Gasoline to LPG or How to trick out your truck on sweet lady propane...

[bake74]

Because of getting ready to move, house hunting, new baby and all I really haven't had much of a chance to run the 425 and compare it to the 300.

      When you do get time I would love to hear your thoughts on the comparison.

[richmond2000]

I know this is a "dormant" topic but some pointers / experience for LPG / propane users
most setups I have seen/worked on just shut off the LPG fuel lock and not bother with the air vent under the mixer and secondly run your truck on petrol once a month and a good fuel stabilizer or your carby will get gummed up and need a rebuild

[Jason S]

      When you do get time I would love to hear your thoughts on the comparison.

Okay, so I've had a chance to run the 425 on the GMC.  It doesn't start quite as quick as it did with the Impco 300.  Overall, it runs great with the 425. I attribute the starting issues to: 1) there is quite a bit more distance for the vacuum signal to travel as compared to the 300.  That is, with the 425 there is the large volume of the mixer to carb adapter and then to from the mixer to the regulator; and 2) The engine is pretty loose; I haven't checked cold compression, but figure it certainly doesn't help the situation any.

As for the 300 mixer on the '74 K10: Much faster starting as compared to using the same mixer on the '73 GMC.  The engine in the '74 is much tighter, so I'm sure that helps.  It drives well and will lug down much lower than when on gasoline. For example, when in granny low, you can keep engine speeds low and not have to slip the clutch. It's possible the 425 would be a better match on the '74 since it has the tighter engine.

I know this is a "dormant" topic but some pointers / experience for LPG / propane users
most setups I have seen/worked on just shut off the LPG fuel lock and not bother with the air vent under the mixer and secondly run your truck on petrol once a month and a good fuel stabilizer or your carby will get gummed up and need a rebuild

   
My setup is using electric propane fuel lock-offs, but a vacuum operated lock-off would be an option.   You're right about running on gasoline to keep the carburetor from gumming up. I try to run the truck on gasoline every so often.  At this point in time, I really need to get some fresh gasoline in the tanks of both trucks.

[Stewart G Griffin]

Thank you for the detailed write-up.  i guess, selfishly, all i want to know about is how much mpg do they get on LP and how much does it cost per gallon?  The numbers.

[Jason S]

Thank you for the detailed write-up.  i guess, selfishly, all i want to know about is how much mpg do they get on LP and how much does it cost per gallon?  The numbers.

Thank you for reading and the inquiry.  On gasoline the GMC (the one I have driven more regularly) will get an average of 10 mpg city or highway.  On LPG (propane) the GMC will get an average between 8-9 mpg.  As a comparison my 2005 Chevrolet 2500 4x4 gets 11-14 mpg, depending upon city or highway driving. My driving is usually at the speed limit and usually no "jack-rabbit" starts.   

LPG here is currently $1.75/gallon. 

For 2012,  I was purchasing LPG at around $2.15 - $2.19/gallon. Gasoline prices were fluctuating. Comparing the 1973 to the 2005 and driving the same routes, etc.; weekly operational costs for the '73 ranged from break even to 20% less than when operating the '05 truck.
 
For the numbers.  You might double check my math...

Using last weeks fuel prices:
-Gasoline at $3.33/gallon (87 octane-100% gas)
  --At 10 mpg using gasoline= $3.33/10 = $0.333/mile
  --At 14 mpg using gasoline = $3.33/14= $0.23785/mile
  --At 18 mpg using gasoline = $3.33/18= $0.185/mile
  --At 20 mpg using gasoline = $3.33/20= $0.1665/mile

-LPG at $1.75/gallon
  --At 8 mpg using LPG= $1.75/8= $0.21875/mile
  --At 9 mpg using LPG= $1.75/9= $0.19444/mile
  --At 12 mpg using LPG= $1.75/12 = $0.14853/mile
  --At 14 mpg using LPG= $1.75/14= $0.125/mile
  --At 16 mpg using LPG= $1.75/16 = $0.109375/mile

Comparison of savings per mile and savings over 3,000 miles (one oil change interval) using current prices:
10 mpg on gasoline versus a low of 8 mpg on LPG = $0.333/mile - $0.21875/mile = $0.11425/mile.  $0.11425/mile X 3,000 mi. = $342.75
20 mpg on gasoline versus 16 mpg on LPG = $0.1665/mile - $0.109375/mile = $0.057125/mile.  $0.057125/mile X 3,000 mi. = $171.37

Straight cost comparisons will vary upon fuel prices and vehicle fuel mileage.

