Thursday, January 12, 2012

Can Mechanical Fuel Injection Be Run On The Street?

Converting Mechanical Fuel Injection for Street Use

Mechanical fuel injection (also known as constant flow) is a type of fuel delivery system, which there is constant fuel flowing in one circuit or the other. This allows for control of the air/fuel ratio by increasing or decreasing the flow rate (pressure) of fuel against two fixed orifices. One orifice sends fuel to the intake (spray nozzles) and the other back to the storage tank. The spray nozzles are not controlled with electronic solenoids. With the electronic type, the air/fuel ratio is controlled by the time the electronic solenoid (injector) is energized and the fuel pressure remains relatively constant. The electronic system uses electronic fuel injectors where the mechanical system uses spray nozzles.  While this might be an over-simplified explanation and comparison, understanding the basic concept is simple.

I have been running  Enderle mechanical fuel injection on my hot rod since 1997 and have seen, up close and personal, both the pleasure and pain in pioneering the concept and refining it to near perfection.  There certainly were times when it was hard to stay motivated, spending what seemed like endless amounts of money and time on research and development to develop the concept’s first proof.  However, I was insistent that it could be done and in the end, persistence was well worth all of the effort.

Nothing draws a crowd to a boulevard more then the sound and look of a blown and injected engine. No matter where you go, people seem to know that something is drastically different about your car. Even with all the refinements, though,  this system is not for every one but if you are looking for “elite status”,  this is the way to go.

My engine is a 468 BBC with a stage four Danekas 6-71 blower and two Holley 750's.  The car is tubed and has all of the usual pro-street amenities but I wanted to take it to the next level and needed something that would set both myself and my car apart from the crowd. I wanted something rarely seen on the street while sitting at a stop light or in a rush hour commute to work.

I first started building my own blower parts in the mid 70s This is a picture of my oldest son Jeff and I in 1979 I have continued building and redesigning parts to this day.

I have been a mechanic since 1968 and have been an auto mechanic's instructor at Saint Paul College since 1987.  In 1996 I posed the question to my students, "What do you think I should run for a fuel system?”  I gave them two choices: A) electronic fuel injection or B) mechanical fuel injection.  The topic turned into a lively debate in class for a few days; much discussion regarding the important differences as well as the pros and cons took place.  We decided to go with the mechanical system, which caused a lot of excitement for the class that was challenged with overcoming the pitfalls running this system on the street presented.

The look of mechanical fuel injection is like no other. There is no other component that you can put on your engine that will give it as much awe-inspiring looks, and demand as much respect, as mechanical fuel injection. There are electronic conversions available that will give you the look but they will always fall short in the cool department. However, when considering what’s best for your own application, it is important to remember that there are pros and cons to each system. With the electronic set up, the system is controlled by an ECU, Idle speed, idle mixture, off idle mixture and power enrichment are metered based on electronic sensors. This gives you the idle quality and drivability of a modern day engine. There is nothing wrong with this, however, for the perfectionists out there, there is nothing like doing the tuning yourself; the mechanical system and all that tuning data is in your head...right or wrong.                                                               
Once you have the system dialed in, it almost takes care of itself. Of course, there will be situations were the electronic system is superior but these are few and far between and should not give the true enthusiast much cause for concern.
 A normal trip in my car goes like this. I prime the hat with ether carb cleaner or gas. It may take a couple of times in the morning with a cold engine. Once the engine is running I back out of the garage and let the engine warm-up.  I check the fuel in the fuel cell and I am ready to go.

 When I get to work or a car show I will turn off the ignition first and then push the fuel lever to off. By doing the shut down this way I will not have to re prime the system unless I am stopped more then a couple of hours.  
I normally don't have to adjust any thing I just get in and go. It really is that easy.   My hot rod was not out much in the last two years because I have been busy with customer hot rods, But I hope to make a lot more shows this summer.
Lets discuss a few of the drawbacks presented by the mechanical system and, later, I will explain how to minimize these.  One of the most important things to remember when venturing into the world of mechanical fuel injection is this: If you buy a system from a race manufacturer, it will come set up for one thing, racing.  When you install it out of the box, the system will have to be modified to your specific application and there are four key challenges that the user must overcome.  First , is getting the engine to idle at a reasonable “street” RPM;  second, is adjusting the fuel curve so it is not too rich from off idle through full throttle; third, is getting the engine started (this is easily overcome with a priming bottle and a squirt of fuel directly into the butterfly), and; finally, you will need a storage tank mounted as close to the mechanical fuel pump as possible. Remember, the fuel pump, in most applications, is mounted on the engine. With this storage tank you must have adequate venting. If you think you have enough venting, add one more vent line.

