I finally had time to start on my propane conversion for my 98 GMC. It is from the netherlands and is pretty cool. It reads the factory injector pulses, lambda (o2) and tach. It takes the info and uses it to fire another set of keihin vapor injectors. It compensates for fuel pressure and temperuature. Here are a couple of pics of my first attempt I only had a couple of hours. I tied in the injector simulators and connected the propane computer to the gm harness for the injector signals, tach and lambda. Here is a pic.
Installed new Thorley headers today. Nice headers no problem installing them either. Also put new water pump. It is supposed to be a Milodon high flow, but on the end of the shaft it is stamped gmb. guess it will work ok.
I figured that most people haven't seen many propane carburetors so I thought that I would post some of the one that I am using so you can see what I am talking about.
This carb was made by borg warner. They were in a hurry to put it out to market and didn't get all the bugs worked out. They developed a very bad reputation because of this. They finally fixed most of the problems but by then it was too late no one wanted them.
The carb works by vacuum and is designed to sit on top of a gasoline carb. The air is drawn in over the doors on either side of the carb. The doors are hollow, so as the air flows over them the fuel is mixed with the air. These doors are attached to rod that determines the fuel mixture depending on air flow. There is also an accelerator circuit that is tied into manifold vacuum.