Boost Logging Gear

Recently I posed a question to someone about a boost chart they had created inquiring about the gear the car was in when the log was generated.  In their response they had stated the gear was not a matter of concern as the chart was showing boost rise versus engine speed, where if it had been boost pressure versus time then it would have mattered.

This answer contradicted results I have recorded on my car but I did not have a good comparison set of data to use to illustrate my point, that gear does matter.

So I set out to collect some data when accelerating wide-open-throttle (WOT) in third gear and sixth gear and commencing the acceleration from a very low engine speed, 1000 rpm.

Recently I have been trying to refine the tune on my S4 for the actual wastegate duty cycle generated boost levels, an effort that has involved operating the turbochargers with fixed wastegate duty cycles.  I loaded up a tune that uses a fixed 95% WGDC that would allow the turbochargers to spool up at maximum rate to see how spool up compared between gear selections.

What I recorded with this purpose generated data confirmed other observations I’ve made, boost ramps up more quickly in 6th gear versus 3rd gear when plotted versus engine speed.

3rd vs 6th gear boost rise
3rd vs 6th gear boost rise

The difference is quite dramatic, by 3000 rpm the 6th gear boost pressure is 10 psi higher than at the same engine speed in 3rd gear.

On the other hand, plotting the boost rise versus time shows boost rising much more quickly in 3rd gear versus 6th gear:

3rd vs 6th Boost rise over time
3rd vs 6th Boost rise over time

 

Returning to charts plotted in the more common format, against engine speed, it can be seen that Airflow rises following the rise in Boost pressure.

3rd vs 6th MAF rise
3rd vs 6th MAF rise

 

Also rising with Intake Manifold Pressure is the pressure in the Exhaust Manifold, again following the boost pressure rise pattern for 6th and 3rd gears.

3rd vs 6th Exhaust Manifold Pressure Rise
3rd vs 6th Exhaust Manifold Pressure Rise

 

So a question now could be, if MAF and Exhaust Pressure increase with the rising Intake Manifold Boost Pressure, why is the Boost Pressure rising more rapidly in 6th gear?  What is driving the faster Boost increase in 6th gear as compared to 3rd for the same engine speeds (RPM)?

The answer probably comprises a number of contributors, but I suspect the most dominant influence is from the Exhaust Gas Temperature.  As the ‘versus time’ plot from above shows, in 6th gear the time is substantially longer for boost to rise, this would mean that there is more time to generate higher temperatures in the exhaust gas due to the components along the exhaust path heating up.  By heating up, these parts are drawing less energy from the exhaust gas stream leaving more heat energy to be extracted by the turbocharger turbine.

Taking a look at the Exhaust Gas Temperature, shown below, it can be seen that when accelerating in 6th gear the exhaust gas temperature rises a greater amount than when in 3rd gear.

3rd vs 6th EGT rise
3rd vs 6th EGT rise

 

Finally, with the Intake Air Temperature contributing the the rate of boost rise I tried to ensure that both cases were tested using similar IAT’s.  I was mostly successful as shown below.

3rd vs 6th IAT rise
3rd vs 6th IAT rise

 

Finally, what’s the point to take away from this?  That when looking at a boost log that is plotted versus engine speed it is important to consider what gear the S4 is in as that selection can greatly (10 psi difference in this case) impact the performance produced.

Thermal Coated FrankenTurbo

Back from having thermal coating applied to the FrankenTurbo F21 turbine housing.

Next for these will be reinstalling them, date TBD, to try and determine if any changes can be measured that arise from applying the thermal coating.

FrankenTurbo F21 turbine housing with Thermal Coating applied
FrankenTurbo F21 turbine housing with Thermal Coating applied

 

FrankenTurbo F21 turbine housing with Thermal Coating applied
FrankenTurbo F21 turbine housing with Thermal Coating applied

White Dog Racing RS4 TB/Bipipe

Another product from White Dog Racing was sent to me for flow testing and comparison to the White Dog Racing bipipe products that I previously flow tested, along with the few other Audi B5 S4/RS4 bipipe options.

This time I received a 60 mm bipipe with RS4 throttle body.

White Dog Racing 60mm Bipipe on Flowbench
White Dog Racing 60mm Bipipe on Flowbench

I was interested to see how much of a difference adding the RS4 throttle body would make to the flow performance of the 60 mm WDR bipipe versus the S4 throttle body that was used with the prior tests, and also compared to the full RS4 intake setup.

Results:

White Dog Racing 60mm RS4 Throttle Body Bipipe Combination
White Dog Racing 60mm RS4 Throttle Body Bipipe Combination

 

The flow through the WDR-60/RS4 product far surpassed that of all the other bipipe combinations I have flow tested thus far.

Curious about how the flow would be affected by adding the silicone adapter/couplers to the inlet of the pipe, I compared three setups: bare metal, a 2.5″ coupler, and a 2.5″ to 2.25″ hump hose coupler.

WDR Bare Metal Inlet
WDR Bare Metal Inlet
WDR 2.5" Coupler
WDR 2.5″ Coupler
WDR 2.5"->2.25" Hump Hose
WDR 2.5″->2.25″ Hump Hose

Results of these three cases measured at 16″ of H2O were:

WDR Inlet Comparison
WDR Inlet Comparison

The addition of the 2.5″ coupler improved airflow measurably.  The reduction from 2.5″ to 2.25″ caused a small decrease in airflow.

Conclusion:

The White Dog Racing 60mm bipipe combined with the RS4 throttle body has achieved the highest airflow through a bipipe / throttle body combination that I have measured.