Updated May 17, 2001
 There are many ways to add fuel to an engine. Some are covered here.
How do you know if you need more fuel? Get an inexpensive A/F gauge of good accuracy from  DawesDevices

Darren is *not making*any more at the moment, but will pick up production as soon as he's finished improving the build-time to better keep up with future orders.

  Hey, man! You don't need any extra fuel... you're running rich enough already!!

But if you *DO* need extra fuel...
1. Raising the fuel pressure:
    Raising the pressure is good for only small increases in HP.  Item  1is good for people who are happy with their present boost level, and merely want to drop their EGT's a little, or add an extra light on the A/F gauge. It is not  for people looking to add lots of boost. Since we start with a fairly high stock pressure (55 psi over boost), we're already at 75 psi at 20#'s of boost. You need a very good pump and immaculate fuel filter to go much beyond 75 psi. It's not good for the injectors to see much more pressure than that, either.
    If you're looking for a *tiny*bit more fuel, you can raise the pressure to 60 or 65. MAKE SURE that you're still 60 or 65 psi over boost pressure at WOT and high boost. You need a fuel pressure gauge that you can see from the driver's seat.
     You can raise your fuel pressure by squeezing the regulator "can" with the spring in it. That tightens the spring, and raises the fuel pressure.


you have to make a little jig to hold the reg in place as you squeeze it in a vise. The fuel hose fitting must be protected, and the reg must be held by the flange that runs around it's center.
 Find a short piece of exhaust tubing or water pipe that just slides over the body of the reg. You'll have to cut a slot in the pipe to clear the fuel line fitting that sticks out sideways.

Once the slot is in the pipe's side, slide the pipe over the reg body until it butts up against the flange in the center of the reg. The pipe should be just long enough to protect the fuel line fitting (hose barb) that sticks out of the bottom of the reg.
     To protect the little vacuum line nipple that sticks out of the opposite end, use a chromed socket from your socket set. Slip it over the nipple, and center it on the reg. Selecta socket that'll push down on the can just outside of the center recess where the nipple comes out of the reg.
     Now take the entire assembly of the pipe, the reg, and the chromed socket, and place it snug in the vise jaws. Keep that socket centered!
Close the vise approximately 1/8", and your pressure will jump up about 10 psi.

    On NEWER REGULATORS WITH O-ring fittings, instead of hose barbs, like on my '89's, You can just use sockets on both sides of the reg, and don't have to make the home made pipe / jig.

     If you want to set your new pressure exactly, hook a rubber tube from a pressurized air tank to the side fuel fitting that's sticking out of your homemade pipe/jig, add a gauge to the line with a tee, and SLOWLY crack open the air tank valve. You want it barely cracked open, otherwise you'll let the pressure out of the tank too fast, and  get a false reading. The pressure will rise to a point, then begin leaking out of the reg, and will rise no more. You'll hear the air hissing out, and the pressure will stay at the same point. That point should be 55 psi before you squeeze the reg in the vise.

Each turn of the vise will raise the pressure right in front of your eyes, and you can stop anywhere you'd like.
Make sure that you've got high pressure in the air tank; it has to be OVER whatever pressure you're shooting for. Don't go too far squeezing, because you can't back up!
 60 psi will make your injectors flow 4.5%more fuel. 65 psi will give you almost 9% more fuel. 70 psi gives almost13% more fuel. You've got to have a STRONG fuel pump (Walbro Viper pump, or similar) to maintain 70 psi over boost, but any stock pump should handle60-65 psi over boost.

     An alternative to the vise is to stand the assembly on a hard surface, and tap the top chromed socket with a hammer. Don't go wild with the hammer!

     Remember that injectors can be damaged by pressures more than 75 psi over boost, and that you must have a good enough pump & filter to keep the pressure high under WOT. Having 65 psi over boost at 5 lbs of boost is no good if you have only50 psi over boost at 20 lbs of boost. The pump's got to be healthy enough to STAY at 65 over boost at all boost levels. A clean filter is a must.
 Just check your fuel pressure at WOT, under boost, to see if the pressure remains the same amount over boost.

 2. Larger injectors with reduced fuel pressure:
    Now we enter an area where there's room to raise the boost a LOT! If you install injectors that are way too large for your motor, like 42pph or 52pph injectors on a stock computer, you can drop the fuel pressure to make them flow just a little more than stockers.
    You can lower your fuel pressure by making your  present regulator adjustable with an inexpensive conversion. The conversions are now offered at a good price.  You send James a healthy stock regulator, and you get back an adjustable unit.

    Try  JamesRichardson,  of Canada. Price is in the $55 area.

     He does excellent work.

       Remember, you just send him a healthy regulator, and you do no work; it comes back ready to rock and roll.

