This month Project Street Mini unleashed a few ponies with an aftermarket intake and exhau
Let's be honest: Increasing horsepower is always the most enjoyable and anticipated part of a project. In Project Street MINI's case, it's even better because we're playing with a supercharged car, and forced induction generally responds to power tweaks better than standard induction systems.
For this chapter we paid attention to the backside of the engine, testing two exhaust systems-a unit from Magnaflow and another from Supersprint-with the help of the technicians at evosport.
The car was strapped to evosport's Dynojet 248C two-wheel dynamometer, and to ensure the systems were tested in a fair manner, all runs were performed on the same evening and as close together in time as possible, eliminating temperature variations. Also, intake and coolant temperatures were monitored using evosport's Snap-On Graphing Scanner during testing.
The entire one-piece factory system was replaced by the Magnaflow exhaust.
First was a baseline run, a third-gear pull on straight 91-octane fuel. The little guy ripped a best 155.5 hp to the front wheels, with 136.3 lb-ft of twist at 4150 rpm. Considering this car is factory rated at 163 bhp, we were duly impressed. (Maybe the manufacturers are starting to quote horsepower figures closer to the power that actually reaches the wheels.) Whatever the case, we were seeing less than a 5% driveline loss already (but don't imagine this car actually puts out over 190 hp at the flywheel with BS conversion factors, because that's very likely not the case).
We were concerned, though, that on every pull the car seemed to hesitate slightly from 6400 to 6800 rpm. On the graphs it was evident the stock ECU pulled back some timing due to possible detonation on the pump gas (it's a glitch we'll try and sort out in the very near future).
The Magnaflow exhaust was tested first. Magnaflow designs its products in its fully equipped R&D Center, complete with multiple engine and chassis dynos along with flow bench and audio test equipment.
The Magnaflow system features rust-proof 16-gauge steel construction. Two mufflers the firm specially developed for the MINI Cooper S were used to keep our ears from bleeding. The tubing of the system starts at 2.25 in. and widens to 2.50 in., eventually letting the gasses escape out 3.5-in. dual tiops. Magnaflow uses 400-series exhaust-grade stainless steel as opposed to the commonly used 304 grade. The company reports experience with the 304 grade "springing back" after it has been bent into shape, causing fitment problems.
Magnaflow's exhaust system features stainless trumpet-like tips.
The Magnaflow system replaced the entire stock exhaust from the catalytic converter back. With its trick, trumpet-like exhaust tips, this system had a much deeper rumble than the factory's unit. On the dyno, the roar of the exhaust system forced our hands over our ears-this exhaust system is loud. Even so, it sounds great. Magnaflow said it's working on a longer resonator to quiet the system down slightly, probably in hopes of targeting a more general market.
When the numbers came out, however, we were disappointed to see little gain in peak torque and horsepower figures, and there were even some slight losses in the higher rev range.
To be fair, we decided to exclude gains and losses through the 6400 to 6800 rpm rev range where the engine was detonating. Any power spikes there would be heavily influenced by the car's knock sensors.
According to the dyno numbers, the Magnaflow exhaust system offered a 2.2-rhp peak gain at 5450 rpm; the peak 2.4 lb-ft of torque occurred at 3300 rpm. Peak losses were charted at 6300 rpm: 1.4 hp and 1.2 lb-ft of torque.