Engine bay teardown
OK, I was extremely embarrassed and not at all pleased with the dyno testing results of my R28 presented in Part Three of this project car series. The awesome Advanced Motorsports (AMS) four-wheel MAHA dyno beat me fair and square. Sadly, I still have 'My R32 Blues'. Perhaps I was asking a bit too much of the little 2.8L VR6 24V (with cams, chip, and numerous bolt-ons), to put out power and torque numbers approaching the 3.2L R32 engine. Anyway, after such a defeat I felt it was time to go back to the drawing board. It did not, however, take me long to determine that my next plan of action was to go all out. No more modest gains with bolt-ons. This time I would open my wallet for some real performance. That is, to a performance level well beyond even the factory's mighty R32. I reckoned an extra 150bhp or so would turn my lightweight R28 into a lethal track weapon, while still maintaining desirable sleeper status. The time had come for forced induction, and the name of the game was Turbo.
In the summer of 2004, Marcel Horn, president of HPA Motorsport, took me for an exciting ride in his infamous 550 bhp twin-turbo R32. Having driven and been a passenger in many fast cars as a track day enthusiast and performance driving instructor, I climbed into the passenger seat, buckled my safety belt, and thought: "How fast can it be?" It was not only fast, it was beyond a doubt the fastest car I have ever been in (exotics, Vipers and Porsche Turbos included). The twin-turbos' power was bordering on unbelievable and the R32 platform's ability to put this extreme power to the road was equally astonishing. I made a mental note: "I've got to buy one."
The junk pile (or classified section) !
New Turbo Power
Having spent a good deal of hard earned cash converting my front-wheel drive GTI to the R32 4Motion driveline, stepping up to a twin turbo was completely out of the question. A more affordable and conservative solution was required. This was after all, my daily driver. Fortunately, in mid 2005, HPA Motorsport released several new single turbo systems for 24-valve VR6 engines. These use an R30 Garrett ball bearing turbocharger with custom HPG compressor housing, integrated recirculation valve, and custom HPG exhaust housing with integrated wastegate, for reduced turbo lag and therefore improved throttle response. The system I chose was HPA's top-line FT410 Series.
This is configured with a proprietary HPG short-runner cast aluminum intake manifold, tuned cast exhaust manifold with external oxygen sensors, dual side-mount TT intercoolers, custom stainless steel boost piping, a compression-reducing spacer (down to 8.5:1), high-flow fuel injectors, a larger diameter mass air flow (MAF) unit, an auxiliary inline fuel pump, a 100-cell-count 70mm race cat (dual R32/TT-specific 100-cell race cats were used in my 4Motion application for proper ground clearance), and race-grade connecting rod bearings and bolts to deal with the extreme forces of the application.
All this is put together in a beautiful OEM quality package, the software tuning is seamlessly integrated into the factory ECU, and maximum boost set to 14psi. By request, my software was tuned to run on readily available 91-octane premium fuel. The result is a ferocious brute with excellent driveability for a single turbo application. Figures 1 to 8 show the progression from dyno-dud to dyno-dude.
Dyno Results and Interpretation
Head spacer install
HPA provided pre- and post-turbo-install dyno runs on the same two-wheel 248C Dynojet. Peak values for these runs were: 181whp/178lb-ft in normally aspirated form (as previously tested in Part Three), and 314 whp/329lb-ft at 14 psi boost, with the turbo system installed. Please note that while the gains in peak power and torque are quite significant, these values are only a small part of what can be learned from the charts. This will be further explained below. Figure 9 shows all pre- and post- curves nicely overlaid on the same plot for your viewing pleasure. This compilation was created by reading the data off the extremely smooth raw curves at 250rpm increments. Also, both dyno runs were done in fourth gear with the Haldex unit's electrical circuit disconnected for obvious safety reasons.
There is a great debate in the VW/Audi tuning scene with respect to converting such peak values from a two-wheel dyno run to actual horsepower at the flywheel-which I'm not going to continue here. The range of conversion factors for MkIV 4Motion Haldex-equipped vehicles is, at present, 0.78 to 0.85. The reason for this variance is due to the unknown additional drag on the measured value caused by the mechanically-pumping Haldex unit. The final drive attached to the front drive is split mechanically and is spinning the center prop shaft during the dyno run. The rear section, even when unplugged, is pumping oil, generating back pressure and drag on the system. The 'chosen' conversion factor is divided by the measured peak wheel-hp value, thus peak horsepower at the flywheel in this case ranges from 369 to 403bhp (depending on who you believe).
Conversion factors aside, this is still not the full story, as fourth gear dyno pulls of turbocharged engines on chassis dynamometers without proper wind tunnels are most definitely not representative of real-world output. It is critical to understand the effect of measuring the generated load in a fourth gear run (simulating 32mph to over 107mph) when reduced air flow is traveling across the radiator, intercooler and firewall.
New short runner intake manifold
Let's see what else can be learned from the dyno curves. First, look at the relative gains at the wheels: 133 wheel-hp (up a very satisfying 73 percent), and 151lb-ft of torque (up an incredible 85 percent). The initial surge in the turbo TQ curve demonstrates the amazing efficiency of the Garrett/HGP R30 turbo, this is really the key in punching the car off the line. Next, it is important to notice the enormous gains in area under the turbo curves. In fact, the turbo curves reveal that from 3500-6400rpm, while the engine is under full thrust, it does so without dropping below a whp or TQ value of 290 at the wheels (see the red line traced on the chart in Figure 9).
Remember that "torque gets you going and horsepower keeps you going". They work together to propel you down the road. Further interpretation of the turbo whp curve shows that shifting before just 6000rpm will maximize a fourth gear pull. Note that this will differ for each gear as the load on the motor will vary. During a real-world pull in fourth gear, I didn't detect any loss in power until about 6500rpm. This helps substantiate the aforementioned need for proper airflow to achieve real-world power outputs.