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Friday, December 30, 2016

Fuel System for Nissan Skyline GT-R

Fuel.  In order to make horsepower in a Nissan Skyline GT-R, you need fuel and air.  The air and fuel mixture are forced into the combustion chamber by our friend, the twin turbochargers(why have one, when you can have two?), which then produces the horsepower/torque we demand with our right foot.

Stock fuel rail modified by Alex Rodriguez Motorsports. -8 AN fitting

As the horsepower requirements increase, the fuel requirements increase. The fuel system, and that is an important set of words, needs to be adequate enough to supply enough fuel.  If you don't supply enough fuel, you will inevitably end up with a dead engine.  Another very important thing to note is fuel flow vs fuel pressure vs voltage.

Fuel System:
Fuel Tank
Fuel Pump
Fuel Pulsator
Fuel Pump Control Module
Fuel Injectors
Fuel Rail
Fuel Pressure Regulator (FPR)
Fuel Filter
Fuel Lines
Fuel Pressure
System Voltage
Fuel Surge Tanks

If any part of the fuel system is not adequate, you are just asking for problems. So pay careful attention to it. About 90% of the time we are on a dyno with a car, the fuel system is the limiting factor.  Build the fuel system with enough capacity for your horsepower goals.

The questions to ask

  1. How much horsepower are you looking to make?
  2. What kind of fuel do you use?
  3. How much money are you willing to spend?
  4. How is the car used?

How much horsepower are you looking to make?

Horsepower.  Just about everyone wants a 500, or 600, or 1000 hp car. Assuming everything else with handle it, lets just focus on the fueling requirements of the engine.

RB26, we have 6 injectors. The factory injectors are low impedance, and they have a resistor box in the circuit. This is important, as most modern injectors are high impedance, and can eliminate the resistor box. HOWEVER, if you eliminate the resistor box, with a normal ECU, and low impedence injectors, you will probably burn out the injector drivers.  So make sure what you have, before you go eliminating parts.

A fairly safe rule of thumb on a 6 cylinder engine on gasoline is about 1 hp per cc at the engine. So a stock 440 cc(485 cc at 43 psi) injector is enough for about 440 hp (485 hp) at the engine on an RB26. In real life you can push it harder, or see less depending on the condition of the entire fuel system.

What kind of fuel do you use?

If you are on other types of fuel, say E85, then the requirements are much greater. An engine will want at least 25% more E85 compared to gasoline.  B.S.F.C is brake specific fuel consumption - How much fuel you are using per horsepower per hour. For turbo cars, that figure is below.

Gasoline – .60 to .65

Here is an example to figure out what fuel requirements an RB26 would want at a 0.60 BSFC, 280 horsepower, 6 injectors, and 80% duty cycle. An injector is a solenoid, and it needs off time to work correctly. We can not realistically ask it to be 100% open all the time, so we normally use 80% in a fuel injector calculator, to give the injector 20% off time. 

BSFC x HP/6 injectors x .80 duty cycle (%)

0.60 BSFC (Gasoline) x 280 hp /6 x .80 = 35.2 lbs/hr or 370cc

0.84 BSFC (E85) x 280 hp/6 x .80          = 49.2 lbs/hr or 518cc

You can see that even at stock horsepower on E85, our factory 440 cc(485 cc) injectors would be too small to provide the fuel required by the engine safely. If you push fuel pressure, or duty cycle, you could get them to work at "stock" horsepower but don't do that please. 

To convert cc / min to lbs. / hr. - Divide by 10.5
To convert lbs. / hr to gal. / hr. - Divide by 6
To convert cc / min to gal. / hr. - Multiply by .015873

How much money are you willing to spend?

This is obviously all up to you, however if there is anywhere not to skimp out, it would be your fuel system.

