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12/29/93            Revised 01/23/02

 

"HOW TO TWEAK YOUR GN/T"

 

 

2.       FUEL SYSTEM

 

The fuel delivery system is perhaps the single most important component impacting the GN/T's performance and reliability.  Not only can it make the car perform poorly but will cause significant engine damage due to inadequate fuel delivery resulting in lean-out AND BAD THINGS.

The fuel system performance deteriorates with age and application.  This system MUST be in excellent working order to assure maximum, safe, reliable performance.

Gremlins that seriously affect fuel pump performance are ...

·        Excessive wear of pump due to age

·        Running tank level too low, less than 1/4 full

·        Dirty fuel filter

·        Low voltage to fuel pump (possibly high resistance in fuel pump      relay and/or wiring

·        Low alternator output

·        Clogged or restrictive fuel tank vent line

 

The following items will be addressed in this section to help size/select/install and implement your hi-performance fuel delivery system.

·        Fuel System components/locations

·        Fuel Pump requirements/sizing criteria

·        Fuel Pump types/selections/specs

·        Fuel System installations- plumbing, wiring

·        Fuel Pressure Regulators

·        Fuel Injector sizing criteria

·        Fuel Injector types/applications/specs

·        How-To ......

a.  Replace Stock Fuel Pump

b.  Install External Pump- plumbing, wiring

c.  Install Dual Pick-up in fuel tank

d.  Change Fuel Injectors

e.  Change Fuel Pressure Regulator

f.  Change Fuel Filter           

g.  Install & Use CPP Remote FP Gage [Test]

h.  Modify Fuel Rail for Dual Feed

 

2.1  The fuel system consists of the following components.

·        Fuel Pump    [Located in gas tank.]

·        Fuel Filter [Located in front of drivers rear wheel near the frame.]   

·        Fuel Rail    [Located on intake manifold.]

·        Fuel Pressure Regulator [Located on fuel rail.]

·        Fuel Injectors [Located on fuel rail.]

·        Fuel Tank Pick-up assembly  [Located in top of gas tank.] 

·        Fuel Feed Line   [3/8"]

·        Fuel Return Line [5/16"]

 

 

 

[COMMENT1] 2.2     Fuel Pump requirements/sizing criteria                       

There is the age old hot rodding adage ... It takes fuel to make horsepower.   It does not matter how good your heads, turbo, intake and suspension are.  You cannot attain peak horsepower if you do not have enough fuel available.

 

The best way to design your fuel system is to establish a performance level or goal and then design, select, and implement the desired system.  If you plan on growing or evolving to that level over a period of time you can install for example the first side of a dual pump system first and then the second feed at a later date.  Planning now will save you money and headaches then and provide you with the optimum system for your performance needs.

Example: You have decided on a performance goal of 400HP now with the ability to grow to 600HP in the future.

The following correlation can be used to size, select, and design your fuel system.

 

A motor capable of 400HP requires 240#/hr of fuel.

A motor capable of 600HP requires 360#/hr of fuel.

 

Fuel weighs 6.05 #/gallon. [We can use 6# for calculations.]

There are  3.785 liters/gallon.

The equations to calculate fuel requirements are ...

 

 

Therefore it takes 40 gallons/hr [151 liters/hr]  to make 400HP and 60 gallons/hr [227 liters/hr] to make 600HP.

As you can see your fuel needs increase proportionally with your performance goals.  The following chapters will provide proven examples of how to address these requirements.

Example:  We now know that we will need 40 GPH right now and will eventually need 60 GPH capacity in the future.

 

2.3     Fuel Pump Types/Selections

 

Now that we have determined how much fuel is required to meet our performance goals we must now decide on what kind and how many pumps are required to meet that goal.

