Contemplating CNG conversion

[ejp2fast]

I've done quite a bit of reserach in the last few weeks on converting one of my festiva's to CNG. Actually this kit I am looking at just ADDS CNG, so the car will still run off Gas/CNG at the flick of a switch. Here is some of the key points infomation I have learned.
-CNG is 130 Octane, and runs more efficiently with a higher compression ratio engine, and our 9.4:1 ratio for the B3's isn't a bad candidate.
-Since CNG is a gas, MPG wise everything is in "GGE" (Gas Gallon Equivalent). So, i have emailed some people and with my 37 mpg average now on gasoline, i should be around 34-36 mpg CNG gge.
-This is very desirable for the folks in Oklahoma, as the gas is CHEAP ($0.78 GGE) and the fill stations are abundant compared to other states.
(See this link for a map with current CNG prices- http://www.cngprices.com/)
-Few 'issues' with the tanks- 1st is tank space. 2nd is tank prices/certification. 3rd is Tank GGE size and efficiency.

Issue #1- so i'd remove the rear seat, to fit my 16" diamter and 48" long tank(s).

Issue #2- Tank Types are 1 thru 4. Type 1 is cheap/heavy (metal), Type 2 is metal/composite and as weight goes down, price goes up. Certification- I can find Used Tanks on Craiglist for cheap- but their certifcation is either expired or about to expire. I am looking for New Type 1 tanks, and they go for about $1000 for a 9 GGE Tank. Recertification is a bear/ expensive, if you can find some one to do it, which isn't very many folks.

Issue #3 Tank size is in GGE. So as an example, a 9 GGE tank will only hold that depending on temperature outside, and rate of the CNG fill. Faster you fill, hotter you get, and with the tanks rated at 3600 psi (some 3000 psi) you fill at a local station (fast) and your tank is HOT and then has to COOL after you leave, so your 9 GGE is really a 7-8 GGE Tank.
So that means at say 35 mpg GGE for 8 GGE tank is a range of only 280 miles. And a 9GGE tank is on the larger side for a tank. So the CNG guys complain that the range between fill ups is shorter.
But still kind of nice, then just flip switch over to regular gas to make it to the next CNG fill station.

-So I put together an excel sheet that has CNG vs Regular Gas. See attachment.
-My rate of return will happen at 22,000 miles from installation, and then I will be only paying ~$.78 per GGE.... and thats appealing.

-But- this car is already 20+ years old, and I would want to put another at least 100K on the car after now.. (Definitely doable) But other people normally put this CNG conversion on newer cars so then they can fully utilize the CNG cost savings...

There is a kit from EWS http://www.ewsews.com/cnghome.html
that has this kit for $600 minus tank and valve.

Thoughts? Any other things I need to consider ahead of time?

[Pu241]

How many miles on the engine you are converting?
Running on CNG will mean longer oil change interval and cooler running with less wear on your engine internals.
So engine should last a good long time.
Also you can pick another B3 for rebuild to swap in if want a fresh engine to use.
Don't think that is necessary if your engine is in reasonable shape as it is.
22,000 miles is about 4 months or so for me.
But that is because I do a lot of long distance drives, meaning finding CNG fueling stations could be an issue.
If your driving is local could be a while to reach break-even, but I'd do it anyway because I don't see gasoline prices going anywhere but up!

[ejp2fast]

Rebuilt my B3 EFI engine 18K miles ago...
and yes, i forgot to add all of the engine wear benefits....

edit: Oh, and John - click that cng prices link- it will show all of the fill stations in the US, zoom in on your travel routes.

[fastivaca]

Here's a really nice CNG fuelled car drool

[TominMO]

Even if you got half the MPG of gasoline, CNG still wins beause it only costs about 1/4 the cost of gas. And with both gas and CNG tanks, your range would be about 700+ miles. It would take a while for the install to justify the savings per mile, so it depends on how long the car will be in service. Of course, you could transfer the system to another car.

[blkfordsedan]

I see no real issues or disadvantages with it. Around here, farmers have been running LPG on their pickups since the 1980's. As with CNG, there are some minor drawbacks, but you make the best of it and learn to live with it. I say "do it"!

