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Starting next month, Mazda says that buyers will be able to purchase its popular CX-5 crossover with two choices of turbocharged engines. The first is the existing 2.5-liter gasoline turbocharged engine. The second is Mazda's new 2.2-liter turbo-diesel engine. We've been waiting for official specifications for the diesel to appear, and now they have. We found a few surprises.

Mazda CX-5 Diesel vs. Gas Power and Torque
The new 2.2 diesel engine, which Mazda calls SKYACTIV-D, has just 168 hp and produces 290 lb-ft of torque. The 2.5T gas engine trumps both with a whopping 227 hp (on regular unleaded) and 310 lb-ft of torque (on regular unleaded). Both engines produce their peak torque at 2,000 RPM. Clearly, the gasoline engine is the stronger of the two by any measure (on paper).

Mazda CX-5 Diesel vs. Gas - Fuel Economy
The first surprise is that the two engines use almost identical amounts of petroleum per mile or per year. 13.6 barrels for the CX-5 diesel and 13.7 for the gas version. So much for that imaginary efficiency benefit diesel fans always fib about. After the fuel is refined, the Mazda diesel does show an on-paper advantage over the gas turbo. With a combined rating of 28 MPG, the diesel seems to have a decided advantage over the gas engine's 24 MPG. But does it? It is the middle of summer and diesel prices are now at their annual pricing lows. Still, diesel is more expensive. That means that these two vehicles have an annual 15,000-mile fuel cost within $100 of one another. In the dead of winter when home heating oil demand raises diesel prices, that will likely drop to parity, or the gas engine may cost less per mile to operate. There is basically no fuel cost savings by going with the less powerful, lower torque diesel engine.

Mazda CX-5 Diesel vs. Gas - Emissions
Contrary to popular belief (perhaps helped along by the diesel lobby), diesel engines with the same power as gas engines produce dramatically more CO2 per mile. In this comparison, the much lower power diesel engine (which also has less torque) is about the same as the gas engine. The CX-5 diesel produces 365 grams of CO2 per mile, and the CX-5 gas engine produces 370 g/m.

However, CO2 is not the end of any emissions discussion. Smog-creating emissions must also be measured. Here, the diesel scores the lowest possible on the EPA scale. Just 1 out of ten (1 being the worst). The gas engine has little to brag about here with a score of 3 on the smog scale, but it does bust the myth that today's modern diesel engines are just as clean as modern gas engines. At least in this matchup, the diesel is dirtier.

Mazda CX-5 Diesel vs. Gas - Performance
We have yet to find a third-party 0-60 MPH test we can use to compare these two. However, we have tested the Mazda CX-5 gas turbo. We found that the vehicle, despite having all-wheel drive, could easily spin its wheels pulling into traffic. What performance advantage a diesel with less torque and dramatically less power can offer is a mystery. We hope to test the diesel soon to see if we can feel any benefit.

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In addition to seeing him here, John Goreham can be followed on Twitter at @johngoreham.