I've heard on occasion that you can rig a setup that allows you to run propane OR gas in your motor. I hear it's mainly a matter of setting up both a gas carb and a propane carb and having a valve to get fuel to one or the other. I have a spare 460 block that I'd like to do a build up on, and after hearing about the phenomonal fuel economy you can pull out of propane I find myself considering a setup where I could switch back and forth, do the propane across the highway and gas in town where I need the acceleration. Maybe even some form of forced induction could be thrown into the mix. What are all y'alls' thoughts?

The Law
1989 F-250 HD 4x4
460, C6, BW 13-56, Sterling 10.25" (4.10:1), Dana 44 HD (4.09:1), twin K&N's, no muffler, stock lo-flo cat, Bosch Platinum Plugs (0.060") MSD 6A and TFI Blaster Coil

 

I don't know where you heard about phenomenal economy with propane, but it's not that much different than gas. Unless of course you're buying the propane without paying the road tax. Power differences are real but slight enough not to be real noticeable. As in it's not going to be doggy as a result of the propane. In order to run a duel fuel setup you'll need to keep compression and or boost within the limits of the gas you'll be running. This will prevent you from taking full advantage of propane's potential. If you crank up either compression or boost you'll not be able to switch back to gas.

Unless, and this thought just occurred to me.

The waste gate on a turbo can be "cheated" to a higher pressure by causing a controlled leak in the line feeding it. The higher the leak the higher the boost. The controlled leak could be run with a T fitting leading to an adjustable valve or a fitting for a holley jet.

If a solenoid was installed just before that leak it could be turned on and off with the solenoids that controll the fuel and propane lines. Thus you could run low boost gas and high boost propane. Still you'd probably just be wasting time. I can think of no practical reason to do this. If you really want it, just build it for propane and boost.

Propane is roughly 105 octane. Every 3.7 pounds of boost is supposed to be roughly equivalent to a 1.0 rise in compression. Therefore, (and this is just a guess) you could run an engine at 7.0 to 1 compression with 20lbs boost on propane!!! That's right at the line though, probably need water injection at higher boost just to maintain the safety factor.

Of course this is all B.S. theoretical. I don't have a 20lb boosted propane unit to tell you if it works or not. I'm pretty sure they've been built but obtaining anything more than anecdotal evidence is almost impossible.

That enough food for thought for you?

 

i know a guy that had this set up Propane/gas on a truck a long time ago when propane was so much cheaper than gas. He had a propane tank in the back and everytime propane was cheaper he would run it and when gas was cheaper he would run it. The only thing is i heard that about 2 years ago and he never told me the details of how he did it but the point im trying to make is propane has to be a considerable amount cheaper to benefit from it, i dont know what prices are now but i doubt its worth the hasstle of mounting a permanent tank on and having all the B.S. work to do it. Just my opinion. But i would ask yourself is it really worth saving a few bucks and spending a bunch of time getting it set-up.:-X23

 

[updated:LAST EDITED ON 04-Nov-02 AT 05:00 AM (EST)]F.W.I.T. I'll though this out there. I'm no expert but this has been my experience. I bought my truck about 8 months ago and it came with a dedicated propane system. It's a 1975 F350 with a 460. It has the low compression heads. I have a set of D0VE-C heads on the back burner. It was at one time set up with the dual fuel sys. When I first got the truck propane was cheaper than gasoline, but the road tax on propane didn't make it much more economical. Maybe just a little. But it did help me pass on my smog inspection because it burns much cleaner than gasoline. Now gasoline prices have come down and it is cheaper to burn gasoline. I have just finished converting my truck back to burn gasoline. Been running on gasoline for two weeks now. I picked up a used carb. at a wrecking yard, cleaned the tanks inside and out and replaced all the rubber fuel lines. One big advantange to burning propane is that it burns cleaner and your engine will stay cleaner between oil changes with less wear. Being a vapor when it enters the engine, any blowby past the rings does not contaminate the oil. You will also need to have hardend exhaust valve seats installed if you have older heads that used leaded gasoline. Of course with propane you will have that big propane tank sitting in the back of your pick-up bed taking up a large amount of space. Another thing to consider, if you should ever hit a stationary object at a substantial speed there is a chance that it could rip loose. I don't have to tell you that the tank needs to be secured to the bed and I mean SECURED! I have seen some low profile tanks in the back of some trucks but mine is a 68 gal. monster. Thats another reason I'm going back to gasoline. Plus there is some work I want to do on my bed and I need to remove the propane tank anyway to do it. I haven't noticed any better fuel mileage with propane. Propane was giving me 6.50 mpg. Now I get about the same with gasoline in the city. But again gasoline is cheaper the propane right now. I haven't figured highway mileage yet. But I get much better performance with gasoline with a noticable increase in power. You can run a much higher compression ratio with propane but it may become a problem when going back to gasoline. You can also run much more advance on your ignition timing. Again a potional problem when switching back. There are definite advantages and disadvantages to propane/gasoline. After I finish the work on my bed I may go back to propane, hence the D0VE-C heads. It has become my opinion that if you were to run propane in a vehicle it would be best to make it a dedicated system. In order to get the most out of propane you need to run a higher compression ratio, advance the ignition timing, put in a higher temp. thermostat, (propane engines run better when hot), and do away with the gasoline altogether. Depending on the price of propane, to run both systems is too much of a compromise if you want to save money on fuel. This is just my opinion.

