We're in love with the new Mazdaspeed 3. We may have beaten that point to death already. But driving impressions aside, there's a lot of techno-wizardry the brochures and ads don't talk about. Not pressure-sensitive 59-way adjustable seats or AI autopilot parallel parking systems. It's the behind-the-scenes tuning tricks that turn the car's 263 front wheel-spinning horsepower into useable, fast, cold sweat-inducing speed, and hint at what tuners should be looking at when they start wrenching.
The BasicsIf you haven't read about the Mazdaspeed 3 yet, it's not too late. Based on the Mazda 3, it's the fastest front-wheel-drive five-door to date and is destined to be the next definitive hot hatch, as long as enough of them are made. It's the fourth vehicle to wear the Mazdaspeed badge (after the Mazdaspeed Protg, Mazdaspeed MX-5 and Mazdaspeed 6). And at just over $22K for the non-GT model, it destroys potential competitors like Honda's Civic Si or VW's GTI.
The EngineMazdaspeed's 3 uses the same 2.3-liter turbocharged and intercooled MZR engine as its big-brother, the Mazdaspeed 6. So why is it short nine horses-even though it's the same turbo, intercooler and boost pressure? According to Mazda, in addition to differences in the exhaust plumbing, the MS3 is tuned for 91 octane gas, while the MS6 was tuned for 93 octane. Mazda also decided to err on the conservative side and only claim 263bhp for the MS3 (partially on account of the big stink we made with one of its other models a couple of years back). This was a decision to save face and keep bean-counters and lawyers happy.
In reality, the 263bhp is probably as accurate as Nissan's so-called 287bhp that the old GT-Rs made: you'll realize that much the instant you mash the go pedal. And, Mazda claims, with just its Mazdaspeed Accessories cold air intake, three-inch cat-back exhaust) and no tuning, the car will make 30 more wheel-hp. We tried it and were as sold as our butt-dynos allowed us to be.
Back to more empirical realms: Mazda's Direct Injection Spark Ignition (DISI). Gasoline direct injection (GDI) systems shoot fuel directly into the combustion chamber instead of the intake ports. The result is an increase in torque, power, efficiency and emissions. Here's how:
Mazda's DISI system pressurizes fuel in the rail at 1600psi, roughly 40 times higher than the 43psi of most conventional port injection fuel systems. Forget being flattened by a fat lady, this is about the same pressure you'd feel with two M1 tanks on your chest. Under that pressure (about 50 times more than the pressure inside a combustion chamber, because the valves are still open) the atomized fuel immediately expands into a vapor state when injected, since the relative pressure is so much lower.
Just like an ice cube melting or water boiling, this phase change is an endothermic process which absorbs surrounding energy and drops the overall charge temperature, while keeping the fuel thoroughly mixed throughout the intake charge. Even though fuel cooling does occur in conventional port fuel injection, GDI systems do it on a totally different magnitude on account of the immense injection pressure. Mazda claims charge temperatures will drop by 50 to 70 degrees F.
For the same reason we want big intercoolers, lower temperatures mean a denser charge, which occupies less volume. This lets the turbo shove even more air into the cylinder for added volumetric efficiency, yielding up to a 10 percent gain in torque at low and mid engine speeds.
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