Aspirated/Venturi Kits

So if you have made it to this page it is because I have successfully peaked your interest. Hopefully on this page I can show you how the venturi/aspirated kits work and their benefits to using one verses an injected type of kit.

First some of the basic vocabulary

Venturi – This term is used to describe method of fuel delivery used. Venturi is a specific type of mixer that reduces a flow of material (liquid, air, or gas) so that immediately after the disruption a second material is introduced into the original stream that compensates for the original disruption in the flow. This creates a mixing space immediately after the placement of the venturi for the two components. The quantity can be adjusted from the size of the venturi and inlet of the secondary inlet.

Aspirated System - It ultimately means that you are creating an environment similar to a carburated system where the fuel and air are mixed in the physical intake manifold.

Fogged System - Again we are referring to a carbureted system as mentioned above where the fuel and air are mixed in the intake manifold. Sometimes also referred to as a wet manifold system.

CNG – Compressed Natural Gas.

So how does this system operate?

For this type of compressed natural gas or CNG system, it is mixed with a venturi that is placed somewhere along the intake tube. For most vehicles it functions best the closer it is to the butterfly valve on the intake manifold. I say most because there are vehicles that use a bypass valve before the butterfly valve that is used for idling purposes. For these vehicles you need to place the mixer before that bypass intake port to allow sufficient fuel mixing to occur. The primary vehicles that I know of that have the exception are the F-150/250/350 gas trucks. Nearly all newer model vehicles have an Idle Air control module but unlike the fords they pull the air from a port nearer to the butterfly valve to allow for sufficient air for idling purposes.

After the gas is introduced behind the venturi it is mixed and continues to mix as it enters the intake manifold then into the cylinders. This system is how the original CNG systems were based. It works. It is very simple in design and as time has proven it just works.

It will require all of the wiring that I have mentioned in the wiring page and it primarily uses the O2 signal to compensate for fuel amounts at and just above idle speed. The other electrical components consist of either a Closed loop or Open loop feedback controller. These Are used to manipulate your current petrol/gasoline injectors to shut them off and give them a signal that they are running fine without actually injecting any fuel. The difference between a closed loop and an open loop are that the closed loop doesn’t give an adjusted output for the fuel consumption. These controllers can provide feedback to the natural gas system, specifically the open loop systems and allow for minor fuel adjustments when wide open. Other wise they allow a fixed amount of fuel to be released depending on the regulator settings.


The Change over switch is located in the cab of the vehicle and will provide a display for what fuel the vehicle is operating on and what the current pressure of the high pressure tanks are at for a fuel gauge. It can be toggled between fuels without damage to the motor at any time.

The hardware

  • High pressure fuel lines that feed into the pressure regulator/s. These supply the CNG to the regulators from tank/s.
  • The regulator takes the pressure from the the tank and reduces it to working pressure to be released just behind the venturi and mixed with the air as it enters the intake manifold.
  • Low pressure fuel line. This takes the now decompressed fuel at the working pressure and attaches to the venturi. There is typically a step motor in between the regulator and venturi.
  • Step Motor. The Step motor provides small adjustment during idle and full throttle to the low pressure fuel line as the fuel is supplied to the venturi.
  • Coolant lines. There are coolant lines that are connected through the heater hoses to the regulator. These provide coolant to the regulator and heat up the natural gas. This is required because of the heat loss that occurs from the fuel decompressing. These coolant lines prevent the regulator from freezing and maintaining a working temperature in the regulator.
  • Pressure Gauge. This can be mounted in line with the high pressure tubing or mounted to the regulator. This will provide information for the fuel gauge inside the cab on the change over switch.
  • Change over switch. This will be located in the cab of the vehicle and will provide a display for what fuel the vehicle is operating on and what the current pressure of the high pressure tanks are at for a fuel gauge. It can be toggled between fuels without damage to the motor at any time.
  • Mounting hardware and fittings. In the kit you purchase it should come with the necessary mounting hardware to affix these items in place in your vehicle. This is left to your discretion or the discretion of the installer if you choose to pay one.