Fuel pumps can generally be separated into two categories.

a.         Internal [in-tank] pumps

b.         External pumps

 

2.3.a  INTERNAL "IN-TANK" PUMPS

 

The stock fuel pump is located in the fuel tank pick-up assembly.  It is rated between 90 - 110 liters per hour.  As noted in  section 2.2.  This is good for about 280 to 350 HP.  This is adequate for stock and slightly modified engines but does not have enough capacity for heavy duty application.

 

There are several hi-performance aftermarket in-tank pumps available today that fit in the stock location without mods to wiring or plumbing.  They can provide 10% - 25% higher volume­ than the stock units.  These pumps are reasonably inexpensive but may not provide adequate fuel for FAST applications.

 

The dual or tandem in-tank pump  is offered by several companies. ­The pumps "Y" together in the tank and can provide approximately doub­le the fuel capacity of a stock unit. 

Advantages:  The assembly fits in the stock location [in the tank] and does not require external wiring or plumbing to install. 

Disadvantages:  Initial costs are higher, utilizes only the stock feed line, a tight fit in tank, uses stock wiring? (Higher amperage requirements of dual pumps can cause sub-par performance due to low voltage.)

At double stock pump capacity these pumps should support up to 500HP with proper voltage but stock fuel lines and filter may be a constraint.

 

 

2.3.b External Fuel Pumps

 

There are many external pumps available for aftermarket, hi-performance application.

Things to consider when making your selection are: capacity (volume and pressure), cost, mounting requirements/size, connection size/orientation, reliability, and load requirements.

 

The "Bosch" fuel pump is probably the most widely used and recognized external pump in use on the GN/T today.  They were the first units available that offered "both" capacity improve­ments and required rated pressures.

 

"Bosch" fuel pumps are rated by capacity [liters/hr], pressure [BAR= 14.505#] and voltage[11 - 14VDC]. 

 

Example:  The Bosch #286 pump is widely used.  It is rated at 130 liters/hr [35 GPH] @ 5 BAR [73 psig] at 11 to 14VDC.  Bosch makes several units that have higher outputs and ­many units that have lower outputs and are only rated at 3 BAR [43 psig] or lower so be careful with your selection.

 

The following manufacturers offer high volume, high pressure fuel pumps and accessories that are applicable to GN/T performance applications.  There are several others but these are some that I documented.

                                                 

MFG.	Model#	Rating/ Rated [GPH]	Comments
Sx	#18201	135 GPH @ 0 psig or 68 GPH @70 psig
"NOS"	#15765	140 GPH @ 0 psig  or 92 GPH @  70 psig
"Mallory"	# ???	140 GPH @ 0  psig
"AC/Delco [In-tank]	#EP157	29 GPH @ 50 psig	Turbo Regal
[In-tank]	#EP226	48 GPH @ 72 psig	Turbo T/A
	#EP261	30 GPH @ 50 psig
	#EP270	37 GPH @ 50 psig	Syclone
Bosch	#GFP204	30-51 GPH 72 psig
	#GFP208	35-58 GPH 72 psig
	#GFP216	35-58 GPH 72 psig
	#GFP286	29-50 GPH 72 psig
Walbro [In-tank]
Weldon

 

Example:  We now know that any of the hi-performance in-tank pumps will meet our initial needs of 30 GPH but will not meet our future needs.  Several of the external pumps above will meet our immediate need but not future needs in a single pump single system­.  (The "Sx", "NOS", and "Weldon" will meet both goals with the proper sized fuel lines and filter.)

 

Remember that all of the above pumps work well in the appropriate application.  The desired performance potential and installation constraints are the main criteria for fuel selection and fuel system design.

 

 

2.4.1   Fuel System Installations [Types]

 We now know how much fuel we need and know of several pumps that will meet our required specifications.

The following information will attempt to categorize fuel delivery systems by application and desired performance poten­tial.  [I have included my personal preferences.]

 

a.         Stock or slightly modified: [less than 400hp]

The stock replacement fuel pump or HP internal pump works well and will require no wiring or plumbing mods.

