Free Boost/Fuel Pressure Up Mod

by Robert Pina

Free Boost

 This is the quick version.  I assume you know some basic things when it comes to the operation of your engine.  I wanted more boost out of my turbo, without the use of a boost controller or shimming the wastegate.  With my setup I was getting exactly 8 PSI using an aftermarket intake and 2.5" HKS exhaust.  One day I thought to myself, if the manifold is reading 8 turbo, what is the turbo putting out?  I hooked up my boost gauge to my turbo/wastegate line and it read 10-11 PSI.  I then thought if the manifold is showing less boost, what if I hook the wastegate up to it.  Once I did this I was able to get 10.5 psi constant boost, without a spike.

  Here you can see where I put the T pipe and ran to the wastegate.  The hose that is used is thick, similar to the size of the wastegate hose.  This is the closest area to the wastegate that is usable.  Some have put an air nipple on the 3000 pipe to achieve similar results.  I would rather not modify the 3000 pipe.  When I first performed this mod I simply closed the turbo/wastegate hose left over by getting a bolt that would slip snugly into the line and putting a small clamp on it to make sure it wouldn't leak boost.

Fuel Pressure Up Mod

  So here I am again "thinking".  Which in most cases is bad, hehe.  Anyway I thought to myself that the fuel pressure regulator senses boost and raises fuel pressure as necessary.  What if I fed it more boost than was actually there?  This would raise the fuel pressure all the way across the board.  It wouldn't do it much, but in some way it should.  Since my turbo line was just hanging, and it was reading 2 psi more than my manifold, I used this line.  I ran a vacuum hose all the way from the turbo to the fuel pressure regulator on the other side.  (insert laughter here)  Once I did this I did notice a kick in performance.  One thing to keep in mind however is that the turbo never shows vacuum.  The fuel pressure regulator needs vacuum to lower the fuel pressure at idle.  What that means is your idle and starting characteristics may very depending on temperature.  The fuel pressure up VSV which cuts vacuum to the FPR in hot conditions, is no longer utilized.  The only downside to this is the lower gas mileage.

  Here is the line I ran from the turbo nipple to the FPR.  So when the engine is getting 5 PSI, the FPR is getting 7 PSI and thus raising the fuel pressure higher than it normally would.  I disconnected all the vacuum lines that went from the intake manifold nipple to the FPR.  There are 2 of them.  Now you have a free spot on the manifold for a boost gauge.  If you don't have one, this would be a very good time to get one.  Make sure you get some hose that is stretchy enough to fit over the turbo outlet, yet small enough to fit snugly on the FPR.  I suggest you buy some clamps to make sure they don't come off when boosting.

Final thought:

  This is take your gas mileage down.  I went back to stock because of this.  Whenever I hit the races I would put the mod back on.  It only takes a few minutes once you have done it a couple times.  Some have voice concern over the heat of the turbo air going into the FPR because it has not been through the intercooler.  I ran the turbo outlet line into the cabin of the car, to feel the temperature of the air when driving.  It barely even got warm, even under boost.

Idea by Jeremiah Grim:

   Rather than having to choose between normal FPR operation and high pressure FPR operation he had the idea of adding a switch valve to go back and forth.  There is a diagram he created below.  Basically you could put a T fitting to the FPR.  Both direct turbo pressure and manifold pressure would have a chance to go to the FPR.  By using a switch valve you could switch between manifold pressure and turbo pressure to reach it.  This way you can flip a switch when you hit the track for a little extra fuel pressure.

  Any comments or questions email me at: mk3supra@cox.net