SPD Tuning Service

Page down for detailed information. Suggestions, comments and questions are always welcome.

At this time there is some controversy about the performance improvements offered by changing the air filter or exhaust on Subaru 2.2 and 2.5 engines. The basic rule is unless normally aspirated engines have their cams changed, not much will happen. There was a time when certain makes and models would immediately benefit form these types of changes. Times have changed. Subaru intake and exhaust systems are properly matched to the power output of the engine and are merely tuned for quite operation,

SPD Tuning Service is very clear is its position. We will not sell you "presents for your car". These are modifications that have the same effect as giving your wife/husband or girl/boy friend a rose. They may purr louder, but the cooking will not have improved.

The same is generally true of the expense and effort to port and polish or match castings. These are the last little tricks of racing engines. With the modern castings, the finish is seldom even marginal. Someone the other day told me that he had his exhaust off and the ports of the pipe did not match the ports on the heads. He wanted to know what could be done to correct this obvious problem. What he was reffereing to is the fact that if the head pipe is bigger than the exhaut port, a "step" is formed. This "step" is there for a reason. About twenty years ago some body noticed that with that step low RPM torque was improved without any loss on the top end power. Subaru was listening.

The 2.2 and 2.5 engines use about the same air intake filter and air box system as the turbo cars have up to 1997. In 1997 the turbo car's intake plumbing was changed to give better spool-up, less ultimate power potential and better throttle response. As a result the air box entry was moved. This 1997 engine layout is generally considered to be a step away from serious horsepower capability by most tuners. Improved torque and engine response were the goals. It still uses the same air filter, air mass flow meter and throttle plate as the standard motors. The point is that big enough is big enough.

The Subaru intake has either a cold air intake in the fender or an intake placed behind the headlamp assembly in outside air flow. The airflow meter and air box are identical to the pre-1996 WRX engines. On 1.8 engines there is sub-silencer located inside the right front fender, found after removing the forward part of the plastic inner fender. We offer a WRX-RA resonator for improving the tone of the intake that replaces this 1.8 liter unit. It has an intake horn in the fender area. This is a true "cold air" intake, set in a low turbulence area to reduce the likelihood of taking in dirt and other debris. What they found on later models was it did not make all that much differnece.

Exhaust presents a similar situation where the 50mm mandrel bent exhaust system is a suitable match to the 2.5 engine. Sport mufflers will slightly reduce back pressure, but the gains are nothing I would claim as in anyway as effective as spending the money on a new rear sway-bar or towards a real set of tires.If you want a sporty exhaust tone, by all means select the Remus or Scooby Sport systems in the Home,Products, Body Parts and Exhaust section.

To repeat in closing, the basic rule is unless normally aspirated engines have their cams changed, not much will happen. This is universally true except for the VTEC Honda engines, where even if you change your cams, not much will happen. Yet there are people out there who will sell you VTEC after market cams all day long. What does this tell you?

Note that no serious development of the non-Turbo Subaru engine has been done, so we are all a bit out of luck. However, let me say a turbo Subaru engine is worth the trouble.

Send mail to mshields@spdusa.com with questions or comments about this web site.
Last modified: May 23, 2000