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# Thread: Proof of Zero Savings on CNG

1. ## Proof of Zero Savings on CNG (In City)

In City
My car does 100 km in 7.6 kg of CNG
and it does 100 km in 9 Litrs of Petrol
i drive about 500 km in complete month

So i save 9*108 - 7.6*75 = 402 Rs for every 100 km if i use 100% CNG
so in a month i could save 402*5 = Rs 2010/- Per Months

It is not possible to run your EFI car on 100% CNG, i.e No petrol At all
I assume that 5% of fuel is consumed for (Starting and Initial Idling) in any case = 2010*0.95 = Saving 1909/- Rs per Month

But actually in Current CNG outages maximum i managed to get 55% cng and 45% petrol (it is even worse nowdays)
So Savings = 1909 * 0.45 /0.55 = About Rs 1500 Per Month

Now I also waste Rs about 10 km for every CNG Refill from nearest station, which means (if 10km) 5 km of petrol wasted and 5 km of cng wasted = about 60 Rs of Petrol and 40 Rs of CNG and i do about 400 Rs per month WASTE )

So Savings = 1500 - 400 = 1100 Rs Per Month

to mention the idling waste at CNG station waiting in long lines)
about 40 minutes to 1.5 hour i think about 50 rs of fuel is wasted per fill

So Savings = 1100 - 4*50 = 900 Rs Per Month

Now if i am cranking my ignition at every 5 minutes for about 1 hr or so my ignition system is worn out for about 12 turns extra , this wear tear will cause its life reduced, Your Cylinders life also reduces while working on CNG. Lets keep Rs 500 to cover this cost.

So Savings = 900 -500 = 400 Rs Per Month

Now if i have only 4 fills possible it wasted my precious time of about 3-4 hours per month. If i pay any person to go to cng station and fill my car for about 1 hour he would take at least at least RS 100 for it per hour

So Savings = 400 - 400 = ZERO

So i decided to Forget about this CNG stuff and maybe in future i may be able to get a fuel efficient car and also i would try to reduce my driving a bit and Chill

2. Originally Posted by Tanveer_1
@bilalahsan your calculations are tailor made to suit yourself, others might not have similar calculations.
it will not suit to anyone who does not take into account waste and long term effects. If anyone says that he is getting 100% cng and driving with 100% efficiency and has a CNG compressor in his garage and has no value for his and others time, I would say he is ignoring reality.

3. My car goes 200 kms in every tank of CNG i.e. around 7.5 kg, do the maths now and get your car tuned :-)

4. Originally Posted by bilalahm
My car goes 200 kms in every tank of CNG i.e. around 7.5 kg, do the maths now and get your car tuned :-)
Must be doing 300+ on highways 😵

5. Nopes 260 is the current best on GT road on speeds not exceeding 110 km/h. A big thing for some with tiny engines generating hilarious outputs requiring high rpms, not for some though :-)

6. Originally Posted by a_n_memon88
Workshops dont know a crap about tuning. When my car was tuned on CNG by mechanics it used to give 100-110 but when I touched it with my hands the average is now 125-135. You need to have proper timing as well as minimum gas required to run the engine. What mechanics do is tune the engine to run at 5000rpms. I have tuned my engine so that it does not go beyond 5000rpms and on highway the car does not cross 120 on CNG, but on petrol it goes to 6000rpm in 3rd gear and 160+km/h. So it all depends on how you want to use your engine
As much as I admire your insights on self diagnostics and maintenance, I would like to highlight here is that you are actually leaning out the AFR (with CNG) to help get that extra mileage. That lean burn causes general engine burning temperatures to rise up which gives high probability of burnt exhaust vales if not blown gaskets.

No no. I am not speaking of theory. See any CNGed cultus especially those Carby ones. The head rarely lasts a 100k. and we have valve jobs pilled up. Whereas you see "COMPANY OPERATED/ COMPANY MAINTAINED" all petroll driven suzuki's pulling 175~250k. Co-incidence???

My humble advice, dont choke your vehicle under load on CNG. WHat those workshops do is prevent the possibility of lean burn under Wide Open Throttle.

@bilalahsan

Its about time, about time someone came up with detailed break up of why CNG is a big no for a responsibly driving City consumer.

For highway surfers, and for short term vehicle owning businessmen (claiming lack of CNG is a loss whereas in actual its a reduction in PROFIT), CNG is like DOPE. Once hooked, its hard to get off.

7. Originally Posted by rustam54
As much as I admire your insights on self diagnostics and maintenance, I would like to highlight here is that you are actually leaning out the AFR (with CNG) to help get that extra mileage. That lean burn causes general engine burning temperatures to rise up which gives high probability of burnt exhaust vales if not blown gaskets.

No no. I am not speaking of theory. See any CNGed cultus especially those Carby ones. The head rarely lasts a 100k. and we have valve jobs pilled up. Whereas you see "COMPANY OPERATED/ COMPANY MAINTAINED" all petroll driven suzuki's pulling 175~250k. Co-incidence???

My humble advice, dont choke your vehicle under load on CNG. WHat those workshops do is prevent the possibility of lean burn under Wide Open Throttle.