 

 

I have done some checking into propane as I plan on running my 460 on a dedicated propane system. The farting around needed with dual fuel did not make it that attractive, gas and propane both reqiure a different engine timing and advance curve, as propane is a vapor it mixes easily with the incoming air, also because of this it is harder to ignite than a gas mixture so a hotter spark is needed and different heat range of spark plug. Msd does make a dual fuel box that will set up two different advace curves and timing one for each type of fuel. Now on to force induction because propane is a vapor and mixes so easily with air , it is a excellent fuel for say turbocharging, on all the reading I have done it is recommended that for street use 10 to 12 psi boost is as high as one should go. The heat created with boosting the incoming air kills the high octane rating of propane. this is the reason for limiting boost to fight of detonation. I feel that if one is going to run propane the engine needs to be built for propane fuel, to gain the maxium benifit
just my 2c worth. Eric

 

Thanks for the info folks. I must've been smokin' crack or something with the propane fuel economy. I think that all gas is probably the way to go.

The Law
1989 F-250 HD 4x4
460, C6, BW 13-56, Sterling 10.25" (4.10:1), Dana 44 HD (4.09:1), twin K&N's, no muffler, stock lo-flo cat, Bosch Platinum Plugs (0.060") MSD 6A and TFI Blaster Coil

 

Im not professing to be an expert on this, but I have done loads of research on "propane" as a fuel as it is cheap here in Australia and available almost everywhere.

I run propane in my 460 - stock with D3Ve-A2A heads - so its a little low on compression. I have less problems with what you guys call propane (us Aussies call it LPG) than I do with gasoline.

On propane, when its 32F outside it starts and runs/idles without fuss. When its 104F things are a little different. Propane as a gas is very sparse when its above 168F. Consider that your thermostat is somewhere between 160-190F and the water in your radiator is used to stop the propane from freezing your converter - when the propane is converted from liquid to vapour it meets a temp somewhere near that critical point of 168F (As liquid propane expands and becomes gaseous propane it sucks all the heat energy out of its surrounding - a techie science thing called enthalpy of formation I believe, and therefore requires that you run hot water through your converter to prevent it from freezing).

Gas that meets 168F water and then 120-140F underbonnet air is not going to be very dense. This is the major cause for the "loss of power" when running on propane. Fact of the matter is that its density is very dependent on its temperature - the hotter it is, the more sparse it is, the more sparse it is the more space it takes up and the less energy you can obtain from this "space". At normal underbonnet temps, propane is sparse enough that it will produce about 4%-5% drop in power over gasoline. Plummet this temp down to about 82F and propane absolutely hums. In an engine that can only take 1 BAR of boost (14lbs) on gasoline, propane will yield about 1.8 bar or 25lbs. The trick is the temp of the intake, and the temp at the converter.

I currently get about 15mpg on propane and about 12mpg on gasoline. I managed to achieve this by keeping my temps down. (hehe highway cogs help too!)

Stoichiometric for Gasoline is 14.7/14.8 or there abouts - try 15.6 for propane. Lean huh? Gasoline and air - even with EFI is still considered to be a heterogeneous charge, meaning there are rich and lean spots all over the place (less so with EFI than carb, but you get what I mean). One of the benefits of using propane is that given that it's already a vapour when it mixes with air, it is considered to be homogeneous - or completely mixed (no rich or lean spots). This gives you better flame front propagation and a cleaner burn, oh yeah and a bigger bang.

Propane burns slower than gasoline, but not significantly. It is aslo less likely to detonate (try 854F instead of gasoline's 440F) and can handle fairly high compression ratios. Yes it does require a bigger spark to ignite it, but hey dont we all run MSD6ALs?

Dont give propane the flick until you have seen it done right. Otherwise, and I agree, you will be sadly disappointed with the result. I have had a lot of fun with propane on 6 cylinder and V8s, but the big 460 has been the best yet. I love burning off turbo jap racers and love it even more when it costs me less than $20 to fill my tank (as opposed to $65 for gasoline).

Have Fun!
Steve