# Diesel with CNG conversion 55mpg



## seeyal8r (Mar 10, 2011)

Okay so I know that many of you don't have access to CNG. A friend of mine has a 2007 Chevrolet 2500 HD with Duramax Diesel and just installed a new CNG conversion tank etc. He says he is now getting 55mpg diesel and using 2 gallons of CNG. CNG here is $0.75/gallon and diesel is $3.55/gallon. The conversion claims a 100 hp gain at the wheel.

Before the conversion he was getting 17mpg which would be a cost of $0.208/mile at current prices.

and after the conversion its $0.092/mile.

His truck is lifted 6" and on 35" tires. If the numbers are real then a normal truck or diesel car would get even better mileage and cost savings.

My wifes car gets 30 mpg gasoline and with this conversion it'd be cheaper to drive the big diesel truck.

The conversion kit was $3500 installed but he knew somebody who knew somebody so he helped with the conversion and it only cost $2800 for him. Still saving $0.11/mile would add up quick and pay for itself in $30,000 miles. Of course if the price of diesel went down then it wouldn't pay off as quickly but I don't see that happening.

Anybody had any experience with CNG? I'm curious and may be looking at trading off my gas guzzler for a diesel to put the conversion kit on.


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## Highbeam (Mar 10, 2011)

His numbers aren't real. In addition to CNG, there is an established aftermarket industry for propane injection with diesels. The bottom line is it isn't worth it for propane, the lower cost of CNG makes it somewhat more attractive before you factor in that insane price he paid for the equipment.  The engine efficiency is not significantly improved with the gas fuel vs. diesel alone so you still need to supply the same amount of energy to move the large truck. 

The biggest red flag was when he told you that he was getting 55 mpg from diesel which is a rate of consumption (likely from his overhead computer) and then gave you a fixed volume of gas which he of course can't measure since it is in a tank. He does not yet know what he is getting. Let him run a few fillups of CNG, and then do real math with miles traveled and fuels used. Then we have something to talk about.

Bully dog is the biggest aftermarket gas/diesel injection supplier. Check out their website and also the diesel truck websites to see how they like propane injection. It's the same thing except using a more expensive propane.


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## seeyal8r (Mar 13, 2011)

I should have done some research first but a lot of my friends claims are somewhat verified by some forums on other websites. 

in early 2007 they were doing injections with CNG at a 1:1 ratio with diesel. the cng was injected before the turbo. this was a very basic setup.

now they are doing direct injections with 2.5:1 ratio NG to diesel. most claims are of around 50mpg with the diesel and 28 mpg CNG.

With that being said it would be about half the cost (local prices) to direct inject CNG into a diesel motor. The benefits seem tremendous except that the overall power increase is breaking parts outside the motor. Twisted frames, broken drive shafts, clutches, differentials etc are all being broken due to the increased horsepower and no doubt a heavy foot.

With diesel prices climbing and CNG prices dropping (due to summer demand) I can see the financial benefits.


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## EatenByLimestone (Mar 13, 2011)

Once govco figures out they aren't getting road taxes for it, expect the benefit to end.  

Matt


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## benjamin (Mar 13, 2011)

I don't see much wrong with those numbers, except how he gets slightly more miles per btu out of gas than diesel?  With CNG that cheap it's hard to argue, even if he's using 1 gal diesel and 3 gallons (?) CNG per 55 miles. 

What kind of setup are we talking about?  and is this compressed or liquified? how big are the tanks and how many gallons?


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## Highbeam (Mar 13, 2011)

I checked some diesel forums. These conversion kits are nowhere to be found and actually mocked pretty hard as being some sort of scam. Even propane injection, which is the same thing just a different "ane", has fallen out of favor for many reasons including NOT getting enough mpg improvement to justify the kit. Don't believe it until you see it. CNG is not new, people would have been doing it if it really worked. 

Remember when water injection was a mpg craze? Heck, water is hydrogen and oxygen right? Both will burn really well so why not burn water? It's cheap from the tap. Yeah, like that.


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## JustWood (Mar 13, 2011)

A friends son put the propane kit on his big rig. At first he said he was getting better mileage. After a year he took it off and his excuse was it was to hard to find propane on the road. I thought it odd due to the fact that an extra 20lb bottle wood be easy to carry along.
I got a feeling it's hokus pokus but wood like to get some serious details as I have an unlimited supply of free propane in 20lb bottles.


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## gregbesia (Mar 14, 2011)

Every time I visit my family in Europe it is interesting to see LPG being sold at every gas station. They have thousands of regular cars (gas) converted to run on LPG. The conversion kit is pretty neat too , with small tank in the trunk and fueling port mounted on rear fender/bumper . One can even simply  switch between  gas and LPG with one flip of a switch inside the car.    Granted, they are paying $6 a gallon  of gas, with LPG about 1/3 of that , but still I would like to see that option in this country.


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## benjamin (Mar 15, 2011)

Some sort of LPG, CNG, LNG is used in much of South America.  It does work, it's not overly complicated and it is much cheaper than gas or diesel.  I'm not saying it makes sense for any particular person or vehicle, but I'll put more trust in the miles I've ridden than the online mechanics who can fart and burp louder than the rest.  There's no magic here, it's just substituting one cheap and untaxed btu for another one.

I don't think the 55 on 1 diesel and 2 natural gas was accurate, but then compressed natural gas wouldn't be measured by the gallon anyway, would it?


