anyone have LPG tech?

[original balzer]

I have been thinking about going the LPG route on something.
from what I have read you can do much higher compression and its best to build an engine with LPG in mind in specific way to maximise potential.

So is anyone on here LPG savy?

I know the claims of lower HP and some of the other concerns but with an engine built specifically for LPG it shouldnt be an issue.

 

[lectric80]

Talk to kgblazerfive as I know his 1-ton is LPG. Seems like the mileage still sucks from what I remember him telling me.

 

[Mike D]

I am not an expert, but two things to remember: 1) LPG is a blend of propane (a 3 carbon hydrocarbon ) and butane ( a 4 carbon hydrocarbon ). It has a natural octane of 100, therefore a 10:1 compression ratio would optomize its potential horsepower. 2) gasoline is a blend of 8 - 10 carbon hydrocarbons. The energy (BTU) of LPG is about 1/2 the energy of gasoline. That means the engine will use 2 gallons of LPG to do the same work as 1 gallon of gasoline ( aproximately ).
Several years ago the company I worked for converted three vehicles 4,6,and 8 cylinder vehicles to monitor oil additive depletion ,fuel economy, and overall vehical performance. From what I remember ( 15 years ago ) oil additives depleated slower, vehicle performance was a little zippier 0 - 40 mph, a little more sluggish 40 - 80 mph, and the fuel economy was about 1/2 the vehicle got with gasoline. One of the engines ( I don't remember if it was the 4 or 6 cylinder engine ) got better than expected mpg probably due to higher engine compression.
I realise that current engine technology and fuel management could potentially optimize engine performance and fuel economy, however the basic fact is LPG contains 1/2 the energy compared to gasoline.

 

[us74k5]

I run LPG on my big block. Its great, so far gas mileage is about the same as I had before with gas. I am not sure about it being half the efficiency, i think the math is off on that. I know its a little lower, but fairly certain its not half. Also assuming you will only get half the mileage is assuming you are using 100% of your gasoline efficiency. Which you are not. Especially if you are running a carb. The overall LPG system just seems to be much more efficient. I have roughly the same power I did with a carb, much better throttle response, and about the same fuel mileage so far. It looks complicated, but once you spend about an hour looking at other setups, its really easy to get hooked up. If you have any questions shoot me a PM.

 

[rufusbooth]

I have been running 100% LPG on my 73 Jimmy since 1975. The engine was built specifically built for all the things that LPG likes. As far as loss of mileage you do loose some but it is certainly not 50%.

I got about 12 MPG with my SBC 350. No matter what I did long highway runs or pulling a heavy trailer it never changed. The whole setup was dynoed at the rear wheels to be 315 HP and 340 TQ at 5500 RPM. It has a Th350 trans and a 203 transfer case so you can guess at FW HP.

The nicest thing about it is that at sea level or 7000 feet it never needed tuning and there is no choke to deal with. The thing would start with the first turn of the key at 7000 feet at 17 degrees after sitting for 3 days covered in snow.

LPG 95,475 BTU / gallon
Gas 125,000 BTU/gallon

You loose about 10%. That loss can be compensated for by some smart engine choices during construction.

Raise compression. I am running 11.5 to 1 compression ratio. this was using a set of ported steel heads. With aluminum heads you might be able to go up another half point.

Use Stellite exhaust valves. This helps the valve deal with the higher exhaust temps.

A lot of the same rules apply for an LPG intake Manifold as a TPI manifold as the intake charge is a vapor. There are no fuel puddling issue in the intake so you can get away with larger runners without having the fuel dropout issues. Go bigger than you would expect to need on gas.

Make sure your cooling system is up to the task as the motors do run warmer for some reason. use a good 4 row radiator and a quality water pump like an Edlebrock.

Stay away from molly rings. The propane burns so clean that they will never seat properly. This was the one problem we had with our motor. It burned because we could not get the rings to seat. we ended up having to hone the cylinders and replace the rings to get them to seat. After that the oil consumption dropped to nothing. One thing that can be done is build up the motor and break in the motor on gas then swap to LPG. You will need to use some high octane fuel but the rings WILL seat.

Find someone that knows how to build a performance LPG motor and get a custom ground cam, it is worth it.

It will take a bit of dyno time to re curve the distributor to get every last bit of power out of the motor as LPG likes different timing.


The rest of the motor is built just like any other performance build. Hope that helps. If you have any questions feel free to ask. I will try to answer them as best as I can.

Cheers,

Rufus

 

[original balzer]

Thats the stuff Im looking for. Thanks.

Although I am actually seeing a lot on the web sugesting 12.5:1-13:1 compression for Strictly LPG engines. Thats pretty good. I am also seeing a lot that sugests single plane manifolds large runners and big valves.

Alternatly running 9ish:1 and 10-12lbs of boost is also popular with LPG. Especially in Austrailia.

Now why is this appealing? Because in a gasoline engine you would have to run 100+ octane which is over $5 a gallon most anywhere. checking locally I can get LPG for as cheap as $1.80 a gallon. and its already 100 oct equilivent. It is also proven to run cleaner with less carbon deposits. That says to me longer engine life and lower maintainance costs.

I dunno but it all adds up to a better choice to me.