CNG makes a very good fuel, but the logistics are a nightmare. You have to have a pumping station to fill it which is very expensive, and that also makes range very limited because there are not too many around.
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| LPG vs CNG conversion https://www.slantsix.org/forum/viewtopic.php?t=23647 |
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| Author: | haacer [ Mon Jun 18, 2007 3:16 pm ] |
| Post subject: | LPG vs CNG conversion |
I'm considering a conversion of my 1974 Scamp to alternate fuel. Does anyone have experience with the pros/cons of LPG vs CNG? I'm interested in creating a car which I can drive to work, but have a decent amount of power. I'm going to start with a naturally aspirated setup and add a turbo at a later date. I'm also located in California, so cold weather is not an issue. So I'm looking for pointers on: part sources, advantages of each fuel type, suggested compression ratio for future turbo-charging, cam selection, and head mods. Thanks in advance. |
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| Author: | SlantSixDan [ Mon Jun 18, 2007 3:50 pm ] |
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The guy you want to talk to on here is Frank Raso. CNG is not really practical or practicable on a passenger vehicle, especially one originally fuelled by gasoline. LPG can definitely be done. |
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| Author: | slantzilla [ Mon Jun 18, 2007 7:37 pm ] |
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CNG makes a very good fuel, but the logistics are a nightmare. You have to have a pumping station to fill it which is very expensive, and that also makes range very limited because there are not too many around.
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| Author: | argentina-slantsixer [ Tue Jun 19, 2007 4:34 am ] |
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we're among the leader countries in CNG infrastructure. We have plenty of CNG stations, etc. CNG sucks, makes less power and it's like giving your engine cancer so you can save allegedly anywhere from 1/3rd to 1/2 the operative cost. This is only on fuel. Oil changes and scheduled mainteinances have to be "pumped up" since CNG's comustion is "dryer" and due to a comparative octane rating (wich is high octane low energy, lower than gas) you're running too little timiing or too less compression, the motor tends to overheat horribly. Most guys from argentina using this cars (they're "big" cars down here) has to use this conversion because they want to use the car and instead of realizing that they're paying less money for the fuel today and so to say "covering their heads while baring their bottoms" more goes into rebuilding engine, special cooling requirements, taxes if you get your tanks checked legally, loose 1/2 trunk etc.... so they'll try to convince you that "it's the same and makes same power and it's enviromental safe and ..." but the truth is that sucks. LPG is good, good, good, but less practical even... and it's not very widely spread down here... some large industries have their slant sixes (pretty popular industrial engine down here) and other engines converted with no power missing and not as much "side effects" as CNG. My 2 cents. |
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| Author: | argentina-slantsixer [ Tue Jun 19, 2007 4:40 am ] |
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you wouldn't feed your horse with dry grass would you? or with wood chips just because they're cheaper than proper food? I don't get why complain about the gas prices... you're getting better price than we do and our incomes are way down 1/3rd of yours... I do get the complaints about prices and how much they have and keep on raising... don't get me wrong... gas ain't going to be any cheaper until war shadows stops darkening the picture, and this ain't no politic statement. We should enjoy our last years of "free" gas... I don't see how individuals would be more or less "free to use gas" in the future... Now if you pay it you can fill up your tank. If things keeps going this way getting a can of race fuel is going to be more or less like buying drugs... |
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| Author: | haacer [ Tue Jun 19, 2007 1:12 pm ] |
| Post subject: | CNG vs LPG |
Thanks for that input. I hadn't considered the maintenance requirements. I'm thinking that LPG isn't "dry grass" or "wood chips" however. It is a fuel which is widely available with higher knock resistance than most gasoline. The conversion cost a bit for the tank, but otherwise looks like a slam dunk on my 225. The only problems I see are making decisions on how high to go with compression, cam selection, etc... My other car is a Camaro Z28, which only runs on California's finest 91 octane. I'm trying to put my classic together as a car which I'll actually be able to drive to work. That means less expensive fuel and more power are only positives. I haven't checked out CNG availility, but I know a number of local stations offer LPG. However, the price of LPG isn't much less than gasoline. My father-in-law said he was paying over $3 per gallon recently. Is there anyone else in Southern California who is familiar with the price of LPG? Also, I'm still looking for answers on what a engine built specifically for LPG would look like. Thanks all |
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| Author: | argentina-slantsixer [ Tue Jun 19, 2007 2:41 pm ] |
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Actually LPG is a good alternative to gas. I'd say, it's THE alternative. If you have LPG stations in your area go for it! I have a friend who was running 40 BTDC total with LPG and 9.5:1 compression. recurved distributer, cam, headers, lower tstat, etc and it was not only easy on the wallet but pretty darn powerfull, actually better than a tired engine on regular gas. I'd go with bigger valves, good porting, bronze guides on the head (thermal expansion is reduced and this is a good factor when rebuilding an engine that's gonna run hotter than stock) you can have tom at erson grinding you a custom profile (Ask Doc and then charlie_S, there's a crane cam profile that's good and idles not only fair but amazingly "calm"... 11:1 compression or higher... (LPG actually compares to 130 octane gas, is a pretty ballparkish comparation because you can't really compare them, but...) |
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| Author: | haacer [ Tue Jun 19, 2007 11:16 pm ] |
| Post subject: | Lpg |
I read somewhere that LPG was ideal for turbocharging. Any thoughts on that? It seems to me that the denser charge wouldn't have nearly the heat issues due to the temp drop from exiting a compressed container. Also, who supplies LPG conversion kits? |
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| Author: | skraecken [ Wed Jun 20, 2007 12:27 am ] |
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Quote:
The guy you want to talk to on here is Frank Raso.
