Inliners International Forums General Discussion Engines Propane

I just bought a 59 GMC 1/2 ton with a 270. I want to convert it to propane like my 1955 Chev 283. I plan on installing an HEI, hardened valves and seats and an LPG converter and carb?mixer. The Carb I have is a 1 barrel. What size of LPG carb should I get? Should I switch to a clifford 4bbl or clifford dual carb intake? THis would also mean that a fenton dual exhaust manifold is necessary too. Hopefully I can increase my performace and mileage with all of this stuff.

Dear M&M;

Your going to need to do some major research here.

First off; you won't need steel seats or special valves, unless your head is in really bad shape.

Next; For low RPM usage 'headers' won't be needed and I don't think Fenton made an exhaust manifold for the GMC. It they did, it will be a huge cost.

Please check with your Propane/LPG dealer first before you buy anything.

Welcome aboard & Good luck.

John is right,as usual. The later sixes boosted compresion for propane. I don't recall hearing this about the 270s. I'm not sure if Fenton made exhaust headers for GMCs or not,but Patrick's has the Chevy ones machined so they fit. I have a set on my 270. I'd stick to one carb,maybe a 302 two bbl set up. Why mess with multiple carbs in a quest for MPGs? Anyway,as John said,in fewer words, headers won't help at lower RPMs. Do your homework, and keep us informed of how it works out! There are folks here who Know.

Should I go with dual exhaust or single exhaust for this propane set-up? The carb is a single 1 barrel so I will need to replace the intake to install a 2 barrel. Should I go with a 300 or 390 cfm carb? What is better, aftermarket aluminum or factory steel intake? What sixe exhaust should I run for mileage, performance and quietness? I'm definitely new to this. Ha, the old gimy doesn't even run yet and I haven't even driven the truck yet either.

Just stay with the stock manifolds for now, till you see how you like the LPG conversion.

Have you run LPG in the cold weather before??

propane runs fine in cold weather. just run the heater hoses thru the vaporizor. also works good on stock gas compression engines. works better with higher compression to optimise the fuel. tom

Yep. I run LPG in my 1955 chevy 1 ton witha 283. It starts up pretty good at 30 and even 40 below zero here in Montana. The 283 is at about 9.5:1 compression with the timing advanced about 10 degrees. The heads are power pack with hardened valves and seats. This is a dual fuel set up where I can run either gas or LPG but not at the same time. The manifold is Edelbrock Aluminum, exhaust= factory rams head and the carb is a simple Holley 4360 (425cfm I think). I like the performance of this set up and would like to repeat it with my 270 six, or at least keep it from being a dog or gas guzzler. My 283 gets about 11 mpg of unleaded with a bit more snap than the 10 mpg on lpg. But that's with a 4:56 rear end and a 6,000 lb truck with poor aerodynamics.

I'd post some pictures but haven't figured out how yet.