bell- the ohg 450 should be fine for a 400 as long as youre not over-revving it alot (like 5000+ rpm), but id probably go with impco 425 just because of better parts availability- also running way rich on propane is the way to burn holes in pistons, running way lean just cuts down on power- with gas running rich will cool the pistons because its wet- propane is dry and acts differently- at least thats my understanding

 

Remember, an engine built for propane could put out more power because the higher octane rating allows you to run a higher comp ratio. Also, with a truck you could do a bi-fuel setup, so if you run out of propane you could switch to gasoline. And just FYI, propane is really cheap around Pearson Airport in Toronto, it was ~65 cents a few weeks ago.

 

bi-fuel setups are why propane power has gotten a bad name in the past- if you build an engine as a bi-fuel propane and gas when you run propane youll get worse mileage because you have to build the engine for gas first- lower compression- if you build it as a propane only engine thats when you can actually do well with it- if you have to have a bi-fuel then build the engine for propane and have the other fuel be e-85, theyre about the same octane so you could run the same compression

 

I was kinda worried about the bi fuel setup because of the differences between the octane ratings and all the compression that I want for the propane. I was planning on a propane only motor but if its still a high compression engine and able to run on E-85 that would be awsome. Then if I had to travel somewhere I wouldnt be stranded because they dont have any propane. Well it looks like all I have to do now is get some cash together and start on the whole project. Project PropCorn. Propane and Corn fuel. I think I need to get more sleep or something.

 

a few things to remember on the e-85 though... mileage will suck worse than on propane... itll get about 10-15% worse mileage on e-85, and youll have to jet it way rich, and replace all your rubber lines, and it wont start worth crap in cold weather, so youre better off with straight propane

 

OWT plain and simple. A little rich is the worst mixture condition you can have as far as heat goes. This myth is so widespread that most belive it just because it is repeated so much. Cars and trucks (except for some turbocharged diesels) dont have the instrumentation (exhaust gas temperature) to display how rich or lean you are running. I suspect that what you call "a little too rich" is way rich and "too lean" is actually slightly rich (of a perfect mixture, or peak EGT). Detonation burns holes in things, not a lean mixture. Airliners of the 1950's would never been able to cross the oceans without lean mixtures.

Jim

 

Partly true Jim, but what causes "detonation" or more properly pre-detonation? When the mixture is "leaned", or the stoichiometry (sp?) is adjusted to a lower-than-normal A/F ratio, the evaporative cooling effect liquid gasoline has in the combustion chamber is decreased proportionatly, and air temps prior to fuel detonation are increased, in some cases enough to cross the line into compression ignition phase, causing (drum roll please) pre-detonation, or more correctly stated premature-detonation. I agree that a "lean" mixture doesn't burn holes in things, in fact a chronically, and appreciably lean mixture may not even ignite, since fuel vaporization is not significant enough to saturate the air to the point flash-ignition can be triggered by a spark.

Oh and FWIW, EGT monitering has nothing to do with AFR on a diesel, and it IS in fact measured automatically on any new gasoline engine, via the primary Oxygen sensor(s), so optiumum efficiency can be reached, on a diesel there is no need to moniter AFR, the fuel combusts no matter the A/F proportion, since the combustion temps are high enough ANY fuel that enters the chamber will ignite.

 

ok... 2 things- yes what you say is true of gasoline- but this thread is about propane... its already a gas when it comes out of the mixer- no evaporative cooling effect because its already evaporated... this is why when you run propane lean it runs cooler- there just isnt enough fuel to keep the temp up... and when you run rich it will run hotter
the other thing is what you said about diesel- yes whatever fuel you can inject will burn but only to the point that it runs out of oxygen- then you get hydrocarbon emissions- same with gasoline

 

Absolutely correct, and I apolagize for the rant, I forgot this was about propane! And with diesels as you say, when you run out of oxygen, feeding it more fuel will only increase emissions, but this is not the purpose of measuring EGT, which was really my point to Jim about that. I just hadn't seen Jimdandy in a while, and I kinda missed sparring with him, he always did love a good debate! Didn't mean to hijack, again, I apolagize.

 

i have not one but two trucks on the pane. a 85 chev with 270000miles on the motor, and my newest addition to the collection of trucks, the 81 f150. I love propane, in the chev that is, for it gets 12 to 13 mpg, whereas the ford gets 6 to 8. I gues thats the difference between a 305 and a 351. Now the power issue, you do want your compression to be 10.5 to one(Dinamic) or you will lose about 20% of your torque(ouch). Also the chev has a huge tank(about 60gal)(250 letres) and yes it weighs alot(propane is either 1 pound per 1.1 letres or 1.1 pounds per letre can't remember off hand). So it weighs alot full(and empty). The fords tank is only 24 gal(90letres) and is undernieth, i like this for i then have a full box, and less weight, the negative being more stops for fuel. Anyways theres about all i know about it, in the end it is up to you, to me it's good stuff. PS PUD if you wouldn't mind, i would like the info on this propane forum as well, thanks.

 

just about forgot, man i type alot, anyways stainless steel valves and nickle or(i forget the name of the metal off of the top of my head but i'm going to try to wing it)irridium(i think thats a metal) anyways it is harder than nickle valve seets, have thses cut into your heads. Cast iron when hot is softer, the continuous pounding of your exaust valves on this hotter softer iron will alow them to acctually burry themselves into the cast, thus decreasing your valve lift. This over time, along with low compression moters to start with is why propane got such a bad name. Stupid 80's.

 

i always said nothing good came out of the 80s... with the possible exception of the delorean and some chicks born then ;-)