Project GD STI, Improving the Powerband with Precision Turbo and Injector Dynamics

The turbine wheel and the wastegate flapper valve are about as large as you can fit in the OEM footprint.  The wastegate flapper has an anti-rotation feature, it’s the triangular-shaped nub on the valve itself.  It has been found that if allowed to spin, wastegate flappers, can actually saw themselves off the arm and fall off! Another cool thing about the stainless exhaust housing is it won’t turn into a rusty mess when installed!

The Precision turbo comes with a ball-bearing center section.  Ball bearings greatly reduce friction in the center section over plain bearings and reduce spool time by as much as 20%. They also have a long service life and reduce oil heating. The turbo comes with the proper oil feed restrictor installed as the ball-bearing center section needs a lot less oil flow than plain bearings.  Precision uses ceramic ball bearings which have a durability advantage over standard ball bearings used by some other turbo manufacturers.   The Precision turbo also has a water-cooled center section like OEM which is also a good feature to improve turbo reliability.

We ordered our turbo with the optional 20 psi actuator, the standard actuator is a 15 psi unit.  If you have a built engine and want to run higher boost levels, this is essential. However, the minimum boost possible is around 14-15 psi so you want to make sure your engine can take this on pump gas.  It is probably pushing it for the stock engine.

The Precision turbo on the left is obviously a lot bigger than the stock IHI VF39 turbo on the right.  The stock turbo compressor inlet is only 46mm or 12 mm smaller than the Precision turbo. The compressor housing is much bigger than stock and has a clearance flat spot machined in it for block clearance. The engine case also has to be ground slightly for clearance but it’s not that big of a deal.

The Precision Turbo turbine discharge diameter is 56mm vs the stock 48mm, a huge difference!  Precision does not list the specs of this turbo but externally it seems about like what a Garrett G30-770 is like. Note how much bigger the Precision Turbo’s wastegate valve is than the stock turbo.