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Getting more serious about a real CNG car, lots of questions, heart set on Caviler

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  • Getting more serious about a real CNG car, lots of questions, heart set on Caviler

    Due to its low cost and cheap parts, I am thinking the Caviler will probably end up being the vehicle I eventually get now that stations are coming to wisconsin.

    I am looking right now at a cheap 01 Caviler that has a transmission issue.

    My logic behind the Caviler is that it can burn normal gas in areas that CNG isn't handy and still get OK MPGs. A Crown Vic although a Nice land cruiser usually isn't dual fuel and its economy isn't too good. I go between Appleton and Wausau often and since both areas have CNG this should work out for me.

    Being a total nube what exactly is the process of filling up at a Station? Is it as painfull as trying to get LPG, where I wait an hour for an attendant? Or do I just go there, swipe my card and fill up like any other gas station with no hassle.

    I am also curious if there were any econobox CNG cars that had a Manual transmission available (I still want to save "gas" if I am getting a different car) My cobalt gets 40-50mpg averages summer/winter about 44mpg. I will keep the balt but the other one will have to go. The Caviler with an auto only gets about 27ish which I can probably drive up into the low 30's given how I drive. My thought was to change out the transmission with a 5sp off a junkyard special, in these cars its not overly complex but I am uncertain if there is any paticular issue in working on one of these.

    I also wonder if the CNG caviler is tuneable by HP tuners or the like? I don't want HP but would want to tweek it a bit since the 2.2 in there should be capable of about 35mpg tuned. (much like the cobalt which is the same car only 500lbs heavier)

    Next while I wait for realistic filling stations what is the lowest cost, most reliable CNG compressor? What is the lowest pressure I can fill the tank to and still drive? AKA stuff other than PHIL, I know there are things for welders, torches and various other tanks that do not operate at 3000psi. I also wonder what the PSI right off the tap is out of the line? Anybody know of a reliable, abundant, efficient, cheap used pump solution that could handle CNG at possibly lower pressures? It doesn't need to amazing, just easily available so I am not booting thousands of dollars I will never recoup. From experience purpose built continous, lower pressure pumps are almost always more efficient than high pressure (less loss)

    My logic behind this is... I was thinking for local drives it would be far more efficient both electrically and maintenance wise to get a CNG compressor that runs at lower pressure like 500-1500psi. Around town I would be taking short frequent trips, typically under 30 miles. I am wondering what the minimum pressure would be that would allow for that distance? What size tank and specs to Cavilers usually have? What pressure can it suck the tank to before it kills?

    Anyone have a full list of all the different vehicles over the years that have been sold as CNG from the various US companies? (in case I want to consider something else, I prefer byfuel or if my cobalt can be converted that is another possibility since it gets very good MPG to begin with, all the better with cheaper fuel)

    Thank You For Any Data, A Bit Long but some of the info, like a NON-standard pump is difficult to find. I know there are other pumps that would work on low pressure CNG, probably more reliably, efficiently and safely than the typical installs, just have no idea what they were/are.

    Cheers
    Ryan

  • #2
    Re: Getting more serious about a real CNG car, lots of questions, heart set on Cavile

    Boy, a lot of questions---I will try to answer some in order. First, filling is not like filling a propane system. You can (and will) be doing it by your self, most likely following instructions at the station, swiping your card and filling. I can't recall any CNG cars that were mass produced with manual transmissions. Although you could convert the '01 Cavalier to a manual, you will run into some computer issues. Starting with the '01 the transmission went from a straight mechanical controlled 3 speed to an electronic controlled 4 speed. A no hassle car to convert would be a '99 or '00. The 4 speed auto is very reliable and therefore it is pretty easy to find one a a scrap yard for a reasonable price as there isn't much demand for it. For all the trouble to put in the clutch and shift system for a manual, I don't think the return would be there. People do "tune" Cavaliers but the bulk of stuff available is for the 2.2 litre twin cam Eco-Tec engine found in the '03 and '04 cars not the pushrod engine found in the earlier cars. The later CNG Cavaliers are the most desirable because of the engine and the fuel-injected CNG system that is installed on them. This comes at a price as the later cars command a much higher price then the earlier ones. The lowest pressure that you can get a Cavalier to operate on is about 600 psi which is required to reset the system. It will run to about 200 psi before changeover to gasoline. In the 400 psi range between these two presures, the car is unlikely to restart on CNG if it has been shut off because the computer is programmed to prevent cycling between fuels as it approaches the 200 psi changeover pressure. You are not going to have very much range (maybe 10-15 miles). The tank is close to 6 gge with about 5.5 gge usable with a slow fill. I don't have a complete list of vehicles that have been converted, however as a practical matter anything older then late 90's is going to run into tank expiration issues which leaves you pretty much with the Ford or Chevy econoboxes. Your Cobalt could be converted with parts from a late model Cavalier, however you better be good at computer programming as the Cobalt has a Eco-Tec engine with cam phasers that aren't programmed into the Cavalier CNG "calibration". Bottom line, if you are ready to go with CNG instead of jumping in with both feet, why not just dip your toes in the water by fixing the transmission in the '01 and running it for awhile to see how you like it. If it works for you, then dive right in.

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    • #3
      Re: Getting more serious about a real CNG car, lots of questions, heart set on Cavile

      Originally posted by siai47 View Post
      Boy, a lot of questions---
      The lowest pressure that you can get a Cavalier to operate on is about 600 psi which is required to reset the system. It will run to about 200 psi before changeover to gasoline. In the 400 psi range between these two presures, the car is unlikely to restart on CNG if it has been shut off because the computer is programmed to prevent cycling between fuels as it approaches the 200 psi changeover pressure. You are not going to have very much range (maybe 10-15 miles). The tank is close to 6 gge with about 5.5 gge usable with a slow fill.

      If it works for you, then dive right in.
      Could I do the fuel tank level sensor disconnect trick to get it to start below 600psi?

      Also is there an external PSI guage I could get to just tell me the pressure in there?

      By my math the tank capacity is nearly linear
      AKA
      3600psi - (200psi usuable) = full
      1900psi = half full (assuming 3400psi usable)

      This should mean 500psi is only about a half gallon

      This also would mean roughly 800psi-1000psi would be required to meet all my normal driving needs and 500psi would actually meet it more often than not since I don't drive far, assuming of coarse I can get the thing to start

      Too bad I can't drain the tank down to sub 100psi

      And what is ever worse is the prices for the good years of Cavalier $8-$11k sheesh, I paid that BRAND NEW for my cobalt.

      Thanx
      Ryan

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      • #4
        Re: Getting more serious about a real CNG car, lots of questions, heart set on Cavile

        I hear that's a good choice. I'm not too impressed with the CNG system that's installed in my 2001 ford f150.

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        • #5
          Re: Getting more serious about a real CNG car, lots of questions, heart set on Cavile

          Originally posted by rmay635703 View Post
          Also is there an external PSI guage I could get to just tell me the pressure in there?
          Ryan, I put this gauge in my car right by the shifter. It is dead-accurate:
          http://www.speedhut.com/custom_gauge...number-732.htm

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