Category Archives: Turbo Selection

FrankenTurbo, Turbo Selection, Turbocharger

FrankenTurbo F21 Mixed Flow

As I wrote about a few months back, the prototype FrankenTurbo F21 with a mixed flow turbine wheel (referred to as F21MF hereafter) is an update to a product that was already on my candidate list.

When the details of the prototype design started to firm up I became more interested in how this third update to the FrankenTurbo offering for the S4 would measure up to my goals of having a quick spooling turbo with good power potential.

The mixed flow turbine is supposed to have greater efficiency at lower blade speeds, and with slightly less wheel mass the potential for quicker spool up.  I’m interested in seeing how this mixed flow design does with high mass flow rates as I believe the K04 hotside is what is limiting the K04 hybrid turbochargers from delivering better performance.

frankenturbo mixed flow turbine
FrankenTurbo F21 Mixed Flow Turbine

The compressor wheel is also seeing significant changes, even more so than the turbine wheel which was based on the outgoing F21 design.

The new compressor wheel is billet, not in itself all that important, but the design is quite a bit different from other K04 hybrid offerings that I’ve been able to dig up information on.

frankenturbo f21 billet compressor wheel
FrankenTurbo F21 Billet Compressor

The inducer is 45.3 mm, compared to the older F21 size of 42.6 mm, and the exducer is 54.5 mm, versus 56.3 mm for the outgoing model.  The closest comparison product I know of is the JHM RS6-R which I believe uses a 45/56 compressor wheel.  The new compressor wheel also has a slim hub, which theoretically should allow the wheel to grab more air.

With what is apparently an overall larger compressor wheel my concern is how well the product will spool up.  I was not a fan of the boost onset hit that the F21 took relative to its predecessor, the F4H, but if the top end delivers and the boost ramp up does not take too much of a penalty I might keep the F21MF on my contender list.

Some early results I’ve seen on the F21MF show that it doesn’t appear to give up any response compared to the previous product.

f21mf_boost_onset
F21MF Requested vs Actual Boost

The remaining question is still, how will it perform on the top end?

For now the F21MF will stay on my candidate list as it looks to be an excellent option for maximizing the power deliver from a stock motor without giving up (too much) boost response.

The candidate list now stands at:

  • BorgWarner K04
  • FrankenTurbo F21-Mixed Flow
  • ProjectB5 RS6-X
  • SRM Billet K04
  • TTE 550

Next: Project: B5 PB550

The Turbo Engineers, Turbo Selection, Turbocharger

TTE 550 Another Contender

The longer I wait the more interesting things become.

Another option that I’ve recently been made aware of is a product from The Turbo Engineers, an outfit in Germany.  While they have a large product line the turbocharger that caught my attention was the TTE 550 (image below).

The Turbo Engineers TTE 550 B5 S4/RS4 Turbocharger
TTE 550

This turbocharger pair is based off of the BorgWarner K04 with modified RS6 internals.  It’s a pairing of components that I have heard good things about and one that I think provides a great upgrade path to someone with K04’s that would like to max out their stock motor, or even push a little closer to the 500 whp range.

For less than the cost of new turbochargers TTE modifies the used BW K04’s, milling the compressor housing so that RS6 internals can fit into the K04 housings.  This means the turbo’s go right back where they came from in the engine compartment without need to purchase RS6 turbine housing compatible DP’s.

TTE offers a number of additional modifications for this turbo such as:

  • Ported exhaust entry
  • Gasket matched exhaust flange
  • Ported boost outlet
  • Ported compressor inlet
  • Compressor cover painted in black Hi-Temp coating
  • Actuator painted red in Hi-Temp coating
  • Lightened Turbine wheels

I’d like to find some additional performance results from users of this turbo, but the data supplied from the manufacturer looks promising.

My list of turbocharger candidates now looks like:

  • BorgWarner K04
  • FrankenTurbo F21
  • ProjectB5 RS6-X
  • SRM Billet K04
  • TTE 550

Next: FrankenTurbo F21 Mixed Flow

Turbo Selection, Turbocharger

New option from SRM

With the passage of a few months a new candidate has entered the scene.  I noticed that Silly Rabbit Motorsports has introduced a K04 hybrid variant to provide another option for me.

SRM K04 RS4+ (K04 Hybrid Turbo)
SRM K04 RS4+ (K04 Hybrid Turbo)

These SRM turbo’s bring a new twist to the candidate pool because they are similar in size to the FrankenTurbo F21 and ProjectB5 RS4-X on the compressor side, though the SRM uses a billet compressor wheel, but on the turbine side it is using a clipped wheel.

This is a very interesting development since I have theorized that one of the reasons my experience with the FrankenTurbo F4H-BT did not show much gain in the upper rpm’s, despite pushing 25psi out to redline, was that the airflow through the turbine side began to back up lowering the engines VE.  Perhaps a clipped turbine wheel would allow this size turbocharger to hold that 25+ psi and flow better, netting greater top end horsepower results.

Since the product is a recent introduction it remains to be see how they perform, but for now they will stay on the candidate list:

  • BorgWarner K04
  • FrankenTurbo F21
  • ProjectB5 RS6-X
  • SRM Billet K04

Note: As of July 2015 I have yet to see any results of how the SRM billet K04 turbocharger performs.

Next: TTE 550 Another Contender