AMS Brushless Fuel Pump assembly - $2000
NISMO/APEX/Tomei Fuel Pump ~$400
Bosch 044 Fuel Pump - ~$250
Walbro Fuel Pump ~$100
Fuel Injectors ~$600-$800
Billet Fuel Rail ~$400
Fuel Pressure regulator - $120-$250
AN Fittings - $10-$20 each
Stainless Line - 6 ~$6-$10 a foot

From Michael on his fuel system cost

Fuelab Prodigy 1300hp pump 550.00
Fuelab electronic regulator 400.00
Tomei rail 370
Id1700cc injectors 1500.00
Flex sensor 180
Pre pump fuelab 75 mic filter 155
Post pump fuelab 6 mic filter with check valve 210
Fuel cell 220
How is the car used?

Factory fuel pump in its small sump. The return line puts fuel back to the inlet of the pump . Fuel Pulsator is also visible

You can get away with some things on a car that is only street driven, or only driven at a drag strip. There are some fuel slosh issues with an R32 GT-R fuel tank, as it is wide and flat. If you run it too low, then you can lean out the engine and blow it up. The factory pump is in a small sump, and we highly recommend keeping that sump or using something bigger/better.

Buy USA Legal R32 Skylines at! for Nissan Skyline GT-R and GT-R parts.

Fuel Tank

OEM R32 GT-R Fuel tank modified with twin -8 feeds, and 044 Bosch Pumps intank

Cars have one, it is where it is stock. Not a ton you can do about it without some major rethinking.  As you can see the OEM R32 is wide and flat. This means that fuel can slosh away from the fuel pickup fairly easily. Mr. T said to put fuel cell foam in the tank to help prevent slosh, but then it will have a tendency to foul the tank level sensor. The foam also has a finite life, and may not like ethanol much.

Holley has a product called Hydramat.  The Hydramat acts as a reservoir, and will help prevent fuel starvation.  Here is what they have to say about it. We like the idea of it, haven't tried it yet.

  • Fuel reservoir system designed to reduce fuel starvation issues present in hard cornering, acceleration, stopping, inclines, and low fuel conditions
  • Available in various shapes and sizes for installation in stock fuel tanks and/or racing fuel cells
  • Patent pending design that solves the problems associated with traditional fuel pick-ups in stock fuel tanks as well as racing fuel cells
  • Greatly reduces the potential for air to enter into the fuel system which can result in poor engine performance and/or engine stalling
  • Perfect for vehicles experiencing fuel starvation during hard cornering, acceleration, stopping, inclines, and low fuel conditions
  • Surface tension and fluid wicking allow the HydraMat™ to continue to draw fuel from the tank or cell even when part of the mat uncovered
  • As an area of the HydraMat™ is uncovered, tiny pores in the media seal off through surface tension, forcing fuel to be drawn from other areas of the mat where fuel continues to be available
  • Unique internal reservoir assists in keeping fuel available at the pickup even under extreme fuel slosh conditions
  • Eliminates the need for specialty reservoirs, sumps and pick up pumps saving cost and greatly reducing complexity
  • Also acts as a 15 micron pre-filter eliminating the need for a separate filter before the fuel pump

Fuel Pump

Endless R32 GT-R fuel system with two Bosch 044 pumps and a surge tank. Full article here. 

The stock R32 GT-R fuel pump is/was 190 l/hr or 50 gallons an hour.  However that one rating isn't really enough to tell you everything you need to know about a fuel pump.  The problem is that fuel flow decreases with pressure. Normal fuel pressure in most older return type fuel systems is around 3.05 kg/cm or 43 psi at idle.

The Stealth 316 page, is one that I have been referring to for years. Has tons of great information on fuel pumps, and fuel flow.

In the April 2004 issue of Turbo & High-Tech Performance magazine, a stock R33 Skyline GT-R fuel pump was tested to flow 252 lph at 43.5 psi and 13.5 volts.   All three of those numbers are important.  Flow, at pressure and voltage.  Just one number alone may be impressive, but you need to see the whole chart, at pressure and voltage to make good fuel system decisions. 

At a point, many fuel pumps have relief valves that open, and you get no more fuel. This is also something very important to know.

Nissan Fuel Pump tests.

