Frequently Asked Questions about CNG Conversions

Frequently Asked Questions about CNG Conversions

Q. Do I get the same fuel mileage on CNG?

A. The mileage will be close, the sequential systems get the best fuel mileage since they are the most tunable.

Q. How many gallons of Natural Gas will my vehicle hold?

A. Unfortunately the size and weight of a CNG tank is the most misunderstood aspect of CNG conversions.

A 11.4 gge (gasoline gallon equivalent) type 1 (steel) tank may only have 7.52 usable gallons at 3000 psi see explanation below

Important: The capacity of any tank is an estimate, many variables such as temperature, inlet pressure, condition of the compressor and atmosphere pressure will determine the amount of natural gas in the tank. A conservative way to calculate how much natural gas you will be able to fill is below. (this is also an estimate and is not always accomplished):

11.4 GGE of the tank x 0.66 @3000psi inlet pressure = 7.52 usable fuel

11.4 GGE of the tank x 0.83 @3600psi inlet pressure = 9.46 usable fuel

This 11.4 gge type 1 tank is 16” x 49” and weighs 321 lbs.

Tank types

Type 1 Steel (least expensive, most heavy)

Type 2 Steel with fiberglass wrap ( a little more expensive, still heavy)

Type 3 aluminum with composite shell (lighter, least common, expensive)

Type 4 Plastic inner liner with composite shell (lightest, most expensive)

Placement of tanks,


The most common place to put tanks in trucks are in the beds, some may go underneath but will be small and usually there isn’t much room under a truck.


If it is a work van you may but the tank anywhere in the cargo compartment, all lines must be vented to the outside. Family vans will usually put the tanks in the rear.


The tank must go in the trunk, the smaller the car the smaller the space.

As you can see a CNG tank is about twice the size of a propane tank for similar gallons.

Conclusion: To run CNG you must give up trunk, luggage or hauling space.

Q. Will I have a power loss?

A. Most CNG conversions will have a power loss but the fuel savings will make up for it. Aspirated systems may have more power loss than Sequential since they are less tunable. Some conversions have no power loss.

Q. Will I get a check engine light?

A. This depends on the system type and vehicle, as stated above a Sequential system is more tunable and usually has fewer check engine lights. When converting a gasoline vehicle to CNG you are using a fuel that was not intended for that particular vehicle. CNG needs higher compression and advanced timing. CNG still works fine in a gasoline engine but the engine monitoring components are looking for gasoline parameters, thus you may get check engine lights.

Q. Isn’t it illegal to convert a vehicle to CNG unless it is EPA certified?

A. This question as to whether or not a CNG conversion is “illegal” I guess it depends on what a persons definition of “illegal” is. Another question is if something were “illegal” is there any enforcement of that law. Is it illegal for a OEM (original equipment manufacturer) to sell a new vehicle that is not emission compliant? Yes they test their vehicles so they will run clean throughout their useful life (100K, 120K). Do we as vehicle owners need to comply with these new car standards? In those states with emission testing a vehicle will be tested annually or semi-annually. But is it illegal to run a gasoline vehicle on natural gas? Who knows? The shops who do EPA Certified conversions on new trucks seem concerned enough to badmouth aftermarket conversions whenever they can. Does the EPA feel concerned about aftermarket conversions?

I have written the “EPA enforcement office” asking if they have ever prosecuted and fined anyone for converting a vehicle to natural gas, and I am still waiting for their answer.

On numerous occasions I have asked representatives of the EPA if anyone has ever been prosecuted or fined for an “illegal” conversion, they answer no. The presumption that a conversion is “tampering” or “running dirty” is just a presumption, they have no proof. Even if the vehicle was running a little dirtier is that a crime, there are millions of vehicles on the road that are out of tune, running speed equipment, missing catalytic converters, etc., etc..


Is a CNG conversion illegal in and of itself? Does a vehicle run dirty if it is converted to natural gas? Does the EPA have CNG conversion cops running around handing out fines? The answer to the first question is no, the answer to the second question is maybe, but the answer to the last question is a big NO.


Q. Will I be able to make back my investment of the conversion?


A. Yes you will be able to make back the investment eventually but why should that be a question? When you paint your car or do any other improvement do you need to get that money back? Most systems are universal anyway and can be transferred from car to car. Converting a vehicle sometimes is the only way a person can afford to keep driving their vehicles.


Q. Are your systems EPA certified, will I get a tax credit or rebate?


A. EPA certified systems are only available for new Ford and Chevy trucks, they cost $15k to $25k. Tax credits and rebates are tied to EPA Certified systems. No my conversions are not EPA certified.





This entry was posted in Aftermarket converters, Automotive, CNG conversions, EPA, Government, Green, mechanics, Regulation. Bookmark the permalink.

3 Responses to Frequently Asked Questions about CNG Conversions

  1. Larry says:

    I am Looking for Type 2, Type 3 or Type 4 tanks that are no larger than 14″ diameter x 35″ can any one help if so contact me at

  2. Hy here you can get your all answers visit Here.

    Thanks for this nice post.

  3. Pingback: Oldies but Goodies, CNG Articles from the past… |

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