Re: IML: propane conversions to an imperial

["mike sutton" <mikanlin62@xxxxxxxxxx>]

Having actually DONE a few propane conversions, versus having just read 
about them, I can share what I know about this process.  From the standpoint 
of what you have to do outside the engine, its fairly straightforward. I 
would like to  list the steps involved as a general idea of what has to be 
done and add a few words to why some of it works the way it does.

A fuel tank has to be mounted , and they are rather heavy and bulky 
cylinders compared to the average factory tank.  That is the biggest problem 
in most cases, finding a place to mount the tank and plumbing it. The tanks 
are very robust, people tend to be scared of them regarding crashworthiness 
and such, they will usually survive better than the car itself in an 
accident since even if they break away the fuel line is designed to shear at 
the tank and the tank valve will close the tank and the tank will simply go 
on its way.  The fire risk of the tank in an accident is probably safer than 
a gasoline tank.

A hose has to run from the tank to the engine compartment,  again a simple 
task.  There are specially designed hose materials to do this with or metal 
hard lines can be fabricated.  A propane conversion will address this.

Then the fuel goes to a vaporizer - regulator device .  Sometimes they are 
combined into one unit and sometimes two.  The vaporizer uses coolant, 
which is tapped into the cooling system from one of the heater hoses, bypass 
hose or radiator hose depending on the vehicle cooling system layout.  The 
reason is because the propane is a very high pressure liquid state when it 
gets to the engine.  It has to be turned into a vapor and reduced down to a 
low pressure state before the engine can use it.  Simply regulating the 
pressure would result in freeze up of the fuel system when the propane goes 
from liquid to vapor as it boils at about -50 F. .

The regulator steps the pressure down from high pressure to low pressure so 
the mixer can use it to deliver it to the engine.  The mixer is a what the 
propane industry often calls the carburetor.  Usually there is a diaphragm 
that senses load and a mechanical linkage that is hooked to the throttle 
that opens and closes a helix or similar type of variable opening that is in 
synch with the linkage.  You open the throttle and you open the variable 
opening to allow more lpg thru, the diaphragm senses load via vacuum and 
allows more or less lpg as load conditions vary.

Propane is always under slightly higher pressure than ambient at the mixer, 
so it doesnt have to " pull " fuel like a gasoline carb does,  it only needs 
a vacuum reference from the engine to open initially  to allow fuel to flow. 
Usually there will be a solenoid or vacuum valve to positively shut off 
propane flow unless the engine is cranking over or running, so if the engine 
quits for any reason the fuel stops also.  Often the solenoid is controlled 
by an oil pressure switch so that is not a difficult thing to accomplish.

As far as the engine itself goes, propane is a dry fuel and does not 
contribute to washing down the cylinder walls like gasoline does, it doesnt 
contaminate the oil with unburned fuel like gasoline does, but it has 
absolutely no valve seat lubrication properties at all like leaded fuel used 
to and while the octane content is higher the btu values are lower than 
gasoline.

A high quality valve job is essential, hardened valve seats are a very good 
idea for the long term, though since there hasnt been any real amount of 
lead in fuel for so long now, if the valve and seat are in proper condition 
then hardened seats need not be added unless the existing seats are sunk 
into the head to start with.    If the engine has valve rotators on it - 
which for a Chrysler engine in a passenger car should not be an issue - they 
have to be removed. Chrysler typically did not use rotators in passenger car 
usage.

Higher compression is a must if you want to regain the power loss from the 
lower btu value of the fuel , and depending on the year of the engine you 
can shave the cylinder heads , get heads with a lower combustion chamber 
volume - this may not be an option on early engines as they are already 
rather low volume - or get higher compression pistons.

As far as tuning, total spark advance may have to be decreased a bit, but 
the best rule is to consider getting the distributor advance checked and 
recurved per the conversion kit instructions or by a shop that does 
conversion work.  Propane burns much slower than gasoline  and you do not 
want combustion to still be occurring when the exhaust valve opens as it 
will quickly overheat the seat and the valve.

There are some kits that use an oxygen sensor to read the exhaust and then 
vary the mixture just like any gasoline engine via a black box mounted on 
the car and usually a simple solenoid to allow extra air into the mixer to 
lean the mixture further for best emissions and economy during sustained 
cruise.

In the time since I last did these conversions, there are now some very 
complex systems that use multiport injection and are also OBDII compatible 
and are EPA compliant as well....for the type and amount of driving that 
most Imperial owners will do, I dont know if that additional expense would 
be worthwhile or not.

One thing I have not addressed is the dual fuel engine,  since with this set 
up in my opinion you do not get to enjoy either fuel as there are too many 
compromises that have to be addressed to use gasoline or propane in the same 
engine.

http://www.propanecarbs.com/

Here is one link to much more information that I have posted, for those of 
you who couldnt give a rip about this, I apologize for the lengthy post. 
For those of you who are interested, or just want factual information, I 
hope you find it useful

Mikey
62 Crown Coupe 




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