Most of our Nissan Skylines are at least 25 years old. At that age, things wear out, or will eventually wear out. On our NISMO #500, we decided to get preemptive and ordered a NISMO fuel pump to replace the OEM fuel pump. We see it as cheap insurance. The NISMO pumps are great pumps, drop in, and have low failure rates. Stock R32 is rated at 195 L/hr . Nismo replacement is rated at 276 l/hr. More fuel pump info - Stealth 316. The single NISMO pump, at OEM voltages is good to about 500 wheel horsepower and 75 psi fuel pressure. Above that you need to start thinking about some complex fuel systems.

You can double up on the stock intank pumps. AKA two stock fuel pumps. Or one stock and one something else. Or two NISMO, or two Walbro, or two Bosch.  It always seems that even though on paper two pumps should flow double the amount of fuel, real life we don't see that. You might only see 1.5-1.75 times as much flow due to limitations elsewhere in the system.  

We used to wonder about the fuel systems that Toyota Supra guys ran in their cars, to support the horsepower they were running, and honestly they look just the clusterfuck. They may work, but adding complexity and failure points to a system as critical as the fuel system isn't really how you should build a car.  However, compromises when there are no great single solutions. 

AMS Performance Brushless fuel pump vs, Walbro, Bosch, and Bugatti pumps
The Bosch 044 is still such a buff pump. 300 l/hr at 40 psi. About 270 l/hr at 100 psi. This is why in about every serious race car setup I have ever played with, we use the Bosch 044. They are loud, they don't like ethanol much, but they move some fuel.  I have seen them keep right on pumping to 120 psi fuel pressure.  Most normal pumps don't want to suck and push fuel. Most pumps want to not have to do both, but that old 044 will motor on through it. All the old Nissan Skyline GT-R drag cars from Japan would have systems with three or four 044 pumps. Each one enough for about 500 hp. 

Bosch 044 as a reserve pump in R34 N1 Super Taikyu car

We still see it on some of the systems for the R35 GT-R.  However when you are looking to make several thousand horsepower, compromises are made.  We are starting to see brushless pumps, and some other interesting developments, but they aren't for the faint of wallet. 

How to replace the OEM R32 GT-R Fuel Pump with a NISMO fuel pump.

Frenchy's Performance Fuel Pump for stock R32 GT-R fuel tank
The Frenchy's Performance fuel pump setup we decided on for our R32 is a dual pump, dual power -8 supply and feed.

R32 GT-R intank fuel system kits. Unique design, easy installation, plug and play with factory harness. First ever kit to incorporate a baffle inside the tank to prevent surge. All components are E85 safe and many options are available: single pump or twin pump, -6 or -8 fittings, screw on or push on hose fittings, wiring kit. The single pump can support up to 500hp at the wheels and the twin pump up to 1000hp. The kits come with genuine Walbro F90000267 pumps. Comes with a fuel level sender calibrated to work with the factory gauge. All stainless steel hardware, anodised aluminium components, milspec wiring, Siemens sensor.

Walbro F90000267 Flow vs voltage

Walbro F90000267 Flow vs Pressure and amperage

Fuel Pump Control Module

The fuel pump control module (FPCM) slows the fuel pump speed down at idle/low speed. It is one of those OEM parts that sound great on paper, but in real life, when they fail, car no go. It provides a ground to the fuel pump and is controlled by the ECU.

Fuel Injectors

444cc at 42 psi in 1989, or 1990, or 1991. Its not 1989 anymore. Lets just say that each cc of injector - on a 6 cylinder car is good for 1 hp or about 444 hp at the motor. The stock injectors are "yellow" tops. They are also low impedance(2 ohm), so there is a resistor pack located on the right side of the engine compartment. In the chart above you can see at 2.55 kg/cm2 (36 psi) of fuel pressure the injector flows about 440 cc. At 3.05 kg/cm2 (43 psi) of fuel pressure it flows about 485 cc. At 3.55 kg/cm2(50 psi) it flows 525 cc. Don't get too crazy with the fuel pressure. Your fuel pump relief valve might end the fun soon.

Injector resistor pack delete from NZEFI

When I do a GT-R fuel system, I generally only go from stock to 1000 cc injector. I don't even bother with anything in between. With even a very basic ECU, you can get them to idle great on a 1000 cc injector, and leaves you lots of headroom. 

Some good replacements.

