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NaturalDrive CNG Retrofit for 2008 Chevrolet Impala Receives EPA Certification

The US Environmental Protection Agency (EPA) has certified NaturalDrive Partners, LLC’s dedicated compressed natural gas (CNG) retrofit of 2008 Chevrolet Impala sedans powered by 3.5-liter and 3.9-liter V6 engines in models LS, LT, LTZ, as well as law enforcement packages 9C1 and 9C3.

The retrofitted CNG Impala reduces NOx and CO emissions more than 50% compared to gasoline the gasoline versions, and offers about a 15% reduction in CO2 compared to gasoline. With the 3.5L engine, fuel economy is 19 mpgge city and 30 mpgge highway. The retrofit on the LTZ model also leverages GM’s Active Fuel Management (cylinder deactivation) for superior fuel economy.

NaturalDrive’s retrofit package includes a compressed natural gas sequential digital fuel injection system and 10.4 gasoline gallon equivalent storage in Type 3 composite fuel cylinders. An additional optional cylinder provides a total of 13.0 gge storage, for a maximum highway range of more than 375 miles @ 3,600 psi. The 3.5L engine delivers 212 hp and 190 lb-ft of torque.

After conversion the CNG Impala offers 14 cu. ft. of cargo volume.

The NaturalDrive retrofit recalibrates the factory powertrain control module (PCM) to provide exceptional performance with low emissions while retaining all of the engine diagnostics and scan tool capability found in the original gasoline configuration. A new pressure regulator system design allows low pressure natural gas to flow to the engine using existing GM fuel lines while high pressure fuel is contained in the rear of the vehicle in lightweight cylinders. Since Chevrolet Impalas are already designed to run on E85, engine seats and valves are hardened for excellent long term durability while operating on 130 octane compressed natural gas.

The retrofit requires no additional wiring, no cooling to be run to the regulator and minimal tubing to be installed on the vehicle. Authorized conversions can be installed in less than 45 minutes.

NaturalDrive’s 2008 CNG Impala is available now via authorized installers in Oklahoma, Utah, Arizona, Alabama, Colorado and Indiana, with Texas and Florida opening soon. EPA certification for model year 2009 is expected to be complete by year end.

Oklahoma State University (OSU) is scheduled to purchase 10 of the Impala CNG sedans. OSU President Burns Hargis already has said the university plans to build a CNG fueling station on its Stillwater campus.

NaturalDrive is also working on the certification on the 2008-2009 Chevrolet-GMC Suburban-Yukon XL, Tahoe, Yukon, Chevrolet Avalanche and the Chevrolet-GMC 1/2 ton pickups with the flex-fuel 5.3L engines, according to co-founder Kevin Fern.


Alex Kovnat

If one can demonstrate a redeeming social value (i.e. reduced carbon monoxide AND dioxide, lower NOx) to using natural gas instead of gasoline, than perhaps our government should offer income tax rebates to users, especially businesses whose vehicles operate mainly within a limited region, who volunteer to convert their pickup trucks, limousines, and other vehicles to natural gas operation.


With so much CNG in the USA- I am dumbfounded as to why CNG-powered vehicles are NOT ubiquitous on our roads!

Picken's plan (which is far from perfect) calls for a massive shift from foreign-oil based transportation to domestic-CNG based transportation.

Hey, more money stays local (God knows our economy needs it) and less goes to our buddies like: Ahmedenijad and Hugo Chavez. (btw- Hugo's latest is inviting the Russian military to play in our back yard)

Where are all the CNG-refueling stations?


The key is to keep oil as a choice.
Make cars that run on both CNG and gasoline.
But make oil/gasoline SECOND choice that is. That way no one will have range anxity.

Love the thought of filling my car up with CNG in my own garage. Everyone leaves home with a full tank.

john mcgovern

The near future for Natural Gas (methane) promises a fantastically renewable fuel, especially for metro areas, where organic matter, such as food & fecal waste, is concentrated. Both of these waste streams, when decomposed without oxygen, produce methane. This idea of waste equals food/fuel is a premise of sustainability, astutely outlined in W. McDonough's classic, 'Cradle to Cradle'.

@Alex: Yes, emissions reductions are critical and CNG/LNG delivers, especially in the area of fine particle pollution, the bane of many metro areas, natural gas reduces fpp vehicle emissions to nearly zero. Definitive info @


Why aren't the US automaker jumping all over this? Without the huge costs and risks of making plug-in hybrids work, they could convert existing models to CNG or dual-fuel with minimal effort.