[Larry Hampton]

I've kicked it around as well. I'm not worried about certified tanks, we don't have inspections here anyway.

[ejp2fast]

Couple more things:
1. with CNG- there is about a 5-10% power loss over Gasoline
2. When starting your vehicle, you need to crank the engine 8-10 seconds VS the regular 2-3 seconds on regular gasoline (I say, just start car on gas, then flip switch over to CNG)
3. Myth with people is that "CNG Tanks will explode with the high pressure" etc in a crash.. actually CNG Tanks are MUCH safer in a crash vs gasoline tanks. so they say.

About the EWS kit:
-"mixer" is installed in the intake tube from air box to throttle body, and that mixer size depends on size of engine and specs.
-regulator mounted on firewall- high pressure line from tank to regulator, and stepped down to usable pressure.
-wiring involved- has to cut power to fuel injectors (of EFI car) but still have other components working
-"Check Engine Light" will come on, as O2 sensor will see a lean condition with CNG. need to learn a little more about that. Emailed EWS about the 02 sensor, and as our voltage is under 1V and constantly changing, we don't need the special O2 kit.

-There is a PHILL station available for $4500 that compresses your natural gas to your house to 3600psi and you plug your car in overnight and takes 5 hours to fill.

http://wisegasinc.com/wg-phill.htm

[ejp2fast]

I've kicked it around as well. I'm not worried about certified tanks, we don't have inspections here anyway.

I too found that we (Oklahoma) don't have tank inspections, but then doing research have heard of all the guys that buy old tanks for cheap and have an accident with them after the expiration date in the non-inpection states. So my question is, what is the certification based off of? Number of Fill ups? ie. Number of "cycles" from 3600 psi to ~0psi to 3600 psi to 0psi?
Or based off just years? I guess I need to look into that a little more.

[Grey Vw]

Interesting stuff.

[Larry Hampton]

I'm kicking the idea of putting 2 of the tiny tanks in the back. Angle iron cage with 16ga sheetmetal surround, vented thru the floor.

There's a guy in Mustang sells the kit for around $500 IIRC. I've seen the tiny tanks go for about $150ea.

I met a guy about a year ago, had a CNG Caprice, '90? Had the original tanks in it.

My take is, welding tanks get inspected every so many years (I think 3), but I've seen tanks built in the 50's that are still good.

[ejp2fast]

I'm kicking the idea of putting 2 of the tiny tanks in the back. Angle iron cage with 16ga sheetmetal surround, vented thru the floor.

There's a guy in Mustang sells the kit for around $500 IIRC. I've seen the tiny tanks go for about $150ea.

I met a guy about a year ago, had a CNG Caprice, '90? Had the original tanks in it.

My take is, welding tanks get inspected every so many years (I think 3), but I've seen tanks built in the 50's that are still good.

what is the tank gge for 'tiny tanks'? and your comment on welding tanks- they wouldn't have the change in pressure (cycles) as a CNG. But you are right, still 50+ year old tanks still holding up.

edit: Larry- you have the contact for your guy in Mustang, OK? I'd be interested in getting in touch with him for more info. There was a guy i contacted in Moore on various CNG tanks, is this the same guy?

[Larry Hampton]

I just looked on the OKC craigslist searching for CNG.

[getnpsi]

Id do this myself if i found a carbed car. Something about efi just makes me want to leave it alone vs the nightmare such a high percentage of carbie's are especially if you are required by law to leave them OEM.

the PHILL is a steeeeeeep investment but if you added a second vehicle such as the f-150 or a honda the fuel savings after a year would offset.

[ejp2fast]

Id do this myself if i found a carbed car. Something about efi just makes me want to leave it alone vs the nightmare such a high percentage of carbie's are especially if you are required by law to leave them OEM.

the PHILL is a steeeeeeep investment but if you added a second vehicle such as the f-150 or a honda the fuel savings after a year would offset.

yeah, and another item i have been researching lightly is making my own PHILL-like system... stepper compressor.. but by what other people are saying about it.. little bit of safety issues arise. Still need to contact a local compressor place to see what they know about compressing to 3600+psi... safely.