High-Tech Nitrous

First we need to determine our overall HP sought. For the math below we need to use BHP, or the HP at the flywheel. If you have your known N/A hp from a dyno session, we just need to convert it to BHP. This is simple, just take you RWHP number and add 15% (below is a couple other ways to calculate your HP, if no dyno sheet). As per normal, my math is conservative and safe.

RWHP + 15% = BHP     We use one of my past dyno sheets. My peak RWHP was 430, so we add 15% and end up with 494.5BHP. This will be our starting point for figuring out what kind of fuel supply we need. We will want to add my 300rwhp n2o shot to this, and must also convert this to BHP, 300RWHP + 15% = 345BHP. Now we add these two HP numbers together for my sought overall BHP, 494 + 300 = 794BHP. Now we can figure out kind of flow capacity my fuel system will need to feed this hungry monster.

The formula is very simple, but remember to use .6 as the Brake Specific Fuel Consumption (BSFC) for power adder applications (.5 is used for n/a applications).

BHP X BSFC = lbs per hour of fuel required

794 x .6 = 476.4 lbs per hr to support my sought overall BHP, or 675RWHP.

OK, what does this mean. Well now we need to convert lbs per hr to liters per hr. We need to do this because fuel pumps are rated generally with liters/hour. Then when choosing a pump we must also be aware of what PSI (Bar) the pump rates it's capacity at.

An example would be a pump rated at 255 liter/hr will approximately equal 4xxlbs/hr and rated at 4-Bar. I will add the math for the conversion liter to lbs and Bar to psi shortly, and expand a bit on both. Also, additional HP calculation equations will be added. Robert 3-11-08

3-Bar = 43.5psi (Ford);   4-bar = 58psi (GM);   5-Bar = 72.5psi

There are few things we can do to improve the stock fuel system before needing to add a dedicated in-line fuel system.

The biggest improvement, IMO, is adding a fuel regulator and a return line at the rails. Why, because when the demand suddenly hits that we need more fuel, when n2o is activated, the regulator is at the tank and to far away for optimum performance. What happens is slow response. It takes an amount of time for the additional load pulling more fuel to be recognized at the tank regulator, then it takes another amount of time for the reg to readjust and send more fuel, then travel time for additional fuel. So we can clearly see if this was instantaneous we would have no issues if capacity is there. A regulator and return at the rails rails does exactly this, responds in micro seconds, or instantaneously.

We can add this capability quite easily two different ways. First is to install the rails/reg from a '97/98 Corvette, my original choice. Any Chevy dealer can get you these rails, and for the Vette guys, you can also have the dealer order the factory return line and different filter, see picture #5. You'll also need to replace the fuel filter (reg is in the filter) on all C5 and Z06s '98 through mid '03 for a complete factory package. The mid '03 and '04 Vettes do not have this option because of a different fuel system, and the need to go dedicated in-line comes about much sooner as we can't extend the capacity of the stock system. See picture #1 for the '97 rails with an inlet and return line and factory regulator set at 58psi (aftermarket adjustable can replace the factory one). Picture #2 shows the rail installed using the factory return line, and stock '02 Z06 coil covers trimmed to fit. It looks totally factory, and no one has ever pointed this out, probably because it does look factory. The second way is to add a regulator to the end of your stock rail, as in picture #3. Aeromotive (and others) has one designed for this particular need called the Compact EFI. It has one inlet and one outlet and goes right on the end of the rail (the one pictured is the one I am running on my Vic Jr intake and has dual inlets and one outlet, picture #4). The second way will need a return line plumbed to the '97 filter area, which you'll change out for both ways. This line is a 5/16 size and you can have it braided with ends attached or go the cheaper way and use push lock connectors and hose (good to 250psi). I use the push lock system wherever I can and picture #4 shows the push lock in use. So, a system with aftermarket fuel pump (Vette does have a Walbro as stock pump, though not as powerful as the Racetronics Walbro GRJ420 Gerator jet pump style), and a regulator and return at the rails can support 600rwhp with the hot wire trick. The stock system can not support this level. You can leave the stock in-tank pump alone if going to the in-line pump, which is next.

Picture #1, '97 Stock Rail on late manifold, and return.

 Picture #2, a factory look with '97 rail on an '02 Z06, just cutout a new slot with a router. A 700hp stock, lol, fuel system. The only fitting that was anodized is the blue 180° coming out the front of coil cover.

