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my 1977 gmc Sierra crew cab

Posted: Fri Dec 19, 2014 9:18 pm
by Dan350
Friends, here is my project. Recently I was laid off from work and have started my own little transportation company. I already had a 1977 crew cab pickup 3/4 ton and decided to build it up so I could use it to haul. I love driving it and working on it and I am currently using it as a hauler. I tow a 2200 kg 26 foot gooseneck trailer with loads ranging from about 2500 to 4500 kg which totals about 4500 to 6500 kg (10,000 to 14,000 lbs). Yes, that is heavy for a gasoline powered 3/4 ton from this era. I have a 1 ton 14 bolt full floating axle and leaf spring setup in the rear and a th400 trans from TCI that was built for heavy duty towing / RV use. Being a crew cab, it has the 8 inch tall 1 ton frame on it even though it was sold as a 3/4 ton. It is 2wd.The 350 in it right now is pretty much stock with 4 bolt mains, a comp cams hydraulic 255 DEH flat lifter cam with roller rockers, a Performer RPM intake manifold and a Holley 600cfm gasoline carburetor. I have 1-5/8 headers with twin 2-1/4 exhaust, no cats. Power is ok but I need to really put my foot in it for the heavier loads (I leave it in L1 for residential streets, L2 for secondary roads and D for highway only) I have to keep it over 2500rpm pretty much all the time when I'm hauling, I sometimes shift full throttle at 4500-5000rpm to get up the hills in my area. I maintain it well but I know I'm asking a lot from it. I get a lot of thumbs-up from people I meet on the road and I like the attention it gets since people recognize it and that helps with business.
Needless to say, it consumes gas like you wouldn't believe, I estimate twice as much as a late model Duramax/Cummins/Powerstroke and not having any emission equipment what so ever on it, I am concerned with the pollution I create. What I would like to do is convert it to propane only. I have a fully machined 350 block with a forged crank and rods, Dart shp aluminum heads with 64cc chambers and 200cc intake ports with 2.02/1.60 valves and I would like to build it up for this purpose so I will need advise on compression ratio, cam selection and the components I need to convert my truck. I would love to get a 454 but I want to start with what I already have. I plan on buying a 200 liter tank which will be installed in the bed of my truck which I hope can give me a range of at least 400km. I would install everything myself and have it inspected and certified by a local technician to make sure everything is safe and by the book. Reliability is a crucial factor. I maintain it weekly but cannot afford to be stalled at the side of the road. If it ain't turnin', it ain't earnin' (as they say on the speed channel).I would like to advertise openly to my clients that my truck, even though is old, was converted to propane and is helping to keep our air free of the toxic fumes that result from burning gasoline. Hopefully this will reflect positively on me and bring in more clients while lowering my operating costs. I don't mind investing on quality parts and would like to learn about electronic controllers to help the engine run more efficiently and what needs to be considered for our winter conditions (engine coolant heaters / circulators and tank warmers ect which would help starting it in the morning) I have begun reading a lot of what was written in this forum and have found lots of useful information. Also, I really need to know where I can buy the parts I need like a mixer and a convertor ect.I'm looking forward to sharing info with all of you. Hopefully I can complete this project by summer 2015 and document my experience and share with the rest of you. Thanks, Dan.