PES is introducing a Garrett T-28 kit....
03-07-2001, 06:32 PM
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PES is introducing a Garrett T-28 kit....
See Tony's post and follow-ups over on the Performance Forum for a bit of info.<ul><li><a href="https://www.audiworld.com/forum/m/performance/msgs/28053.phtml">PES Mentions new Garrett T-28 Turbo Kit for 1.8T</a></li></ul>
03-07-2001, 07:22 PM
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My 2 cents on bb vs. shaft and lag (turbos)
(no expert)
The infamous LAG issue could be an issue or it couldn't be an issue. If this was a 944t board then lag would be practically non-existant and nobody would talk about it as frequently. If I drove a 944t daily I wouldn't even feel lag less think about it. What I'm saying is the 944t is not turbo dependent like the A4 (granted na944's are slow as, um....)
If you put a bb turbo and a shaft turbo in two 944t's then the difference (driving) would prolly only be noticed by a <i>professional technician.</i> Reason why is becasue both 944ts' turbos hit upstairs between 6.5 and 8k (don't recall exact specs, sorry)
Ball bearing turbos are great turbos..they are excellent turbos...but they lag down LOW. Agrue this if you want but they LAG. You need an excellent exaust manifold to flow the air. APR has done this succesfully and impressivly although some customers have complained of lag. I cannot verify this myself b/c I have not driven a stage 3 car. Back to turbos-> BB's are not instant and they do not hit <b>hard</b> early. Big bb turbos lag more b/c of the increased inertia. There is more **** inside that has to spin but they are claimed to be more efficient. This is simple stuff even I can understand :-/
You want a big turbo? For a 4 pot with a t-belt and interface motor? (gt 25 is not big; no pun) A strong shaft turbo that is sized right for the application (A4) is what I personally look for. Shart turbos are stock in all p-cars relevant or not...Yes and this is before ol' Ferdie kicked the bucket. Shaft turbos are what won and are what win enduro races for p-cars. If something broke Porsche would have looked to another source. There was no need b/c they diddn't break. The turbos were (OMG) shaft. NO brearings. Technology may have not been up to speed. Maybe they cheated and used amsoil, in don know. Bottom line is that they did not break. BB's may be the lastest and perhaps greatest but it really depends on how the car is tuned and what kind of power you are looking for. If you are not going to rip the tranny out like RUF does religously when they do upgrades then there is no need for a big bearing turbo in the a4 in my honest opinion. Those of you that have maxed your chipped A4's know what I'm talking about. What is hp w/o torque in a small powerband?
Post is general, not personal (;
The infamous LAG issue could be an issue or it couldn't be an issue. If this was a 944t board then lag would be practically non-existant and nobody would talk about it as frequently. If I drove a 944t daily I wouldn't even feel lag less think about it. What I'm saying is the 944t is not turbo dependent like the A4 (granted na944's are slow as, um....)
If you put a bb turbo and a shaft turbo in two 944t's then the difference (driving) would prolly only be noticed by a <i>professional technician.</i> Reason why is becasue both 944ts' turbos hit upstairs between 6.5 and 8k (don't recall exact specs, sorry)
Ball bearing turbos are great turbos..they are excellent turbos...but they lag down LOW. Agrue this if you want but they LAG. You need an excellent exaust manifold to flow the air. APR has done this succesfully and impressivly although some customers have complained of lag. I cannot verify this myself b/c I have not driven a stage 3 car. Back to turbos-> BB's are not instant and they do not hit <b>hard</b> early. Big bb turbos lag more b/c of the increased inertia. There is more **** inside that has to spin but they are claimed to be more efficient. This is simple stuff even I can understand :-/
You want a big turbo? For a 4 pot with a t-belt and interface motor? (gt 25 is not big; no pun) A strong shaft turbo that is sized right for the application (A4) is what I personally look for. Shart turbos are stock in all p-cars relevant or not...Yes and this is before ol' Ferdie kicked the bucket. Shaft turbos are what won and are what win enduro races for p-cars. If something broke Porsche would have looked to another source. There was no need b/c they diddn't break. The turbos were (OMG) shaft. NO brearings. Technology may have not been up to speed. Maybe they cheated and used amsoil, in don know. Bottom line is that they did not break. BB's may be the lastest and perhaps greatest but it really depends on how the car is tuned and what kind of power you are looking for. If you are not going to rip the tranny out like RUF does religously when they do upgrades then there is no need for a big bearing turbo in the a4 in my honest opinion. Those of you that have maxed your chipped A4's know what I'm talking about. What is hp w/o torque in a small powerband?
