Carbureted v. EFI

[Carb'dCobra]

First of all, I wanna clear up my end. What I'm hoping to accomplish here is not start a brutal war; carb this, efi that. I want everyone who decides to post, to post with concise and educated facts about each of these induction types, and let whoever is interested in changing the induction on their motor, to have an easy means of learning about which one suits their application better.

I'll start on what I know: Ultimately I believe their are two different routes...

Carburetion, I believe, is most effective in highly modifed, high horsepower, nostalgic(show cars), and "I could give two s**ts less about gas" applications.
EFI, on the other hand, I believe is much better used in street vehicles. Not to say that someone shouldn't use curburetors on the street (I do...Jesus do I), but as far as gas prices go these days, EFI has a clear advantage. Thats not to say that EFI motors can't make big horse numbers as well, but unless this somehow turned into an all-out forum for sanctioned, circuit-run race cars (as opposed to the majority of people here who refer to this site for their daily drivers), I would have to say that EFI is clearly the better choice for the street and shouldn't be highly modified.

Also, you must remember there's not a whole helluva' lot you can tune on EFI. You can fidd'ly fart around with the computer til' your heart's content, but when it comes down to the most efficient way of making more horsepower, theres alot more to be had in basic elements like intake manifolds. Not to say that there isn't a selection of manifold for EFI motors, but there is a much, much greater selection in carbureted manifolds. Also, there are alot more tuneable elements to a carburetor, especially highly modified carburetors. Different modes of induction with carburetors also add to the tunability; air pans paired with scoops, velocity stacks, etc.

Thats my two cents, but I still want to stress my point: Find which one fits you and your application best, and do what you want with it. And for Christ's sake don't go on and on about how certain inductions are superior. Remember, they're superior in their own rights (gas mileage, horsepower, etc.). There is no form of induction that has an ALL-OUT advantage above the rest.

 

[jrichker]

Some basic thoughts about two very different approaches to making power in an internal combustion piston engine:

Carburetors are mechanical devices that depend on pressure differences to meter fuel. The venturi is common to all type of carbs, it is what creates the pressure difference that makes carbs function. The float bowl is vented to the atmosphere just above the venturi in most carbs. The fuel is sucked out of the bottom of the float bowl through a metering system that controls the gross amount of fuel delivered to the engine. That metered fuel is then delivered to the point in the carb where the greatest pressure drop occurs. In some simple carbs, it is the area of the smallest part of the venturi opening. More complex systems may use a booster venturi to aid in fuel delivery.

Notice the emulsifier tube in the diagram: it has two purposes: It helps break up the fuel into tiny droplets and it serves as a suction breaker when the engine isn’t running. That keeps the siphon effect from sucking fuel out of the float bowl when the engine is shut down.
Also present in carbs are separate circuits that meter fuel at idle, a power valve that opens up to provide extra fuel at high power settings, and an accelerator pump to provide extra fuel when the throttle is suddenly opened. All these circuits with the exception of the accelerator pump depend on a pressure drop to make them work.

The primary limitation of carbs is that they are a mechanical device, and have no way to compensate for changes in temperature and atmospheric pressure. These two items can limit the power of a carb’d car. A race to the top of Pike’s Peak on a hot summer day would be an example of how this will affect a race car. Or a trip down the drag strip at Denver, Colorado in the summer compared to one in Los Angles during the winter. Definite power differences would be seen & felt. Adjustments can be made, but it requires some small amount of wrenching to do.

Want to learn more about carbs? see http://www.chevyhiperformance.com/techarticles/83118_carburetor_basics/ or http://en.wikipedia.org/wiki/Carburetor. If that's not enough, do a Google search: you'll find enough information to read for weeks at a time

EFI does not depend on a pressure drop to pull fuel into the intake or help atomize the fuel. The venturi and associated restriction of the intake airflow is eliminated. Instead EFI measures either air pressure or airflow along with air temperature, water temperature, RPM, and throttle position to calculate the amount of fuel needed. The calculation is much more precise than the simple mechanical process of a pressure drop across a venturi. Since a pressure drop across a venturi is not part of an EFI system, pressurized injection is needed. The injectors are capable of consistently breaking the fuel into tiny droplets that flash to vapor and distribute themselves evenly in the individual intake ports. Couple the precision of the air/fuel measurement along with timed, pressurized injection of the fuel directly into the intake port, and you have a superior system.

