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  • Questions on converting a subaru wrx to cng

    hey i am thinking about converting a 06 subaru wrx sti to cng. i am trying to do some research. does anybody have any experience doing anything like this. the engine is a 2.5 liter turbocharged car running around 18 lbs of boost. I know that there will be some power loss with the natural gas but figured that i could switch it back to gas for spirited driving. I am looking to decrease the pain of filling up at the pump for $3+ on premium and geting 15 mpg in the city. what type of power loss would i see. the engine compression is about 8.5:1. I have got a quote from a guy who says he can do it for about 6200 and i am thinking about it. any responce would be gladly appreciated
    thanks
    andy

  • #2
    Re: Questions on converting a subaru wrx to cng

    ldscamaross,

    It has been reported that you get about a 15% reduction in power. I read that in an article somewhere. I'll see if I can dig it up. CNG has an optimum compression ratio of about 12-13:1.
    Jared.
    Mountain Green, Utah
    2003 CNG Cavalier
    2003 CNG Silverado 2500HD

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    • #3
      Re: Questions on converting a subaru wrx to cng

      I drive a 2.3liter turbocharged ford ranger and have been looking into the same thing. One thing you should realize with a turbo motor is that while you may experience a power loss in normal driving, the octane rating of cng is anywhere from 120-130. You could run as much boost as any turbo could push and make up for that loss. That is one thing that really appeals to me. I am just having a heck of a time finding any good info on how to actually do it, as i would prefer to do it myself.

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      • #4
        Re: Questions on converting a subaru wrx to cng

        So nobody on here really knows much about cng on performance applications huh?

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        • #5
          Re: Questions on converting a subaru wrx to cng

          The guys at So-Cal Speed Shop have built a CNG hot rod. Sorry no picts.

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          • #6
            Re: Questions on converting a subaru wrx to cng

            I have heard that an Australian rally team will be running on CNG this coming year. I don't really know any details though.

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            • #7
              Re: Questions on converting a subaru wrx to cng

              They ran on natural gas last year, this year they running it all on biogas.
              Sponsored by OMV, its a CNG Mitsubishi, The first rally race is in Austria this coming week.
              I have a photo of the car on our blog. http://blog.cngaz.com
              LICO Lavanttal Rally, April 4-5
              Last edited by cngaz; 04-01-2008, 08:36 AM. Reason: Adding Race Date
              Dave Clement

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              • #8
                Re: Questions on converting a subaru wrx to cng

                My best guess is that a turbocharged engine would do very well with ngas, but you will likely need some way to pump in extra gas under boost conditions. It probably would take some kind of enrichment circuit (probably using an extra injector) regulated by a pressure sensor mounted in your intake manifold. Boost pressure in a turbocharged system is controlled by the level of work done/heat produced in the exhaust- it is independent of any mechanical coupling with the engine.

                The problem you need to overcome is that because turbocharger's boost is not rpm dependent like a supercharger, which could use the base programming hardware to provide the needed fuel enrichment. It is dangerous to run any boosted system too lean; detonation is the likely outcome.

                I have a twin turbocharged Mustang Cobra that Id love to convert...
                Last edited by rtry9a; 04-01-2008, 03:36 PM.

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                • #9
                  Re: Questions on converting a subaru wrx to cng

                  2 of the guys up at FuelMaker in Toronto, Canada converted their Mustangs, but thats Canada.................................
                  Dave Clement

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                  • #10
                    Re: Questions on converting a subaru wrx to cng

                    Converting the basic Mustang is no problem (could use any kit designed for the F150's). The problem involves tuning the turbochargers tho Im sure it can be done with a wide band O2 sensor and a few "modified" parts.

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                    • #11
                      Re: Questions on converting a subaru wrx to cng

                      If you had a boost referenced Fuel Pressure Regulator like many gasoline motors (turbo and non-turbo) that would not be a problem. As th eboost pressure rises, so does fuel pressure.

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                      • #12
                        Re: Questions on converting a subaru wrx to cng

                        hey thanks for all the replies you guys. i hadnt looked here for a while.

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                        • #13
                          Re: Questions on converting a subaru wrx to cng

                          I am looking into research about what the market is for older foreign vehicles. And the need for EPA certified CNG conversion kits for them. I own a WRX and that's what the first thing that I would be working on. Please let me know about what you think, or how many would buy. :-)

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                          • #14
                            Re: Questions on converting a subaru wrx to cng

                            you could try a impco mixer in the high pressure side coming from the turbo to the intake manifold than feed it with a stove gas regulator run the ng from the hp regulator to the in side than run the out side to the impco mixer now the trick run a line from the out put of the turbo to the vent on the back side of the stove gas regulator it is the hole that has a screen over it pop the screen out and you will find npt theads just hook a line to the pressure side of the turbo that way as the boost comes up it will push against the diaphrame and give the same amount of pressure as the boost and than add whatever pressure that you have the spring set for to the boost if the regulator that you use has a plastic plug over the ajuster you will have to find or make a metal one now I am sure that this is not aproved for on road use but if you are trying to run ng on something off road or a turbo farm tractor it will work well as I have done it you will not want much of a spring as the impco is set up to run zero pressure or very low ie inchs not pounds good luck the best part is no computor

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                            • #15
                              Re: Questions on converting a subaru wrx to cng

                              Oh I have a design that will run just fine with ANY car. I'd need to do some more work for other makes but it'll work. I am trying to find out what the market is for CNG for 35+ MPG cars. :-D

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