TECH: Mechanical Fuel Injection for your SBC...

and your flathead, your nailhead, Dubya-head, in-line, hemi, SBF, BBF, Pontiac... hell, you can put this set up on just about any engine!

First you have a fuel tank, mount it up high, so your cam driven fuel pump is submerged... it'll make starting easy.

Get a high-flow fuel filter. Crap, when in a fuel system like this, can clog your injectors, causing some cylinders to run fat, some lean.


From there, your fuel goes to the pump.

The pump is the thing below the thing I am pointing at.

As engine rpm's increase, so does pressure and flow.

The fuel comes out of the pump, and goes to two places from a common orafice, also called a manifold.

One of the places is through the shut off valve... that's the little blue thing I am pointing to.

Once past the shut off valve, the fuel goes to the barrel valve. I'll explain what Mr. Barrel Valve does later.


The pill holder is the other place the fuel goes to once it comes out of the fuel pump's common manifold.

Inside the pill holder is a pill.

Think of the pill (it's really a jet) as the end of a garden hose and your thumb (over the end of the garden hose) is/are the different sized pills that you have.

Hold your thumb over the end of the hose, and the pressure increases inside the hose.

If you let your finger come off the end of the hose a bit, the pressure decreases inside the hose.

Now because the pill and the injectors all share a common bond, i.e. they are plumbed to the same outlet (common manifold), the pressures all past the pump all stay the same to all of the orifices.

If you DECREASE the size of the pill, you effectively increase the pressure inside the entire system, therefore increasing the amount of fuel that comes out the injectors.

Also, if you INCREASE the size of the pill, you effectively decrease the pressure inside the entire system, therefore decreasing the amount of fuel that comes out the injectors...

Smaller pill = richer mixture to the engine
Larger pill = leaner mixture to the engine



The barrel valve... ah, the barrel valve. The barrel valve is an "on and off" switch of sorts.

The voo-doo behind the barrel valve is what screws people up who want to run these things on the street... don't ask me how to run one on the street, 'cause that's a whole 'nuther can-o-worms.

The barrel valve, as I said, is an on and off switch.

There is a cam inside that either closes off the fuel flow to the injectors, or, when opened wide open, allows all the fuel from the fuel pump go to the injectors.

The barrel valve (actually the cam inside the barrel valve) is actuated by a lever that connects it to the throttle shafts.

Open the throttle blades and the barrel valve open.

If you close the throttle, the barrel valve closes.... well, ALMOST closes.

You need a little fuel for idle, and some air too... so there is a stop that holds the butterflys cracked open at idle, and a "leak down" setting that you set the barrel valve to when the butterflys are "cracked open".

A leakdown test is a differential pressure test. It tells you, in a percentage, how much something leaks.

I learned all about them when I was an aircraft mechanic working on piston driven aircraft... and then put that knowledge to good use when I set up my barrel valve!

But basically, the manufacturers of the injection system know how much air the barrel valve needs to leak in order to have a proper idle "air fuel ratio" at a given "crack of the throttle blades".

Here's a pic of the barrel valve and a clear shot of how it is opened and closed by the arms coming off of the throttle shafts. Notice the hoses are not connected to any injectors... as I have them out in this shot.


Once the fuel makes it past Mr. Barrel Valve, it goes through the hoses (always buy new hoses) to the injectors, the injectors are just little pieces of brass, machined a bunch, that have a little hole in them to squirt the fuel into each port.

Ours have screens on them, I think it breakes up the fuel a bit. Some have a deflector... they spray the fuel in a desired direction in a fan pattern. Either way, your engine is being injected with fuel.


So, that's basically how it all works... if you're still lost at this point, go outside, poke eight holes in your garden hose...

turn the hose bib on, and then hold your finger over the end...

Now watch how the water comes out of the eight holes as you move your finger in front of, and out of the way of, the big hole in the end of the garden hose....

do this before your mom comes outside and smacks you in the head for poking holes in her garden hose.

Sam.

 

Nice tech post. I am thinking about running mechanical inj on my hopefully dry lakes car. I'm going to run a 283 sbc. I dont see the same problem a carb posesses with the small engine trying to pull fuel thru it. I've always liked them, but didn't know how it worked. Thanks.

