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IDI Propane Setup

Don Lambert (Zigg)

An inexpensive alternative to turbocharging for the IDI Owner who wants more from his machine.

I first heard about the addition of propane to a diesel engine from some of the threads on Why Propane injection??? Diesel engines burn approximately 75% of the fuel that is sprayed into the cylinder. That unburned 25% is either exhausted from the cylinder or it finds its way into the crankcase. Either way fuel is wasted and does not produce power. One method or regaining the potential BTU output of the unburned fuel is to inject propane (LPG) into the intake air. Propane acts as a catalyst and enhances the burn of each cylinder firing. The result is a cleaner burning engine (less soot, cleaner oil), increased fuel economy, and increased power for any given volume of fuel.

I was intrigued, so I checked into it. I found a few companies that offer after-market bolt on systems, most of them in and around the $500 (U.S.) price range. Unfortunately, most of these are designed for turbocharged engines. Since mine is not a turbo, I was hoping to find a system that would work on a non-turbo application. A company named Bully Dog Technologies returned an email, and said their system would work on a non-turbo application. Regrettably, it was still $600 (U.S. [about $900 Canadian.]) and I figured I could build something similar that would be significantly less expensive. I read many of the threads at on this modification and found one that described a homemade system designed for a turbocharged PSD. I liked the way this system was constructed and decided that it was a safe reliable system that I could adapt for use in my non-turbo application.

WARNING! Propane can be very dangerous if not used properly. Abuse can lead to death or injury.

I decided to design my system to supply Propane only when maximum power was required. This way I would conserve propane, which can become expensive when run all the time.

Equipment required...

  • Vapor-type propane tank (BBQ style 20lb'er works fine)
  • High to low Pressure regulator (Acetylene regulator works great)
  • Hobbs pressure switch
  • Electric solenoid Lock-off switch
  • Micro switch for throttle activation
  • Various hose & fittings
  • Dash mounted toggle on/off switch

The total cost for all this stuff was less than $250 (Canadian.) I did scrounge some of it second-hand. To purchase it all brand new would probably run closer to $300 (Can.)


A long (10ft.) extension hose connects the tank sitting in the back of the truck to the Acetylene regulator mounted at the front of the bed on the driver's side in a Plywood box. I had to wire wrap the hose fittings to connect the high-pressure hose to the regulator. (Don't want any leaks here!)

The box I constructed for the regulator is accessible, and safe from things bouncing around in the bed of the truck. I put the lock-off valve on the low-pressure side of the regulator so that if it somehow didn't completely close off the flow, the leak would at least be a low pressure one. Some setups have a second lock-off valve connected to a separate on/off toggle on the dash, which might also be a good idea. I set the regulator to 4psi measured in a closed line. When the flow is activated, the low side of the gauge drops to less than 1 PSI.

I then ran 1/4" fuel rated hose from the Lock-off valve through a solid brass fitting mounted at the forward drivers side corner of the truck bed. The hose continues along the inside of the frame rail, up over the top of the engine where it further continues along the firewall, and finally connects to the to the air intake hat. The connection to the intake was made with brass 3/16 I.D. fittings equipped with 0-ring seals and a small 4" length of copper tube. The copper tube is placed on the inside with eight (8) holes drilled through one side to disperse the Propane into the incoming air stream.

The electrical connections consist of running a wire from positive power through a micro switch mounted alongside of the fuel injector pump. The micro switch is attached in a fashion so that it is barely coming into contact with the timing advance lever. Mounting in this manner allows the switch to activate the Propane flow once the lever moves out/away from the pump. I set mine to allow the switch to activate when the throttle is at about the halfway point.

I then ran the wire from the micro switch to a Hobb's style pressure switch. The two switches shown to the right are plumbed into the oil pressure gallery. The switch on the right is the one I used for the Propane system. It is normally an “open” switch, therefore it allows current to flow when the oil pressure is above 15psi. The switch on the left is for the previously installed "idiot" light that I have on my dash. It is not related nor required for the LPG setup. It is a normally "closed" switch and only allows the idiot light to light up if oil pressure drops below 15 PSI! I use that one for sake of paranoia.

