Why the CX-9 Doesn’t Offer Engine Stop-Start, and More
Much of the magic in the 2016 Mazda CX-9‘s 2.5-liter turbo-four engine happens in the exhaust manifold. Its first trick is to plumb two paths into the turbo, a big one with a flow-control shutoff valve, and a smaller one. Mazda tech guru and former Sport Compact Car colleague Dave Coleman explains that at low engine speeds the valve shuts so that the smaller amount of exhaust gets forced through the little opening and onto the turbine a whole lot faster. He likens it to holding your thumb over the garden hose to spin that paint roller you’re cleaning way faster than the open hose would.
Coleman describes the engine’s next trick with another paint metaphor. You know how compressed air is used to suck paint out of a reservoir when airbrushing that rainbow and unicorn onto your custom van? That same trick leverages the initial burst of high-velocity flow exiting a cylinder whose exhaust valve has just opened, to help suck the residual exhaust out of an adjacent intake runner serving the cylinder that fired immediately before it. It’s called the “ejector effect,” and a unique, ultra-short four-into-three-into-one “pulse converter” manifold makes it happen.
All of this helps boost efficiency and broaden the torque curve, but Mazda wanted to ensure the 2016 CX-9 would deliver on the fuel economy promised by the EPA’s gentle testing, something most downsized turbo engines have trouble doing. To do this, Mazda needed a better way of keeping the cylinders cool during hard use than spraying in extra fuel that can’t contribute to propulsion (most hard-working turbos do this). The answer? Route some exhaust up to an intercooler in front and pump this cooled EGR back into the intake. This greatly increases the load point where fuel enrichment is required for cooling. Mazda expects the 2016 CX-9 to earn 21-22/27-28 mpg (11.2-10.7/8.7-8.4 L/100km) city/highway.
Oh, and after spending all that money to add an EGR cooler that doesn’t help on the EPA cycle, why didn’t Mazda invest in engine stop-start tech? Not enough payoff. This 2.5-liter doesn’t burn enough fuel at idle, and because most Americans don’t idle their cars for very long, the tech doesn’t warrant the couple hundred dollar expense of doing auto stop-start right. Coleman’s list of what’s needed to do it right: an extra 12-volt battery and a fancy crankshaft-position sensor that knows precisely where the engine is, even when it’s not spinning. This allows the starter to get the crankshaft into precisely the ideal position so that a cylinder is ready to fire, assisting a faster, less noticeable restart.
|2016 Mazda CX-9|
|VEHICLE LAYOUT||Front-engine, FWD/AWD, 7-pass, 4-door SUV|
|ENGINE||2.5L/227-hp*/310-lb-ft turbocharged DOHC 16-valve I-4|
|CURB WEIGHT||4,050-4,300 lb (mfr)|
|LENGTH X WIDTH X HEIGHT||199.4 x 77.2 x 67.6 in|
|0-60 MPH||7.2-7.5 sec (MT est)|
|EPA CITY/HWY/COMB FUEL ECON||21-22/27-28/23-24 mpg|
|ENERGY CONSUMPTION, CITY/HWY||153-160/120-125 kW-hrs/100 miles|
|CO2 EMISSIONS, COMB||0.80-0.83 lb/mile|
|ON SALE IN U.S.||June 2016|
|*87-octane fuel rating; 250 hp with 93 octane|