 

kickass sam... so now that we understand how fuel delivery and distrobution works, how about linkage?

thats where i tend to get a bit confused

 

Well, there are two throttle shafts. One for the four throttle bores on the right bank, and one for the four throttle bores on the left bank.

They are tied together with that hex bar you can see in picture four.

There are little arms that clamp down on the shafts, and then the hex bar connects those via heim joints.

There is another hex bar that you see directly in front of the longer one. It is the one that controls the barrel valve.

We have a throttle cable; you can see it in the lower part of the fourth picture. It is gray, and is ribbed. It connects to the front of the right bank's throttle shaft... again, with a little arm and a heim.

Then there is a return spring on the system too... right now, we do not have a stop directly on the arm that the spring is connected to.... kind of a no-no. The stop is back halfway through the mechanism... which allowes the spring to actually bend the throttle shaft at idle... just enough that the cylinder closest to the spring runs rich at idle.

We'll fix it soon enough...

Sam.

 

EXCELLENT post, Sam!!!

I've wanted to run a mechanical fuelie on a street car since Chris Buttera did it in the early 80s on his big block Camaro, he and his Dad (Lil John) came up with a few innovative tricks to make the set-up more "street friendly"...wish I could find that old article again!

Thanks for the pictorial and informative text...keep us posted!!!

 

Thanks for the info and pictures. Excellent explanation, for a knothead like me.-MIKE

 

Awesome tech man!

 

Excellent Sam. Could this be a techomatic canidate? Or even tech of the week?


jerry

 

Your saying that the fuel is not metered at the injector but by the pill in the pill holder?

Looking at the pictures I assume the pill holder is the black tube/box in the return line to the tank? If this is correct then doesn't that mean that it is a blow off/bleed to meter the fuel pressure in the whole system?

How big is the hole in the injectors? Does it matter what size they are?

How similar is mechanical fuel injection to a nitrous oxide set-up? Don't they run 'pills' and injectors to meter the fuel?

 

Thanks Sam - This is excellent, I know there are a bunch of us who want to run this set up on the street, mechanically. I was going to post a request for this very subject.

Sam or anyone have suggestions for running on the street?

I can add the street combo used in the Rodders Digest (Feb 05) article if anyone else is interested.

Thanks

 

I'd like to see the Rodders Digest article.......

 

me too!

 

i have seen this question come up before about running mechanical injection

IMO - its almost the same as running a magneto on the street - you can, but you probably dont want to since the fuel pressure rises as engine rpms increase.

these pieces of equipment were designed for high rpm use, you would probably get better results from a 6x2

 

Here's a few other things that might help....

The barrel valve is actually a cam lobe. As the lobe is adjusted one way or another, it either opens or closes the ramp, increasing or decreasing the flow of fuel at idle. Thjat is where the leakdown tester comes in.
Hilborn used to tell you to back the barrel valve down until the idle went flat then start back the other way until it "cracks" when you rap the throttle. This is the (pardon the analogy) "Old School" way of adjusting it. My dad has always taught this method to new guys and so I challenged him to see how close it was to the gauge.......we were 2% apart.
So you can get pretty close by ear.

Another setup gauge is a piece of Saran Wrap. When you setup the injector butterflies, you can gauge the amount of seat pressure against the injector bores by dragging a piece of Saran Wrap between the butterflies and the wall. Use the Saran Wrap like a feeler gauge of sorts. A piece of paper will work also.

If the pill issue still confuses you, just remember that the more fuel that goes back to the tank, the leaner it will run. That is how the hole size corresponds to the jetting.

The less fuel that goes to the tank....the more that goes to the motor= richer.

 

The holes vary in size depending on the amount of fuel you need. The pill size is usually a drill size. EX: 125 pill is .125", a 135 jet is .135"
I may be wrong on this but I'll research it and let you know for sure.

 

like stated the pills are incremental and meter the return fuel tot he tank,you can also change the spring tensions with in the retun block to effect the retuning fuel. there is also a high speed by-pass on the hilborn pg pumps, most guys don't use them but in racing application that will add a third retun line to the tank. the jets in the manifol are also sized incrementally as well as by fuel (gas/alcahol etc) the pumps are also rated by flow GPH and by gas/alcahol/nitro etc)
I run a pg-150-O pump with a single retun on my rail with 4" stacks, the length of the intake stack also dictates bottom end /top end performance.
injector maintenance is critical (cleaning the screens in the jets) this is limited greatly by using a quality FI filter and filtering the fuel when it goes into the tank (using a funnel with a brass screen is great for lint trapping).
I have all of my injection pumps reflowed by gene adams, gene told me as far as filters go "if you have to pucker your lips to blow air threw it,it's to restrictive".
well thats my $ .02
very well written and detailed sam!