If prices stay at $1.75/gal LPG and the vehicle gets 10 mpg on gasoline and 8 mpg on LPG, LPG would result in a cost savings at anything above a price of $2.1875/gallon of gasoline.  The formula would be LPG operating cost x Gasoline fuel mileage = $0.21875/mile x 10 mpg.

Same scenario, LPG at $1.75/gal, but with a vehicle that gets 18 mpg on gasoline and 14 mpg on LPG - the break even point would be  $2.25/gallon of gasoline [ $0.125/mile (LPG) x 18 mpg (gasoline)]. 

[gehidore]

I realize this is a bit old but since it's specific to the thread I have to ask:

Do you have any before pictures of your tank? And I didn't notice you stating how you cleaned your tank.

I'm about to undertake a very similar conversion on my 69 IHC Travelall, though rather than use a gas carburetor I'll be using a 2bbl MotoCraft, yes f*rd, TBI from a 1985 LTD. I have an Impco 425 mixer, a model E converter ( electric LP choke ), an impco fuel bonnet, and an 80 Liquid Gallon Manchester tank from 1975. My tank has seem some hard years and there is a minor layer of pitting / rust on the lower corner. My local LP guy certified the tank even with this to my surprise so I am planning to have the tank drained then I'll line the bed of my other truck with thick plastic and put the tank back into it in a bath of water and washing soda so I can use some electrolysis magic to remove and neutralize the rust.

-Beaver

[Jason S]

Thanks for looking and asking gehidore.




originally posted here:
http://forum.73-87chevytrucks.com/smforum/index.php/topic,23323.msg194272.html#msg194272

The LPG tank in the tractor bucket is the one used for the '74 K10 LPG conversion, the photo is what it looked like when I purchased the tank.

I used aircraft paint stripper, sandblasting and hand sanding to strip the tank down.  The tank wasn't really pitted and actually had a little LPG and thus pressure when I bought it.  In general all was good with this tank, so  I repainted using Rustoleum Rusty Metal Primer and Ace Hardware Aluminum paint.   I upgraded the tank valves on this particular tank, as well as replacing the rubber o-ring on the fuel level gauge.

The pressure inside the tank at 60 degrees F is 92 psi; at 80 degrees F it is 128 psi and at 100 degrees F it is 172 psi; at 130 degrees F the pressure is 257 psi.  Therefore, keep the tank a light color to keep pressure down on sunny days.

LPG tanks will have a pressure release valve.  Looking at the second photo of the tank in the tractor bucket, to the right of the valves is the pressure relief valve. If pressure inside the tank increases beyond the hold back pressure of the spring within the valve, the valve will release excess LPG pressures. Once the pressure is relieved, the valve will close back down.

As for the carburetor setup on the '74 Chevy K10, it has a Quadrajet from an '85 Dodge D-30, the engine or the mixer haven't complained to me yet...

You may already know that if straight LPG is desired, the 425 can be directly bolted to a Holley butterfly assembly, if you have one laying around or adapted to other butterfly baseplates. In both of my trucks, LPG and gasoline were originally desired and an adapter for use over a carburetor or TBI (in your situation) assembly was used.   

Take lots of photos of what you did during the conversion process, I would be interested in seeing the electrolysis route you're using and details of parts used/modified/created. Additionally, while the Chevy/GMC forum may not be correct location to post the full conversion on a Cornbinder, I would imagine an IHC forum would be interested (if you're not already a member).

[gehidore]

You may already know that if straight LPG is desired, the 425 can be directly bolted to a Holley butterfly assembly, if you have one laying around or adapted to other butterfly baseplates. In both of my trucks, LPG and gasoline were originally desired and an adapter for use over a carburetor or TBI (in your situation) assembly was used.   

