High power Propane

Let's hear all the gory details about your car and how it became alternative fuelled.
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Posts: 10
Joined: Sun Feb 18, 2007 11:55 am

High power Propane

Post by stroker » Mon Feb 19, 2007 11:35 am

Hi, I had to talk with someone that might have gone though the same type of high performance teething pains that I am now going through. First I built a 4x4 1 ton 79 GMC camper-van and then converted to propane, this was 5 years ago. The motor was a 350 30 over 250 cam 1.5 rockers 9.5 compression heads mildly ported and of course balanced. I was running the largest Vaille vaporizer made, along with a 650 cfm Tecnocarb mixer. This system gave me 50,000 miles of trouble free service and I do mean trouble free, -20 +35 C easy to start, plugs were changed at 35.000 miles and was not necessary, went through air care without ever having any problems, however being a bit of a gear head wanted more. So I did my research and designed what I think is the correct motor for my application. 383 Stroker with 11.2 compression X4254H cam with 1.6 roller rockers, lift corrected to .477 / .492 / RHS Vortec heads ported to flow 260 in 184 ex at .500 lift, Along with the this I went to 0 dec height, used Beehive springs, total seal gapless rings. Now you have an idea I might have a bit of knowledge, I will tell you about the dyno and road test.

The builders suggested that I break the engine in on the dyno on gas, this produced 416 HP at 4900 RPM & 494.9 TQ at 3800 RPM however 477 TQ AT 3000 RPM. Now we hooked up the aforementioned propane system and were building good power until 3600 RPM and then just like too small a fuel pump the engine leaned out and lost power. I had a very good idea this was going to happen, so contacted Tecnocarb, drove out and picked up a new Vaporizer and Mixer. Once installed and back on the dyno the engine produced 386 HP and 452 TQ, I was happy with the results and installed in my van. Another thing I should mention is this engine developed 19.5 inches manifold vacuum at 900 RPM. The van was already running headers and mandrel bent 2.5 stainless exhausts, so just a straight forward install. I have since drove this vehicle 2000 miles and it is hard to start, vaporizer freezes at plus three C, will not idle, as in you can set idle at 900 RPM and turn engine off restart and now the rpm is 1600. I realize this sounds like a vacuum leak but I disconnected trans and brake vacuum hoses and but a plug in manifold, re-torqued intake, removed mixer installed new gasket and there was no change in the results The only thing this system does well is go fast, under full throttle pulls strong, no hesitation from stop, however if I accelerate hard and slow down to 10 miles an hour engine tries to die and I have to feather gas peddle so engine does not die. I talk with another propane guy that told me to run my old vaporizer on the front of my mixer and run the new tecnocarb vaporizer on the rear and turn the idle screw all the way in. This is not what I want to do; I will go back to my old motor and use the new motor with an injection system on a vintage ride before I do this. I am beginning to wonder whether I have a faulty vaporizer or if it needs to be electronically controlled. Okay, does anyone :? have any ideas to help steer another propane guy in a new direction to sort out this problem.

Thank You in advance for any and all thoughts
Sincerely Gerry Vass

Posts: 1019
Joined: Fri Sep 09, 2005 11:23 pm
Location: Winnipeg, Canada


Post by C3H8 » Fri Feb 23, 2007 1:03 am

You need to post this in the propane forum part of this forum if you want to get some good feedback. This area is kind of specialized for showing off some of the vehicles. Yours sounds pretty neat but you are getting a limited audience here.

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