Picture #3, Aeromotive Regulator on stock rail. This is the dual inlet used if you run your new pressure line into the test port (should be a single inlet, single outlet if just running the stock pump, or having the new pressure line tap into existing pressure line, but a dual inlet will work if we plug one inlet side). Also use this style mount if you plug your new pressure line into existing supply line with a "T", and use test port as your new return, also a single inlet/outlet could be used (remember, the option of a '97/98 return line). 

Picture #4, Dual Inlet regulator plumbed utilizing both inlets, and push lock connectors. Fitting on bottom is my new return line.

Picture #5, Stock '99 to mid '03 C5 filter. The '97/98 has one less barb, just an inlet and outlet. Whereas, this late model filter has the regulator internally, so has additional return to tank (and is very close to tank). Once changed, the new return line from engine bay reg goes to the tank where existing return line from filter went.

This how to is primarily directed at the C5 Corvette; however, this can certainly be adapted to the F-bodies, GTOs and trucks. The principals are the same, but specific mods are little different.

The first step is to get the gasoline out of the tank. A pretty simple step, but be careful, as we all know how dangerous gas can be. Bleed the fuel pressure off at the shrader valve on the stock rail, drivers side. It's at the end of rail and has a cap, underneath is a valve just like on an inner tube. Just depress this valve, with a container or rag to catch the gas, then discard.  We now need to identify the supply line going to the engine on the drivers side tank, picture #6. Locate the black paint marked hose barb. To this connect a hose like in picture. run the hose to a suitable gas container of adequate size. Next we must locate the fuel pump relay, picture #7. You'll find it in the fuse box next to the battery. As per the picture, we need to insert a jumper with a fuse, be careful as soon as this is inserted the fuel pump will turn on, so be ready. Note in picture which holes to use. Pump as much fuel out as you can, though some will be left behind. Now disconnect the battery for safety.

Picture #6, notice the black paint marked hose barb-supply line (you'll have a green, blue and Black)

Picture #7, the fuel pump relay removed and jumper wire inserted.

First we can take the aluminum cover over the top rear of the fuel tank off. Also at this time remove the aluminum cradle that holds the tank up. Don't worry, the tank will drop an inch or two and no more, and the rear end of tank will hang lower and be self supporting. Now we need to remove the inner fender liner. This is a very easy step. There is about 6 or 8 , 8mm screws that hold it in, remove them and just wrestle it out. Now we will be drilling the tank for our pick up hose. This is an area we need to be careful again, as there is still a small amount of gas in the tank. USE AN AIR POWERED DRILL, SO THERE IS NO SPARKING. I do know of one guy who did not have an air drill, what he did was use a cordless and tape all the vent holes with duct tape so no spark to the atmosphere. I DO NOT RECOMMEND THIS. Be prepared with a pan to catch all residual fuel.

Picture #8 shows the original fuel cell bulk head fitting I purchased from Jegs; however, because the tank is such thick plastic, you won't be able to get the nut on the back side. The cure for this was/is to use a national pipe thread tap. You can use a 3/8" NPT and 9/16th drill bit, or you can up the size to ½" NPT and appropriate drill bit. I chose to go with a ½" NPT as the Bosch requires ½" hose feeding the fuel pump (some use 3/8"). Here's the fitting used: ½" male pipe x ½" male JIC 90°, and can be seen in picture #9. Just don't tap the hole to deep, as the taper style of the pipe thread will self seal as it's an interference fit style fitting, though do use a little Teflon soft seal on the threads. Tighten the fitting down pretty good and we are ready to move on, it works very well, trust me. Picture #10 shows the location to drill on the tank.

Picture #8, the blue fitting is the one not to use (at least on plastic Vette tanks); Also shown is the Push Lock and standard hose barb fittings I used on hose ends.

Picture #9, the 1/2 M/P x 1/2 M/JIC 90° used in the NPT taped tank.

Picture #10, here is the spot to drill. Get it as low as you can so it will fill the pump through gravity, or be self priming. This is under car looking up. Mine could have been lower, but due to trying the wrong fitting (blue one above) that needed a flat spot...

Now that we have our tank fitting installed and the inner fender removed, we can move on to mounting the pump. The first photo, picture #11, shows how the brake cooling duct on the Z06 can help with the pump install. We do not need to mount the pump as deep as I did in this photo, but chose to do it to allow the pump to be at it's lowest without kinking my ½" cheap fuel supply line. A better hose will allow a tighter radius and also allow the pump to be mounted where it's easy to get at through the fender liner, once it's removed. Some have even mounted the pump a little higher, on the frame (option for non Vettes also), to have more hose routing options, it's really your choice for a final location, as it will work fine mounted higher.