I will walk you through the modifications that the racing system will need for good street performance and reliability later. To understand what changes would be needed you must first understand a few laws of physics.  

First Law: Liquids and solids will not burn. Gasoline must vaporize before it will ignite. In order for it to vaporize it  must first be broken into small  particles (atomized as small as possible). A particle of fuel must absorb enough heat so it will boil and change its state. (liquid to a vapor)  there are two main factors influencing this. Heat and pressure. When you reduce the pressure on a liquid you reduce the boiling point. This works in our favor. High performance engines typically have camshafts with large amounts of valve overlap (intake and exhaust valve open at the same time). At low engine speeds (idle and just off of idle) this overlap allows exhaust to go into the intake system causing the intake pressure to increase (vacuum decrease).  This increase in intake pressure then raises the boiling point of the fuel particle. This works agents us.

The smaller the particle the easier it is to vaporize and the less time it will take to change from a liquid to a gasses state. With the mechanical system this is very hard to do.(create small fuel particle size at low fuel delivery pressure (idle, off idle).  This is one reason they don’t work well on the street.
 When there is poor vaporization fuel economy drops and hydrocarbons go off the chart HIGH (hydrocarbon is the stuff that burns your eyes).  When you hear some one say (Man is that running rich) that is an inaccurate statement. You can not smell rich. Rich mixtures are indicated by high levels of carbon monoxide. This is a tasteless odorless gas. What you are smelling is unburned gasoline that has gone throw the combustion process (Hydrocarbon). Unburned gasoline has a very distinct smell  before and after the combustion process.

When you order your mechanical fuel system It will not come with everything you need to get it running! Depending on which manufacturers system you purchase the list below may very.

The system consist of:

A. 1 injector hat.  Size isn't that important at this point. Order the one that looks right on your car.
B. 8 spry nozzles
C. 8 metering jets.
D. 8 nozzles fuel lines.
E. 1 barrel valve.
F. 1 fuel distribution block.
G. 1 idle check vale.
H. 1 high speed check valve.
I.   1 jet holder and assorted jets.
J.     Stainless fuel line from barrel valve to fuel distribution block.

With that said lets look at the components you will need to supply, to run well on the street, but are not part of the kit:       
A. 1 Fuel pump. This is a mechanical pump that is typically belt driven. On gas, an 80A                pump or equivalent will be sufficient to handle all of your requirements. You don't need a big pump on the street because you are returning most of the fuel any way. This can be ordered from the manufacturer of your system.
B.    An electric pump at or near the rear fuel tank.
C.    Fuel storage tank mounted up by the mechanical fuel pump; this is typically custom  made  your application and should be mounted higher than the mechanical pump inlet.
D.  Fuel pump mount and drive kit.
E.  An assortment of nozzle metering jets to tune your system from racing only to street use.
F.  8 “B Nozzles”. These are non-vented.
G. 1 Distribution block. (used to add 8 additional nozzles).
H. 8 Fuel lines. (I prefer flexible over stainless steel in case something is in the way).
I.   1 Pressure check valve. (used to bring on the additional 8 nozzles).
J.  1 Fuel line to connect the pressure check valve to the barrel valve.
K. 1 Shut-off valve to adjust part throttle fuel mixture.
L.   Fuel on/off cable.
M.   High pressure fuel filter.
N.   Miscellaneous fittings and hoses to connect every thing  together.


This is a none vented "B" nozzle.

This is a "B" nozzle and a metering jet.

This is a jet holder I made to organize all the jets I used to tune the system. After dividing up the fuel delivery system into two basic circuits (primary and secondary) I used #18 jets in the primary and  #24s in the secondary.

    This is how I mounted my fuel pump. I kept it low so the
   fuel storage tank outlet would be higher then the pump inlet.  

