A reader asks: “I’ve got a 2008 Mazdaspeed3 with 2.3L turbocharged engine. My engine is modified to put out around 330 horsepower and 400 ft lb of torque. On a Mazdaspeed3 forum (where many posters have similar mods), some use Shell Rotella T6 5W-40 diesel engine oil. Does AMSOIL offer an equivalent of this product and would it be good for my car? Also how often should I change oil if using your product”

Answer: For those not familiar with this model, “Mazdaspeed” is Mazda’s performance division. The Mazdaspeed3 is a turbocharged and souped-up version of the regular Madza3. The stock Mazdaspeed3 model puts out 263 horsepower and 280 ft lb of torque, so our reader has added some serious ponies to an already potent car.

AMSOIL Signature Series 100% Synthetic 5W-30 Motor Oil

The perfect synthetic 5W-30 motor oil for Mazdaspeed3 engines.

Mazda’s engine oil recommendation for the Mazdaspeed3 is 5W-30 and as AMSOIL’s application guide follows OEM specs, they also suggest 5W-30. A well-appointed synthetic like our Signature Series 5W-30 is designed for turbo duty and will provide the utmost in protection when your car is under load and during especially hot operating temperatures.

Even with the added horsepower and turbocharger, we see absolutely no upside to going with a thicker 5W-40 diesel engine oil. A good synthetic 5W-30 will easily withstand the rigors of your engine and it is the viscosity that your engine was designed to use. Thicker oil doesn’t automatically mean improved protection, so instead of using a 5W-40, go with a premium synthetic 5W-30 like our Signature Series.

As far as an oil change interval length goes, as your car is heavily modified, it is difficult for us to offer a concrete recommendation. While an oil like Signature Series Synthetic 5W-30 is quite capable of ultra-long drain intervals in relatively stock engines, offering a service interval for highly modified engines would be mere guesswork. So stick close to Mazda’s prescribed oil change interval in this case and there will be no problem.