Picture #11, looking through Z06 brake duct

You can clearly see in picture #12 the fuel filter mounted in the supply line between the tank fitting and the pump itself. Use one that has enough flow capacity for at least 700hp, and pressure capability to handle EFI pressures. Picture #12a shows how the inner fender panel was notched out to fit around the hose/filter for future servicing and ease of access. Make sure you look carefully and measure twice on where and how you want to notch the panel to make it nice looking. Some will just cut the entire corner out and that is the easiest, but I was looking for better mud control. Picture 12b shows how the aluminum top tank cover should be notched, some leave this piece off completely, your choice

Picture #12, fuel filter and fender well notching. You can see extra fuel line tie wrapped around supply line for added safety.

Picture #12a, this where the fender ling needs notching for filter and hose to fit. The tab is to keep the liner tight. Most just cut this area out, though I like it tight to keep debris out and a support base for filter.

Picture #12b, the tank cover that goes on top of tank. This can be eliminated as it is for keeping debris out of tank area. The right notch is for the 90° fitting, and the left notch is for the hose heading to the filter.

After choosing mounting location and where you want the filter, it's hose making time. We can do our hoses in a number of ways. Full braided and anodized aluminum fittings is the generally accepted way to plumb the fuel system. However, I chose to be a little more frugal, even though these fittings and hose I get free through work connections. We can save literally hundreds of dollars here; Using nylon braided hose, which is as tough as SS braided, and brass push lock connectors. The push locks are good to 250psi with out any hose clamps or crimping. I did use a mix of SS, brass and aluminum on my setup. The engine bay was the only place that I really wanted or needed the full trick look of anodized and/or braided SS. Some of the brass fittings we used were standard hose barb style and thus the need for a crimp connection. So, don't be confused when you see crimped and non crimped connections in the photos. Picture #8 shows the difference between push lock and standard barbs. The one with the yellow plastic ring is a true push lock with sharper barbs. Do not used a crimp or a hose clamp on a push lock, it will cause the hose to be cut and compromise the connection, as it actually gets it sealing strength when line is pressurized. The barb with out the yellow ring will need a clamp or a crimp connection as I used. Hose clamps are not recommended on high pressure side of the EFI system, use the push lock or standard SS braided line reusable connections. Sorry for the extra confusion, but I didn't want anyone thinking they could use a standard hose barb with no crimp or clamp.

Wiring schematic can be found below, picture #13,. We used 10 gauge main power supply to the pump for our home made Hot Wire Kit. The real key to the Hot Wire trick is having wire of appropriate gauge, so as not to have a voltage drop which will skew pump performance (remember the 15/18% increase using the appropriate gauge wire). We chose to put the main fuse in the engine bay right at the alternator, picture #14, for ease of service.

Picture #13, wiring schematic, click link below for larger version. 

CLICK HERE-Upsized Wiring Scematic

Picture #14, fuse and 10 gauge wire at alternator.

The main power wire, and supporting trigger wire, along with fuel line, were run inside the drivers door sill. Picture #15 shows where the bundle was tied off in the front tire well, there is an access panel on the Vettes. You can see the red wire going into the firewall, there is a grommet in this location, so no drilling of firewall needed. The only wire going in this location will be the number 86 wire to the relay. This is the trigger wire from the MSD RPM activation SW, and will send a small voltage to relay, to trigger contacts and allow the main 10 gauge wire to have and send the full voltage to the pump. The MSD unit is in the drivers foot well, see picture #16, and is very easy to get to for changing the RPM pills.

Picture #15, shows wiring and fuel hose at front fender access.

Picture #16, MSD switch in foot well.  

Picture #17 shows where I chose to put the wiring and relay. You can put this in the engine bay, but IMO, it's much cleaner to have the bulk of the wiring hidden. The relay is a 40 amp unit and can be purchased at radio Shack. This will not hinder performance having the relay at the rear, compared to the engine bay area. Make sure you clean a good spot on the frame for the ground as this is paramount to pump performance. One of the areas that the EFI GM products have odd glitches, the grounding system, so I added another ground from the relay ground to an existing factory ground near the fuel fill (all in a junction together on the frame). Also, we added another ground from the rear area to the forward area on the frame. These additions are really only a safety insurance measure on my part.

