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Contacting Us for Technical support

Our goal is for you to be 100% satisfied with your product. If you have any questions or issues please contact us.

1. Please look through the Techincal Articles below for a solution to your question.

2. You may email us for a prompt response at this link: email tech support here,
    or call Accufab Racing M-F 8am-5pm PST at: 909 930-1751.

Throttle Body Installation. General Instructions.

Replacing the original throttle body and installing an Accufab throttle body is considered a “bolt-on” modification. In most cases it is an “off with the old and on with the new” process.

In some cases, some minor modifications are required. If, for instance, the new throttle body is larger than the inlet hole in the intake manifold, some minor grinding or chamfering of the inlet hole may be required. On the 1996-1998 Cobra installations, the bridge between the dual-hole intake manifold must be ground or cut out so as to permit the installation of the larger single blade Accufab throttle body. It will be necessary to remove the upper intake manifold lid to accomplish this.

All of these tasks are relatively easy to do, however, if any part of a throttle body installation is thought of as being difficult, or if you are uncomfortable with doing it yourself, we recommend getting advice or consultation from a professional.

In general, here are some generic throttle body installation instructions. Disconnect the ground cable from your battery. Remove the Throttle Position Sensor (TPS) from the original throttle body. If the original throttle body also has an Idle Air Control motor (IAC), remove that too. Remove the original throttle body (typically, four bolts). If the vehicle requires any modifications to the intake manifold, do that now. When that is complete, install the new Accufab throttle body. Then, re-install the IAC and TPS, reconnect the battery cable and follow the directions outlined in the TPS Adjustment section.

See below for instructions that may be model specific for your throttle body.

Throttle Body Installation. Mustang 3.8L

Click here to view printable throttle body installation instructions for the 3.8L.(pdf file)

Adjusting the TPS.

Click here to view printable instructions for adjusting the throttle position sensor. (pdf file)

Fuel Pressure Regulator Instructions.

Click here to view printable fuel pressure regulator instructions. (pdf file)

Ford GT XPIPE Installation Instructions.

Click here to view printable Ford GT xpipe installation instructions. (pdf file)

Accufab Ford GT Rear Axle (half shaft) Bolt Instructions.

Click here to view printable Ford GT Rear Axle (half shaft) Bolt Instructions. (pdf file)

CFM Air Flow Data of Accufab Products.

Click here to view CFM air flow data for Accfab products.

Mustang Cobra 1996-1998 Throttle Body Instructions.

The Accufab Ford Cobra set-up uses a large single blade throttle body instead of the original “2-hole” throttle body that was installed at the factory.  Because the inlet transition from the throttle body into the stock intake manifold was originally cast for two smaller holes rather than one large one, a slight modification to the intake manifold will be required.  The bridge or wall between the original two holes will need to be relieved (cut out) slightly, just enough to provide clearance for the larger, single throttle blade.  This is done by removing the several bolts that hold the throttle body adapter to the intake manifold, removing it, and grinding or cutting the area between the original two holes enough for the clearance required. Hardly rocket science.  There is no “wrong” way to do it, either. 

Why do I Need a Larger Throttle Body?

Let’s start at the beginning. An engine can be defined as an air pump. That is, it moves or pumps air, starting at the air inlet to the air filter and basically ending at the tail pipes.  The more air that can be moved through the engine, the more horsepower potential it will have. Everything that can be done to an engine to increase horsepower (other than strengthening the rotating components on a race engine) is related to moving additional quantities of air.  This includes adding larger flowing cylinder heads with larger valves, cylinder head porting, higher lift camshafts, more efficient intake manifolds, higher flowing exhaust systems (you can’t get more air in unless you get the old exhaust out), and a larger throttle body (or carburetor if the engine is non fuel injected).

Additional ways to move greater quantities of air may also include using a larger displacement engine or increasing the displacement of the existing engine (boring and stroking).  Bigger engines can move more air than smaller engines.

