electronic fuel injection

hi im doing a report on EFI and i need to get as much info as i can...i need to know things like how its helped the car industry and pretty much why have they switched from using carbs? whats the big deal with efi??? so any info would be greatly appreciated thanks

efi is alot more fuel efficient and allows you to use different fuel curves for partial and full throttle and various engine speeds. Also, EFI requires alot less maintenance than a carb.

http://auto.howstuffworks.com has alot of info on how both work.

Sounds like a fun report. I think it had a huge impact on the car industry. Carbs were great, but in the smog crunch starting in 1973, car companies were asked to do the impossible; comply with nearly impossible emissions requirements. To do this they had to drastically reduce compression ratios, cam durations, and power outputs. They had very little knowledge of the emissions equipment like EGR and Catalysts, but they smacked them on there without any real idea how to properly tune it. People were frustrated that for two years the most HP you could order in a corvette was 180.

EFI came along and revolutionized the automotive industry. Its more accurate, better atomized fuel metering allowed much more flexibility. Keep the mild cams and compression for an economy car, or go ahead and push the limits a little with cams and compression and use EFI to be able to keep the emissions acceptable.

In the early 70s, HP ratings went from "gross" hp ratings to SAE net, so its hard to compare apples to apples, but the early 70s caused the death of the muscle car as we know it. No longer could you get a 450-hp Chevelle. Power numbers dipped deeply in the 70s and 80s, but now look at whats out there. You can buy mustangs and corvettes with 400 hp off the showroom floor. Much of that is due to computer modelling of heads for increased efficiency, but it would not be possible without EFI

uh don't you mean oranges?

Whats the difference between SAE net and gross ratings?

Nope, I mean apples. I used the phrase in the double negative so to speak. Ideally you want to compare apples to apples, so I said in that analogy its hard to do that using gross and SAE net ratings.

The difference in the ratings is this. Prior to SAE (Society of Automotive Engineers) ratings, power outputs were measured in gross HP. This was an ideallized number based on an engine dyno with no accessories. Just an engine with headers, big straight exhaust, no alternator or air pump, and usually no smog equipment (not that it was common to have any smog equipment in that day). Since there were no protocols, there was ample room for "fudging" numbers. Different dynos used at different locations, corrections for atmospheric conditions, and downright lying made HP ratings almost comical in some cases.

The 1970 Chevelle SS 454 with the LS6 option was rated at 450 gross HP. If you bought one new, pulled the engine and put it on a dyno, it actaully made more like 515 gross HP, but Nobody's insurance would touch a car with over 500 hp. Chevy chose to test it in the hot desert with manifolds instead of headers and came up with the 450 number. Conversely, I had an AMC inline six rated at 120 hp. That was a load of bull. It made 85, tops, but no one would have bought an 85-hp wagon, so the choice was made to idealize the rating.

Later, SAE stepped in and created standards to level the playing field and make more realistic numbers. Manufacturers are now required to test engines under specific conditions, including all of the belt-driven accessories, air intake box, manifolds, smog equipment, and a full chassis exhaust that duplicates the one used in the vehicle. There are still discrepancies in ratings and actual outputs in today's cars, but they are very minimal. Production tolerances, mistakes, or slight changes from the prototype to the production model account for these. There are rare cases where there were big problems, like recent Mustang Cobras. Some were shipped with a different intake manifold that were thought to not affect power. They actually cut about 60 hp from the total output and they had to recall them.

By 1974, that same Chevelle 454 could only be ordered with 235hp. That lower number is partly due to the switch to SAE ratings, and partly due to smog restrictions.

Given the inaccurate nature of gross HP ratings its hard to say that "SAE is XX% lower than gross," but in general SAE is typically 15-30% lower than gross for the same engine. The actual power the engine makes is the same, its just different ways of measuring it.

What really killed the carbs was the emission demands and the catalytic converter which required an air fuel mixture of lambda 1.

But fuel injection also had advantages since its computer could calculate the fuel needed, and later also the ignition timing based upon more factors what control the flow though a carb. This makes it possible to operate the engine closer to where detonation would occur.

Fuel injection also doesn't require any pressure drop to work like the carbs do, this increases VE and also makes the engine run better at low engine speeds with more extreme cams. For example that have make it possible for a racing engines with someting like 330 degree cams to idle almost normally.

Excellent points, SaabJohan. Totally escaped my post :)

so whats lambda 1? and what does ev stand for? thanks for all the posts their helping out alot

is it better to have sequencial fuel injection or just regular?

Lambda is the air fuel ratio. A perfect mix (meaning that there are the perfect number of O2's and Gasoline molecules that if they all burned there would be no left over of each. More gasoline and there would be extra gas in the exhaust. More air and there would be extra O2 in the exhaust.

This ratio is 14.7:1 air/fuel. For every pound of fuel, it takes 14.7 pounds of air to supply the right amount of oxygen. 14.7 is sometimes expressed as a value of 1 on a "lambda" scale. The reason for the lambda is the number 1 is easy for computers to understand. When an O2 sensor for instance is giving the computer a value of 1 on the lambda input, it knows its at 14.7:1

VE stands for volumetric efficiency. It is a ratio of how much volume an engine displaces vs. the amount of air it takes in. Lets say you have a one-cylinder engine that displaces one liter. Let's say its fed with a straw instead of a carburetor or EFI. If you turn it by hand really slowly, there is time and adequate flow such that the cylinder fills the whole way. This would have a VE of 100%. If you spin it really fast, there is not enough flow to fill the cylinder before its on its way back up, and therefore it would have a VE of less than 100%.

This is a very simple explanation, but VE in an engine is a very complex thing having to do with port flow, cam timing, and other factors. By this rationale, you can see that engines with turbos and blowers can achieve more than 100% VE

In theory, sequential is better. Batch fire fires one set then another set instead of each one for each timing event. In actual practice, there is rarely a difference in the two as far as MPG, proper lambda, and drivability.

Typical fuel injection system uses pressure from an electric fuel pump to provide fuel. A carburetor uses engine vacuum to draw fuel into the engine. Fuel injections gains its advantages in allowing an improved atomization (fuel is being sprayed into the intake manifold under pressure) which will help bring the fuel in as a fine mist. Better atomization improves fuel distribution into each cylinder and more efficient combustion of the fuel. This leads to many advantages over a carburetor. Better fuel economy due to more precise fuel metering, distribution, atomization. Emissions can be maintained better since you can run a lean air-fuel mixture [a mixture greater than stoichiometric: 14.7:1, for instance: 20(air):1(fuel)]ensuring a better percentage of fuel is burned. Cold weather drivability is improved. And the biggie, an overall increase in engine power. Of coarse having a proper engine setup will increase the efficiency. Engine setups such as lean burn engines use correctly shaped pistons paired with correctly located intake manifolds to generate more swirl in the combustion chamber. This process allows the fuel to mix even better increasing air-fuel ratios as high and 25:1. Multi-valve engines also improve this process. Then you also have direct injection systems where fuel is injected directly into the combustion chamber under high pressure prior to ignition allowing an even more precise control the the charge.

One of the best books on fuel injection that I know is the Bosch book. It goes into therory and the evolution of fuel injection from mechanical to full electronic. It can be found at most bookstores including amazon.com