Project GD STI: Making More Power with Cobb Tuning and Precision Turbo Part 2!


Wow, after some minor tweaks to reduce power (to be mindful of our stock engine with its fragile cast pistons), our STI rocked AntSpec's dyno with 384 whp and 404 lb/ft of torque. 

This was 62 more whp and 60 lb/ft more torque than previously. Our boost was now spiking to 18 PSI and holding at 16 PSI. This is where our power gains were coming from. We were reaching this boost without having to mess with the wastegate solenoid duty cycle at all, so there is plenty more boost on tap when we build the engine's bottom end.

The EJ257 is a notoriously weak engine in stock form, so Mike actually took steps to limit the torque by strategically reducing the timing about the engine's torque peak to reduce the peak cylinder pressure. Normally running E85 means that you can make tons of additional power on pump gas, but in our case, it was to assure that there would be no way that we could get any detonation.  At this power level, detonation would surely break the ring lands of the stock pistons right away. 

The only concession to get more power on E85 over pump gas was adding a small bit of advance over 5500 rpm to flatten the power curve as VE was dropping and the cylinder pressure was declining.


As a reference, here is our previous dyno chart taken at Cobb Socal so you can see the across the board gains we are experiencing. 

So we are very impressed with how our STI is now running. We are beginning to exploit the power gains that our ball bearing Precision Turbo is capable of, and we are at about the safe limit of our car's stock bottom end. 

We are using the high octane and high latent heat of vaporization of our E85 fuel, not so much to make more power, but to help save our weak stock engine from the harmful effects of detonation. 

From our data logs, we can see that we are now out of injector, out of airflow meter and out of fuel pump. To get more power, these parts will need to be upgraded in addition to our engine. Our platform is maxed out!  This is fine because we are at the high end of what the stock bottom end can take. 

Our car is now really fun to drive, it feels about as fast as our Project EVO IX now, and the driveability with E85 is excellent. Idle and small throttle responses are much improved as well. The only negative we have seen so far is that the engine cranks a few revolutions longer from a totally cold start situation. This is hardly noticeable. 

Some interesting observations are that our engine is much quieter on E85 with the exhaust note having a much quieter bark.  Also, our launch control and no lift to shift functions are now very quiet with no popping or banging- just a light bubble. 

Our car is now working so well that we are reluctant to take it apart, but we have acquired an EJ257 long block and we have plans to build a strong motor for our car so we can take advantage of our turbo and the E85 fuel safely.  We figure we can get another 60 hp possibly with no bad side effects once we do this.

We will be converting to bigger stainless core injectors, a bigger ethanol safe pump, filter, and also to Speed Density to get rid of the MAF.  Cobb assures us that the Access Port can do this with absolutely no issues. 

Stay tuned we are pretty excited about our car!

Read more about Project GD STI !


Precision Turbo

Cobb Tuning


MXP Performance

Perrin Performance

Turn 14 Distribution

KW Suspension


Race Comp Engineering

Injector Dynamics

Crawford Performance

AEM Electronics


Radium Engineering 


Koyo Cooling Systems

HPS Silicone Hose

Synapse Engineering

Afterhours Automotive


Mackin Industries Advan Wheels

Falken Tires

West End Alignment



PLX Devices – Kiwi Bluetooth

Palmer DashCommand

3M Window Films (Renewable Energy Division)

Frank Garrido – Owner
Tint Factory Solar Concepts Inc – 3M Authorized Dealer
2033 South La Cienega Blvd.
Los Angeles, CA 90034

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