Post is general, not personal (;
03-07-2001, 09:00 PM
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My add'l two cents, and I will not post about it again.....
Lag is not just about the characteristics on one component of a system. That is failing to see the forest for the trees.
Here is an excerpt from the infamous GT25/K04 war. It was directed as a response to one person, but look at it for it's information. It does NOT get any better:
<i>(1) Power is not solely a function of boost pressure.
(2) Turbo lag is not solely a function of turbocharger size (when other variables are changing.)
Until you can accept these facts it will not make sense!!!
It is very easy to bring a car to one level, given certain hardware. However, transitioning to the next level requires more effort. These methods may or may not be understood by the general public.
For example, it is easy to accept the statement that a larger turbo automatically means more turbolag. But by accepting this generalization you are limiting yourself to that statement.
There are many factors at work here. Remember that flywheel torque (or power) is equal to the internal engine torque minus pumping losses minus internal friction minus losses caused by auxiliary components. We will start by throwing out losses caused by auxiliaries and internal friction, these are not factors here that we can control. When we replace major engine parts (exhaust manifolds, turbos, etc.) we have some control of the other parts of the equation (internal engine torque, and pumping losses.)
Internal engine torque - This is directly related to the area under the curve of the instantaneous cylinder pressure versus crank angle. Specifically we are talking about the cylinder pressures during the power stroke. The more charge mass that we can inject into the cylinder the more power. The closer that our spark advance timing is to the ideal spark advance angle, the more power that we can make. (In our applications we are always going to be limited by the octane rating of the fuels used. IOW, it is a good rule of thumb that we are always going to want to advance the timing as much as possible without detonation.)
Pumping losses - The best way to visualize this is the energy required to expel (or ingest) gases from the engine.
Backpressure
Backpressure is one of the key factors to consider when comparing the K04 to our stage 3 system. Backpressure has two big negative effects- (a) it effects pumping losses, and (b) it effects cylinder scavenging.
Backpressure and pumping losses - It's very simple. The more backpressure that you have, the more energy is wasted on expelling the exhaust gases. Hence, with more backpressure you have HIGHER PUMPING LOSSES.
Backpressure and cylinder scavenging - This affects the internal torque in two ways. First of all, a reduced scavenging effect will mean less fresh air charge in the combustion chamber. Less fresh air charge means less oxygen which means less fuel which means less power. Also, the residual exhaust gases will add heat to the subsequent cylinder charge. A hotter charge means less timing advance which means less power. More exhaust backpressure means LESS INTERNAL ENGINE TORQUE.
Fact: A K03/K04 turbocharger utilitizing the stock exhaust manifold will have much greater exhaust backpressure then our stage 3 setup at any given airflow.
Enhanced scavenging / Reduction of cylinder-to-cylinder pulse interference
By utilizing a paired runner design in our manifold and being careful with the geometry, we are reducing the pulse interference effect and enhancing cylinder scavenging. This allows us to run more ignition advance for a given load condition and means that we are getting a fresher air charge. Also, exhaust manifold internal volume is kept to a minimum to aid turbocharger spoolup time. The exhaust manifold is constructed of Inconel, a material with one-fourth the heat conductivity of a standard cast iron, to keep the heat in the charge which maximizes the amount of energy available to spool the turbocharger (minimizes lag.) The inconel is also very stable and resistant to cracking when undergoing severe thermal cycling.
