Community Speak: Pros and cons of installing a CNG kit in a petrol automatic?

With the recent hike in petrol prices, many petrol car owners are looking at alternative ways to bring down their running costs. One of them is obviously converting the car to CNG (compressed natural gas), which is much cheaper than petrol and just slightly cheaper than diesel. How will CNG fair in a car with an automatic transmission?

Latest news! Honda City CNG-ready sedan launched! Click for full details (24 October 2012)

CarToq member Varu Var says he wants to convert his Honda City automatic into CNG by installing a sequential CNG kit in his City i-vtec automatic. By doing this, he wants to know what the pros and cons could be.

Here are some of the replies from CarToq experts and community members.

honda city front left
Photo: Honda City automatic is a good candidate for CNG conversion

CarToq expert Roshun Povaiah says, “Pros are obviously the low running costs of CNG (even after the price hike). Cons are a loss of power and drivability in the City. Also make sure you get the conversion done from a reputed garage. There will be higher wear and tear on the engine. Make sure you drive it on petrol for the first few minutes every day at least, till the engine warms up before switching to CNG.”

Impact on performance

CNG in cars reduces the total power output by about 15% and reduces the torque as well by a similar amount. In an automatic car like the City, this can affect performance in weird ways. The Honda City makes 116 bhp of power and 146 Nm of torque from a 1.5 litre petrol engine. On CNG, peak power output can come down to about 99 bhp or so, which is slightly lower than an SX4’s output, but still more than the regular petrol Linea’s.

CarToq expert Shreyans Jain says, “Drivability does reduce a bit but as your car is an automatic, it will not be much of a bother as you do not have to shift gears anyway.” He has a point. An automatic won’t really hamper drivability too much, but shift points can change and will take some getting used to.

CarToq expert Rishabh Nair, advises against converting an automatic to CNG. “I would advise you against getting CNG in an automatic car. There is a certain amount of loss in power when the car is driven on CNG. It might not work very well with your auto box. Although you won’t have to shift gears your car may not downshift when you need it to,” he says.

Shreyans agrees there is an impact on performance, but also says, “I know a few people who have CNG kitted automatic i10s. I have driven them myself and there are no issues whatsoever as long as you are not in a hurry.”

Impact on running cost

However, it is hard to ignore the impact on running cost and the convenience value of the City on CNG. As Shreyans points out: “In any case, the City automatic comes with paddle-shifts so that is not going to be an issue anyway. Frankly, a CNG automatic is the best combo for regular city driving if you ask me. All the convenience of the auto box with the running costs of CNG. It’s like having your cake and eating it too.”

On petrol, the City’s running cost, assuming a mileage of 13 kmpl works out to Rs. 5.62 per kilometer. However, if it’s run on CNG, and taking a very conservative estimate of 15 km per KG of CNG, the running cost works out to just Rs. 2.48 per km, which is less than half the cost compared to petrol.

Final take

Even if you factor in higher maintenance costs and slightly lower performance, overall it does seem like a good bet to convert the City automatic to CNG.