 

Dude your car is the business.........


One other thing is that the shutoff needs to be on the output side of the pump so that when you shut the fuel off, the pump doesn't run dry and ruin the bearing surfaces.

 

Thanks Roothawg and Shadow - Shadow that car reminds me of a few that would run at Dover (NY) and Connecticut dragway. I like short wheelbase diggers.

I have heard that you really can't run mechanical injection on the street, but I want to give it a shot.

Since photocopying a magazine article and posting it here is breaking some copyright I'll give the part numbers used. From 2/05 Rodders Digest.
Credit for the article - Simon Watts
Credit for the pain, suffering and financial stress - Chad Everett (Jalopy Shoppe)
Engine: SBC 400/327 small journal crank;300cu in ford rods; custom pistons high compression.
461 heads - heavy port job.

Intake - Hilborn PN 265-C-8E (2 1/16 bore)
Nozzles - Hilborn PN 702AD
Metering Rotor - Hilborn PN 77 (200 cu in sprint car)
Pump - Hilborn PG 150 A size 0 (.8 gal per min at 50 psi 1800rpm)
He tried a super 0 (S0), but was too much.
Primary Bypass Parts;(also Hilborn numbers)
Main Body PN 511
Poppet Valve PN F513A
Spring PN F514
Jet (aka pill) PN 115
Seal PN 410
Cap PN 512

Hilborns site (http://www.hilborninjection.com/) has some tech stuff and pics of the PNs described above.

I have some of the parts; manifold, pump drive, etc., but need more.
I am interested in learning if the secondary bypass can help streetability, since it is only supposed to have an impact on part throttle conditions not idle or full.......?

Anyone have a better recipe?

Steve

 

I thought about this today and how the pill defied the laws of physics. Now that I read Root's response, the garden hose analogy makes more sense. The pill orifice acts as a bypass pressure regulator. The variable speed pump will try to build head pressure as the rpm increases, and the pump is able to flow a higher volume. The fuel will take the path of least resistance. A larger pill size will bleed off more of this volume and thereby lower the pressure (and fuel flow) the engine will see. It will work in this universe.

Like Homer Simpson says: "In this house we we obey the laws of Physics."

 

Right-oh!

Except for the part about the fuel taking the path of least resistance... that an eee-lec-tri-zity rule. The pressure rule we are talking about is the hydraulic principle that says something to the effect that pressure is exerted in all directions equally and evenly.... then you let your finger off the end of the hose and the pressure drops.

Sam.

 

All matter in nature will flow in the direction of least resistance. Water doesn't flow up hill. Heat travels form hot to cold. The pressure on a confined fluid will remain constant if the volume (and temperature) of its container remains constant.

Yes, the pressure is applied equally in all directions. If you open a valve on a pressure vessel the the fluid will always flow from the higher pressure area to the lower pressure area taking the path of least resistance. The nozzels at each cylinder are fixed. If you install a larger opening in the bypass (return line), the lines downstream of that bypass opening will see less pressure and flow.

The water pressure in the garden hose remains constant. Is does however have a choice of where it will flow. It would rather flow through the large opening at the end of the hose, than the little holes you poked in the wall of the tube. If you close-off the easy path it will be forced to take the hard way.

 

Great stuff, guys! Now I have a question for you guys who've been running these things for a while: I have an idea for priming the injector on my alchohol car, that someone may have already tried - I want to wire an electric fuel pump to my starter switch, so that when I hit the starter, I get a shot of gasoline into the mechanical fuel pump. The line from the electric pump would have a check valve installed in it to keep the alky from running into the gas tank, but I don't know what valve to use - how much pressure should this thing be rated at? The idea is to be SURE this car fires at the starting line - I have a steel one piece lift-off front end (the injector stacks don't poke through), and if I have trouble starting it on the line, I'm screwed! I've had many episodes of being shut off at the line because of trouble elsewhere on the track, and although these systems USUALLY start okay once warmed up, I can't afford to take a chance - I want a sure fire starting system. Any comments on this???????

