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Old 06-28-2008, 02:03 AM   #1 (permalink)
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Partial natural gas converion

Natural gas burns clean and is inexpensive. There is a station that sells it locally. So I'd like to use it in my car. After much research, I find that doing a complete conversion is a big job. So I'm thinking of a partial conversion that would work like this:

I use a small engine (10HP range) carburetor modified for natural gas. Kits are readily available for this (regulator and jets).

I get a small NG tank (say a couple gallon equivalent) + high pressure regulator and mount it in the trunk.

I run a 1" tube from the car intake manifold to my new carburetor.

Somehow hook up the throttle linkage on the new carb.

The idea is that up to 10HP would be from NG. On acceleration, this isn't much, but in steady state cruise, it might be 50% of fuel usage.

Ideally, a NG conversion would include higher compression and spark advance. But perhaps by only using partial NG, this wouldn't be such an issue. The car is largely unmodified and easy to put back to normal. The existing engine computer and air fuel mixture tuning remains in place. I don't worry about running out of NG.

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Old 07-07-2008, 04:23 PM   #2 (permalink)
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I think when switching back and forth the car would stumble creating rich and lean bumps. the air fuel ratio of natural gas and gasoline is slightly different too. I would find a way to turn off the fuel injectors and run a larger "carb" that is enough to supply at highway flat land speeds, more like 20-25-30 hp.

On the other hand if everything is working great and you were able to use both at once, most ecu's do not like to pull out that much fuel out of the trim. you might have to add some sort of map/maf signal altering hardware like tuner cars. The problem with this is it messes with your timing.

You will also need a tank you can fill that is dot approved and all of that stuff. If there was a way to compress the gas at home from a tap in your garage that would be the ultimate way to go about it. if i was able to do that id go 100% ng. From my personal experience at the gas station when I throw the guy a $20 Ill buy a soda snickers bar etc so not all that cash made it into my tank. Home fillups save on more than one front.

I think there are a few used honda civics that are being sold to private people now. I saw one with "tuner" rims and a full unpainted bodykit out here in socal. YUCK i know.
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Old 07-07-2008, 06:59 PM   #3 (permalink)
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Not sure about this but I have been considering CNG for a while, sadly legal varieties are too expensive.

Anyway in Mexico there are various converters that convert and sell full systems $800 installed, sadly you obviously have to go to Mexico in said car, you can specify you want to be setup to be able to burn both fuels, CNG or Gas.

Issue is how would you fill once you get here?

Furthermore when I read the law it said something akin to all OBII2 need an EPA certified... Does this mean all of my oldies are exempt?

Too bad the government is standing in the way of progress, there is obviously something wrong if nearly identical systems can be installed with a factor of 10-20 difference?
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Old 07-08-2008, 08:18 PM   #4 (permalink)
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Since I am putting on a NG carb, it will keep the mixture about right and the ecu would do little to no triming of the A/F mix. Ie, I'm adding CNG fuel and air at the right mix.

I'm hoping that my ECU will advance the timing a little automatically when it sees no detonation (due to partial use of the high octane CNG).
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Old 07-09-2008, 03:15 PM   #5 (permalink)
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I dont know what year your car is, but a pulse width of next to nothing combined with your throttle for example being at 20% and your speed increasing and decreasing all the time could confuse it, even if the a/f is dead on. Computers still look at the load of the engine and change the timing advance accordingly. Your vehicle could end up being a total dog, if the ecu assumes you are rolling downhill all the time. Are you going to weld a plate onto your plenum to make the carb sit there and route air from the intake plumbing? Im NOT saying this can't work, if it does work id love to do something like that on a truck we have in the family.
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Old 07-10-2008, 12:26 AM   #6 (permalink)
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I will be using a small engine gas carb - ie, a mixer and throttle valve. This will be tied into the intake manifold (not sure about direct mount or a hose yet). I'll probably add a small separate air filter for the gas carb (vs tying into the existing one).

I think that the ECU thinking I'm going down a lot of hills is a good way to describe it.

The goal is a 50/50 mix of nat gas and gasoline at normal cruise.
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Old 07-13-2008, 11:47 AM   #7 (permalink)
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Looks like I will drill holes into the intake manifold and run hoses from there to the carb. I found a K&N air filter that fits the Beam T502 carb. First and second stage pressure regulators are on the way (3000 psi to 100 psi, then 100 psi to slightly negative pressure).

Using used parts, I expect the total to be under $600 and have a 1.5 year payback. Plus it's cleaner for the environment and the engine.

Last edited by jonr; 07-13-2008 at 11:56 AM..
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Old 07-16-2008, 11:38 AM   #8 (permalink)
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I'm leaning towards using a IAC (idle air control) valve for the throttle on this small carb. An electrically controlled throttle would be much easier to tune than trying to somehow connect the throttle linkage. No idea how much restriction an IAC causes.
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Old 07-16-2008, 02:44 PM   #9 (permalink)
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Does an iac valve close when more air is coming thru the system when the regular throttle body is opened up? Maybe youd want a second tps system where you can reference voltages. i think an iac is backwards of a tps. the user isnt changing the voltage of the iac. when you press on a throttle the tps tells the ecu how much throttle is applied. with an iac the engine sucking tells the computer its story. maybe you can get a tiny throttle body like off an ITB application that can be placed inline.
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Old 07-16-2008, 08:43 PM   #10 (permalink)
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My little gaseous carb has a throttle body, but it's a mechanical butterfly. An IAC does the same thing, but is electrical. I may just put a switch or variable resistor on the gas pedal to activate it.

There won't be any connections to the current computer or sensors.

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