EFI Conversion - The Reason For It All: -

Date	Discussion
Dec 2022	A question often asked is, "Why does Rhapsody have a petrol engine in favour of a diesel unit?" and, given that diesel engines do have some advantages, it's a reasonable question. The first reason is very simple. I chose a petrol engine because I already had a suitable unit "in the shed". It was fully marinised and ready to go - (or so I thought, but more of that later). The alternative was to source a new 80hp diesel engine, plus a suitable gearbox, that would not have left much change from $20,000. So, the decision was quite simple. It should be noted that Rhapsody was originally intended to be solar powered, and that option was also dismissed eventually, not only on the basis of cost, but efficiency. It is true that in the intervening fifteen years, or so, the technology has improved as dramatically as the prices of solar panels, electric motors and batteries have declined. If one were designing a new boat now, perhaps the decisions would be different. The decision process that led to the abandonment of the solar approach is discussed in excruciating detail elsewhere. Whilst diesel engines do have some advantages over petrol, such as fuel efficiency, low end torque, longevity and, sometimes, simplicity, they also have some major disadvantages. Diesel engines in boats, in my experience, vibrate badly and are both noisy and very smelly. They are simply not pleasant things to be around in the confines of a boat. Also, whilst I have considerable, albeit amateur, experience with petrol engines, I have absolutely no experience with Mr Rudolf Diesel's creations. The petrol engine installed in Rhapsody is from a 1965 Holden (GMC) model "EH". It is an early example of an Australian designed series of engines, known as "Red Motors", that were used in all Holden cars from 1963 to 1980. (They weren't actually all red!) It has a capacity of 149cu in (2,443cc), although in later models this was increased in stages to 202cu in (3,310cc). It is a six cylinder unit that generated 100hp when new, with seven main bearings, that earned itself an enviable reputation for being simple, quiet, smooth and practically "unbreakable". Also, Holden made so many of these engines, over the years, that replacement parts are still readily available, if needed. Note: - the Red Motor installed in Rhapsody is now painted blue - well, why not? The original carburettor was a single throat downdraft Stromberg, which was selected more for economy and reliability, rather than performance. As a result, many people re-carburetted their engines, "back in the day", to improve that performance and this has turned out to be quite useful, given that many "upgrade" parts are still available. Why is a carburettor a bad idea? Carburettors meter the volume of fuel going into an engine very carefully and convert it to a vapour at the same time. Part of the process requires the incoming fuel to be at atmospheric pressure and whilst there are many other factors involved, such as ambient temperature, let's ignore those for a moment. The fuel pressure is controlled by a "float bowl" that works much like the water cistern in a toilet. Fuel is pumped into an open container that contains a float connected to a valve. As the level of fuel in the bowl rises, the float also rises and eventually stops the flow. As fuel is consumed by the engine, the level in the bowl drops and the float valve opens to admit additional fuel to maintain a constant level. It is a continuous process that was invented in 1875 and works very well. However, consider what happens when the engine is turned off. The float bowl is still full of petrol, and this is where the problem occurs. (You can avoid the problem by switching off the petrol supply before the ignition and letting the engine empty the float bowl - but are you willing to gamble your life on you, or worse still, someone else, remembering to do that?) Once the engine is stopped, the petrol remaining in the bowl evaporates over time and becomes a vapour, which, being heavier than air, falls and collects in the lowest part of the engine compartment, where it lies in wait for the merest spark to trigger a fire or even an explosion. There have been many attempts, over the years, to seal carburettors against leakage for environmental reasons, as much as anything else. The undersides of car engine bays are always open to the air to let any lost petrol vapour escape safely, but none of these systems is perfect and leaks can occur from other parts of the fuel system over time as well, of course. In a car, these leaks don't usually cause a severe problem, but in a boat, with a closed engine space and sealed bilges, they can be fatal. In contrast, a fuel injection system doesn't have an open float bowl or any other opening from which fuel vapour can escape (mechanical failures notwithstanding). It uses a closed pressure regulator and one or more electrically operated valves (the injectors) to deliver measured doses of fuel into the engine at high pressure, which has the effect of vaporising it as well. Significantly, when the engine ignition is turned off, the injectors simply don't open anymore and there is no fuel wasted or left "hanging around" exposed to the air. In a perfect world, a fuel injection system, once it's turned off, is completely sealed against leakage and that's what makes it so desirable for application in a boat.