EFI expands itself into engine management: not only does it control fuel delivery, but ignition timing as well. The computer can add or remove timing advance while the engine is running, according to the need of the moment. Inputs from sensors can detect detonation and retard the timing, or add timing if the engine can handle it. With an aftermarket tuner and a laptop computer, you have an infinitely tunable machine that can make changes on the fly while you are racing. Consider the possibility of the computer detecting a sudden increase in RPM due to wheel spin. The computer could reduce the timing advance to the point that the wheel spin was minimal and then increase it as the car picked up speed.

See http://en.wikipedia.org/wiki/Fuel_injection for more information on fuel injection or Ford Fuel Injection & Electronic Engine Control 1988-1993 by Charles Probst :ISBN 0-8376-0301-3.

It's about $20 from Borders.com see http://www.amazon.com/ . Select boo...very good, and I found it to be very helpful.

 

[85_SS_302_Coupe]

June '06 5.0 magazine, page 62, "Animal Unleashed"....1047hp 427 stroker, totally streetable and carbed. The engine is built with a Procharger F2 blower with a carb hat, pushing only 19lbs of boost. The engine revs to 7k and is tuned very conservative...they say in the article that with more ignition and a leaner tune, more boost and race gas, the engine could easily make 1300hp. All while being carbureted and streetable, because it doesn't have a ridiculous cam.


I think a lot of people forget that while EFI is superior in many many ways, carb tech has come a LONG LONG way since the days of them being used on production cars. Today you can have a very high tech carb, even if it's built around old school tech, and you can make just as much power as any EFI setup, and it can be tuned to come very very close to what an EFI setup can bring. As far as power production between the two, there is really no bias on either side. The fact is you CAN do it cheaper with a carb setup, but you'll gain more efficiency with an EFI setup. The driveability comes down to the tune.

The reason you see more serious racers running EFI is because these days it has become easier to maintain consistancy with an EFI setup because it's all ran by computers and can be tuned via a laptop or whatever...there's less user tuning, which is becoming a lost art.

If you don't have that issue i can take some pics and post them for ya.

 

[brin0357]

Carb allll the way. I see dudes running EFI with problems alll the time. Sure we have to jet and adjust more often, but its totally worth it. More power

 

[8950HO]

Doesn`t EFI produce more torque in most cases compared to a carb?

 

[Carb'dCobra]

Doesn`t EFI produce more torque in most cases compared to a carb?

It depends on how well the driver can tune for the most part, but in any one application, if you had an ideal EFI setup and an equally set up carbureted setup, you wouldn't necessarily have more torque.

I know I'm probably wrong, but my big deal with carbs is that I like the idea that my fuel and forced air is RIGHT there, but to me it seems like there's a lag with EFI since when you step on the gas, it has to wait (under a second, but still...) til' the new forced air reaches the top of the intake runners on the heads (the placement of the fuel injector nozzle) before it will inject a proportionate amount of fuel.

I don't know much about EFI, but one thing I do know is; I'm a simple guy, and to me it just adds way too much electronic crap that isn't needed when a carburetor of equal performance will work just as well if not better.

 

[1Bad88notch]

In my opinion if the car is your daily driver leave it EFI. If its your toy and you play around with on the weekends and just go to the track with it carb it, unless you like the smell of gas inside your car when your sitting in traffic. thats just my 2cents

 

[Carb'dCobra]

Carb allll the way. I see dudes running EFI with problems alll the time. Sure we have to jet and adjust more often, but its totally worth it. More power

Thats the stuff I'm talkin' about. I'm not trying to be a d**k, but what I was aiming for was for people who wanted to know to read this thread and decide for themselves which type of induction THEY like better and not be swayed by either group, be it Carb or EFI guys.