Picture #17, wiring and relay in rear tire well area looking forward (red wire goes to a factory ground, and comes from the ground junction on frame, brown is from relay and black is from pump, not shown is another ground going to engine bay area).

My testing so far shows system is working fine. The pressure with the '97/regulator stays at a nice 58psi like it should. I didn't get a chance to do an in depth testing procedure, as we have now torn the top of the engine apart for some intake/head/fuel mods. One of the mods is a Vic Jr manifold. So, fuel return is being re plumbed, but am still using existing '97 return line and stock plumbing from engine bay back. System is virtually the same except now it will be running an Aeromotive regulator and Vic Jr fuel rails. Updates on performance of the fuel system and reaching my goal of 700/800rwhp coming real soon. We will see how far I can push this system. The stock fuel rails are known to be able to support 700hp, but now I have aftermarket rails and should be able to go for higher HP. We will post some logged fuel pressure curves, with aux pump, and without. Check back later for more.

Robert Weaver,

AKA Robert56

F-Body Fuel System

            The fuel system of an f-body, while more capable than some, is extremely lacking as the seemingly endless quest for horsepower advances. My initial fuel system consisted of an upgraded fuel pump, aftermarket rails, and aftermarket fuel injectors. This was sufficient until my power levels reached over 500+rwhp. Judging by my airflow numbers, fueling, and track times, I estimated 530-550rwhp naturally aspirated. The fuel system would support my setup in this manner, however, I was forced to “fudge” several numbers in my PCM to attain richer WOT air/fuel numbers. This “fudging” was done in order to offset the effects of dropping fuel pressure. Dropping fuel pressure is certainly a culprit in leaning air/fuel ratios, and is a prime suspect when inspecting a F.U.B.A.R.’d bottom end. Not sure on F.U.B.A.R.? Google is your friend. I will now elaborate on fuel pressure problems associated with the stock fuel system present in an F-body. Many of the principles here seem specific to an f-body; however, the concepts behind these principles are mostly universal.

            The factory F-body fuel system employs a “fake” return system. Shortly after leaving the tank, the factory feed line runs into a Tee fitting. The run of the Tee continues on to the front of the car, while the branch of the Tee returns to the fuel tank. On the end of this Tee’s branch (back to the tank) there is a small fuel pressure regulator. In this configuration, the fuel pressure regulator in the system only maintains a 58psi fuel pressure at the Tee. Downstream of the Tee (that continues to the engine bay), the pressure drop of the increasing amount of fuel flow is not accounted for. Pressure drop across a piping system, also known as line loss, is dependent upon several factors. The most influential factors are flow rate, cross sectional flow area, and minor losses due to restrictions in the line. As your engine begins to consume more fuel, the actual amount of fuel flowing from the Tee to the fuel rails increases. This increase in flow rate promotes an unwanted excess fuel pressure drop, detrimental to any tuning work, or safe air/fuel ratios.

            When speaking of the stock f-body system, most people consider it’s maximum output to be around 450rwhp. While this is the extreme upper limit of even the largest factory injectors, it is not the upper limit of the fuel pump. If the fuel pump was attached directly to the fuel rails, the stock pump could support much more horsepower. The problem lies in the treacherous path the fuel must take from the pump to the engine, and the fact that the pump must supply enough fuel to maintain nearly 60psi at the Tee. The stock pump has the ability to support an incredible amount of horsepower, but not at 60psi. As the pressure demand increases, the flow rate is sacrificed. With this in mind, designing a fuel system capable of running 1000rwhp at 60psi seems daunting, but it’s easily do-able.

            The first problem we must deal with is the regulator placement. The stock fuel pressure regulator, while convenient for manufacturing, is extremely inconvenient for the average hot-rodder whose only concern is making massive amounts of horsepower. Locating the regulator downstream of the fuel demands is key to building a reliable and performance oriented fuel system. This can be accomplished several ways. The easiest way is to run the stock feed line (plugging the Tee branch originally leading back to the regulator) as intended, but running the fuel after the rails to a fuel regulator, then back to the tank using the factory EVAP line as the return. After this is completed, the factory “return line”, which was originally connected to the branch of the Tee, can be used as a new EVAP line, simply venting to atmosphere, or running (via rubber fuel hose) to the front of the vehicle and plugging into the EVAP solenoid (located on the driver side of the manifold, connected to the intake manifold behind the throttle body).

