Direct Bolt on GT25 Turbo for A4 1.8t
02-13-2001, 03:52 PM
#21
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There have been no head stud problems on Stage 3 cars.
Even in extreme testing. Stage 3 has been out for a long time, we have a lot of miles on it and so do many our customers. There has never been a hint of a problem.
Nonetheless, we are investigating this issue on the transverse Stage 3 due to the higher forces and the increased mass of the assembly. If people are worried, then that bracket may be added to the A4/Passat Stage 3 kit.
Nonetheless, we are investigating this issue on the transverse Stage 3 due to the higher forces and the increased mass of the assembly. If people are worried, then that bracket may be added to the A4/Passat Stage 3 kit.
02-13-2001, 04:20 PM
#22
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Heck I am not worried-
I just dare that head to give me a reason to pull it off again. I'll do even more work to it this time. MMMMM, maybe some money wasting coatings would be in order. Actually I am not an engineer like APR but there are quite a few studs holding the manifold to the head. Looks plenty strong to me.
02-13-2001, 06:03 PM
#28
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Everyone says the APR manifold is so important to the kit
I would stick with APR for that reason right now. BTW, I belive the GS kit will come with injectors.
02-13-2001, 06:16 PM
#29
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Well it seems we need to insert some logic here (novel intended for defensive Stage 3 owners)...
The stock manifold is NOT the problem with the K03/04 setup - the scroll and wastegate in these turbos are! The bottleneck always has been and always will be the turbo itself. The "scroll" of the turbine is too small and its efficiency decreases even at moderate flow levels. On the upside, this design produces almost no lag at all. There was talk last year of KKK redesigning the Inline 1.8T K04 turbine housing with a much larger scroll and maybe a 55mm turbine (this never materialized).
As for manifolds - let's look at what they do! Aside from their small supporting role in holding up the turbo (sorry about the pun), they act in concert as a series of tubes that transfer energy. To maximize efficiency in this transfer, one must first minimize the distance that the individual exhaust pulse must travel. The further the distance, the more the pulse/charge loses its energy. Equal length headers are efficient only in 500+ hp setups where pulse interference/cancelling occurs or when extremely high RPMs are being run (but even the validity of that second argument has come into question).
The second way to maximize the efficiency of the energy transfer is to maintain the (circumferal) volume of the tubes. That is not to say that each tube needs to have the same total volume, but the total pulse/charge needs to be contained in a space of consistent volume as it moves through the "tube". The "volume" of the charge (the length most specifically) is determined by the smallest circumference it passes through which in this case is the point at which the head meets the manifold also known as the port. This is the constant that cannot be changed (without porting of course).
So, if we allow the exhaust charge/pulse (of a given volume) to enter a chamber of an ever increasing volume, the potential energy of that charge will be much lower when measured at any point past the intial small entry port. We see this somewhat in two stroke motors where there is an "expansion pipe". The expansion pipe actually aids in cylinder scavenging becuase the loss of energy downstream creates an area of low pressure in the exhaust port theoretically pulling out extra gasses (and some intake mixture) into the pipe for a more complete cylinder fill. Using an expansion pipe (an extreme example) with a turbo would result in a significant loss of the potential energy contained in the charge/pulse by the time you "funnelled" it back into the turbine scroll. Not very efficient!
If one were to progressively decrease the volume of the tube, the charge/pulse would actually pick up potential energy as it passes through. This is becuase the charge/pulse in an exhaust manifold already has a specific volume and therefore occupies a given length of the tube as it travels downstream. If the volume of the tube is decreased and the length of the charge is not allowed to increase (because it is preceded and followed by another pulse/charge) then it is forced to compress which generates additional heat. Heat is the potential energy that the turbine harnesses and therefore, any additional heat is just additional energy.
So the way I see it, the stock manifold will do just fine, especially if it is Extrude Honed because it has a pretty even circumferal volume and almost exactly matches the exhaust port circumference. What I'd really like to see are the flow bench numbers for an APR manifold compared to that of an Extrude Honed stock manifold. Will the APR flow better? Probably. Will this increased flow mean anything at power levels below 500HP? Probably not!
As for the cracking issue...all manifolds crack! If they don't, then they are made of a material that has a very low tensile strength (becomes soft and mushy like a soft serve cone in August) at high temps. If someone claims their manifold doesn't crack, I'd like to see the metallurgy on that alloy because I bet it has no tensile strength at 900C!