This is my fuel storage tank. There is a number 16 fuel line at the very bottom that feeds fuel to the pump. The three lines on top are for venting. At wide open throttle you want atmospheric pressure on the fuel in this tank. The two lines below the sight glass are fuel return lines from the various valving.  Always return  liquid fuel below the fuel level in the storage tank to keep the fuel in the Storage tank as stable as possible. (to avoid caveatting)

I must emphasize that there is more then one way to do this. What follows is the result of my
fourteen years experience running an Enderle Buzzard Catcher system.  My blower is under
driven 15% and I limit my engine rpm to 4,500. This reduces the total amount of air the engine
will need and allows me to run less fuel through the entire fuel curve.  Also, remember we are
De-tuning the system so it will operate good on the street. Even with engine RPM limited and the fuel system DE-tuned it will pull very hard and you will be able to smoke the tires any time you wanand as long as you want.

Now lets get started with the conversion!

    First, figure out how much air your engine can handle and how much boost you want to run. Some of the factors you are going to want to take into consideration are: engine cubic inch displacement, strength of the bottom end, cylinder head efficiency, blower drive ratio and blower efficiency. Not all blowers are created equal. There are different sizes and efficiency levels. The blower is key to the success of running mechanical fuel injection on the street. A good blower will have tight clearance and allow very little leakage from the high pressure side to the low pressure side. A tight blower running slow will make a huge difference in over all performance and system efficiency
Resist the urge to run the blower any faster then absolutely necessary to produce adequate boost levels. The blower drive ratio and efficiency will influence the fuel curve from idle to wide open throttle. We want the fuel curve to be lean when there is light load on the engine and enrich when load increases.  How this is done will be explained as we go through all the modifications that will be made.

Modifying the hat

After calculating air requirements, The hat must be modified to limit the incoming air to that specification. I used a Buzzard Catcher hat because it fits the size and look of my car however, it’s air flow capacity was much too large for running on the street.  Remember that any air that enters the engine must be mixed with the proper amount of fuel. As you open the butterflies from idle to part throttle, the inlet sq. in. area increases dramatically and you must add fuel to keep from leaning out. Keeping this sq. in area as small as possible helps you to achieve better fuel economy and crisper throttle response. Reducing air= reducing fuel! The air flow calculations you made earlier were for wide open throttle!

There is a couple of ways to limit the air allowed through the hat. One would be to create a restricter plate below the hat. The opening  of the plate can be cut to allow the exact amount of air you need.  The problem with this method is that all the nozzles must be placed below the adaptor or fuel will puddle on top of it; Remember liquids do not burn.

The next way to meter air through the hat would be to block off the outside two butterflies. This is done by making two filler panels and welding them on the inside of the hat. This is not as accurate as the first way because you are left with the center holes air flow capacity.  In my case, this is a five inch diameter throttle plate. A five inch bore equals 19.6 square inches. 19.6 square inches equals lots of air at wide open throttle. The actual CFM of air flow will depend on your specific set up.
Now, you have to tune all the nozzles to give the correct air fuel ratio at wide-open throttle. The idle and off idle circuits will have to be re-calibrated to give them the correct air fuel ratio.(or close)

Modifying The Idle- Off Idle and part throttle Circuits

I have divided my fuel delivery into four circuits through the use of valving and dividing the primary distribution block into two separate sections connected through a small metering hole.
This allows the fuel to be brought on in four stages. Each stage adding more fuel until the throttle gets to wide open throttle. At this point you are running the amount of fuel you calculated for earlier.

For now the idle air fuel ratio is controlled by the position off the barrel valve. This is accomplished by increasing or decreasing the length of the leakage on the side of the barrel valve. Longer makes it richer and shorter makes it leaner.  
There is a check valve (idle check valve) that closes to keep fuel from returning to the storage tank during start up. Once the engine is running, and fuel pressure increases this valve will open and allow excess fuel from the pump to return back to the storage tank. For good idle mixture control you want this valve to open under very light pressure. Just enough pressure for good starting properties. From Enderle this pressure is set at about 15-20 PSI . For street driving this is why to much pressure(too rich).  You will want to reduce this to about 3-5 PSI. This lighter spring pressure will reduce fuel pressure and volume in the primary distribution block. The primary block will now fill half way and the engine can be run on four of the eight fuel nozzles instead of all eight. This light closing pressure allows you to use more of the idle slot on the barrel valve before you start to go rich. you must now increase the main check valve spring pressure to about 7-10 PSI. From Enderly it is set at about 1-2 PSI. Remember that the engine is idling approximenty half the R.P.M. that is was intended to so this throws off the entire fuel curve .                                                       

This is a view of the secondary fuel supply from the barrel valve. The steel lines from the distribution block feed the primary nozzles and the rubber lines feed the secondary nozzles.

