Anyone know about CNG or Propane conversions on Gas engines?

I am considering running CNG or Propane in my 03 3/4 ton Suburban. The more I think about selling it, the less likely it seems that I will get a decent amount of money out of it. Therefore, I would like to make it cheaper to run. Both are a little cheaper than gasoline locally at the moment and I suspect will continue to be cheaper (substantially) as the inevitable creep of gas continues.

Anyway, what I can looking for is a way to run both gasoline and propane or CNG in my GM 8.1L V8. The idea is that I will use gasoline for long hauls and the other for anything in the state. What does the hive mind say?

Edit: Just ran some pricing and the tank itself might price me out. The cheapest 14 gallon tank (not likely big enough as that is only 120-200 mile range) is like $1500 and weighs 600 lbs empty (this is for CNG). I suspect the much lighter tanks to cost several times more. LPG is still possible as that is only stored at <100 psi but since is carries lower energy, I would need to see how much cheaper I can get it.

What you're looking for is a Bifuel kit, which will let you run either or, depending on availibility.

I don't see the 2003 8.1 as having an EPA approved conversion available per this list, but there is a list of converters at the bottom that you can contact.

NGV America Link

Having said that, the ROI is pretty steep, even if doing your own conversion (and having to deal with any possible legality issues if your state does emissions inspections). Remember also, natural gas cylinders have an expiration date, and must be replaced after that date for your vehicle to remain road legal. Buying used cylinders is a crap shoot some times, especially for composite (type 2, type 3) cylinders, as UV exposure degrades the wrap and can severely compromise the cylinder's integrity. Do your research - there are benefits and drawbacks.

If the contacts on that list can't help you, do a google search for Tom Sewell of Tulsa Gas Technologies, he is very experienced in conversion and many other things regarding NGVs. He may be able to point you in the right direction.

Well on the propane front, I can get 100 lbs tank for $150 new. I live in Missouri and there are basically no rules here for emissions type items. A quick search makes me believe that all I need is a $75 decal since there isn't a fuel tax on propane. Missouri is about as lax as any state on these things.

Duel fuel vehicles don't take advantage of the 2nd fuel. Both CNG and Propane have very high AKI's but since you need to fall back on gas, you really can't build for it.

I am not sure about the newer kits, but some of the older kits did not give good cylinder-to-cylinder mix and I have seen some engines burn a piston as a result.

Yeah, if I was going to go so far as pulling the motor apart, I would likely plan for e85 (easy enough to find most places with planning) and then one of the others. This truck might make 2 trips over 300 miles in the next 3 years but that means I need a regular fuel available for that. I am just investigating at the moment.

We've done a bit of alternative fuel tuning at DIYAutoTune. You're going to need the following:

1. Some sort of separate gaseous fuel delivery on the engine side. Could be a second set of injectors, could be a mixer - the equivalent of a carb. Drilling the intake for a second set of injectors would give better fuel distribution. Some of the injectors are similar to conventional gasoline injectors; others are more like industrial pneumatic solenoids. The injection option generally needs a control box. Most appear to be devices that take and modify pulses from the stock ECU, but they can also be run off a

2. The fuel tank - looks like you've done your homework there.

3. If running liquid propane, you'll need an evaporator. Unfortunately most of these are sized for smaller engines; finding one in big block sizes is a pain. CNG does not have as much of an issue.

4. For best results, you'll want a way to remap the ignition system. The optimal timing curves aren't going to be the same for gasoline.

In reply to MadScientistMatt:

Yeah, I ran across a number of threads for using MS3 in a dual fuel setup. The more I research though, the more I realize that until gas hits $5 a gallon, there is zero reason to do this for financial purposes. For the hell of doing it though, I am going to keep researching.

I would much prefer CNG except for the extremely cost prohibitive fuel tanks. If not for that (or a sub $500 option) I would probably go ahead and do it. The benefits of LPG aren't high enough for me though.

Propane cars used to be a "Thing" here in Ontario since the Gov was paying for the conversion. Friend ran a fleet of 20 or so cars on propane for about 10 years. The upshot was that the engines did not last as long as they did on gas. If you live in cold weather hood, the stuff does not work well when it is really cold. Getting a fill-up can be a pain if you travel out of the pattern.

They maintained their own filling station and save further, but overall it was pretty much a wash.