Turbocharger Technological Enhancements
The ball-bearing design of the turbo in our kit decreases spoolup time. The wheel designs on this turbo are cutting edge.
Also, with our kit the turbocharger is being run in its' sweet spot. This means that the compressor efficiencies will be high. Higher compressor efficiencies equate to lower intake charge temperatures. Lower intake charge temperature mean more ignition advance and a denser intake charge = More power.
CONCLUSION
As you can see, we are changing and affecting many things. It is much more complicated than 'this turbo is bigger than this one.' We would also like to point out the fact that there can be HUGE differences between two kits utilizing the same turbocharger depending on the rest of the kit.
The increased backpressure of the K03/K04 will mean more pumping losses at a given mass airflow. The increased backpressure will also effect the cylinder charge decreasing the amount of air actually reaching the cylinder and increasing the charge temperature. Thus, our setup will be always be able to generate more power than a K03/K04 setup would at a given boost level. This also means that we can produce the same power as a K03/K04 setup at a lower boost pressure.
Even though the boost onset point of our kit utilizing a GT25 turbo may be slightly higher than a K04, the power from 2500RPM's and on will greatly exceed the outputs of a K04. Why? Because power is not solely a function of boost pressure. Also realize that we do not need as much boost pressure to make the same amount of power.
The responsiveness of our setup past the boost onset point will always exceed that of a K04. Why? Because turbo lag is not solely a function of turbocharger size. At the very lowest engine speeds (2000rpm and below) the engine feels very much like a naturally aspirated car- very responsive and drivable yet not overwhelmingly powerful. The power outputs with our kit below 2000rpms are very comparable to a chipped K03 or a K04.
Thanks,
Brett
APR
</i>
Here is an excerpt from the infamous GT25/K04 war. It was directed as a response to one person, but look at it for it's information. It does NOT get any better:
<i>(1) Power is not solely a function of boost pressure.
(2) Turbo lag is not solely a function of turbocharger size (when other variables are changing.)
Until you can accept these facts it will not make sense!!!
It is very easy to bring a car to one level, given certain hardware. However, transitioning to the next level requires more effort. These methods may or may not be understood by the general public.
For example, it is easy to accept the statement that a larger turbo automatically means more turbolag. But by accepting this generalization you are limiting yourself to that statement.
There are many factors at work here. Remember that flywheel torque (or power) is equal to the internal engine torque minus pumping losses minus internal friction minus losses caused by auxiliary components. We will start by throwing out losses caused by auxiliaries and internal friction, these are not factors here that we can control. When we replace major engine parts (exhaust manifolds, turbos, etc.) we have some control of the other parts of the equation (internal engine torque, and pumping losses.)
Internal engine torque - This is directly related to the area under the curve of the instantaneous cylinder pressure versus crank angle. Specifically we are talking about the cylinder pressures during the power stroke. The more charge mass that we can inject into the cylinder the more power. The closer that our spark advance timing is to the ideal spark advance angle, the more power that we can make. (In our applications we are always going to be limited by the octane rating of the fuels used. IOW, it is a good rule of thumb that we are always going to want to advance the timing as much as possible without detonation.)
Pumping losses - The best way to visualize this is the energy required to expel (or ingest) gases from the engine.
Backpressure
Backpressure is one of the key factors to consider when comparing the K04 to our stage 3 system. Backpressure has two big negative effects- (a) it effects pumping losses, and (b) it effects cylinder scavenging.
Backpressure and pumping losses - It's very simple. The more backpressure that you have, the more energy is wasted on expelling the exhaust gases. Hence, with more backpressure you have HIGHER PUMPING LOSSES.