@bilalahsan

Its about time, about time someone came up with detailed break up of why CNG is a big no for a responsibly driving City consumer.

For highway surfers, and for short term vehicle owning businessmen (claiming lack of CNG is a loss whereas in actual its a reduction in PROFIT), CNG is like DOPE. Once hooked, its hard to get off.
Well that's something new for me that lean mixture can cause engine damage. All I thought was that richer mixture is not good for an engine. Will search that and look into the fact that am I really damaging the engine, if that's the case I will retune my vehicle.

Sent from my GFIVE President(G9) using PW Forums mobile app

8. I can give you a little example of Economics in Pakistan.

Lets assume a machine using pillow bearings for shafts, the machine makes Rs 5,000/hour each pillow (saddle) costs Rs 10,000/- and takes 4 hours to replace. Usual life of recommended pillow bearing is 500 hours.

downtime to repair is equal to Rs 20,000/- in operating loss and then Rs 10,000/- for part and more in labor.

For some reason the Pakistani accountants will purchase the Rs 2000/- pillow bearing which has a life of 100 hours only and all will be perfectly cool, nice n dandy. They would even get promotions.

ECONOMICS at its best - desi ishtyle.

I had such arguments in Pakistan where I would see some so called ISPs masquerading as RF install entities whose technicians and mechanics would have worn out, sloppy, underpaid slave labor made tools, literally I once saw a guy using a 1 ft long adjustable spanner to tighten a 10mm sunken nut. Their office arguments were that "ozaar ozaar hota hai, china ka ho ya germany ka, adjustable sub size pe set hojata hai"

9. Originally Posted by a_n_memon88
Well that's something new for me that lean mixture can cause engine damage. All I thought was that richer mixture is not good for an engine. Will search that and look into the fact that am I really damaging the engine, if that's the case I will retune my vehicle.

Sent from my GFIVE President(G9) using PW Forums mobile app
A rich mixture causes speedy carbon build inside combustion and exhaust areas. Its a disaster for catalytic converter. However, a rich mixture keeps the combustion chamber cool and engine temperatures under control.

Reason being, fuel vapors, when they enter along with air inside the hot combustion chamber during intake stroke, provide a cooling effect. Sort of someone sprinkles water over you in a hot summer day . Evaporation causes cooling remember!!!

This is another factor that is missing in CNG use. That increases temperature of exhaust gases and while the engine is within safe limits, the exhaust gases burns the exhaust valves on their way to header.

10. Originally Posted by panicslayer
Drive in your 1.5 million car and spend half of your life rolling the windows up and down, means?
You are getting personal now

11. Originally Posted by Xulfiqar
I can give you a little example of Economics in Pakistan.

Lets assume a machine using pillow bearings for shafts, the machine makes Rs 5,000/hour each pillow (saddle) costs Rs 10,000/- and takes 4 hours to replace. Usual life of recommended pillow bearing is 500 hours.

downtime to repair is equal to Rs 20,000/- in operating loss and then Rs 10,000/- for part and more in labor.

For some reason the Pakistani accountants will purchase the Rs 2000/- pillow bearing which has a life of 100 hours only and all will be perfectly cool, nice n dandy. They would even get promotions.

ECONOMICS at its best - desi ishtyle.

I had such arguments in Pakistan where I would see some so called ISPs masquerading as RF install entities whose technicians and mechanics would have worn out, sloppy, underpaid slave labor made tools, literally I once saw a guy using a 1 ft long adjustable spanner to tighten a 10mm sunken nut. Their office arguments were that "ozaar ozaar hota hai, china ka ho ya germany ka, adjustable sub size pe set hojata hai"

Atleast its still better than using a flat head screw driver and a hammer to create a notch and rotate.

12. Originally Posted by rustam54

Atleast its still better than using a flat head screw driver and a hammer to create a notch and rotate.
That would be epic facepalm time.

13. Originally Posted by a_n_memon88
Well that's something new for me that lean mixture can cause engine damage. All I thought was that richer mixture is not good for an engine. Will search that and look into the fact that am I really damaging the engine, if that's the case I will retune my vehicle.

Sent from my GFIVE President(G9) using PW Forums mobile app

if you want a vehicle that has a low fuel intake - rather than underfeeding it, get a smaller engine. In farm terms you are trying to pull your wagon with your horse but are feeding it like a goat.

WONT WORK - the horse will die.

speaking of lean burn - once you get hit by a proper repair bill you will never go lean burn again, proper repair bill does not mean "buthole kharad masheen owner grinding junk steel valves and guides and then slapping the head with plumbing washers under the headbolts to take up stretch"

14. Originally Posted by xulfiqar
if you want a vehicle that has a low fuel intake - rather than underfeeding it, get a smaller engine. In farm terms you are trying to pull your wagon with your horse but are feeding it like a goat.

Wont work - the horse will die.

Speaking of lean burn - once you get hit by a proper repair bill you will never go lean burn again, proper repair bill does not mean "buthole kharad masheen owner grinding junk steel valves and guides and then slapping the head with plumbing washers under the headbolts to take up stretch"
and also lean burn was also abandoned by honda due to evironmental concerns

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