Or, if adding displacement is not feasible, spinning the engine to a higher RPM can increase airflow.

The term most used to measure the quantity of air moving through an engine or through it’s independent components, is CFM, or Cubic Feet per Minute.

We used the term “horsepower potential” above. That is because there is one other element that is connected with increased CFM when discussing horsepower, and that is gasoline.  If you recall from your high school physics class, “fuel” is actually made up of approximately one part gasoline to ten to twelve parts of air. To increase horsepower significantly, the engine must burn additional fuel, and because the primary ingredient in fuel is air, we need to figure out how to move more air through the engine.

Is this all starting to make sense?

In the “old” days when everybody relied on carburetors, installing a larger carburetor increased the CFM.  Installing a larger CFM carburetor also required an increase in the gasoline supply. This was usually done by changing to larger jet sizes.

Today, things are a lot easier.  With electronic fuel injection, the on-board computer or “fuel management processor” handles this for us, and much more efficiently than was ever possible with a carburetor.  For instance, all electronic fuel injection (EFI) engines have a series of sensors that notify the computer as to what is happening inside the engine. There are specific sensors that notify the computer if the engine is running too rich or too lean.  With this information, the computer controls the amount of gasoline injected into the engine in order to maintain the correct air to gasoline ratio (not too rich, not too lean) in a real time atmosphere.

So, if we add additional airflow potential to our engine in the form of a larger throttle body, the sensors will notify the computer of the increased CFM and the computer will then add additional gasoline into the engine.  Simple, eh?

In a high performance street type application with an EFI vehicle, there is generally little reason to modify the gasoline side of the “fuel” equation. The stock computer will, in most cases, handle this for us. Most OEM computer systems, fuel injectors, fuel pumps and fuel pressure regulators can handle greater horsepower potential than the stock engine produced.

Our job in the quest for additional HP is to concentrate on the “airflow side” of the equation. And that is where Accufab, Inc. comes in. We design and manufacture one of the most important components in the airflow path, the throttle body. The throttle body is the “door” that the air needs to get through before it can get into the engine. Any air restriction at the throttle body will invalidate almost anything else that you can do to increase CFM. No additional airflow; no additional horsepower, it’s that simple.

Therefore, if you want to increase performance on your EFI vehicle, start by installing a bigger throttle body.

Not all throttle bodies are alike (you knew that was coming, didn’t you?). For instance, all stock OEM and most aftermarket throttle bodies are manufactured using cast aluminum (or pot metal in some cases) to save money. At Accufab, Inc., the cost of the product, while an important consideration, is secondary to the quality of the component. We use aircraft quality, CNC machined billet aluminum, polished to chrome like luster for our throttle bodies. The Accufab throttle body is a work of art, and would look good on your coffee table if it weren’t so effective on your engine.

In addition, we use the most expensive internal components, including sealed roller bearings, heavy-duty throttle shafts and machining to tolerances way above OEM specs. Nothing but the best, to insure a lifetime of trouble free performance.

We know that our customers expect a high quality product, at an affordable price, whether it’s for high performance street driving or all out racing. An interesting side note regarding Accufab throttle bodies is that the 200 MPH all out racecar is going to use the very same throttle body that anybody can purchase off the shelf for their street machines. The race engine may require a larger size throttle body (more CFM), but other than that, all throttle bodies for the same applications are identical. We don’t manufacture beefier or heavy-duty throttle bodies for a race environment and cheaper ones for street use. Other than the different sizes available, all of our throttle bodies are built to the same high tolerances, using the same CNC billet aluminum, the same internal components, and the same attention to detail.

What Size Throttle Body Should I Use?

Bigger than what came on the engine from the factory.

