Why weren't K04's designed with larger compressor wheels? (Theory pros/cons of Hybrid Turbos)

VR_Life · 09-15-2004, 01:25 AM

Assuming Hybrids are larger K16 or RS6 Compressor wheels on K04 shaft, retaining K04 Exhaust Turbine and fittings.

So is it correct to say:
- they are more efficient, pushing more air at lower shaft speeds
=> they can reach higher PSI, at lower Exhaust Manifold & Turbo temps
=> they will be stronger than vanilla K04's in the mid range

- they have a bigger rotational mass on the shaft
=> so they are slower in ramping up
=> (significant?)more lag than std K04's

Any other downside to having a larger compressor wheel ? If this is more efficient, why was the original K04 compressor so small ?

What am I missing ?

VerrÜckt · 09-15-2004, 03:10 AM

J.Moss@TorqueFactory · 09-15-2004, 04:51 AM

Edit.

AntiSocial · 09-15-2004, 04:59 AM

Ideally, you want as small a turbocharger as you can get away with for your application. In Quattro GmbH's case with the RS4, they wanted something that hit hard in the midrange with almost diesel-like torque. The K16 hybrids you see coming out now are designed to yield more horsepower. You have to also look at the pressure ratio that the RS4 K04's are run at in the RS4 application. So long as they do their job, there is no reason to go bigger.

That is, unless you want to make these pigs fly, in which case, all bets are off.

AntiSocial · 09-15-2004, 05:02 AM

At a recent ricer dyno day, I noticed that EVERY time the cars hit their boost spike, that was EXACTLY where peak torque was, which makes sense, considering peak cylinder pressure and all that. Just my 2 peso's.

Ray Khan · 09-15-2004, 06:45 AM

VerrÜckt · 09-15-2004, 06:53 AM

because each car has a different output. There is a difference, but it is very hard to tell by the seat of your pants. To field the questions...

-Yes, an MBC will help spoolup because of its "on-off" behaviour at low RPM's. The wastegates are fully shut until the requested boost level is met. I believe the N75 behaves differently.

-The downpipe's effect on torque ramp is very complex and difficult to judge. Larger downpipes likely evacuate gasses quicker which helps spool up. However, they also run "cooler" which hinders spool too.

-Turbos definitely affect torque ramp. It's known that the K04's spool quicker, but from behind the wheel the difference is not dramatic.

And yes, my sig still makes me laugh too. :-P

SLPR S4 · 09-15-2004, 07:20 AM

Oo.et.oO · 09-15-2004, 07:32 AM

so i don't like it so much. ;-P

but i'm getting a "new" machine on friday so it should alleviate my "problem".

Skydive@AI · 09-15-2004, 07:47 AM

09-15-2004, 01:25 AM	#1
VR_Life Guest Garage is empty, add now Join Date: Jul 2003 Posts: 9,718	Why weren't K04's designed with larger compressor wheels? (Theory pros/cons of Hybrid Turbos) Assuming Hybrids are larger K16 or RS6 Compressor wheels on K04 shaft, retaining K04 Exhaust Turbine and fittings. So is it correct to say: - they are more efficient, pushing more air at lower shaft speeds => they can reach higher PSI, at lower Exhaust Manifold & Turbo temps => they will be stronger than vanilla K04's in the mid range - they have a bigger rotational mass on the shaft => so they are slower in ramping up => (significant?)more lag than std K04's Any other downside to having a larger compressor wheel ? If this is more efficient, why was the original K04 compressor so small ? What am I missing ?

09-15-2004, 03:10 AM	#2
VerrÜckt AudiWorld Super User Garage is empty, add now Join Date: Feb 2003 Posts: 16,414	Very little difference in lag. I can't complain about 25 psi around 3000 RPM.

