F21 on E85

There’s not been much activity in the turbocharger selection area recently, but that has changed with the receipt of this data showing a F21 equipped B5 S4 operating with E85 fuel and measured on a Dynapack dynamometer.

It’s good to see a F21 car operating the turbocharger at a boost level consistent with what I believe they are capable of, steady 23-24 psi out to redline.

Details about the car: 2001 Audi B5 S4 on Stock Engine, FrankenTurbo F21 turbochargers, 72 lb injectors, 85mm MAF and intake, 2.5″ catless downpipes, Silly Rabbit Motorsport Intercoolers, tuned by Epic Tuning Group on AU Tuning’s Dyno.

Chart of Frankenturbo F21 using E85 fuel
FrankenTurbo F21 on E85 (Dynapack Dyno)

And some results of the F21’s on 91 octane fuel.

FrankenTurbo F21 Turbocharger on 91 octane fuelIn terms of selection criteria these results show that F21’s are going to be able to push the edge of my comfort zone with the stock motor.  With 93 octane instead of 91 I’d expect the horsepower and torque to nudge up another 15-20.

The contenders still are:

  • Borg-Warner K04
  • FrankenTurbo F21
  • Project B5 RS6-X


PreTurbo Air Temperature

After relocating the Auber air temperature sensor to a fitting on the turbocharger inlet pipe, a position just forward of where the exhaust manifold and inlet pipe are running parallel and close by one another, I logged the temperatures again.

The point was to try and determine how much of the pre intercooler heating of the intake air is taking place in the inlet pipe that runs alongside the exhaust manifold as well as through the turbocharger.

The chart below shows the results:

Pre turbocharger intake air temperature chart
Comparison of pre versus post turbocharger/exhaust manifold air temperatures

The lines are a bit busy, so I will try to explain what the chart is showing.

The lighter shaded lines represent data that was collected this morning when the ambient temperature was about 66F.  The darker lines represent data collected midday when the ambient temperature had risen to 79F.  The green lines show the respective ambient temperatures in relation to the other temperature readings.

IAT is the temperature of the intake air as reported by the car’s intake air temperature sensor located after the Intercooler inside the Intake Manifold.

CIT is compressor inlet temperature, the intake air temperature before it goes into the turbocharger, and also because of the placement of the sensor the air has not yet passed alongside the exhaust manifold.

COT is the compressor outlet temperature, the temperature of the air after it has exited the turbocharger, but before it passes through the intercooler.

The morning temperature trend is similar to what I recorded yesterday (IAT Problems) and about a week ago when I looked at IC Efficiency.  The temperature exiting the turbocharger steadily rises well above ambient temperatures even when the car is not being driven hard.

The midday data introduces the pre-turbocharger air temperature and shows this value tracking right along with the post intercooler intake air temperature.

While the intake piping and airbox are contributing some to the temperature rise of the intake air, the greatest climb in temperature is taking place within the inlet pipe that runs alongside the exhaust manifold and the turbocharger compressor housing.

What’s next:

I’d like to narrow down further the location where the temperature is being affected greatest.  If I can identify specific locations of great heat addition I can then investigate possible ways to mitigate the heat addition.  If the exhaust manifold is a significant contributor a few easy options would be ceramic coated exhaust manifolds, ceramic coated inlet pipes, and wrapping the inlet pipe with a thermal shield.

If the turbocharger compressor housing is identified as the greatest contributor finding a remedy will be much harder.