For instance, the popular 5.0 Ford Mustang typically was equipped with a 60MM throttle body from the factory. This equates to a flow rating of 495 CFM. The Accufab 5.0 Mustang replacement throttle body sizes start with 65MM. The 65MM unit flows 664 CFM. This is a CFM flow increase of 34%. The Accufab bolt on replacement throttle bodies are available with units up to 105MM for the 5.0 Mustang.  The 105MM unit will flow 1550 CFM, way more than triple the stock flow rating.  Of course, only a serious race engine could even come close to benefiting from that amount of airflow.

A word of caution here regarding throttle body size. While the throttle body is the most important component controlling CFM, it is by no means the only component. In other words, if you install a large, high CFM throttle body on an otherwise completely stock engine, don’t expect a giant increase in horsepower. Simply put, if the engine is unable to make use of the increased airflow because of other air restrictions in front of or behind the throttle body, it won’t be able to produce much of an increase in horsepower. In the case of a dead stock engine, the larger throttle body probably won’t hurt performance, but it may not help it much, either.

Our tech staff will be happy to work with you in selecting the throttle body size that will most benefit your specific engine combination and driving requirements.

What About Fuel Injectors? Do I Need Bigger Ones?

For most situations in normal high performance street applications, the factory injectors will handle the additional horsepower created when you install a larger throttle body.

Electronic fuel injectors are usually measured in pounds of gasoline per hour (Lbs/hr) at maximum flow conditions or at 100% duty cycle. In most applications, the flow rating or lbs/hr at 85% duty cycle is used. One gallon of gasoline weighs 6.2 pounds.

A typical 5.0 Mustang is equipped from the factory with eight 19-lbs/hr fuel injectors. Some Mustangs are equipped at the factory with 24 lbs/hr injectors.  If you calculate the gasoline flow from the 19-lbs/hr injectors, at full duty cycle the eight fuel injectors would go through 24.5 gallons of gasoline in one hour. That’s a lot of gasoline.  It would take a very high horsepower engine to use that much gasoline, and remember, that’s just about 1/10th of the total amount of actual fuel, considering that you would need 10 to 12 times the amount of air to gasoline to arrive at the correct fuel ratio.  Engines don’t burn raw gasoline. They burn fuel.

But, if you are contemplating the requirement for larger flowing fuel injectors here are a few things to consider. First of all you must remember that we are dealing with both volume and pressure when we discuss gasoline as it relates to EFI, two distinctly different issues. The volume side of the equation comes into play where the fuel pump is involved. The fuel pump (always electric and typically mounted inside or very near the gasoline tank with EFI applications) will need to move a greater volume of gasoline if we are going to develop more horsepower.  Most stock fuel pumps will handle this increased volume requirements, at least up to a point. After that, an aftermarket High Volume Fuel Pump will be required.

The second part of the equation is the pressure side. All (or most) EFI systems have a return line built into the fuel line system.  In essence, the gasoline is picked up from the gas tank and driven forward to the engine (and eventually to the fuel injectors) by the fuel pump. But before it gets to the injectors, it passes through a device called the Fuel Pressure Regulator (FPR). The FPR, by blocking the free flow of the gasoline directly from the pump, raises the fuel pressure.  It works like the nozzle on your garden hose. With no nozzle to interrupt the flow, the water gushes out with plenty of volume, but with little ability to create much of a high-pressure stream.  As soon as you install the nozzle on the hose, the volume is held back but you can now shoot a stream of water quite a distance.

The FPR raises the pressure by creating a restriction, just like the nozzle does on the end of the hose.  As it turns out, there is usually a greater volume of gasoline going to the engine than it can use. This extra volume is re-routed by the FPR back to the gas tank via the return line. To achieve more fuel pressure to the injectors, the FPR creates a restriction on the return line. It kind of acts likes a vice grip on the return line, if you will. The less fuel allowed to return, the more the pressure builds up.

There are now some new vehicles where the fuel pressure is completely controlled by the engine management system (the computer) and a return line is not used. In situations like this, any major adjustment or change in fuel pressure from the stock settings would need to be re-programmed into the computer via a chip.