09-15-2004, 04:51 AM	#3
J.Moss@TorqueFactory Senior Member Garage is empty, add now Join Date: Jan 2001 Posts: 5,077	Re: Very little difference in lag. I can't complain about 25 psi around 3000 RPM. Edit. __________________ Sport Compact Car 2007 Ultimate Street Car Challenge Winner Jeff Moss, ASE Certified (A1, A3, A4, A5, A6, A8) <a href="http://www.torque-factory.com">Los Angeles area GIAC dealer for Audi, Bentley, BMW, Mini, Porsche and VW. Torque-Factory, Inc.</a> Torque-Factory Support Forum

09-15-2004, 04:59 AM	#4
AntiSocial AudiWorld Super User Garage is empty, add now Join Date: Nov 2002 Posts: 8,514	The RS4 K04 wasn't designed for top end HP, it was for huge midrange torque. Ideally, you want as small a turbocharger as you can get away with for your application. In Quattro GmbH's case with the RS4, they wanted something that hit hard in the midrange with almost diesel-like torque. The K16 hybrids you see coming out now are designed to yield more horsepower. You have to also look at the pressure ratio that the RS4 K04's are run at in the RS4 application. So long as they do their job, there is no reason to go bigger. That is, unless you want to make these pigs fly, in which case, all bets are off. __________________

09-15-2004, 05:02 AM	#5
AntiSocial AudiWorld Super User Garage is empty, add now Join Date: Nov 2002 Posts: 8,514	About torque... At a recent ricer dyno day, I noticed that EVERY time the cars hit their boost spike, that was EXACTLY where peak torque was, which makes sense, considering peak cylinder pressure and all that. Just my 2 peso's. __________________

09-15-2004, 06:45 AM	#6
Ray Khan AudiWorld Super User Garage is empty, add now Join Date: Apr 2000 Location: Melrose, MA Posts: 20,310	yep....this is true for me __________________ Ray Khan 00 1.8T QM APR stage 3+ APR Exhaust APR Intake DUH FMIC Southbend OFE Stage 4 clutch SPEC 12 lb flywheel Greddy Profec B electronic boost controller Porshe Boxster calipers BIRA stage I brackets Hawk HPS brake pads A8 rotors, SS lines V&S Short Shifter Vogtland Coilovers Neuspeed 19mm rear sway 18x8 Flik Lex 235/40/18 Falken GRB 451 17x7.5 B5 S4 Avus 205/50/17 Dunlop Wintersport 3D Sony XM 7554 amp with 5.25" and 6.5" Infinity kappas MTX 801D amp with 2x10" kenwood sub enclosure Xenons Fog light relay mod VDO boost gauge in custom vent pod Clear corner mod S4 wheel well liner RS-4 grill AIM and MSN messenger:rakha77

09-15-2004, 06:53 AM	#7
VerrÜckt AudiWorld Super User Garage is empty, add now Join Date: Feb 2003 Posts: 16,414	For these cars...the slope of the line is what is important, not the actual numbers because each car has a different output. There is a difference, but it is very hard to tell by the seat of your pants. To field the questions... -Yes, an MBC will help spoolup because of its "on-off" behaviour at low RPM's. The wastegates are fully shut until the requested boost level is met. I believe the N75 behaves differently. -The downpipe's effect on torque ramp is very complex and difficult to judge. Larger downpipes likely evacuate gasses quicker which helps spool up. However, they also run "cooler" which hinders spool too. -Turbos definitely affect torque ramp. It's known that the K04's spool quicker, but from behind the wheel the difference is not dramatic. And yes, my sig still makes me laugh too. :-P

09-15-2004, 07:20 AM	#8
SLPR S4 Member Garage is empty, add now Join Date: Jul 2003 Posts: 4,378	How much boost are they pushing? What is a "safe" # for K04's? __________________

09-15-2004, 07:32 AM	#9
Oo.et.oO AudiWorld Super User Garage is empty, add now Join Date: Nov 2003 Posts: 5,889	your sig brings my machine to its knees whenever it's on the screen so i don't like it so much. ;-P but i'm getting a "new" machine on friday so it should alleviate my "problem". __________________ Gone but not forgotten: 2001 Brilliant Black S4 Avant 6spd. c'mon AoA, where is the B8 A4 3.0 TDi?

09-15-2004, 07:47 AM	#10
Skydive@AI Senior Member Garage is empty, add now Join Date: Dec 2000 Posts: 7,818	Geezus David... S#it or get off the pot, already! ;) __________________ -Skydive 2001 S4 Avant - Now Returning to Stock! 450 Vertical Feet in a B5 Audi Chassis Plan the Work. Work the Plan.

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