 

b.         Mildly modified: [400hp - 500hp]

Option #1: My minimum recommendation is at least [2] two 30+GPH pumps [OR BIGGER] fed from two [2] pick-ups in the tank feeding into a "Y" merging into a HP filter feeding a new 1/2" main fuel line to the fuel rail.  I also like to use the old main fuel feed line for the return line.  This helps prevent over-riding the regulator at idle.  (The 3/8" line flows more than the 5/16" line.)

Option #2: A single high volume pump [like the Sx, Bosch or NOS] feeding into a new single 1/2" fuel line and HP filter.  Make sure the fuel filter can handle the added volume AND pressure.

NOTE: For high output application I feel it is essential to run a new 1/2" main fuel line to the rail to reduce line loss .  The pressure drop and volume loss is significant.

Question: How much fuel can flow through a 3/8" line 10 feet long?

 

c.         Highly modified: [500hp - 650hp]

For 500HP+ and higher I prefer dual pick-ups in the tank, dual external pumps, dual 1/2" fuel lines, dual HP filters and dual feeds at each end of the stock fuel rail.  [See fig.2.4] The old main fuel line should be used for the new return line from the regulator.

 

This is the same system that was used on Tweaked @ 9.50's.

 

                                                   ­

d.         FAST/FAST: [700 - ???]

 

The following fuel system is used on Tweaked @ 9.??'s.

 

 

2.4.2   Fuel System Installations [Wiring]

The previous section covers the plumbing to and from the fuel tank and fuel rail but does not address the very important fuel pump wiring.

Always remember that a  voltage drop of even 2 volts can reduce pump performance by over 15%.  Therefore we want to insure that our pumps are performing at peak performance electrically.

There are several ways of electrically enhancing pump perfor­mance. 

a.         Raise voltage:  This can be done by selecting an alternator with a higher output or by changing the internal voltage regulator with one that is on the upper limit.  [Output is normally between 13.8v - 14.5v.]  The higher the better.

b.         Raise voltage to pump: There are several manufacturers of devices that provide a higher voltage surge to the pumps under boost conditions. [Many people are using these units with initial success.] However, I feel that this is like running a 120v light bulb at 150v. It will burn bright for awhile.  Also, remember that no amount of voltage will save a failing pump.

c.         Reduce voltage drop in fuel pump wiring:  After years of use it is not uncommon for voltage to the pump to be as low as 11v - 12v.  This significantly reduces pump performance.

 

The following examples reflect several methods of assuring maximum electrical performance of your fuel system. 

 

Schematic "A" reflects changes to your stock wiring to enhance  single pump performance. This can be used for both the in-tank or external pump systems.  An aux­iliary relay is mounted at the rear of the vehicle.  A heavy gage wire [#14 or heavier] is run from the alternator [+] post --> thru a HD fuse holder --> to the relay contact --> to your [+](pump)[-]--> to chassis ground.  The gray wire to your stock pump can be cut and terminated at the [+]relay coil to activate the relay.  The [-]relay coil terminal can be grounded to the chassis.

 

 

 

 

 

 

 

Schematic "A"

 

 

 

 

Schematic "B" demonstrates how to wire a dual pump system for maximum street/strip performance and maintenance free ­operation.

 

Schematic "B"

 

 

To implement Schematic "B" the following is required.

·        Install ONE[1] NEW relay near pumps.

·        Run TWO[2] #14AWG or heavier wires the length of the vehicle.

·        Wire TWO[2] NEW HD fuse holders from the alternator post[+] per Schematic "B".

·        Mount NEW pressure switch in the engine compartment and plumb to a boost source

·        Run wire from other Relay #1 contact to the pumps[+] post.

·        Run wire from pump[-] post to a good chassis ground.

·        Terminate wiring from Fuse#2 to pressure switch contact     and from other [PS] contact to Pump#2 [+]. 

 

[Note: The pressure switch will turn on the secondary pump at a specific boost pressure. This prevents over-rich conditions at idle and low speed operation.]

