Project GD STI: Getting More Power with Precision Turbo and Cobb Tuning! – Part 1


With our part throttle calibration greatly improved, Mitch carefully worked up to wide open throttle full pulls, checking the data logs and making changes to the fuel and spark maps along the way.
Our fuel maps were pretty spot on once the MAF compensation was figured out.  Our turbo spools a little later so Mitch added more timing to the lower rpm areas of the spark map that now had less boost.  Mitch added more cam advance in those areas as well.  Since our turbo has less backpressure, thus less heat retained in the combustion chamber, Mitch gave the entire map a little more timing.  Our car was running about 3 lbs less boost than it had before with the stock turbo so Mitch added wastegate duty cycle to up the boost.  However the big wastegate flapper was being forced open by exhaust backpressure and Mitch could only get another pound of boost out of the turbo. Our turbo would spike to almost 14 psi then fall to a little over 11 psi. To get the turbo to hold boost better we would have to get an even stiffer actuator. So currently our 14 psi spike is about two pounds less boost than before and our 11 pound top end boost is 3 lbs less than before.
Even with less boost our Precision Turbo made much more power than the stock turbo.  The Precision turbo with its bigger wheels and housings was a little more laggy, making less power than stock below 3500 rpm. With the STI's gearing we honestly could not tell it was more laggy! The ball bearing turbo felt a lot more responsive and zippy than stock so we could have sworn it was less laggy!  At 4100 rpm the Precision Turbo made 30 more hp and 38 more lb ft of torque with 2 psi less boost!  At 6800 rpm the Precision Turbo made 15 more hp and 18 more lb /ft of torque with  3 pounds less boost.  More power with less boost means a much more efficient turbo!

When driving Project STI the new Precision turbo feels a lot more responsive and lively with faster transients even though the onset of boost is about 300 rpm later.  To be honest you could not even really feel this delay in the boost.  The latest tuning revisions have given us really great driveability, smoothness and slightly improved fuel economy as well. 

We really liked the new launch control and the improved no lift to shift features and feel that these really help drivetrain life by reducing stress on the parts on drag starts and during WOT shifting. The launch control allows a little boost to be generated off the line and helps with really quick starts while not being so aggressive you melt your cat. Push in the clutch and floor it and the engine stutters around 5500 rpm, let off the clutch and let it slip a little and the car burns out just slightly for around 20 feet with all 4 wheels then goes.

When it's time to shift, leave your foot to the floor and shift.  The engine stutters a couple of times when you move the lever maintaining  full boost and when you clutch out, the car rushes with full acceleration with no turbo lag at all. 

So far we are really pleased with our turbo but to be honest, we were expecting more power.  In the next edition of Project STI we will upgrade our Access Port to the latest Version 3, add Cobb's 3 port boost control solenoid and go to a 20 lb wastegate spring.  We want to spike our boost to 16 psi and hold 14 across the board.  That should give us a really decent gain in power with our new turbo.  Stay tuned!

Read more about Project GD STI !


Precision Turbo

Cobb Tuning

Cobb Tuning So Cal

MXP Performance

Perrin Performance

Turn 14 Distribution

KW Suspension


Race Comp Engineering

Injector Dynamics

Crawford Performance

AEM Electronics



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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