As you can see, the fuel pressure is a very important factor in determining the fuel flow at the injectors.  Because pressure rises as the square of the flow through an orifice, to double the flow through an injector takes four times the pressure. This is assuming that the injector can actually flow that amount.

The stock factory FPR has a range or window of fuel pressure capabilities built into it and adjusts itself automatically based on engine vacuum. This is more than acceptable for most street type applications but if really high horsepower is needed, such as for racing, a larger, stronger and more adjustable FPR is usually required.

Did we mention that Accufab, Inc. also manufactures heavy duty, adjustable FPR’s for many applications?

But, we initially were asking about fuel injector size, before all this other stuff came up.

And wouldn’t you know, there is a formula for this.  Here it is.

“Maximum engine output, times brake specific fuel consumption, at peak power time, divided by the number of fuel injectors, equals the flow requirements per injector.”

And you thought that this was going to be easy, didn’t you?  Well, it actually is.  Let’s simplify this equation first.

For Maximum engine output, lets substitute “horsepower”.

For Brake specific fuel consumption, lets substitute the figure “0.5” for naturally aspirated engines.

For peak power time lets use the figure “1.175” which is a conversion factor for the 85% duty cycle.

For the number of injectors, obviously it’s going to be “8” if the engine is a V-8.

Let’s assume we are looking to produce 400 horsepower in street trim.

So, we take 400 x 0.5 x 1.175 divided by 8, which equals 29.37 lbs/hr. When we round off the number it looks like 30 lbs/hr injectors would be needed to support 400 HP. But, you should also remember that the engine won’t always be making a “foot to the floor” 400 HP if it’s street driven (unless you want to pay a ton in traffic tickets) so a slightly smaller injector size might be a better overall choice.  A 24-lbs/hr injector size might be more appropriate for a 400 horsepower street driven vehicle.

What About Fuel Pressure?

You must remember that we are dealing with both volume and pressure when we discuss gasoline as it relates to EFI, two distinctly different issues.  The volume side of the equation comes into play where the fuel pump is involved. The fuel pump (always electric and typically mounted inside or very near the gasoline tank with EFI applications) will need to move a greater volume of gasoline if we are going to develop more horsepower. Most stock fuel pumps will handle this increased volume requirements, at least up to a point. After that, an aftermarket High Volume Fuel Pump will be required.

The second part of the equation is the pressure side.  All (or most) EFI systems have a return line built into the fuel line system.  In essence, the gasoline is picked up from the gas tank and driven forward to the engine (and eventually to the fuel injectors) by the fuel pump. But before it gets to the injectors, it passes through a device called the Fuel Pressure Regulator (FPR).  The FPR, by blocking the free flow of the gasoline directly from the pump, raises the fuel pressure.  It works like the nozzle on your garden hose. With no nozzle to interrupt the flow, the water gushes out with plenty of volume, but with little ability to create much of a high-pressure stream. As soon as you install the nozzle on the hose, the volume is held back but you can now shoot a stream of water quite a distance.

The FPR raises the pressure by creating a restriction, just like the nozzle does on the end of the hose.  As it turns out, there is usually a greater volume of gasoline going to the engine than it can use.  This extra volume is re-routed by the FPR back to the gas tank via the return line. To achieve more fuel pressure to the injectors, the FPR creates a restriction on the return line. It kind of acts likes a vice grip on the return line, if you will. The less fuel allowed to return, the more the pressure builds up.

There are now some new vehicles where the fuel pressure is completely controlled by the engine management system (the computer) and a return line is not used. In situations like this, any major adjustment or change in fuel pressure from the stock settings would need to be re-programmed into the computer via a chip.

As you can see, the fuel pressure is a very important factor in determining the fuel flow at the injectors. Because pressure rises as the square of the flow through an orifice, to double the flow through an injector takes four times the pressure. This is assuming that the injector can actually flow that amount.