 

That's a good idea Jangle. You need to know the maximum pressure the alcohol pump will put out. Choose a check valve that can hold back that max pressure plus 20% or more. When the engine dies the alcohol pressure will drop to zero. Start the gas pump and.....................

I changed my mind. you would need another check valve in the alcohol line and that would screwup the flow of that system. keep the two fuel systems separate. run a separate gas line to your injector hat, or each tube, depening on what brand of fuel injection your using.

You might consider a setup like an old John Deere tractor. hit a button on the dash that would squirt a little starting fluid into the intake.

 

You are talking about Bernoulli's principle.

Bernoulli's principle thus says that a rise (fall) in pressure in a flowing fluid must always be accompanied by a decrease (increase) in the speed, and conversely, if an increase (decrease) in , the speed of the fluid results in a decrease (increase) in the pressure. This is at the heart of a number of everyday phenomena. As a very trivial example, Bernouilli's principle is responsible for the fact that a shower curtain gets ``sucked inwards'' when the water is first turned on. What happens is that the increased water/air velocity inside the curtain (relative to the still air on the other side) causes a pressure drop. The pressure difference between the outside and inside causes a net force on the shower curtain which sucks it inward. A more useful example is provided by the functioning of a perfume bottle: squeezing the bulb over the fluid creates a low pressure area due to the higher speed of the air, which subsequently draws the fluid up.

 

JG I had the same problem with My Dart when I used alcohol. But my injectors were exposed so we just sqirted some gas in them.
I have heard of guys using windshield washer pumps for this with success.
60s Mopar winshield pumps and resivours are one piece and made from some plastic. You could use small plastic hose from the pump to a vacume hose splitter then run 4 or 8 hoses from there to your tubes. Hit the button and prime it. I quit the alcohol deal and went back to gas NO starting problems at all!! I lost some torque but it idles better cracks the throttle way better and now I dont have to worry about getting old fuel. A small percentage of water in alcohol makes it all but impossible to start when cold. And with gas I dont have the maintenence of flushing the lines and oiling the pump after each race. --FEDER

 

Damn Root... you sound like a text book!

As far as priming... you want to make sure your pump is alcohol compatable... but yea, I think that would work great.

Run a second feed line off of the tank... a 3/8" line would be adequate. "T" it into the line that comes out of the pump. I would run a second shut off valve, OR a one way check valve before the "T". A check valve would be a safer bet... then you won't forget to shut it off. Then, hit the pump switch, put the pedal to the floor for a couple second.... foot off the pedal, shut the pump off... then hit the starter switch and varoom!

Sam.

 

Jeez, thanks for all the feedback, guys. Plenty of ideas to keep my head spinning for a while...Didn't mean to hijack your post Sam, just seemed like a good place to ask a question I've been wondering about for a while. I'll take all this info into consideration. Thanks again...

 

It was in the Dec. '79 Hot Rod.

Photo caption: The two-quart Moon receiver tank was fitted with a removable Holley float bowl (and float assembly) to control the fuel level. Fuel is pumped into the top of the tank so gravity can be used to help prime the injector pump. Bottom line (arrow) goes to the pump, while the top lines are bypass returns.

Lil' John said, "The only problem we ran into was finding a cheap and simple way to prime the injector pump. The way we solved that item was to take a two-quart Moon aluminum tank and bolt a Holley removable float bowl to one side of the tank. It was simply a matter of hooking up a Carter competition-type electric fuel pump near the stock gas tank and running a fuel line from it to the firewall-mounted 'receiver' tank. What happens here is that the electric pump fills the receiver tank until the float shuts it off. A No. 12 steel-braided line is run from the bottom of the tank to the injector pump, which always keeps the injector pump primed. Two return lines (one a high-pressure relief valve on the pump and the other the bypass jet) are rerouted back to the top of the receiver tank. It's all very simple and works just as easily."

 

This is the article I used to run my Hilborn on the street...!!!

After I gathered all the parts to put it together..., I sold it to a friend who stripped it down for the Dragstrip...!!! (that's when I purchased and learned about Weber carbs)

So I never got to test the system in the magazine..., however..., it started well (on gas) just by opening the Shut-off valve and doing a little "Hokey-Pokey"!

 

Thanks Goober! This helps all of us...