Project GD STI – Improving the Fuel System with Injector Dynamics and Other Details


We wanted to reuse the stock turbine heat shield.  To clear the Cobb downpipe we had to trim part of it off.
We had to cut away the lower half of the shield and open up the semicircular part to accommodate the Cobb’s larger pipe diameter.
The shield in place gives our install a clean look.  Cobb has a stainless shield available as well.
With our downpipe in place we hit the dyno at Cobb SoCal to see what our improvements had done.
Mitch McKee determined that we were out of injector and fuel pump so he could not do much to exploit the free flowing downpipe.  With our big intercooler we had zero knock count and we could lean on the motor a little more but Mitch was reluctant to do so until we could get him more fuel.
You can see that the Cobb downpipe spooled the turbo quicker and gave us more boost.  Because of fuel and choking the small stock turbo, Mitch tapered off our boost back down to where it was originally before 6000 rpm.  The turbo spooled much earlier and faster giving us 18 lb/ft more torque and 4 more peak hp for a tiny blip.  If you notice that our power numbers don’t exactly jive from our last dyno session, Cobb had replaced the dyno computer and changed they dyno software since our last test.  The dyno now reads a little lower for some reason and we had to establish a new baseline from the conclusion of our last test.  We badly need to upgrade our fuel system.

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