This section explains our views on some of the various popular external engine modifications that are in the aftermarket. Unlike the normally aspirated engine, where bolt-on engine modifications only produce marginal acceleration gains of a three to five tenths of a second and only affect engine power in the last 1500 rpm before redline, the WRX engine is, as I explained in the previous section (UP!, please), just a convenient hot gas generator for a turbine. If we can make more hot gas to drive the turbine and stay out of trouble inside the engine, we get lots more power, pretty much everywhere in the turbocharger's efficient operating range. This translates in to significant midrange torque as well as higher rpm power gains. In fact their is a saying, "You buy horsepower, but you drive torque." As we drive the WRX, we learn we drive torque, and that is why turbo motors are so much fun. They have lots and lots of torque and a very wide power band. My 1996 "260hp" WRX accelerates in third gear from 3700 to 7000 rpm at about a constant rate from 45 to 80 miles per hour. Great for pulling on the freeway. Stock ecu, stock intercooler, stock everything. How do they do it?

The Japanese ECU is set to run higher boost and more advanced timing as the fuel and weather conditions permit. The Japanese ECU will turn down the boost and pull back the RPM as it learns to run on lower octane gas. The US does the same thing, but it is set to a lower maximum power target and it is set strictly for best emissions including the avoidance of nitro oxide emissions under full throttle running. These two sentences are really the whole story on the power differences. SPD Tuning has been waiting to gain control of the factory ECU to bring it into a more capable level. Relatively few parts will need to be added to the engine peripherals to extract all the possible power from our gas. This is now a reality in the ECU Tech computer software. This is covered in another section, but please read on here to fully appreciate what to do and NOT DO to your WRX engine.

The stock engine mods section will explain how we think new engine peripheral parts should be applied with regard to budgets and reliability considerations running on pump gas. The preceding engine sections have gone to great length to explain the very real limitation of fuel quality with regard to power in turbo engines, so our views are always tempered by this reality. Give me 96 or 98 or 100 octane gas on a daily basis and I will tell a different tale. Please remember, if we are running a high octane 320-360hp engine there is a different story to tell, but for a daily driver on pump gas we look to what modifications are effectively making better power.

Many products are available to increase the power of the WRX EJ205 227hp engine. But, how is it that the same engine in Japan as 22 more hp and 50 ft-lbs more torque some 1000 rpm sooner without any difference other than variable valve timing? Better gas and less stringent emissions regulations, and an engine management system tuned to make the power, nothing more. The information here is somehow one of the best kept secrets in the American aftermarket. 

Many owners assume that it is easy to emulate the high torque and the full 280+hp (or the WRX-RA 320hp) performance of the 1997-2000 Japanese WRX versions. We are not interested in attempting this with our customers for reasons explained High Power elsewhere. We can get close to 280hp on a cool day with 94 octane gas and can easily reach it with ~95 octane. Power levels fall as we bring the octane into the 91 octane level. 

Now remember we are not building  a 100 octane rocket motor here, we are talking about pump gas daily driver cars. This section is going to tell you about what you do not need to put on your motor and why. This may seem very strange advice from a company that wants to sell you tuning parts. But it is as important to understand what is not needed as it is to understand  what the engine needs. Please select from the side menu to read about each part we do not sell for pump gas engines.

We do not recommend the popular blow-off valve, the front mount intercooler nor turbo timers on a mildly (up to 250-280hp) tuned engine. Please push the side bar buttons to find out why the stock by-bass valve is important for a road car, what a good top mount intercooler does and why engine shut down timers are an unnecessary expense.

Please note that we do not recommend intake kits and most of the filter kits that we have seen to date. Intake kits are not recommended if they replace any parts after the air flow sensor. 

Long term, we are more concerned with getting clean air to the engine and turbine than more air. Turbine impellers are very sensitive even to the smallest dust particles, so clean air is critical for long engine lift. The intake kits do make a nice noise though. But, I thought I get more power with and intake kit? Our point is it is relatively simple to turn the boost up .2 pound and get more power with clean air rather than use a filter that does not have at least one 90 degree bend to the air flow ahead of the filter to remove the larger entrained particles before they hit the filter. This is what the stock cold air intake does and those turbocharger impellers are very sensitive to clean air for long life. So we recommend giving it every chance by staying with a proper air box. We are looking for a larger, low restriction airbox, but with ABS it is difficult to fit one in the space provided!

The following "Stock Engine Mods" section looks at mild tuning for a road going WRX engine on pump gas.