            Another way of accomplishing a downstream regulator, and the way that I selected, is to run a new fuel feed line to the front of the car, through the rails, into the regulator, and use the stock feed as the return back to the tank. A regulator acts as a “vent” that diverts any excess fuel back to the tank while maintaining a set pressure. A general overview of my system is below.

            In my system, I removed the fuel tank pressure sensor, and stock wiring harness connector from the sending unit. These holes were drilled to ½” to accept the ��an 90* bulkheads. The fuel pumps send fuel via high-pressure 5/16” hose, into ¼” NPT female x 5/16” barb fittings. These attach to ¼” NPT male x ��an Female adapters, which then attach to the bulkheads. After removing the wiring harness connector, I was forced to drill new holes to run my wires through. There are 6 wires going through the fuel pump sending unit “hat”, two for each pump, and two for the fuel level sensor. After these are run through, their holes were sealed with JB Weld “Quick-Set”.

The bulkheads send a ��an fuel line to the large fuel block, which employs ��an x ½” NPT adapters and a ��an x ½” NPT adapter.

 After the fuel block the fuel continues to a ��an Magnafuel high-flow filter, and then to the front of the car. The line is run along the stock fuel line and zip-tied into place; the black wire loom contains the dual 10awg wires from the back of the alternator. You can see the placement of this here.

From here the fuel continues to the engine bay and enters a Tee, one side enters the fuel rail, the other side sends fuel to the fuel solenoid of the nitrous system. Here you can see the top fuel line (feed), zip-tied to the return line (smaller line). The feed Tee is attached to the back of the passenger side rail.

After the nitrous solenoid fuel demand, and he passenger side injectors, the fuel crosses over to the driver side via ��an line. The flow rate at this point in the line is extremely depleted, and the larger size line is no longer needed.

After the fuel passes by the driver side injectors, it is diverted to the fuel pressure regulator’s inlet port. In these pictures, the small line leaving the rail is the return line. The pressure regulator vents out the bottom. There is a ��an male x 3/8” quick connect adapter screwed into this vent port allowing for easy installation and removal of the regulator on the stock fuel feed line.

Once the fuel has passed through the regulator, it is on its way back to the tank. The fuel continues toward the tank and runs into the factory Tee fitting. From here it can either go back-wards through the factory filter, or through the factory “return line”. This dual flow-path ensures that the 5/16” return line, or the presence of another fuel filter flowing in the wrong direction, does not impede the flow of the fuel vented back to the tank. A restriction here would not allow the pressure regulator to properly maintain fuel pressure at a steady state.

The second key thing to having a successful fuel system build is sheer power. Electricity, just like fluid, has pressure drop across its transmission device. In electricity, the “pressure” is measured in volts, as opposed to PSI. If you increase the voltage, you increase the power output available. The alternator put out roughly 13.5 volts. If you measure the voltage of a 18 gauge wire attached to the alternator at the alternator, you will get 13.5 volts. If this wire is 100’ long, and you measure the other end, you will get less. This is due to a voltage drop across the wire. The only way to defeat this problem is to either shorten the wire used, or to use a larger wire; much in the same way we increase fluid flow system performance. A “hot-wire kit” does just this. It helps deliver the maximum amount of power available to our all-important fuel pumps. In my system, I employed two 10awg wires from the alternator to a convenient relay location. The wire travels along the stock fuel lines from the alternator, and through the rubber grommet located below the passenger side rear seat bucket. From there it runs under the carpet to the relays, which are located where the rear passenger side seat belts used to be. They can be seen in this picture. The small red wire coming from the front of the car in the picture is used to activate the second relay, and thus the second pump, only when the nitrous is activated. The main fuel pump relay is activated by using the stock fuel pump power wire as a trigger attached to the fuel pump relay. It comes on and primes the system when the key is turned on just like the stock setup, but is designed to handle more electrical power. From the relays, I chose to run 12awg wire the short distance over to the pump sending unit and down to the pumps.

Keep in mind that this is a custom system. I enjoy thinking about, planning out, and installing these kinds of things, so it may not be for you. I drew the system on graph paper, labeling all fittings/components needed and made a list on Summit Racing’s website using their shopping cart feature. Fuel system parts seem cheap, but it’s deceiving. Sure, a fitting is only $20, but there are 30 of them, they add up quickly. The dual Walbro setup has been proven to over 1000rwhp several times with a properly setup return system. With a little thought, little dough, little ingenuity, and a lot of time spent reading; you can build pretty much anything, including a wee-little fuel system.

-Casey Spears - “TheBlurLS1”