Finally, the wire runs through a toggle switch on the dashboard (In the picture it is the little blue one down low). The switch is also connected to the little green LED on the steering column to indicate when the LPG is being activated. From the dashboard switch the current runs to the Lock-off valve located in the box mounted alongside the regulator.

Well, that's it!

Does it work you might ask??? You Bet! It took a bit of fiddling to get the micro switch set where I wanted it to be, and some more fiddling to find the best pressure to run the system at. Once I got it right, there was no turning back. The difference in power was immediately noticed and very impressive. One desirable feature, inadvertently designed into this system, is that it doesn't instantaneously develop power and "snap on.” Instead, it comes on smooth and strong. I believe this is because the distance from the regulator to the intake is about 11 feet. At most, there is about 1 second delay, but it is barely noticeable when the demand for power is required.

To put the power increase in perspective I conducted a few tests to get some numbers. On the flat, shifting through all 4 as fast as I could, 0-60mph, without the LPG, I could do it in about 22 seconds (3 tries averaged). When I turned the LPG on and did the same test, I spun out in 1st, and was still able to make it to 60 in roughly 16 seconds. Climbing a local hill, about 5% grade, with about 2,000lbs of gravel in the back, without LPG, I couldn't hold 55mph in 4th, and had to shift down after about 1/2 mi. When I did the same thing with the LPG on, I had to back off the throttle at about 3/4 mi, because I was pushing 65mph!! (Speed limit 55.)

Long Term Review of the Installed Components:

I have had the Propane system in constant operation for a few months and I found the following: I have not noticed any increase in fuel economy, in fact, my fuel mileage has gone down significantly, and I am pretty sure I know why… I can't seem to be able to get my foot off the "go pedal"… It's so hard with all that available power!! Furthermore, I was surprised how long the Propane lasted. The 20 pounder that I started with only needed a refill after 8-10 tanks of diesel fuel were emptied. So, to me, for 15 bucks to fill the Propane tank, it's well worth it for the amount of additional power return.

I had to make a couple of changes to the original system. I found that the single stage "acetylene" regulator that I used was a little difficult to control. I was always adjusting it, to find the "sweet spot." I'm convinced this problem is caused by changes in tank pressure due to ambient temperature variations. To address this problem, I installed a second small regulator in the low-pressure side of the regulator. I plumbed the second so that it is closer to the engine. This drops the tank pressure to between 10-15psi with the 1st stage, and then it further drops the pressure with the second stage. I can run the system at about 5-6 PSI through a 5/32(instead of the original 3/16) inch orifice to the engine. Tank pressure will fluctuate normally, and the pressure at the engine remains more consistent with less adjustment required. I collaborated with one of the guys here on and he had done much the same thing to compensate for these pressure variations. He used a Sears Craftsman model 359H, two-stage regulator. (See Photo) I liked the simplicity of this regulator and attempted to find one like it, but I couldn't locate one here in Canada.

Additionally, I have found that if the micro switch is set to allow flow of Propane at very heavy throttle applications, the result is a lot off black smoke. It comes with lots of power too. Instead, I found that if I set the switch so that the Propane flows at a throttle position just over that required to lightly accelerate on the highway from 60mph, it allows the Propane to flow as power is required, and the black smoke (over fuel) doesn’t appear until the pedal is nearly at the metal. Since moving the micro-switch, I have also noticed that my foot only goes to the floor on those long steep hills.

One undesirable feature I found: When the Propane hasn't been on for a long time, the first time or two that it is turned on, there is often a lot of black smoke for a bit. The black smoke clears up very quickly, and I am guessing that it is due to built up carbon/soot deposits being "blown" out of the exhaust system when the Propane is being used. Once the Propane has been on for a few seconds, the exhaust clears up, and there is hardly any smoke out the exhaust at all, even with heavy acceleration.

Overall, I still feel that this is the single most significant thing I have done to my Naturally Aspirated engine to get more power without having to spend the big bucks, and have the added stress of a turbo. I will mention again, this stuff is great if used properly and respected, but we know that Propane can do some serious damage to life and limb if abused. Double and triple check your system for leaks before using it. Perform a leak-down test and use soapy water at the connection points. Better yet, have it inspected!

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