OEM injectors have a 10.5 mm top.
Most aftermarket rails are 11mm or 14mm.

With an inline 6 fuel rail, it is easy to get an o-ring cockeyed, or an injector not fully seated. Always prime the fuel system and check for leaks after fuel injector replacement.

NZ EFI has drop in 1000cc high impedance multi hole injectors.  With the above approximations, assuming the rest of your fuel system is up to task, you should have enough injector to cover 1000 hp at the engine on gasoline, about 750 hp at the engine on E85. Your actual hp will vary.  The modern multi hole injectors do a better job of atomization. This helps idle, and mid range power. 

Fuel Rail

Stock fuel rail modified by Alex Rodriguez Motorsports. -8 AN fitting
The OEM GT-R - RB26 rail isn't bad.  It takes a 10.5 mm top fuel injector. Most aftermarket are 11 mm. More recently it is possible to get 10.5 mm adaptors or injectors to direct fit the stock rail.  It is large feeds from rear, fuel pressure regulator(FPR) is on the front, where it returns to the fuel tank.  The Super Taikyu race car had a stock type rail that had been modified with a -6 fitting on the supply, and a -6 fitting on the outlet of the FPR.

Most "billet" rails are smaller internally than the OEM rail. If pretty colors are your thing, then go right ahead with the billet rail. If you want to double feed the rail, or add other ports, then billet may be what you want. However up to 800+ we don't see an issue with a modified stock rail.

Fuel Pressure Regulator

Fuel Pressure. Normal fuel pressure in most older return type fuel systems is around 3.05 kg/cm or 43 psi at idle with the vacuum line disconnected.  The OEM fuel pressure regulator is a 1:1 regulator. How that works is this. As 1 psi of pressure is in the plenum, where the injector fires, it raises the fuel pressure 1 psi to overcome this pressure. So at 43 psi base pressure, plus 10 psi of boost, your actual differential fuel pressure is still 43 psi, but your fuel pump needs to supply fuel at 53 psi. At 20 psi of boost, 63 psi of fuel pressure, 30 psi of boost, 73 psi of fuel pressure.   If you didn't raise fuel pressure vs boost pressure, you would end up with a lot less fuel though the injector.  Some great fuel pressure and flow charts here. As you can see as pressure increases, flow decreases. At a point, many fuel pumps have relief valves that open, and you get no more fuel. This is also something very important to know.

It is VERY important that you don't lose this boost reference line. NOTHING else should be tapped off this line.  If you need to add boost gages, or BOV control, do not under any circumstances use this line. Failures in real life happen. If you add one additional item on this line, you are adding three additional points for failure.

Fuel Filter

OEM R32, R33, R34 GT-R fuel filter. 

Somewhere in there, in the fuel system there should be a filter. Maybe two or three. The first line of defence is on the fuel pump. A screen. From there you will probably have another filter inline.  These filters help prevent getting anything clogged in the injectors.  The injectors themselves actually have small screens in them, but that really is a last line.

Fuel Lines

Fuel lines pass the fuel. OEM lines will support OEM power well. Once you go up from OEM then you need to do some figuring.

AN line sizes
ID= Inside diameter
OD= Outside diameter
-4 hose has an I.D. of 1/4"  or 6.35 mm
-6 hose has an I.D. of 3/8"  or 9.52 mm
-8 hose has an I.D. of 1/2"  or 12.7 mm
-10 hose has an I.D. of 5/8"  or 15.87 mm
-12 hose has an I.D. of 3/4" or 19.05 mm
-16 hose has an I.D. of 1"    or  25.4 mm

-6 AN line to about 500 hp
-8 AN line to about 800 hp
-10 AN line to about 1100 hp

We have actually had the fuel lines in the tank fail in an R33 GT-R. When they failed, with a full tank of fuel, the car would run fine. However as the fuel load decreased, the car would run progressively worse, until it would just shut off under boost at a point. We finally figured out that the lines in the tank were collapsing.  The R33 uses a saddle tank. It is taller and narrower than an R32 GT-R tank. It is behind the seat vs under the trunk in an R32.

