How Much Power Can Stock Subaru Drivetrain Take?

Most people who begin to modify their WRX/STI begin with bolt-on modifications, and safe, Staged tunes. And everyone wonders at some point - just how much more power can stock Subaru drivetrain take while maintaining stock longevity and reliability?

Generally, whenever you modify your car and increase the power level, you are increasing the stress on car’s drivetrain components, which were designed from the factory to reliably work under a certain amount of stress/power. So technically, with increase in power comes risk of failure.

The good news is that Subarus are very well and strong built cars. In fact, stock WRX/STI drivetrain (engine, transmission, axles, differentials, etc) is exceptionally strong, stronger than most performance cars on the market today.

WRX and newer, 08-up STIs do have a ‘weaker’ point - transmission. Stock WRX 5-speed transmissions are known to be fairly weak when it comes to abusive launches and hard shifting, suffering from stripped gears. Newer STI transmissions have problems from the factory it seems, suffering from ‘popping out of gear’ and other issues.

04-07 STIs seem to have the stronger transmissions, with ‘07 transmission being the preferred one due to longer gears.

So, what are the relatively safe power levels for the stock drivetrain components? Based on our experience, the list below represents the relatively safe power levels for WRX and STI stock drivetrain components, assuming a safe tune. Keep in mind that modifying your car to these power levels greatly increases the risk of component failure due to increased stress. It doesn’t mean that the components will fail, just that there is an increased risk, especially if you abuse the car:

• WRX Engine: ~ 400 chp
• STI Engine: ~ 450 chp
• WRX/STI clutch: ~ 400 chp / 350 ft.lb torque - clutch will last, but not long at these power levels
• WRX transmission: ~ 350 chp / 350 ft.lb torque
• STI transmission: ~ 600 chp / 600 ft.lb torque
• WRX axles, differentials: ~ 400 chp / 400 ft.lb torque
• STI axles, differentials: ~ 450 chp / 450 ft.lb torque

As you can see, stock Subaru drivetrain components have their limits for the amount of power the car can handle from the factory. What we are saying is depending on your power level and driving, you’re going to need to upgrade components.

To sum it all up:

• Subaru WRX cars are weaker than STI cars, which are well built to a point;
• WRX / STI can fairly reliably take some more power than factory levels, but should consider upgrades appropriate to their power, before drivetrain failures begin to happen;
• Your car must be tuned safe in order to have any degree of reliability and longevity.

If you abuse your car, it will break, without sufficient upgrades!

Call us to discuss your upgrade options, before it breaks.