I am glad that Allied Signal stepped up to the plate! The direct bolt on will be a huge win for the tuner scene. We will surely see variant turbines and compressors in this housing over time and might see well over 300HP before we know it.
Mike O.
"I've never heard of turbos before but I did stay at a Holiday Inn Express last night!"
As for manifolds - let's look at what they do! Aside from their small supporting role in holding up the turbo (sorry about the pun), they act in concert as a series of tubes that transfer energy. To maximize efficiency in this transfer, one must first minimize the distance that the individual exhaust pulse must travel. The further the distance, the more the pulse/charge loses its energy. Equal length headers are efficient only in 500+ hp setups where pulse interference/cancelling occurs or when extremely high RPMs are being run (but even the validity of that second argument has come into question).
The second way to maximize the efficiency of the energy transfer is to maintain the (circumferal) volume of the tubes. That is not to say that each tube needs to have the same total volume, but the total pulse/charge needs to be contained in a space of consistent volume as it moves through the "tube". The "volume" of the charge (the length most specifically) is determined by the smallest circumference it passes through which in this case is the point at which the head meets the manifold also known as the port. This is the constant that cannot be changed (without porting of course).
So, if we allow the exhaust charge/pulse (of a given volume) to enter a chamber of an ever increasing volume, the potential energy of that charge will be much lower when measured at any point past the intial small entry port. We see this somewhat in two stroke motors where there is an "expansion pipe". The expansion pipe actually aids in cylinder scavenging becuase the loss of energy downstream creates an area of low pressure in the exhaust port theoretically pulling out extra gasses (and some intake mixture) into the pipe for a more complete cylinder fill. Using an expansion pipe (an extreme example) with a turbo would result in a significant loss of the potential energy contained in the charge/pulse by the time you "funnelled" it back into the turbine scroll. Not very efficient!
If one were to progressively decrease the volume of the tube, the charge/pulse would actually pick up potential energy as it passes through. This is becuase the charge/pulse in an exhaust manifold already has a specific volume and therefore occupies a given length of the tube as it travels downstream. If the volume of the tube is decreased and the length of the charge is not allowed to increase (because it is preceded and followed by another pulse/charge) then it is forced to compress which generates additional heat. Heat is the potential energy that the turbine harnesses and therefore, any additional heat is just additional energy.
So the way I see it, the stock manifold will do just fine, especially if it is Extrude Honed because it has a pretty even circumferal volume and almost exactly matches the exhaust port circumference. What I'd really like to see are the flow bench numbers for an APR manifold compared to that of an Extrude Honed stock manifold. Will the APR flow better? Probably. Will this increased flow mean anything at power levels below 500HP? Probably not!
As for the cracking issue...all manifolds crack! If they don't, then they are made of a material that has a very low tensile strength (becomes soft and mushy like a soft serve cone in August) at high temps. If someone claims their manifold doesn't crack, I'd like to see the metallurgy on that alloy because I bet it has no tensile strength at 900C!
I am glad that Allied Signal stepped up to the plate! The direct bolt on will be a huge win for the tuner scene. We will surely see variant turbines and compressors in this housing over time and might see well over 300HP before we know it.
Mike O.
"I've never heard of turbos before but I did stay at a Holiday Inn Express last night!"
02-13-2001, 07:20 PM
#30
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every turbo has lag
Lag is a momentary under-performance of the engine under acceleration due to the turbo needing more time to spool up to match the increased airflow.
Every turbo has lag because the turbo spin up is driven up by the exhaust.
I'm sorry, but from those pictures, there is no way the GT25 has less lag than a K03. Increased turbo spool size leads to increased spool mass which leads to slower spin up.
Higher boost also creates more lag because you have to lower compression ratio to reduce knocking. Lower compression ratio means the engine produces less power when off-boost, thus it produces less exhaust gas, so it spools the turbo up even slower.
Turbo boost is alive and well. Keep your revs up and you'll minimize it as much as possible.
Every turbo has lag because the turbo spin up is driven up by the exhaust.
I'm sorry, but from those pictures, there is no way the GT25 has less lag than a K03. Increased turbo spool size leads to increased spool mass which leads to slower spin up.
Higher boost also creates more lag because you have to lower compression ratio to reduce knocking. Lower compression ratio means the engine produces less power when off-boost, thus it produces less exhaust gas, so it spools the turbo up even slower.
Turbo boost is alive and well. Keep your revs up and you'll minimize it as much as possible.