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We have now decided on how much fuel we need.  How many and what kind of pump[s] we need.  How to install, plumb, and wire the system.  We now need to be able to adjust the fuel pressure for different driving needs.

 

2.5       Fuel Pressure Regulators [Fig.2c]

The following functions are performed by the fuel pressure regulator in your fuel delivery system.

 

1.         Maintain  a set  fuel pressure in the fuel rail. 

2.         Maintain the same differential pressure between the fuel rail pressure and the intake manifold pressure.

3.         Provide a mechanical means to richen or lean the fuel/air mixture.

 

Contrary to popular belief the regulator is NOT a pressure reducing regulator.  The fuel does not flow through the regulator to the rail and injectors.  The regulator is used to maintain a desired backpres­su­re  [or pressure] in the rail by ­relieving excess fuel pressure back to the tank through the return line.

 

The second function of the regulator is to maintain the same differential between the fuel rail pressure and the intake manifold pressure.    The rail pressure will increase at the same rate as the boost rise and decrease at the same rate as the vacuum.  Always keeping the pressure differential between the manifold and the fuel rail the same­.

 

i.e.  If the initial fuel pressure is set at 37 psig [stock] at idle [With the vacuum line disconnected from the regulator.] and the boost increases 10 psig the fuel pressure should increase 10 psig to 47 psig.  Every one [1] psig increase in boost will raise the rail pressure one [1] psig.  At idle the fuel pressure will decrease proportionally with vacuum. .

 

 

The third function of the regulator is optional but desirable. It provides a manual method of "Tweaking" your fuel/air mixture.

The fuel pressure has a direct impact on the fuel delivered to your engine­.  The higher the fuel pressure >> the richer your mixture.  The fuel pressure can and should be used to trim you air/fuel ratio for optimum performance.

 

For example the stock Turbo Regal regulator is preset at 37 psig.  A regulator off of the Buick "Somerset", Pontiac "Turbo T/A" or GMC "Syclone" is preset at 43 psig thus providing higher pressure to the injectors resulting in a richer fuel mixture.

 

The amount of enrichment can be calculated by the following equation.

 

 

Example:        If the stock regulator set at 37 psig is replaced with the Sumerset regulator set at 43 psig we can expect approximately a 7% enrichment throughout the entire rpm range.

 

% Enrichment = [SqRt(43­/37) - 1] x 100 = (1.075- 1) x 100 = 7.5%

 

Regulators can be generally be grouped into two [2] categories:

Non-Adjustable and Adjustable.

 

The advantage of the adjustable fuel pressure regulator is the ability of one unit providing the flexibility to meet all of your performance requirements.  The only disadvantage is a slightly higher initial price.

 

The following chart reflects part numbers, initial pressure settings and applications of some of the more common regulators.

 

 

2.6       Auxiliary Regulator [fig.2.6]

 

The auxiliary back pressure regulator [or FMU] allows the use of BIG injectors without having to resort to an aftermarket fuel management or other special computer system.

The auxiliary regulator provides the capability to ramp up the fuel pressure rapidly as boost increases.  Whereas most fuel pressure regulators have a pressure rise or slope of 1:1.

i.e.  A one [1] pound rise in boost pressure results in a one [1] pound increase in fuel pressure.  The auxiliary regulator usually has a slope of three [3] or five [5].  It raises the fuel pressure 3 to 5 pounds for each one pound increase in boost.  Its main use has been on aspirated motors modified with aftermarket superchargers or turbos.  It force feeds undersized injectors by significantly raising the fuel pressure as the manifold pressure increases.

The main drawback of the auxiliary regulator is that it does not have the ability to lower fuel pressure at idle or high vacuum conditions.  Therefore, it must be used in conjunction with a stock type regulator to provide drivability at low speeds AND ample fuel enrichment under full boost.  It should be installed in fuel return line downstream of the stock type regulator.

 

 

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