frequency, your car will blow up.
Almost any automotive aftermarket performance business will either sell boost controllers or have a contact for you. They can range from simple vacuum solenoids or check valves that are so inexpensive you would consider the price negligible, on up to electronic fuzzy logic computers for several hundred. If you want more info let me know and I will send you my boost controller file, but info is everywhere.
Just don't go goofing up your turbo systems' sequencing and sizing unnecessarily, and don't jump without a parachute.
Larry Witherspoon
Torrance (Los Angeles)
ADVERTISEMENT
<http://rd.yahoo.com/M=168643.1620686.31 ... Fcid=12715>
<http://rd.yahoo.com/M=168643.1620686.31 ... Fcid=12715>
<http://us.adserver.yahoo.com/l?M=168643 ... =210698084>
To unsubscribe from this group, please send an email to:
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zZz <http://docs.yahoo.com/info/terms/> .