Fuel pressure 45 PSI 40 PSI 35 PSI 30 PSI
Flow of 52 pph "+40% injectors" 47 pph 44 pph 42 pph 38 pph
Flow of 42 pph "+20% injectors" 38 pph 36 pph 34 pph 31 pph

    Example#1: Let's say that you have 27 pph T1 injectors, and you want to upgrade for big power in the future.  You can run42 pph (+20% injectors) units at 30 psi, and they'll act like 31 pph injectors.
    When you raise the fuel pressure to just 35 psi, with your pump still *loafing*, you'll have the flow ofT2 injectors.
    Example #2: You have stock 33 pph T11 injectors, and you swap for +20% injectors. Run 40psi fuel pressure, and they flow like 36 pph units.  Roughly 10% over normal, which is easy for your computer to idle clean & smooth.
    Example#3: You have stock 33 pph T11 injectors, and you swap for +40% injectors. Run 30 psi, and you get 38pph injectors, which is a big improvement over stock.. People often question the quality of the spray pattern at 27 psi, which I run. I can only tell you that I get good gas mileage and pass emissions with those big 52pph units running at 27 psi. Other car companies run their fuel pressures way below our stock55 psi.
    In any of the above examples, you can now go to a few more pounds of boost before leaning. When you raise boost above the "leaning" point, it's time to raise your fuel pressure.
    Of course, the hot trick is to get the fuel pressure to rise all by itself, whenever it's needed.

 3.Gettingthe pressure to rise on it's own, as you need it.
     You can gradually close off the return line as the boost rises with an adjustable gain regulator.
     The way Slug runs is with an adjustable gain regulator.

  CARTECH is selling this adjustable gain regulator for $209, plus shipping. This model is number 20002. It is fully adjustable from 1-7 psi of fuel pressure per pound of boost. My car likes 3:1 gain; your car might like 2.5:1, or 4.1:1. No problem!

  Remember that we're dealing with high fuel pressures, and therefore need fuelinjection fuel hose. Normal fuel hose is much weaker than F.I. hose.
  Here's a sample of how the fuel curve works on a car running big injectors with 30 psi fuel pressure and a 3:1rate on the rising gain regulator:

4. Extra injectors.
    My second favorite technique, and also the cheapest, is to add extra injectors.($20- $40 per set of junkyard injector, new pressure switch, and "tee" with fuel line.) Pressure switches turn them on as needed, and your car runs a totally stock fuel system when you're not at WOT, so gas mileage and emissions are unaffected.

    DarrenDawes is selling pressure activated switches.

     COLD START INJECTORS: You can look at old VW's and Saabs in your local junkyard. On the intake manifold you'll see that there are 4 injectors neatly in a row, and one more injector all by itself. The lone injector is the cold start injector .Cut off the fuel line with snips or cutters, and unbolt the two little bolts on the injector flange. It lifts right out, with no effort.
     There's a banjo fitting on the top of these Bosch injectors. Leave it on, and leave the first couple inches of hard skinny fuel line on the banjo fitting. You can slip 3/16ID fuel hose right over the 2 inches of line already on the injector, and clamp it on.
     To supply fuel, you'll need to get brass fittings from NAPA to make a "tee" that has 5/16" hose barbs on each end, with a 3/16 nipple in the middle.
     You splice the tee into the rubber fuel line that feeds your fuel rail. I use 3/16" rubber fuel line to run from the tee to the injector.  You can use metal line if it makes you feel better. Then connect the metal lines with short pieces of 3/16" fuel line and clamps.

     The cold start injector has a nozzle that squirts out the fuel. Drill a hole into the intercooler tubing that's just slightly larger than the nozzle, then slip a half-inch long piece of fuel line over the nozzle.(5/16 ID)  Lower the injector nozzle into this hole, and use it's flange as a template to mark where the 2 mounting holes will go. Then drill small holes in the intercooler tubing where your marks were made. When you tighten the two sheetmetal screws into the holes you drilled, the fuel line will compress and conform to the shape of the intercooler tubing, making an air tight gasket. Now the injector is mounted.

    Years ago the NOS company did flow testing to find the best placement for their fogger nozzles. They wanted the gasoline/air to have time to mix well before reaching the intake valves. They found 6" before the TB to be the best place for good dispersion.

Pressure activated switch; use one to activate your extra injector.

       You will note that there's a vacuum line barb on the switch. These switches DON'T LIKE vacuum! Use a pressure source that doesn't see vacuum. Use an intercooler tube; epoxy a small vacuum line barb on it.
          ...Or use the intake manifold for a source, but put in a one-way (check)valve so that it doesn't see vacuum. Then install a tiny pinhole vent to atmosphere between the check valve and the pressure switch (about .015"to .020")

        The switch will work on higher boost when the adjustment screw is turned clockwise; it will work at lower boost when the screw is turned counter-clockwise.

      The polarity of the 2 injector wires doesn't matter; it'll work no matter which color wire goes to positive. Send one wire directly to positive, and have a pressure switch send ground to the injector at 14 psi or so.

     Watch your rich-lean gauge; keep about .9V on the gauge. If you don't have one, get one.  Go to   DawesDevices for a great

     Don't have it come on early unless your rich-lean gauge tells you it's needed. (less than .9V) The extra injector will allow a few more psi of boost. That's when you really feel the difference.

     Flow rates of these injectors commonly support either 15 (usually the VW units) or 30 HP (usually the Saab units). Apply 12 volts to click them open, then blow through them. The ones that are slightly harder to blow through are good for 2 psi more boost (15 HP) The injectors that are slightly easier to blow through are good for 4 psi more boost (30 HP) Strangely, the ones with the smaller looking injector holes flow more, and are the "30 hp" units. These seem to be mainly in old Saabs...