Part throttle
 This is where most of the time and money will be spent!

The off idle circuit is where you will probably spend most of you time cursing.  As built, there is no compensation for light part throttle operation. It is pretty much pump speed, barrel valve/throttle plate position and nozzle jet size. What is really needed is a load sensing fuel control device. There is none available so the air fuel ratio in this operating range must be set conducive to clean and efficient engine operation and enrich as load goes up. Here is how I went about it.

The spray nozzles supplied with the system will most likely be eight vented nozzles. These must be removed and replaced with eight "B" type (none vented) nozzles. The holes in the vented nozzles acts like a throttle air bypass and is the main reason for high idle speeds.  The venting holes allow for the atomizing of the fuel as it travels through the nozzle. It also serves as a siphon brake. With vented nozzles fuel will drip out of the vent holes if you don't purge the system on shut down, (shut the fuel of first). If you shut the Ignition off first it keeps the fuel system charged with fuel and makes restart much easier.

The atomization must still take place so fuel vaporization will continue at the highest level possible. To do this we will move the atomization function to the primary fuel distribution block because the system is now running on such a low amount of fuel at idle the fuel distribution block only fills half way and this now makes it act like a fuel bowl.                                                 

Only the bottom ports on the distribution block are exposed to fuel. What this means is that if air is plumbed into the primary fuel distribution block, below the fuel level, it will be drawn in and atomization will take place here instead of at the nozzle. This atomized fuel will now travel to the nozzles and be discharged into the low pressure area above the blower. This is not as efficient as a nozzle air bleed but it helps the engine idle at a reasonable speed for running on the street.

To achieve the above, first remove the cap on top of the distribution block. Drill a hole in the cap to install a 1/8 by number three 90 degree elbow. (see pic) enlarge the lower portion of the fitting to 3/16.

Take a piece of 3/16 tube long enough to reach  within ⅛ to ¼  from the bottom of the distribution block. Solder one end shut. On that end, drill four small holes that go all the way through. Press the other end into the fitting. This fitting is now connected to the fuel storage tank venting. This is were the air for atomization comes from. You must also install a one way check valve in this line so when fuel pressure in the block rises fuel will not leave the distribution block and return to the storage tank through this line.

If you look closely right behind the "H" you will see the vent line I am talking about. If you follow the steel line down you can see the one way valve that allows air for atomizing to enter the distribution block but keeps fuel from leaving. The fuel pressure regulator in the picture is used to reduce fuel pressure feeding the storage tank to about three pounds.


Before re installing the modified cap, install a ¾ expansion plug with a ¼ hole in the center of it for the emulation tube to go through. Install this plug about half way down the distribution block. This will serve two functions:  A) It restricts fuel from moving up the block when the throttle is opened quickly causing a rapid increase in pressure in the lower portion acting like an accelerator pump and B) It causes a slow rise in fuel pressure in the top half.  As fuel rises into the top half the top four nozzles start to flow crating a steady enrichment.
What has been achieved by splitting the eight primary nozzles into two groups of four, Is a lean mixture for part throttle (running on four of the eight).  And two stage part throttle fuel enrichment by bringing on the top four as the throttle continues to open to wide open throttle.  The total flow of these eight nozzles will not be enough to achieve the proper air fuel ratio at full throttle. This is accomplished by the secondary nozzles.The hole in the expansion plug works in conjunction with the secondary nozzles check valve.

This valve is used to achieve a third stage of enrichment. The secondary check valve crack pressure is set to open when all eight primary nozzles have become saturated. This timing is very important for smooth operation to full throttle.  I use a lean out check vale that will open just under my crusing rpm of three grand.The full throttle air fuel ratio can be further tuned with the help of a Kinsler dial a Jet. The wide open by pass (pill) plays a very miner roll on a street drive car.

Like I said, I have been running this system for fourteen years in one configuration or the other. What is listed above is what works the best for me.  I love running it and have a blast every time I take it somewhere.

If you have any comment's or questions please e-mail me at

(UPDATE) I have added a primmer system and no longer have to squrt gas in the hat or use carb cleanner) Here is a link to a cold start.
Thanks Mike

This is how I did my fuel system.