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Old January 23rd, 2008, 14:56   #31
TDIMeister
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The GT40 I spec'ed out was already too big for 400 HP in the 1.9 TDI; the S200 takes big to a whole other level. While it's a stretch to make 400 BHP from a 1.9L 4-cylinder TDI, I could definitely see a realistic possibility to use either turbo to make that power level in a 5-cylinder TDI.

But as GoFaster warned, care must be taken in the boost control to prevent the possibility of the boost rising to sufficient levels to cause the engine to go BOOM!

Using an R5 engine as a baseline, I would lay out the hotside like in the BMW x35d, meaning in parallel with the stock GT22V used in the R5. The pair of turbos will also be connected to a large capacity external wastegate that begins open at a fixed EMP, say, 2.5 bar and fully open at, say 3 bar. The turbine of the LP turbo would have to be dimensioned for A/R ratio such that with its characteristic boost threshold, it would be impossible for it to spool with the 3 bar EMP limit to make enough boost at the low-end RPM for damaging surge and boost pressures to occur.

The N75 still controls the VNT on the GT22V, but a MAP sensor that will operate over the full range of MAP will be required (I recall DIESEL DAZZLER telling me there's a GM part that goes to 4 bar or something...). Remapping would obviously be necessary.

On the cold side, the inlet of the LP turbo is connected to ambient, the outlet to the HP turbo and then off to the IC.

400 HP can be achieved in an R5 using no cheaters with 3.5 bars (50 PSI)of boost (4.5 bar absolute) if maximum power is produced at 4750 RPM.

BTW, the map of the S200 suggests that is has a ported shroud. It has a wide flow range between the surge- and choke lines, while sacrificing some efficiency.
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Old January 24th, 2008, 05:22   #32
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Quote:
Originally Posted by TDIMeister
BTW, the map of the S200 suggests that is has a ported shroud. It has a wide flow range between the surge- and choke lines, while sacrificing some efficiency.
Yes indeed it has a ported shroud. Thats the main reason the map is so wide. I'm pretty sure it will work out just fine in the end.
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Old January 24th, 2008, 14:53   #33
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Quote:
Originally Posted by GoFaster
…you will want to repeat the calculation for lower RPM points, with a view towards making the turbochargers *smaller*...
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I would suggest that the next iteration would involve one size smaller on the inner turbo (VNT17?) and one or maybe two sizes smaller on the outer one.
One caveat that you must be careful about specifically when rematching the HP turbo for a yet smaller one is that the smaller turbo is dealing with some factor more mass flow, in the calculated case more than 2X more. Compressor work will therefore increase by at least that factor. If you assume constant shaft RPM, that means that you’re transmitting more than twice the amount of torque through the scrawny shaft of the GT17-ish frame size turbo, something that is already well known to be marginally adequate for stock duty. Your turbo selection will therefore be a compromise (isn’t it always) between the best response and something that looks correct in calculations and plotted points on a map to one that will stand the rigors of use. I would hesitate using a GT17 for practically *any* serious performance application unless I see one with a stronger shaft.

Furthermore, we assumed that shaft RPM remained constant even though we drive more than twice more air through the turbo. After all, that’s what the map says, doesn’t it? Well, it’s quite clear that shaft speed simply cannot be constant! With geometrical constraints fixed, doubling compressor work at constant RPM demands doubling the impulse at the turbine. This is impossible given a certain P5 (turbine inlet pressure) and T5 (turbine inlet temperature). That means that to a large extent, the maps go out the window for the second stage. In matching the second stage, you likely need to pay more attention preventing over-revving the shaft and problems with excessive boost and boost creep than clearing surge and choke.
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Old February 4th, 2008, 03:12   #34
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Santa,
I just thought I'd add my 2 cents. I have a great book on turbocharging and thought I might recommend it to you. It covers a lot of fundamentals of turbocharging but doesn't go overboard with the physics/calculus/engineering stuff. It may seem a bit dated in some sections but it's good info. I think the latest model road car was a 90's era corvette, but all the same principles used today are discussed. I thought the real-old stuff was an interesting jump into the way-back machine. I've had this book for ~ ten years they very well could have newer versions.

Anyways, you can get a lot of perspectives and concepts from motorcycles to tractor pulls to v-12 3500hp marine engines and just about everything in-between. covers design, choosing turbos, gas-diesel, water injection, controls, twin/triple/staged/parallel turbos, inter-cooling etc. and has lots of charts/turbo maps to go with the text. It's a real easy read too.

Book is called "Turbochargers" by Hugh Macinnes and is published by HPBooks.

Last edited by bchezick; February 4th, 2008 at 03:15.
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Old February 4th, 2008, 10:49   #35
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That's a good suggestion. You can read a preview with several pages of the book on Google Books, but the chapter on tractor pulling and staged turbocharging that are relevant to this thread are not in the preview.
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