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## seeyal8r (Mar 15, 2011)

CNG is measured by a gasoline gallon equivalent (gge) which is actually a bunch of cubic feet depending on the size of the tank and pressure. NG cannot is not compressable to liquid form under normal circumstances. The CNG tanks are compressed to 3600 psi. I'm finding more and more websites for the installation of diesel CNG injection websites. Some sound crude and maybe false but it appears there is some truth to it. The reason (it appears) that propane is not viable is the cost of propane in relation to the cost of diesel fuel. I'll post links to some of the websites i've found.


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## seeyal8r (Mar 15, 2011)

Natruell CNG Conversion Kit - Diesel

As I understand it this is the kit he bought with an 18 gallon tank? not real sure on the tank.


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## seeyal8r (Nov 17, 2011)

I'm seeing more CNG Dedicated and dual Fuels in our area. That could be because the fuel is already so available.
Locations and Prices Here

There are even some dealerships popping up that are only selling CNG equipped vehicles. 
Auto's for sale

If you get a Honda Civic and 30mpg and buy CNG at $0.78/gal then you could drive 500 miles for $13. I think I could easily live with that.


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## peakbagger (Nov 17, 2011)

Be carefull of mixing Btu contents as a gallon of propane does not have the same btu content of gasoline or CNG. The best way is to stick to GGE (greenhouse gas equivalents). CNG does have a bonus effect that the octane ratio is higher than gasoline. In theory if the engine only burns CNG, higher compression ratios can be used but if its a dual fuel or a conversion then this isnt normally done. A higher compression ratio means higher engine efficiency if its done right. 

Generally a lot of the dollar savings for alternate fuels is getting around gas taxes. CNG is popular in some areas in the US as you can install a compressor in your garage and fill up the tank with no gas tax. One of these days as electrics and other non gas vehicles get more popular, we are going to see tax per mile fees. 

When I visited New Zealand last year the taxi driver was going through the cost to run a vehicle, they pay very high gas tax (less for diesel), an annual mileage fee, and yearly excise taxes.


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## blades (Nov 17, 2011)

Fed gas tax 18.4 cents /gal,  Diesel 24.4 cents/gal,   Wisconsin fuel tax 30.9cents /gal either type + 2 cents/gal ust.


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## Highbeam (Nov 21, 2011)

I buy off-road red dyed diesel for the tractor because I save 40 cents per gallon once you include all the fed and state road taxes. I drive a diesel truck and know I can run the off road in an emergency. Surely, folks do run the off-road fuel on road and cheat the system. I could see why, just fill er up.


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## MasterMech (Nov 21, 2011)

Highbeam said:
			
		

> I buy off-road red dyed diesel for the tractor because I save 40 cents per gallon once you include all the fed and state road taxes. I drive a diesel truck and know I can run the off road in an emergency. Surely, folks do run the off-road fuel on road and cheat the system. I could see why, just fill er up.



You do NOT want to get caught with dyed fuel in the tank. Not only is the officer annoyed you were doing whatever he/she pulled you over for, but now you've cheated the tax system?! You'll never be heard from again.... Rumor has it you have to run over-the-road fuel for quite awhile before all traces of the dye disappears.


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## maverick06 (Nov 21, 2011)

haha  I have a diesel Jetta, sometime i dont think anyone would ever check for. And a heating oil tank in my basement... That would be great to use for my car. BUT a) its illegal, b) I use 30 gal of heating oil a year so who knows what nasty stuff is in that tank as the tank is 60 years old and the fuel is 4 or 5 years old. 

So I dont.... but I suspect a lot of people do. I also suspect that typically only the trucks get checked for fuel, not pickups or my little jetta.


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## Hass (Nov 21, 2011)

maverick06 said:
			
		

> haha  I have a diesel Jetta, sometime i dont think anyone would ever check for. And a heating oil tank in my basement... That would be great to use for my car. BUT a) its illegal, b) I use 30 gal of heating oil a year so who knows what nasty stuff is in that tank as the tank is 60 years old and the fuel is 4 or 5 years old.
> 
> So I dont.... but I suspect a lot of people do. I also suspect that typically only the trucks get checked for fuel, not pickups or my little jetta.



My propane supplier said he buys old heating oil from customers that are switching to propane for $.50/gal and removes it for them + the tank (instead of them having to PAY to get it removed)... Then he runs it all in his truck.

I wanted to do WVO for a long time... I will some day.
My father bought a RV that had a chevy 454 that could run on gasoline or propane. He actually bought the RV on ebay for 4500 sight unseen. The seller was a small dealership that knew nothing about the RV... So we were surprised when we found out it could run on the propane tank! The propane tank was 50gal, and could be filled up at most campgrounds or gas stations... Even better to fill it up at the reservation a few miles away from my house where propane is still $2/gal. It ran INCREDIBLY smooth on propane, however it wouldn't start on propane. So it would always have to be started on gas.... and when it was switching from Propane -> Gas, it ran very rough. But Gas -> Propane was smooth. He ended up selling it at the start of this year for a little more than he paid for it.

My grandfather said when he worked at GM that all new engines were tested on Propane because it was less volatile than gasoline. I don't know the truth to this however.


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## granpajohn (Nov 22, 2011)

Be careful comparing NG to LP.
Propane has about double the energy content of NG... at least as it is delivered at the pipe.
This pops up when folks hook the propane grill up to the gas line and find it cooks much slower/cooler. (there are special burners available to make this conversion)

http://www.propane101.com/propanevsnaturalgas.htm

There used to be a Hearth member who had a CNG chevy he bought from Balto Gas and Electric company. He had the comparison costs (savings) down very well. But he was fortunate to live near a fueling station at BWI airport.


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## blades (Nov 22, 2011)

Gm assembly plant in Janesville Wi, guys used to get hazard pay for driving units off end of line.


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