DFI? EFI? What's The Difference

[nightstalker]

I see outboards advertized as DFI (direct fuel injection) and EFI (electronic fuel injection). Can someone tell me what is the difference between the two and which injection system is best? Are there DFI and EFI 2 strokes, 4 strokes?
Thanks,
Nightstalker

 

[steelespike]

Re: DFI? EFI? What's The Difference

basically EFI is the injection of fuel into a port near the cumbustion chamber.
DFI injects directly into the cumbustion chamber at the exact computer controlled time.Used on Diesel motors dating back probably to the early 1900s,of course without the advantages of computer control.

 

[DJ]

Re: DFI? EFI? What's The Difference

For now, DFI is essentially limited to two strokes. DFI injects fuel directly into the cylinder as two strokes have no intake valves as we think of them.

EFI is primarily on four strokes (although there have been some EFI two
strokes). EFI, essentially, (now) injects fuel into the intake manifold just ahead of the intake valve(s).

Some auto manufacturers (Mazda/Ford, to name one) have developed DFI for their four stroke engines. Many claim that DFI is more efficient because you eliminate losses in the intake manifold.

In the outboard world, DFI (2-stroke) was developed to present an efficient, lightweight engine. Oil is still injected but at vastly lower rates, than in the past. The DFI 2-strokes do not have a valve train, thus allowing for the lighter overall weight.

 

[nightstalker]

Re: DFI? EFI? What's The Difference

Thanks for the info. I understand it now. The few EFI 2 strokes would not be as efficient a a 2 stroke DFI correct?
Nightstalker

 

[DJ]

Re: DFI? EFI? What's The Difference

Thanks for the info. I understand it now. The few EFI 2 strokes would not be as efficient a a 2 stroke DFI correct?
Nightstalker

Correct. In theory and in application that has proven to be correct.

 

[Silvertip]

Re: DFI? EFI? What's The Difference

At wide open throttle it makes very little difference whether an engine is carbureted, EFI or DFI contrary to what the manufacturers would like you to believe. It still takes "X" amount of fuel to make a certain amount of HP. EFI and DFI have a fuel consumption advantage over a carbureted engine at idle and in the mid RPM range. So when you use the term "efficiency" be careful as it is not the same as "economy". This topic has been beat to death so I won't get into the actual "economy" of operation.

 

[JB]

Re: DFI? EFI? What's The Difference

Correct, stalker.

DFI offers several advantages in both 2 and 4 stroke engines that EFI (and carburetors) cannot match.

Most prominent is the complete prevention of fuel being scavenged out with the exhaust. This allows more radical port timing in 2 strokes and more radical valve timing in 4 strokes.

Next is the use of a stratified charge. This allows the fuel/air mix to be richer right at the point of ignition and leaner as the flame front advances. The results are that the fuel charge is more completely burned and more power is developed with less fuel.

I am not sure of this, but I also think they will burn lower octane fuel without preignition or detonation.

There are several cars now on the market with DFI 4 strokes. The specs are remarkable for engines of those displacements and most run on regular gas.

FORD and Mercedes Benz (and maybe others) are developing DFI 4 strokes with compound turbocharging that make Racecar power per cubic inch with diesel-like fuel (gasoline) efficiency.

Great engines are on the horizon. They will be showing up as outboards eventually. Could be they may be badged Johnson?

 

[Chris1956]

Re: DFI? EFI? What's The Difference

As JB has stated, the most important advantage about the DFIs is that gasoline is injected into the combustion chamber after the exhaust port is closed. No unburned gas (and its high hydrocarbon content) makes it into the exhaust. In addition, only gasoline is injected since the oil is seperately injected into the intake air at the throttle bodies, as it makes its way thru the reed valves and into the crankcase. The DFI motor is similar to an EFI motor, except the gas and oil are not mixed in the fuel pump, and the gasoline is diverted to the injectors on the cylinder head.