The stock factory FPR has a range or window of fuel pressure capabilities built into it and adjusts itself automatically based on engine vacuum. This is more than acceptable for most street type applications but if really high horsepower is needed, such as for racing, a larger, stronger and more adjustable FPR is usually required.

6.0L Diesel Elbow Instructions.

Click here to view printable instructions for 6.0L Diesel Elbow. (pdf file)

Modular Crank Trigger information.

Accufab produces two Modular Crank Triggers. One is for use with Electromotive engine management systems (Accufab part number CTE), the other, for any other (stock or aftermarket) engine management systems (Accufab part number CTS). Either can be used on any 1996-1998, 2-valve or 4-valve 4.6L or 5.4L engine. These crank triggers will also fit on other year 4.6L or 5.4L engines PROVIDED that the ’96-’98 chain sprocket is also used. These chain sprockets (Ford part number XL3Z-6306-BA) are interchangeable with all other non ’96-’98 4.6L or 5.4L chain sprockets.

Throttle Body Custom Applications.

Accufab, Inc. does not recommend our products to be used on any application other than what they are designed for.  We constitute such use as a Custom Application.  There is no warranty, expressed or implied, on an Accufab product when used in a custom application.
This article is for informational use only.  If you have decided to purchase our product for use on a custom application, please consider the following before installation.

A throttle body is a simple device with only one moving part, which rotates about 90 degrees.  Under normal conditions, including racing, the throttle body will last a lifetime and NEVER fail.

However, listed below are a couple of non-warranty conditions where a throttle body will fail:

1. A nitrous explosion behind the throttle body (usually in the intake manifold) can bend the blade and/or break the shaft.
2. When a throttle body has been incorrectly mounted on an engine for which it wasn’t designed.

In every case of a broken or bent shaft, it has been as a direct result of the 2 situations above and/or one or more from the following list.  This list contains six non-warranty situations where any throttle body may or will fail:

1. If you have to change (increase) the diameter relationship between the attachment point of the linkage and the center line of the shaft, you may break the shaft.
2. If you have any tension on the throttle cable greater than what is required to overcome the throttle body return spring (with the engine at it’s fully torqued position), you may break the shaft.
3. If you have to remove the built-in stop bracket for any reason, you may break the shaft.
4. If you have to bolt, weld or attach a secondary throttle bracket to the existing bracket, you may break the shaft.
5. If at any time there is not reasonable slack in the throttle cable, even at wide-open throttle, you may break the shaft.
6. If the throttle is pulled open at any angle other than perfectly in line with the throttle linkage, you may break the shaft.

First, let’s discuss the dynamics mentioned above.  On a Ford V8, and most other V8 engines, under hard acceleration the engine torques over to the right (passenger side).  This causes no problems, added tension to the throttle cable.  Also, each of our throttle bodies are designed around the exact requirements, geometry and range of motion of the throttle pedal for the correct application.  What this means is that at full throttle, when your foot is hard on the floor, the cable bracket attached to the throttle shaft on the throttle body is both fully open and not quite touching the built in “throttle stop” on the throttle body.  The cable is NOT under tension, and uses only enough force to overcome the return spring.

Now, let’s look at some of the things racers have done when adapting an Accufab throttle body to a custom application and specifically, to a cross mounted engine combination.

In some cases, in order to get the correct range of motion between the throttle pedal and fully open at the blade, the throttle body linkage geometry has been altered.  This takes the form of several things, including attaching a secondary cantilevered linkage to the original throttle body linkage. Because the new linkage is extended further away from the bearing, more load is put on the shaft, and because the cable attachment points may be further out from the centerline of the shaft, this too can cause increased load on the shaft (sort of like using a crank handle on a Model T that is larger in diameter, to give you more twisting torque).

The next problem that we have seen is that some racers remove the built-in throttle stop on the Accufab linkage bracket.  Because of the design of the throttle blade (slightly elliptical) the blade will NOT be able to go over center, and if you try, it will usually result in breaking the shaft.  The built-in throttle stop is there to keep this from happening.  The throttle stop on the linkage is specifically designed to open the blade precisely 88 degrees, 2 degrees from perfectly vertical.

