Impreza WRX/STI GC8/GF8 (1998 – 2000)

Chassis Code Body Trim Engine Power* Torque* Rev Limit
GC8 Sedan WRX EJ207 276 bhp @ 6500 rpm 250 lb-ft @ 4000 rpm 7600
GC8 Sedan/Coupe WRX STI EJ207 276 bhp @ 6500 rpm 260 lb-ft @ 4000 rpm 8000
GF8 Wagon WRX EJ205 237 bhp @ 6000 rpm 228 lb-ft @ 4000 rpm 7200
GF8 Wagon WRX STI EJ207 276 bhp @ 6500 rpm 260 lb-ft @ 4000 rpm 8000

*OEM published rating

Revision Production Dates
F 09/1998 – 09/1999
G 09/1999 – 09/2000
Engine Turbo Peak Boost (bar) Max Airflow (g/s)
EJ205 TD04HL-(15T?) 0.74 215
EJ207 Rev.F VF28 1.08 (WRX 1.0) 255
EJ207 Rev.G VF29 1.08 (WRX 1.0) 255

These cars come with either the EJ207 or EJ205, a turbo 2.0L boxer engine. The EJ205 (GF8 WRX only) is the same 9.0:1 compression engine used in the JDM SF5 Forester. The EJ207 is an 8.0:1 compression engine used in all other WRX and STI models. The WRX ECU tune has slightly less boost and torque than the STI model. The ECU is a 32-bit model made by Unisia Jecs Corporation.

Improving reliability and common problems:

ECU tuning: The main source of problems for these cars is fuel octane. The JDM ECU is tuned for JDM fuel, which has a 98-100 RON octane rating vs Canadian 91/94 AKI (~95 – 98 RON). The lower octane range and engine condition usually result in detonation, which sounds like a crackle, or metallic rattle from the engine bay under medium to heavy throttle. projectLAMBDA has tunes for these ECUs to work properly on either 91 or 94 octane Canadian gas. The tune also increases the knock sensitivity of the ECU so that it can respond quickly to detonation before any damage occurs.

Ignition system: A very high percentage of these JDM engines have misfire issues under boost caused by old spark plug wires. If you still have the original wires, replacement is mandatory before tuning. Recommended spark plug is BKR7EIX at 0.8mm gap.

MAF sensor: A lot of these cars still have the original ~20 year old MAF sensor. They usually fail at higher airflow first by reading 10%+ too lean, which causes the ECU to run leaner fuel mixtures and higher spark timing without triggering the engine light. This leads to detonation and is the 2nd leading cause of damaged engine bearings on these cars. This can be checked by datalogging the ECU.

O2 sensor: Pre 2002 ECUs do not have any OBD2 capability cannot detect a failing O2 sensor unless it is unplugged. The ECU will overcompensate for a bad O2 sensor by adding up to 25% extra fuel, resulting in poor fuel economy. This can be checked easily by datalogging the ECU.

Upgrades:

Fuel pump: OEM 440cc injectors will max out the fuel pump above 85% duty cycle. Upgrading the fuel pump will allow you to run higher boost at high rpm without running out of fuel.

3-port wastegate solenoid: The stock 2-port solenoid limits how fast the turbo can spool. Using a 3-port solenoid in interrupt mode will help the turbo spool faster and reach higher peak boost.

Catback exhaust: +5-10 whp, faster spool. Tuning may be required to prevent boost spikes/oscillation.

High flow downpipe: Faster spool, higher peak power potential. Reduces EGT.

Aftermarket header: Faster spool if insulated properly. More torque over entire powerband.

Air intake: Aftermarket cone filters that bolt directly onto the MAF are not recommended. This sucks hot air from the engine bay reducing the engine’s knock resistance and reduces the max airflow that the MAF can read. MAF sensors also don’t seem to last as long with the cone filter. The stock airbox with the fender well snorkel box removed is adequate for OEM turbos.

Turbo: Larger aftermarket turbos are also available and will require bigger injectors. Intercooler and turbo inlet upgrade is recommended as well to handle the higher boost.