I was thinking of converting my 01 Sierra to propane, does anyone know if there any conversion kits that allow me to keep my current fuel system and allow me to change between them? If so where can I find them?
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We used to use Impco (Imperial) propane conversion kits and loved using propane. You can run some wild parts because there is no octane issue. You do have to run your timing on a different curve. This is important.
In a standard Carb unit, the Impco carb fit between the ar cleaner and the carb, using the throttle plates as normal and drawing the propane in a demand system, something like a scuba outfit. You would shut off the gasoline and switch over to propane, just like that. However, I have seen carbs melt down internally...melt the throttle into a pool at the bottom of the intake manifold and I always attributed that to too much heat in the intake manifold. Block off the cross-over to reduce this. I always felt that part of the reason for this was that gas on the float bowl absorbs heat and contributes to cooling the carb...no gas, no cooling...but the old man said I had rocks in my head, so there ya go. I would keep your intake as cool as possible. I knew several people that kept spare carbs for the day theirs melted down. The old man kept one in his truck.
The problem could come if you have to have it inspected. We used to do this to get a special note on the title "Propane". We also had to show it was a permenant conversion, but I always figured that anyone with enough ability to add a propane system would be just as able to pull it back off, but I what do I know? However, the laws in Washington State have changed and now propane has to be OEM. Anyway, you had to put a "Propane" sticker on the back of your truck, mainly for firefighters so they would know if they were fighting a fire that could contain compressed gas cylinders. As a former firefighter, I understand this and need to point out that if they are required in your state and you don't do that and there is ever a problem they won't be very nice about it, especially if someone gets hurt. Propane/LPG is a fine fuel and fairly safe 99% of the time, but if line or valve gets damamged in an accident, you better have your paperwork clean.
That said, propane has been offered by GM on many vehicles for many years. There is no reason why you can't get something fairly bolt-on. It is a safe, clean fuel and can be run as a racing fuel. It's cheap, at least for now...I have seen the price rise and drop against gas prices, sometimes being as expensive or more expensive than gasoline.
As far as that goes, Energy = Mass, and propane has less mass than gasoline. As I recall, gasoline is 6.8 lbs. per gallon while propane is about 4. something. Within certainlimits, you will need to burn the same number of pounds of fuel to get the same horsepower, so you can expect a drop in mileage, which is ok as long as propane is significantly cheaper than gas. In Seattle that is about $3.50/gallon for gas and $1.79/gallon for propane. It is a savings that is hard to ignore.....
If you can make it work, you will love LPG. Good luck!