Date

Discussion

Dec 2022

A question often asked is, "Why does Rhapsody have a petrol engine in favour of a diesel unit?" and, given that diesel engines do have some advantages, it's a reasonable question.

The first reason is very simple. I chose a petrol engine because I already had a suitable unit "in the shed". It was fully marinised and ready to go - (or so I thought, but more of that later). The alternative was to source a new 80hp diesel engine, plus a suitable gearbox, that would not have left much change from $20,000. So, the decision was quite simple.

It should be noted that Rhapsody was originally intended to be solar powered, and that option was also dismissed eventually, not only on the basis of cost, but efficiency. It is true that in the intervening fifteen years, or so, the technology has improved as dramatically as the prices of solar panels, electric motors and batteries have declined. If one were designing a new boat now, perhaps the decisions would be different. The decision process that led to the abandonment of the solar approach is discussed in excruciating detail elsewhere.

Whilst diesel engines do have some advantages over petrol, such as fuel efficiency, low end torque, longevity and, sometimes, simplicity, they also have some major disadvantages. Diesel engines in boats, in my experience, vibrate badly and are both noisy and very smelly. They are simply not pleasant things to be around in the confines of a boat. Also, whilst I have considerable, albeit amateur, experience with petrol engines, I have absolutely no experience with Mr Rudolf Diesel's creations.

The petrol engine installed in Rhapsody is from a 1965 Holden (GMC) model "EH". It is an early example of an Australian designed series of engines, known as "Red Motors", that were used in all Holden cars from 1963 to 1980. (They weren't actually all red!) It has a capacity of 149cu in (2,443cc), although in later models this was increased in stages to 202cu in (3,310cc). It is a six cylinder unit that generated 100hp when new, with seven main bearings, that earned itself an enviable reputation for being simple, quiet, smooth and practically "unbreakable". Also, Holden made so many of these engines, over the years, that replacement parts are still readily available, if needed.

Note: - the Red Motor installed in Rhapsody is now painted blue - well, why not?

The original carburettor was a single throat downdraft Stromberg, which was selected more for economy and reliability, rather than performance. As a result, many people re-carburetted their engines, "back in the day", to improve that performance and this has turned out to be quite useful, given that many "upgrade" parts are still available.

Why is a carburettor a bad idea?

Carburettors meter the volume of fuel going into an engine very carefully and convert it to a vapour at the same time. Part of the process requires the incoming fuel to be at atmospheric pressure and whilst there are many other factors involved, such as ambient temperature, let's ignore those for a moment. The fuel pressure is controlled by a "float bowl" that works much like the water cistern in a toilet. Fuel is pumped into an open container that contains a float connected to a valve. As the level of fuel in the bowl rises, the float also rises and eventually stops the flow. As fuel is consumed by the engine, the level in the bowl drops and the float valve opens to admit additional fuel to maintain a constant level. It is a continuous process that was invented in 1875 and works very well.

However, consider what happens when the engine is turned off. The float bowl is still full of petrol, and this is where the problem occurs. (You can avoid the problem by switching off the petrol supply before the ignition and letting the engine empty the float bowl - but are you willing to gamble your life on you, or worse still, someone else, remembering to do that?) Once the engine is stopped, the petrol remaining in the bowl evaporates over time and becomes a vapour, which, being heavier than air, falls and collects in the lowest part of the engine compartment, where it lies in wait for the merest spark to trigger a fire or even an explosion.

There have been many attempts, over the years, to seal carburettors against leakage for environmental reasons, as much as anything else. The undersides of car engine bays are always open to the air to let any lost petrol vapour escape safely, but none of these systems is perfect and leaks can occur from other parts of the fuel system over time as well, of course. In a car, these leaks don't usually cause a severe problem, but in a boat, with a closed engine space and sealed bilges, they can be fatal.

In contrast, a fuel injection system doesn't have an open float bowl or any other opening from which fuel vapour can escape (mechanical failures notwithstanding). It uses a closed pressure regulator and one or more electrically operated valves (the injectors) to deliver measured doses of fuel into the engine at high pressure, which has the effect of vaporising it as well. Significantly, when the engine ignition is turned off, the injectors simply don't open anymore and there is no fuel wasted or left "hanging around" exposed to the air. In a perfect world, a fuel injection system, once it's turned off, is completely sealed against leakage and that's what makes it so desirable for application in a boat.