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| Author: | Mister Twister [ Wed Jun 20, 2007 5:07 am ] |
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Hello all. Our Propane fork lift motor was 8 years old when we put some gaskets in it WOW  The motor was so clean. The guy told me cause it's propane fueled? Something to think about. Hope this helps Don
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| Author: | Charrlie_S [ Wed Jun 20, 2007 5:13 am ] |
| Post subject: | Re: Lpg |
Quote: I read somewhere that LPG was ideal for turbocharging. Any thoughts on that?
I have had plans for a turbo propane slant for many years. Maybe next year I can start on it. I have the engine parts, the turbo, and the propane system. Major parts still needed are the tank, and new propane lines. I am not doing it to save on fuel (propane is not any cheaper per mile), or for more power ( propane is less then gasoline, everything else being equal). Just happened to find the parts for the right prices, and the fact of being different.
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| Author: | slantzilla [ Wed Jun 20, 2007 8:49 am ] |
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Quote: Hello all. Our Propane fork lift motor was 8 years old when we put some gaskets in it WOW
I can tell you for certain that service interval and oil type play a much bigger role than fuel. I was in the lift truck service industry for 13 years and saw about every kind of damage you can believe. LP is cleaner, but stretch out the service intervals and see what you find. Left too long, the oil turns gooey faster than with a gasoline engine. The motor was so clean. The guy told me cause it's propane fueled? Something to think about. Hope this helps DonLP fuel grade is another problem. LP has oil in it for top end lubricant, and cheaper LP has more oil (and just plain dirt) in it. That leads to heavy deposits in the intake and on the backs of the intake valves. I personally liked CNG for a fuel better. I was involved with a couple CNG conversions. However, filling equipment is expensive and hard to find on the road. LP filling staions are not as common as they once were either though.
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| Author: | haacer [ Wed Jun 20, 2007 1:18 pm ] |
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Quote: I personally liked CNG for a fuel better. I was involved with a couple CNG conversions. However, filling equipment is expensive and hard to find on the road. LP filling staions are not as common as they once were either though.
I've heard but not verified that there is a local CNG station. Assuming that fuel is readily available, it sounds like you're advocating CNG. I'm interested in power and operating cost. Are these goals which can be accomplished with CNG?The articles that I've read talk about power loss, expensive tanks, and general misery. Maybe CNG has just gotten some bad press... I think slantzilla and argentina-slantsixer need to hash this one out. |
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| Author: | slantzilla [ Wed Jun 20, 2007 4:29 pm ] |
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The customer that I was involved with used CNG exclusively. It was a paper company and the engines were 4.3 V-6 GM's. They did not require any more maintenance or repair than a similar 4.3 on LP. You also ahve to take into consideration that the 4.3 has the biggest POS heads of any engine I've ever seen. It was not unusual for them to have sunken exhaust seats and cracked exhaust valves in under 2000 hours (1 year). I could actually listen to a 4.3 idle and tell you how long it would be before we saw it for a head rebuild. (GM quality my azz) CNG did not seem to aggravate that problem. The problem with LP here is fuel quality. Since industrial LP is sold by weight, suppliers find it too easy to use oil, dirt, and rust as filler. The main benefit to LP used to be lower cost, even though you will use twice the amount compared to gasoline. I think now it is not as low cost as it once was. I have seen 9 second drag cars both running on LP and CNG. Both were very successful after they went through the pain of getting the fuel systems figured out. Me personally? There is not enough benefit to either CNG or LP to warrant the cost of changeover, but then I am pretty set in my ways. 
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| Author: | Daddiojoe [ Fri Jun 22, 2007 7:45 am ] |
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Has anybody else had trouble with the site? I've been trying to reply to this for two days. Anyways, I've been running on sweet lady propane since late April. It runs all right, but the gas mileage has been pretty dismal. Best so far was 11 mpg on the highway. But remember I'm running a '71 truck w/ a 3:23 rear. The conversion itself is super simple easy. Easier w/ a truck because they make tanks that fit in the bed specifically for that purpose. Beyond bolting on regulator, vaporizer, and mixer, all that was needed was a little fabrication for brackets. I'm using the throttle plates from a Carter BBD, as I had already super-sixed my engine. And that has been the biggest problem. I have SEVEN (7!) BBD carburetors in my garage with wallowed out throttle shaft housings. So until I broke down and got a real machine shop to re-bush the thing, I was having vacuum leaks. The throttle plate, with the help of an adapter you'll have to make yourself or get a shop to do, bolts right onto the bottom of my Impco mixer. PROBLEM--- I have a computer, etc. to make it a closed system. But can't get a reasonable reading from the O2 sensor which provides it with feedback. I'm getting a 1.8 - 1.6 volt reading, and according to my lpg guru Franz Hoffman, that is way too rich. But I don't think this reading is accurate, because the engine starts to miss if I adjust it leaner. As far as I know the engine is in good mechanical shape. ANY SUGGESTIONS? Franz Hoffman can set you up w/ parts, etc. PM me for his email. He is down the road from me in Lockhart, TX. In the future I plan to do some head shaving to get the compression up, as propane will definitely take it and benefit. The only other things I've done are on Franz' recommendation--loosening up the valves for less duration/heat transfer, and gapping the plugs down between .030-.035. As far as CNG goes, the one big advantage it has in my mind is political. We've got lots of natural gas here in the good old US of A. On the other hand, it is under A LOT more pressure than sweet lady propane, so is harder to handle and you need a very expensive tank to contain it, etc. Even w/ this long post I'm sure I'm leaving something out. Let me know if I can help further, Joe |
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