Things to consider/Tips

  • Leave the regulator/s semi accessible, there are adjustment dials on the regulators to adjust for idle fuel flow and high end fuel flow. Make sure you can access these dials for tuning purposes. Try to mount them as close to the venturi as possible. It will still operate if you have to mount it and the low pressure lines have to span a distance but it will operate better if it is close to the venturi.
  • Mount the stepper motor as close as possible to the venturi. This fine tuning will be more responsive the closer it is to the venturi.
  • Make sure every thing that is mounted aftermarket with this kit is completely free and tied up well that it won’t become tangled in the moving parts. For instance, I was asked to fix a system that was installed on a Chevrolet suburban. What happened is the installer never tied up the extra slack in the electrical connections and several wires drooped down and into the steering stem. These wires got caught one day and as the customer turned it entangled these wires and pulled them from their connections. I simply had to reconnect them and secure them out of the way of the steering column but it could have been prevented and the damage could have been worse.
  • If you are installing a venturi on a Ford truck. Locate the Idle air control bypass hose and either relocate the hose to a position behind where you decide to install the venturi or install the venturi 3-4 inches before the bypass hose. This will allow it to idle smoother and transition from idle to full throttle smoother or with out lag.
  • When installing the venturi get a high temp RTV/silicone to place around the venturi. The system won’t run properly if you have any leaks around the venturi!
  • Purchase a high flow aftermarket air filter at minimum if not an entire intake system. This will reduce the amount of air flow that is restricted from the venturi installation and will help recover some of the loss in power.
  • A tip for regions or areas with emissions. If you live in an area with emissions testing and you install or have a CNG system installed on your vehicle it will likely fail the emissions test because it isn’t really an emissions test.Surprised Its really a scam!  They are simply plugging into your OBDII and checking for any codes to see that your vehicle is operating without any error codes, instead of actually pulling the particulate count from your exhaust. (They do this but it isn’t decided by the counts your vehicle puts out.) Since the CNG system will more than likely cause the lean error code to go off it will fail the test with that code. The way around this is simply by purchasing an OBD scan tool from your local autoparts store (the cheap one that can clear codes). Clear the code and drive on regular gas for at least 50 miles before having the emissions tested. Leave it on regular gas until you pass the test then switch it back over to CNG. (it sounds silly to burn a dirtier fuel and pollute more in order to pass the test but thats is what you have to do.) The reason for this is because they need to have a history in the cars ECU to reference if it is operating correctly and clearing the codes immediately before going won’t give them the history they need.

High pressure tubing and fittings. After you have mounted your regulator and tank you will need to link it to a fill nozzle and the regulator. When you are attempting to plumb the system you need to spend the time to get the angles correct with the tubing. The more time you spend with lining up the tubing to where it will be connected the first time the more time you will save yourself from leaks.

  • Tip one – If you are using the 6mm zinc plated tubing. check to see how soft the plastic covering is. If it is hard or brittle, send it back and request some newer tubing. It isn’t worth the time you will spend trying to keep it from leaking.
  • Tip two – Do not use pliers, of any sort to attempt to bend your tubing to line it up. Using them will create a flat spot in the tubing that will be very difficult to seal. Use your fingers. Give yourself atleast 2 inches of a straight shot into the fitting to line it up. Make sure it lines itself up without any external force required. Spend the time and line it up correctly, it will save hours of time trying to fix the leak you will cause if you don’t line it up. I will try to post a video of this later but again get it lined up perfectly without any external pressure and don’t use pliers or a tool to straighten it. You will only be causing yourself more of a headache.

Some of the Pros and Cons of the venturi style system


  • They run. It is a proven method for conversion to natural gas and they run.
  • Very simple mechanics of how the system runs. Fewer parts than the injected systems and less install time.
  • Less Expensive than the injected style systems which allows for a quicker recovery in fuel savings.
  • Can be electronically tuneable depending on the system and the program if it has one.
  • Part replacement is fairly inexpensive. Most common part to replace is the step motor ($20-$50).
  • You aren’t burning petrol/gasoline and are burning a clean fuel with nearly zero emissions.


  • Can have rough spots in the RPM spectrum. Little hiccups or delays in throttle response.
  • Noticeable power loss from regular petrol/gasoline.
  • Less efficient in terms of fuel consumption as opposed to the injected systems. (very minor)
  • Some Venturi systems aren’t tune-able. They don’t have a program that allows the user to make minor adjustments in the program itself to compensate for their specific vehicle.
  • reduces air flow when running on regular petrol/gasoline because of the venturi that is installed.
  • Probably cause your check engine light to come on because you will have a “lean signal”. Very common and it won’t hurt your car.

Overall I like these systems for earlier make and model vehicles. You can’t contest the fact that they run and by running at least this system you aren’t burning regular petrol/gasoline and you are saving money and you are not producing the harmful emissions and contributing to pollution. When choosing a supplier for a kit make sure they have been in business for a while and you will be able to ask questions. There are a couple places i’ve seen that specifically request you to not bother them for technical questions. I think this isn’t a good sign because they should be willing to help customers trouble shoot when ever possible.

I hope you have found this helpful and it provides any input you were looking for. Best of luck on your install.