 

[Carb'dCobra]

In my opinion if the car is your daily driver leave it EFI. If its your toy and you play around with on the weekends and just go to the track with it carb it, unless you like the smell of gas inside your car when your sitting in traffic. thats just my 2cents

Valid point. That's one thing I did like back when I had mine 'Injected, the only thing I could smell while idling was the old rotting Ford carpet...GOD I love that smell

Mine is my daily driver and I like the setup carbureted because specifically, for me, the guy who owned the car before me used to have a Holley 750 4150 double pump carb on it. When gas prices started going up he had the brilliant idea to, instead of go to a vac. secondary carb, pull an old junker EFI computer, harness, upper & lower manifold, etc. out of an '88 GT. My problem was, he was a f**kin' deedeedee and had no idea what he was doing, so I went through a mess of electrical problems before I had enough money to buy a decent carbureted setup. Thats why I went carbureted. I love my setup and I wouldn't ever go back to EFI just because it's not really my bag, but the point I'm trying to get across is, everyone has a different reason for their induction system, and it's up to them to decide which one suits them the best.

(P.S. I wasn't joking, I really do like the smell of old Ford interiors).

 

[EMW150]

If you're talking naturally aspirated, a properly built and tuned carb will outperform EFI in peak hp figures consistantly. EFI cannot atomize fuel as well as a carb. EFI fires a spray directly before it enters the cylinder whereas a carb has fuel drawn from the bowl with air and has the entire runner of the intake to mix and refine the droplet size before it enters the cylinders. The finer more mixed the air/fuel mixture is, the more powerful the burn. Check out this article, they list some other pretty interesting reasons. http://www.pro-system.com/scoop92102.html

 

[jrichker]

Bravo! more input!

Interestingly, no one has responded to my satement "The primary limitation of carbs is that they are a mechanical device, and have no way to compensate for changes in temperature and atmospheric pressure. These two items can limit the power of a carb’d car. A race to the top of Pike’s Peak on a hot summer day would be an example of how this will affect a race car. Or a trip down the drag strip at Denver, Colorado in the summer compared to one in Los Angles during the winter. Definite power differences would be seen & felt. Adjustments can be made, but it requires some small amount of wrenching to do." How do you make a carb do that on the fly? EFI is all weather, all the time, even while you are racing towards the finish line.

 

[EMW150]

Bravo! more input!

Interestingly, no one has responded to my satement "The primary limitation of carbs is that they are a mechanical device, and have no way to compensate for changes in temperature and atmospheric pressure. These two items can limit the power of a carb’d car. A race to the top of Pike’s Peak on a hot summer day would be an example of how this will affect a race car. Or a trip down the drag strip at Denver, Colorado in the summer compared to one in Los Angles during the winter. Definite power differences would be seen & felt. Adjustments can be made, but it requires some small amount of wrenching to do." How do you make a carb do that on the fly? EFI is all weather, all the time, even while you are racing towards the finish line.

I would tend to agree that for a race up pike's peak, yes EFI is the way to go. But how many of us race up pike's peak? You can take the carb and tune it for the altitude changes or atmosperic pressure. Since drag strips or road courses are flat, you don't have a variable altitude change on an outing. Just weather changes which can be compensated with a jet change.

 

[Boss 351]

Doesn`t EFI produce more torque in most cases compared to a carb?

I have a rag article, that compares EFI to carb. On the same engine, same dyno, same day there was a 1HP difference (in favor of the EFI) between the two!

 

[mstngjoe]

An interesting comparison here:

http://www.popularhotrodding.com/enginemasters/articles/hardcore/0305em_holley/

 

[Boss 351]

interesting...

 

[jrichker]

I would tend to agree that for a race up pike's peak, yes EFI is the way to go. But how many of us race up pike's peak? You can take the carb and tune it for the altitude changes or atmosperic pressure. Since drag strips or road courses are flat, you don't have a variable altitude change on an outing. Just weather changes which can be compensated with a jet change.