My 425 actually came with the square to spread adapter and a Holley spreadbore throttle plate already installed and I was originally going to run 100% LP, due to prepayment of road tax based on vehicle weight in this state AND the fact that there are no stock 4bbl intakes for an IH 266 I've decided to go bi-fuel, I finally received my fuel bonnet thanks to eBay so I have already removed said adapter and butterflies.

Take lots of photos of what you did during the conversion process, I would be interested in seeing the electrolysis route you're using and details of parts used/modified/created. Additionally, while the Chevy/GMC forum may not be correct location to post the full conversion on a Cornbinder, I would imagine an IHC forum would be interested (if you're not already a member).

I'm a member, albeit inactive, in a few... I did decide though I'm going to use the http://www.arduino.cc/ and write my own engine management software for the TBI / sensors as when I had this rig previously converted to the same injection setup sans LP the computer would sometimes get confused after entering closed loop as it expected different o2 readings with the EGR in play, which I didn't even bother to try to use in the setup.

My thought is that, although I may take many months if not a few years to perfect it, it will allow me to use a wideband o2 sensor and hopefully get lambda values back for LP as well thus making it so I only have to shut off the fuel to each of the two systems to make a switch between LP or Gas.

Thanks for the reply and I'll take tons of photos and write lots of documentation I'm sure as I go along.


Also on a side note, since that looks like a Manchester, were those screws that hold the gauge on hard to remove? mine look pretty sketchy and she's got 40 of her 80 gallons full and a pinhole leak at that gasket site... Trying to decide if it's worth the extra money to have the company who is going to drain the tank for me do the valves and seals since if it breaks they'll have the know-how and equipment to fix it...
-Beaver

[Jason S]

since that looks like a Manchester, were those screws that hold the gauge on hard to remove? mine look pretty sketchy and she's got 40 of her 80 gallons full and a pinhole leak at that gasket site... Trying to decide if it's worth the extra money to have the company who is going to drain the tank for me do the valves and seals since if it breaks they'll have the know-how and equipment to fix it..

 

The tank on the '74 Chevrolet was manufactured by Western Tank & Equipment in Lubbock, Texas.  The screws on the gauge for this tank gauge came out easily.  Also, I did not experience any issues with the gauge screws when I replaced the O-ring on the '73 GMC tank. However, both of these tanks spent most of their lives in a more arid climate.

Once the screws come out, the gauge just slides out of the tank. There is a square shoulder O-ring on the backside of the gauge. To replace, just remove the old o-ring and slide on the new o-ring. 

I did find photos of the tank disassembled for cleaning and painting. If I get some more time, I'll try to get them uploaded.

In my opinion, it would be a good idea to ensure the seals in the valves and the gauge o-ring are in working order before the parts go into regular service.  I think it would be more of hassle to have to go back and replace those parts after everything else is put back together.

FYI, I have another posting on here with links that may interest you, just search "Alternative Fuels".

[Dirty Offio]

This is an awesome article!  Thank you very much for doing such a good job on it.

[Jason S]

This is an awesome article!  Thank you very much for doing such a good job on it.

Thank you for the compliment.  I tried to show cover most of the steps in case anyone was interested in running LPG on their truck. 

[gehidore]

Finally got mine up and running with the 425 valve body, Impco Fuel Bonnet, and Model Ep Vaporizer.

[youtube]https://www.youtube.com/watch?v=Ub6Xqoi5Xus[/youtube]

[impco lpg]

lpg is the way to go runs mint on gas and half the price. in the uk its 49.7 a ltr
mines a  impco  modle E vaporiser with 300a mixer  f-380 filter,180 ltr tank just fits in. with flash lube
next mod is to fit vacuum power vale
http://www.ebay.co.uk/itm/181048925618?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

[Jason S]

lpg is the way to go runs mint on gas and half the price. next mod is to fit vacuum power vale

Until recently here, LP gas has been quite a bit less than gasoline.  The engine runs great on LPG, plus the plugs and oil are so much cleaner. I'd be curious to know if you get that power valve and how it works out.

[impco lpg]

mine is just pure LPG i have removed all the petrol side ie; tanks/pipes/pump. i had to mod the 25mm  feed pipe and fit a shut off valve at the end, so it starts quicker
 http://www.ebay.co.uk/itm/231313637799?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT
your oil will stay clean, and the flash lube helps clean the engine. i will let you know if the power valve works