Backpressure and cylinder scavenging - This affects the internal torque in two ways. First of all, a reduced scavenging effect will mean less fresh air charge in the combustion chamber. Less fresh air charge means less oxygen which means less fuel which means less power. Also, the residual exhaust gases will add heat to the subsequent cylinder charge. A hotter charge means less timing advance which means less power. More exhaust backpressure means LESS INTERNAL ENGINE TORQUE.
Fact: A K03/K04 turbocharger utilitizing the stock exhaust manifold will have much greater exhaust backpressure then our stage 3 setup at any given airflow.
Enhanced scavenging / Reduction of cylinder-to-cylinder pulse interference
By utilizing a paired runner design in our manifold and being careful with the geometry, we are reducing the pulse interference effect and enhancing cylinder scavenging. This allows us to run more ignition advance for a given load condition and means that we are getting a fresher air charge. Also, exhaust manifold internal volume is kept to a minimum to aid turbocharger spoolup time. The exhaust manifold is constructed of Inconel, a material with one-fourth the heat conductivity of a standard cast iron, to keep the heat in the charge which maximizes the amount of energy available to spool the turbocharger (minimizes lag.) The inconel is also very stable and resistant to cracking when undergoing severe thermal cycling.
Turbocharger Technological Enhancements
The ball-bearing design of the turbo in our kit decreases spoolup time. The wheel designs on this turbo are cutting edge.
Also, with our kit the turbocharger is being run in its' sweet spot. This means that the compressor efficiencies will be high. Higher compressor efficiencies equate to lower intake charge temperatures. Lower intake charge temperature mean more ignition advance and a denser intake charge = More power.
CONCLUSION
As you can see, we are changing and affecting many things. It is much more complicated than 'this turbo is bigger than this one.' We would also like to point out the fact that there can be HUGE differences between two kits utilizing the same turbocharger depending on the rest of the kit.
The increased backpressure of the K03/K04 will mean more pumping losses at a given mass airflow. The increased backpressure will also effect the cylinder charge decreasing the amount of air actually reaching the cylinder and increasing the charge temperature. Thus, our setup will be always be able to generate more power than a K03/K04 setup would at a given boost level. This also means that we can produce the same power as a K03/K04 setup at a lower boost pressure.
Even though the boost onset point of our kit utilizing a GT25 turbo may be slightly higher than a K04, the power from 2500RPM's and on will greatly exceed the outputs of a K04. Why? Because power is not solely a function of boost pressure. Also realize that we do not need as much boost pressure to make the same amount of power.
The responsiveness of our setup past the boost onset point will always exceed that of a K04. Why? Because turbo lag is not solely a function of turbocharger size. At the very lowest engine speeds (2000rpm and below) the engine feels very much like a naturally aspirated car- very responsive and drivable yet not overwhelmingly powerful. The power outputs with our kit below 2000rpms are very comparable to a chipped K03 or a K04.
Thanks,
Brett
APR
</i>
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03-07-2001, 09:53 PM
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I saw that original post and looked at it..
I remember reading it real fast. Yeah I read it again and from what I've seen, hmmm... 'efficiency' and 'smooth' is all I can come up with. I've seen the numbers and they tell me it's fast. Driving/Riding one may spill several other words in hundereds per min depending on the following impression.
Exaust manifold: how can so many variables be placed into it w/o the car even feeling like has a turbo? Is it smooth, like na smooth? Do you feel_the_boost?
That post made very good sense. Has me thinking about all of the internals, pistons, fire order, intake and exaust flow and direction; etc.
I think that we will have a second strong kit on the market very soon and the bad part is that I know it will be difficult for me to choose between the two :-/
Exaust manifold: how can so many variables be placed into it w/o the car even feeling like has a turbo? Is it smooth, like na smooth? Do you feel_the_boost?
That post made very good sense. Has me thinking about all of the internals, pistons, fire order, intake and exaust flow and direction; etc.
I think that we will have a second strong kit on the market very soon and the bad part is that I know it will be difficult for me to choose between the two :-/