Let’s take the race to Pikes Peak and expand it a bit…

One of the important things is consistency: that’s why automatic transmission cars are so good at bracket racing. With a little effort on the driver’s part, they get off the line the same every time. Transport that idea to EFI and carbs: the EFI system is like the auto trans, and the carb is like the 5 speed. It can be much more difficult to get consistent 60 foot times with a 5 speed than an auto trans.

Large changes in temperature or barometric pressure can affect power output due to the change in air/fuel ratio in carb systems. EFI takes care of that problem by getting input from the sensors and adjusting the injector pulse duration .

Sample examples:

Carb: You take your new hotwheels 351 with a carb, fancy heads, hot cam, built C4, etc., etc. to the local tuner whiz. He’s a little peculiar, one of those hair on fire, can’t stand still kind of guys, but he gets results. He also gets $100 an hour plus $300 for dyno usage, so wasting his time isn’t healthy for your wallet. It’s 60 degrees and dry as dust as you pull into the dyno shop. The first pull is terrible, and he shakes his head and makes some insulting remarks about your hat size. Out come the tools and 15 minutes later he’s ready for another run. This one is better but flattens out near the top. He’s thinking a different power valve is the fix. More tool turning, another 15 minutes and he’s ready to go at it again. Next run looks really good on top end power, but the mid range torque is down and isn’t what he wants. Time to change more parts… Out comes the jet kit and he finds the proper size, along with another 15 minute slice of your wallet. Fire up the engine, re-adjust the idle and accelerator pump linkage and run it up. This one makes him smile – a little. He tells you that this isn’t the ultimate, but it is good. Pleasantries are exchanged, along with $400 of your money. Weeks pass and spring turns to summer, along with several trips to the track. The track results have been good, but the times seem to increase as the temperature rises. Today it’s 95 and so humid that everything has a layer of sweat. First run, power is down, the car seems to bog, the trap speed is down and the ET is up. You check the timing, tire pressure, fuel pressure, all OK. Second and third runs produce similar results. Another run and you do a clean cut at the last light. Coasting into the return lane, your pit crew buddy meets you with a plug wrench and some extra bodies to push the car out of the way. Plugs come out, inspection is done and you conclude that the engine is running rich. A call to the tuner guy results in him digging out the dyno sheet and looking at his notes. More insulting remarks follow, and he asks you if you expected the same tune that ran good at a dry 60 degrees to run the same at a sweaty 95 degrees. You say yes and then he tells you to get a life and some more education on how temperature and humidity affect engine performance. He offers a retune for the current weather at a discounted $300 flat rate. A sudden pain in your wallet springs to life as your credit card starts to throb like a stubbed big toe…

EFI: Your new EFI 351 is all ready to go, hot HCI combo, 70 MM TB, 30 pound injectors, 80 MM MAF, built C4, stock computer and a lot of time and effort. A trip to the dyno is scheduled and it’s a fine day, 60 degrees outside and bone dry. You pull up to the dyno shop and are greeted by a little guy with frizzy red hair that looks like and explosion in a mattress factory and a T shirt that says “DynoGuys” on it. He seems a little weird, but he is supposed to be the best. Five minutes later, he has a laptop connected to the computer port and is ready to roll onto the dyno and prep for a run. Tires, timing, fuel pressure & idle are checked and pronounced acceptable. First run is a baseline and shows there is more on the table. “DynoGuy” shakes his head, mumbles something and does a tap dance with his fingers on the laptop keyboard. Two more up and down runs and he smiles, showing the braces on his teeth. The engine returns to idle and it seems a little rough. “DynoGuy” dances on the keyboard some more and things smooth out. Another run up and down and he hands you the dyno sheet and asks if that was what you had in mind. You say yes, he shuts everything down, disconnects the laptop and heads for his office. Five minutes later he is back with a little black box that the plugs onto the car’s computer where his laptop was plugged in. He plugs in the black box, secures the loose pieces and kick panel. So far so good – then he hands you a bill for $475. You look and see $300 for the dyno, $50 worth of his time and $125 for the custom chip he just installed. Ouch! Well, at least your air miles on your credit card just went up.
Weeks pass and the miles go by. The car even passes the gas stations, something it never did before. Several trips to the track prove fruitful, the car just keeps getting better. You decide to make a July 4th bonus race, even though it is 95 degrees and so humid that even your cat is sweating. Off to the track: first run good, second, third and forth runs are good too. You look in the glove compartment at your previous time slips. All are tightly grouped with about a 1/10 of a second between the highs and lows. Bonus time comes up & you win $75 for the most consistent times for the season. You think back on it all, and "DynoGuy" doesn't seem so weird after all...

