Part III, Tuning, Dyno Results & Driveability
Paul Shaw Shares His Own Experiences
Following Xmas and New Years, a month passed by before the next major phase of the project got underway. Shawn fired up the M5 and we went straight to the dyno to confront the biggest challenge of all. When forced air is crammed into cylinders along with increased fuel, the big worry is detonation, especially with the M5s high compression engine. Detonation is a BIG deal. When air fuel charge is ignited out of sequence, it can break rings, pistons, split heads and can even fry engines completely.
Our expectations were that we were on the ‘safe side’ because we selected a Vortec pulley that would produce a relatively low boost of 6psi. Subtract the parasitic effects of the intercooler – an assumed 2 psi – and the resulting boost might be a very safe 4-5psi. Indeed, Shawn speculated that at this low level of boost, no reprogramming of the engine management system may be necessary, allowing full piggybacking of the SC kit on the existing system.
While 4-5psi may sound highly conservative for a performance oriented team, a key compensating factor is the intercooler. By cooling and condensing the blown air from the SC, the intercooler not only reduces chances of detonation, but increases the ‘bang for the buck’ because it crams a more condensed air/fuel mixture into the cylinders. In our thinking, a good intercooler combined with 4-5psi should out-perform 6-7psi without an intercooler (as used, for example by Dinan in it’s SC kits for 540i’s).
The first set of dyno results produced a lot of excitement. Maximum rear wheel HP was 345, a gain of about 100 RWHP over the stock M5 (and a gain of 75RWHP over my M5 with Jim Conforti Chip). This was achieved with a registered boost of only 3.5psi! When this gain was “translated” into flywheel or BHP, and then compared to stock HP and torque figures for an M5 (with no chip), the increase in flywheel HP went from 311 at 6800 rpms (stock) to 426 at 6800 rpms; while torque increased from 266 ft/lbs at 5000 rpms (stock) to 340 ft/lbs at 5000 rpms. Furthermore, these gains were achieved without modifying the air/fuel ratio through out the rpm band, with the strong implication that tuning would generate more performance. But then we hit a snag – oil leaks – presumably caused by the increased boost, combined with seals that had probably shrunk or dried out because my M5 had largely been a garage queen..
Once the oil leaks were fixed by master BMW mechanic Rudolf Buchler at CG Motorsports in Vancouver, we were back at the dyno. This time Shawn worked his magic by modifying the air/fuel ratio through major portions of the rpm band while still maintaining 3.5psi.. Compared with a stock M5, the supercharger was now adding 123 rear wheel horsepower, or 50%, and about 76 ft/lbs of torque over stock, for a gain of about 36%. Translated into flywheel or BHP, the supercharged M5 was putting out 465 HP at 6800 rpms and 361 ft/lbs of torque at 5000 rpms. The full spectrum of performance results is contained in the accompanying data table.
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