Except CNG AND Gasoline (dual use) means nearly no cargo area except in very large vehicles. Also CNG refueling terminals are basically non-existant (unless a local taxi fleet owner is willing to let you fuel up at their station).

Natural gas at the house + some type of refueling station (at home) meets some of the same problems as a pure EV in that you have to go home to refuel.

If you make a dual fuel vehicle you end up compromising on one or both fuels and have a less efficient engine overall. I bet a 3.5L tuned specifically for CNG could get better gas mileage and horsepower/torque (maybe at a cost of higher NOx emissions than the present tuning provides).

Alex Kovnat

Micro Batman suggests that cars should be designed to operate on either compressed natural gas or gasoline, with CNG as first choice.

My view: No Can Do. Natural gas operation already compromises available room in the trunk, and demanding the kind of "flex fuel" capability MBM suggests would make matters worse. And besides that, if you require the engine to operate on gasoline as well as CNG, you can't take full advantage of the latter's higher octane rating.

That is why I believe compressed natural gas conversion programs should focus (at least at first) on non-personally owned and operated vehicles like limousines, school buses, government (state, federal, local) motor pool vehicles and others, which operate mainly within a defined region. Within such regions, it would be easier to provide CNG refueling facilities.

Since "compressed" as in compressed natural gas means 3600 psi, it would be best to locate refueling facilities near a natural gas pipeline, where the gas is already at high pressure.

I know there are those who advocate filling CNG-vehicles using a natural gas compressor located in one's own garage, tapping into the same gas line which feeds one's home heating furnace and clothes dryer. Problem is, you then have to use an electrically-operated compressor to to compress the gas to 3600 psi or more, thus increasing the total system's energy consumption.


I think our #1 priority as a nation should be to get off foreign oil, and I want to do my part. I also like the fact that the exhaust pollution (that which causes SMOG and respiratory problems, not CO2) is less than a hybrid. Does anyone know how much that kit costs and how much it costs to get it installed?


Alex K is absolutely right.
Since the Obama transition team is requesting suggestions and questions about energy policy, I have recommended to them the following:
Retrofit all diesel buses (school, public transport, and non-profit owned) to natural gas.
This would
1. be relatively inexpensive per vehicle,
2. be used by vehicles that have a central parking location and therefore refueling location,
3.use Domestic energy,
4.reduce emissions,and
5. create a jobs program for people who build and install the systems throughout the country.


JMartin makes good suggestions. CNG is best suited for fleet buses near term. Better if they are supplemented by high cycle batteries in a hybrid drive trains. The lithium titanate NanoSafe batts and competitors are best but a test of Zebra might be good. These buses can then be recharged at route end points - increasing AER and dramatically lowering fossil fuel consumption.

The problem with CNG conversion for light duty vehicles is they must meet strict safety standards mandated by DOT and EPA. There are very few certified CNG conversion shops around today for this reason and those that are will charge in the $8-12K range for certified (without which vehicle is un-insurable) converts.


A few comments....

What about CNG and E85? Doesn't E85 have high octane? I'm not sure that optimization (a whole new engine for a new, marginal fuel source) is worthwhile at this point. How much MPGs would really be lost? A bigger issue in any case would be a vehicle design that could accommodate the tankage (like Ford's hydrogen vehicle that incorporates the tanks under the rear seat).

A compressor is needed for home refueling, but the cost of electricity is tiny. And even if it wasn't, it's still worthwhile as it is being used to displace oil. A specious argument from Alex in my opinion.

If the automakers had taken the time to make a reasonable flex-fuel CNG/gasoline vehicle that they have WASTED on hydrogen, we'd have a very good platform by now.

Also, one must remember that these can be fueled via biomethane as well, so it's not just about substituting one fossil fuel for another.

Henry Gibson

Dual fuel cars have been around for a long time. CNG can be integrated into a vehicle with many small tanks. There is not any theoretical weight advantages for large pressure tanks. You can even make yuor own NATURAL gas, methane that is, from all kinds of waste material including sugar bought from a local store. ..HG..

Roger Pham

More BANG for the BUCK to convert fleet vehicles or heavy-duty vehicles to CNG-only operation at the present.

Once the momentum is going strong for CNG-commercial-vehicles, with CNG filling infrastructure sprouting up sufficiently, we will see more people naturally want to acquire a privately-owned CNG car or converting their existing gasoline vehicles.


The problem with CNG is that is finite. Trading one finite source of energy for another would not lead to a solution. Our natural gas resources provide the U.S. a way to ease off of gasoline by powering larger fleet vehicles and equipment that need the power electricity cannot provide. I thought the article about using computer modeling to test emerging technologies for consumer vehicles viability was promising. A great deal is lacking from our understanding of resource flows for materials use in making the next generation of consumer vehicles. It is the stroke before midnight. We cannot afford to make the wrong choice. Be mindful of what you preach.