The point is EFI is a consistent performer, hot or cold, rain or shine. Differences in temperature and humidity are accommodated by the computer’s programming. No jets to change, no linkages to adjust, no power valves to tinker with. No getting stinky smelly from gasoline while playing with tiny parts that seem to want to run away and hide from you.

Consistent all weather performance, good gas milage, and no failing the smog check because of non standard equipment are the pluses of and EFI car. Cars that were EFI and have been converted to carb will not pass smog testing. That may not be a problem now, but if you move or sell the car to someone in a emissions regulated area, it will be.

 

[Carb'dCobra]

Interestingly, no one has responded to my satement "The primary limitation of carbs is that they are a mechanical device, and have no way to compensate for changes in temperature and atmospheric pressure. These two items can limit the power of a carb’d car. A race to the top of Pike’s Peak on a hot summer day would be an example of how this will affect a race car. Or a trip down the drag strip at Denver, Colorado in the summer compared to one in Los Angles during the winter. Definite power differences would be seen & felt. Adjustments can be made, but it requires some small amount of wrenching to do." How do you make a carb do that on the fly? EFI is all weather, all the time, even while you are racing towards the finish line.

Carbs are also a pain in the ass just in case, say, you wanna' take a trip next January from Florida up to Hickory, North Carolina for a trade show called KartFest. Unless you've brought a set of different power vavles, jets, and wrenchs, you're SOL. Which is why I like my 750 4160 vac. secondary carb; no changeable jets or power valves

 

[dragnazz5.0]

i look at it more as a price issue. lets say you have a stock motor with some bolt ons and a cam. you have a carb setup with a decent carb and you decide to get some decent heads. put it all together and hmm...youre running a little lean. time to pull the jets and swap them out. how much does that cost...5 bucks. take the same combo but put efi on it and you find out you are running lean and the computer cant comensate for it and neither can more fuel pressure. so you buy new injectors and a maf and possibly a fuel pump. youre looking at 500 bucks minimum. the tuning capabilities with a carb are endless and much less expensive. the only reason manufacturers got away from carbs is because of emissions regulations and gas mileage regulations

 

[jrichker]

i look at it more as a price issue. lets say you have a stock motor with some bolt ons and a cam. you have a carb setup with a decent carb and you decide to get some decent heads. put it all together and hmm...youre running a little lean. time to pull the jets and swap them out. how much does that cost...5 bucks. take the same combo but put efi on it and you find out you are running lean and the computer cant comensate for it and neither can more fuel pressure. so you buy new injectors and a maf and possibly a fuel pump. youre looking at 500 bucks minimum. the tuning capabilities with a carb are endless and much less expensive. the only reason manufacturers got away from carbs is because of emissions regulations and gas mileage regulations

The increase in fuel pressure can accomodate a fair range of change. Increasing the pressure will effectively increase the flow rating. Example: a 19 lb injector will flow 24 lbs at 63 PSI, and a 24 lb injector will flow 30 lbs at 63 PSI.

 

[Modular2v]

I think you guys are debating the wrong issues. . . Both of them have very similar performance #s given the same atmosphere! But the COST is a completely different issue! Being a broke college student , my race car will not have a efi system on it period!