Since Sam asked us to post photos of using the HICAS lines as fuel lines, here are a few photos of the R32.4. This will obviously only work if you delete HICAS. We don't mind HICAS, think it is just a misunderstood system, with mostly steering wheel gasket issues.  Fix those steering wheel gaskets, and it is a good system.
-8? AN fittings adapted to the HICAS lines. 

Using old HICAS lines as fuel supply lines. OEM line was used as a return. 
HICAS lines went to a Y, with a filter on the outlet, that then feed the back of a modified stock style rail. The quick disconnect in the picture is for the release bearing. 


Look, it is a magic box, dissected partially. 
It all is controlled with some magic box, the ECU(engine control unit) This magic box takes voltages from one source, chews them up, and spits out other voltages and grounds. A magic box is only as good as its inputs.  It is only as good as the numbers that are put into it.  Our current advice on ECU, are use whatever your tuner likes. If you pick something they don't have experience with, you are just paying them to learn, and perhaps hate what you have given them. With a magic box they are used to, they can get started, and troubleshoot any issues that might come up.

Fuel Pressure

Fuel pressure is important. The problem is that fuel flow decreases with pressure. Normal fuel pressure in most older return type fuel systems is around 3.05 kg/cm or 43 psi at idle with the vacuum line disconnected from the fuel pressure regulator (THIS IS IMPORTANT). Most modern non return systems run about 50 psi base pressure. This supposedly helps with fuel atomization.

Fuel Flow vs Pressure Calculator

Fuel Pressure Explained

System Voltage

This is something else that isn't given much thought normally. A battery in a vehicle is designated as 12 volts. This voltage is potential, or standard voltage, but in real world a vehicle that is running is taking its electrical power from the alternator. The alternator is producing a voltage/current, normally in the 13.5 volt range. As a straight measurement, voltage is generally easier to measure than amperage, as amperage normally requires the meter to be in line with the supply and load.  As above the FPCM actually slows the OEM fuel pump down, by supplying less voltage at low speed. This quiets the pump down a little. On an all stock car it might be fine, but on a modified car, it is a good thing to eliminate.

As an example, the Toyota Supra Denso pump at various voltages from 12v to 18 v showing the relationship between flow and voltage pretty clearly.

Fuel Surge Tanks

R34 N1 Super Taikyu Fuel cell, surge tank, and 044 reserve pump

They sound great on paper. However in my real world experience, nearly every single one manages to reek of fuel. On a race car, not a big deal, but on a street car, it is normally enough to have someone not happy with the car.

Dual 044 in an externally mounted Surge tank. Patricks setup

Most of the time you see them mounted in the trunk of the car. The issue with the trunk being, there is no airtight barrier between the trunk and interior.   Some guys, like Patrick, have a surge tank mounted under the car, but you don't see them much there.  Stainless lines over time will have some permeability based on our experience. The ethanol in pump gas seems to put a bit of a hurting on most lines.  The latest and greatest stuff may last a bit longer, but if you have lines that are 5 or 10 years old, you may have a permanent 91 cologne.

Dual 044 in an externally mounted Surge tank. Patricks setup
We do see people do surge tanks in all hard line, and that is fine, just need to be supported properly. They also need to allow for some expansion and contraction, and rough roads. On a hard oil line to a turbo on the R34 race car, we actually developed a crack, that flashed to a fire at Sebring. We lost a bolt that helped support the line. Never had that issue before or after, but Sebring is a rough track.

When we race we want to minimize failure points. Adding a surge tank to most systems, just adds many times to the complexity. In order to get fuel to the surge tank you need a lifter pump (normally oem). Then you have one, two, fifteen pumps in the surge tank, or an externally mounted pump that has the suction side on the bottom of the surge tank.  In the surge tank will be a lot quieter than externally mounted. A couple 044 in the trunk sound like you have a swarm of angry bees chasing you.

With one setup we had with a Weldon pump, it was louder than front row center at an AC/DC concert. You had to wonder if the 2.8 liter 4 inch exhaust, GT42R RB26, with the 280 cams was running, over the racket that the Weldon produced.

Trunk mounted surge tank

1 comment:

Rick said...

Thanks for the mention on the external surge tank!

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