CNG can be co-fired (with minimal engine modification) with diesel in existing diesel engines. A small amount of diesel is used as a liquid spark plug to ignite the gas.

A turbo diesel hybrid with electric launch assist, start / stop, regenerative breaking and this dual fuel system would be responsive to drive, low emissions, good fuel economy. As batter technologies improve it would be easy to add 10 - 50 miles all electric range (which would replace about half to 80% of all miles driven)

It would make use of domestic natural gas and would open a market for producing bio-gas for transportation (much better EROEI than corn ethanol and can make use of non food crops and waste, as well as returning the digestate to the soil.)

Hydrogen will never be a major energy player, but 5-10% by volume of the gas can be used with natural/bio gas in existing infrastructure and the electrolysis could provide a fast responsive dump load to help balance the grid, the oxygen from the electrolysis can be burnt with gasification of coal in a combined cycle with solar steam assist.

Natural gas can also be stored in an adsorbed state in a carbon membrane without the need for high pressure tanks.

Niel Young's LinkVolt has a natural gas rotary engine (mazda) serial hybrid installed in a 1959 Lincoln. Gets 70 mpg apparently.

Sorry that link should be


130 octane fuel and a 3.5 liter engine to move an Impala!! Not the optimal solution.


Here's a news flash. CNG was used quite extensively in public transportation during WWII, at least in my community.


Another news flash, certified CNG conversions as of last year quotes for 6 cylinder engines run from $10k - 15k per vehicle. Insurance costs increase also. BUT, in some States there is a tax credit of up to 50% conversion cost. So you could get this Impala conversion down to $5k per vehicle.

The other caveat is CNG availability in your area. There are several web sites that track CNG stations according to zip code. Unfortunately for many of us driving 40-50 miles to the nearest CNG pump does not make eco-sense.

And then there's the conundrum that replacing gasoline with non-renewable fossil CNG, is a troubling choice for greens.


Common people, this is not a technological issue, it is a control issue.

Australia has had dual fuel vehicle’s, made by Ford and GM for YEARS. The United States and Canada should have the same, regardless of cost, octane, convenience, or safety, it is possible now.

I don’t know this company, but they better explain the laws that prevent them from making the vehicles dual fuel!!

We need to have dual fuel NOW. Do not let yourself be controlled by corrupt politicians and auto companies. Demand the right answer


I think the ultimate vehicle (end game) is a PHEV powered with CNG and small liquid fuel tank (gasoline or E85). Such a vehicle can be powered with electricity, natural gas, biomethane, gasoline or ethanol. Liquid fuel allows the vehicle to work with extant infrastructure while NG filling stations are added.

Leave biodiesel to our trucks and aircraft.

Some vehicle design is needed to accommodate space needed for tankage and battery packs.

All-electrics have only a niche market unless and until they can be recharged quickly, which is probably technically infeasible.

Hydrogen is hopeless.

We should work toward developing the here and now viable, instead of pipe dreams.

Max Reid

Already there is a fit like this for E85, now CNG, its very good. I hope the fuelmaker sell the CNG refuelling device to households, so that many people can make use of it.

Oil production is any way declining and its time to jump out.

Dick Duffy

The selling point for bi-fuel vehicles (gasoline/CNG)is that they provide peace of mind during a period where CNG refueling stations are scarce. Working for a gas utility promoting NGVs, I must admit I was dead set against bi-fuels. Many public and private fleets using CNG can tell you that their drivers - if not under threat of disciplinary steps - would always use the gasoline. With the recent run-up in gasoline prices, that was no longer a concern. There will be a day when gasoline and diesel will climb again in price...never to return to today's prices. Then, when it means significant savings, you will see natural gas flowing like water.
Although it's a little nit picky, I would say that natural gas (methane, at least)is, technically, a renewable fuel. Microbial organizms found in shale recently have demonstrated they eat shale and pass methane gas. And, although seemingly impossible to harvest or produce, methane hydrates are estimated in quantities that are astounding: some estimates are 3,000 years supply of methane.
I agree with the cargo space issue when it comes to extended range packages. This is simply because no carmaker selling vehicles in North America have taken the time and spent the money to build a platform desinged for sufficient CNG storage tanks. They cram tanks onto existing platforms. The funny thing is that they are willing to design completely new cars for EVs. Trunk space (and bed space on pick-ups) should be considered sacred to maintain.
I'm happy to pontificate further, but fear I'm boring most everyone.

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