Finally, the cross mounted engine torques forward under full power (yes, even with solid type engine mounts there is some flex), not to the side as is the case with an engine mounted front to rear.  When the racer is first setting up his adapted throttle body, he will want to insure that the throttle body gets to a fully open (wide open throttle) position, and typically has someone sit in the car pushing the gas pedal to the floor (with the engine off), while he insures that the blade opens all the way.  The problem is that engine torque is not taken into consideration.  As the engine torques forward, it can increase the tension on the throttle cable (like a bow string), and given the typical modifications done to the linkage on the throttle body, eventually, the shaft will break.  The cable or rod used to open the throttle MUST be in line with the linkage and not at any angle.  All modified applications, in most circumstances, will require a pedal stop, to insure that the throttle blade and the gas pedal reach wide open throttle at the same time.

Accufab does NOT have a problem with throttle shafts breaking, which is why virtually all serious racers that know what they are doing use an Accufab throttle body.  We have our throttle bodies mounted on engines, including single and dual turbo engines, making serious horsepower.  For instance:

Ed Thornton’s 3000 HP twin turbo big block Chevy Pro Mod Dou

Sikora’s 2500 HP twin turbo Ford 10.5 Outlaw Mustang

John Mihovetz’ 2500 HP twin turbo Ford 4.6L Pro Street Mustang

Clint Hairston’s 3000 HP twin turbo small block Chevy powered Pontiac

The racers listed above and many others have taken the time to understand the dynamics involved with adapting our throttle body to their racing applications.  Furthermore, they have NEVER broken a throttle body shaft.

These are the same throttle bodies available to everyone, all out race cars and street machines alike.  Accufab does not make separate throttle bodies exclusive to racing.  When installed correctly, the shafts do not break.  It’s not difficult to adapt a throttle body from one application to another as long as you understand the dynamics and geometry involved.  If you follow these guidelines, you should not have problems with breakage. 

Vent Tube Restrictors. Installation Instructions.

There are three basic styles of Accufab’s VENT TUBE FUEL RESTRICTORS.  All are the same internally and work the same. 

 The standard units (anodized black) can be used on any application. 

 The “Off Road” versions (anodized red) can also be used on any application, and have connectors on the top for racers that link the vent tubes together with a ¼” rubber hose.

 The Marine units (anodized blue) work exactly like the standard units, except that instead of venting straight upward, the vent is downward at an angle, so that any fuel that might dribble out will go right back into the carburetor, as required by the U.S.C.G.

Installation procedures are the same for all units.

 The VENT TUBE FUEL RESTRICTORS are designed to slip over any standard 5/16-inch vent tube, which are found on the vast majority of racing carburetors.  The vent tube MUST be at least ½-inch tall, from the base to the bottom of the diagonal cut at the top.  The vent tube may be taller but it cannot be shorter.  If your vent tube is too short, you will need to acquire a longer vent tube from your carburetor manufacturer and follow their vent tube installation instructions.

 The vent tube MUST have a straight cut on the top.  If it has an angled or diagonal cut at the top, it must be cut off flush.  It might be better to remove the carburetor and hold it upside down while making the cut so as to keep any metal dust from entering the float bowls.  Make sure that the top of the vent tube is smooth at the top after the cut and has no “ridge” which may impede the installation of the VENT TUBE FUEL RESTRICTORS.

 Slide the units over the vent tube, push them down as far as they go, and tighten using a 9/16-inch end wrench on the center section and another 9/16-inch end wrench on the bottom.   Do not over tighten.

Because dust and other contaminants may affect the internal operation of the units, it is suggested to periodically remove and wash them in some type of carburetor cleaner. 

For any questions or additional information, feel free to call Accufab at (909) 930-1751.

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