ozarks06

Actually, an EFI system will outperform a carburator at every point in the RPM/torque curve except one. A carbed engine is designed and tuned for peak HP or torque at a single given load/RPM, thus at any speed/load other than that one point it is not optimally tuned. (For example, at any load above peak torque you actually gain power by leaning out the mixture slightly, something that is impossible with a carb unless you can change the jets while the car is going down the drag strip.) The advantage to an EFI system is that the mixture can be adjusted for any given RPM and load to provide optimimum torque, fuel economy, emissions, etc. EFI cars have much flatter torque curves, which is why they are better for daily drivers/cruisers. If you combine this with distributorless ignition (which you can't on a 5.0/302) you can also adjust spark timing precisely at different RPM/load points as well. That's why cars like the 2011 GT get heaps of flat-torque curve power from a 5.0 motor, have a smooth idle, and great mileage too (the vict helps too!).

Another advantage is that with factory-type EFI intakes the runners are all the same length (or close) which means that each cylinder is 'tuned' to make the same power at all RPMs. With a conventional carb intake the runner lengths usually aren't the same, which means the cylinders with shorter runners are making more power in the upper RPM range and the cylinders with longer runners are making more power in the lower RPM range. However, the different-length runners in a carbed intake tend to flatten the torque curve somewhat, though it does so by reducing power and efficiency across the board.

The biggest advantage to EFI in a daily driver/cruiser - click the key and it starts in any weather, can't flood it, burns clean, and gets great mileage.

Your heads shouldn't be an issue with EFI but your cam might not be ideal. EFI engines and intakes usually prefer slightly different cam grinds than carbs, but probably not enough to worry about.

Granted, factory EFI doesn't look as 'classic' but personally, after seeing the umteenth vintage Mustang with a carbed small block at a car show or cruise-in, I like seeing an EFI conversion. To me it says the owner appreciates classics but recognizes that newer technology can improve the old girls, but that's just personal preference (like carb or EFI).

Starfury

That '93 EFI system should work fine with the cam and heads you're using. It's a mass-air system rather than the old speed-density type, which means it'll adjust to most things you throw at it. Take a look at James W's website (google 'James W Mustang') for a good reference on an EFI swap into a classic.

I'm not anti-carb, but if I had a working EFI setup and more time, I'd happily swap a mass-air EFI system onto my car.

MustangFTW

^this.

ive drivin my stang in -20F weather and its not fun with a carb, has to warm up for like 10 mins before even think of driving, then it konks out at stop lights :P
i would consider getting EFI if it didnt cost 2k.

67mustang302

I swear, some of you people are so ignorant it's mind boggling. Stop repeating the same old crap you hear "everyone saying" and actually learn what's really going on in an engine. If you actually care to learn something, then read below. If you're not going to take the time to read it, then do everyone else who wants to learn a favor, and stop repeating the same bad information that's floating around. The reason people keep thinking the same wrong crap is because others keep repeating it.

The way an engine runs has to do with what's happening the the combustion chamber, not the fuel delivery system. The engine doesn't know whether it's carb'd or EFI, it simply operates based on combustion. An engine doesn't know that it has EFI and is therefore supposed to run better. As long is combustion is close to "ideal" for that engine, it'll run the same regardless of EFI or carb. The goal is to get the fuel system to deliver the proper AFR of well mixed air/fuel charge. EFI uses a computer to do it, carbs use fluid flow to do it. But they both do it.

If a carb runs dry(after sitting for 1-2 weeks) it takes a few seconds of cranking with a mechanical pump for it to fill enough to start. With an electric pump that self primes that's a non issue, since the carb fills before the engine starts. And I live in the mountains, where it snows. I've driven and started my car in freezing weather. My carbureted engine starts faster in sub-freezing weather than my parents 2011 Honda CR-V does. And it drives the same whether it's 0*F or 110*F when it's tuned right.

As far as fuel ratios, that's mostly a non starter as well. Contrary to popular belief, most engines, especially street engines, generate no measurable power changes if they're within +/- 3-5% of "ideal" target fuel ratios. Engines are largely insensitive to minor changes in AFR. You'll never notice a power difference between 13:1 and 13.3:1 on a street engine, not even on the track. You might see a change on a dyno, and people say "Oh look, that leaner AFR made 3 more hp!" Well, 3hp on an over 300hp engine is a less than 1% power increase. You'll never notice that, and it's also well within the margin of error for dynos. And as far as EFI adjusting for the proper AFR....it runs off of base fuel maps, under x conditions it delivers y fuel. And most systems run in open loop at WOT, so there is ZERO adjustment to the fueling at WOT, it runs ENTIRELY off a pre-programmed base fuel map. And if the base fuel map is on target to begin with, then even in closed loop there is little to no adjustment under normal driving conditions and it runs almost entirely off the base fuel map.

A properly set up carburetor will provide the correct AFR across the whole rpm range of engine operation. That's what the emulsion system is there for. If you have a carb that gives the correct AFR in one spot and not in others, then it's either the wrong carb or it's not setup properly. The air bleed and emulsion circuitry in a carburetor is there to introduce air into the fuel before the booster to cause it to deliver the proper amount of fuel across the full range of load and rpm. It uses the physics principles of fluid flow to control fuel delivery, whereas EFI simply looks at input data and generates an output(injector pulse width). But the both deliver a given quantity of fuel based on engine conditions.

Carburetors generally make more power over a wider rpm range than EFI. Typically the entire mid and upper rpm range. There are several reasons for that. First is something called the Joule-Thomson effect(http://en.wikipedia.org/wiki/Joule%E...Thomson_effect). Basically when the air/fuel charge passes out of the carburetor barrels and into the manifold plenum, it tries to expand freely...that results in a rapid cooling of the air fuel charge, which has 2 advantages. 1 being the cooler induction charge is much less prone to detonation, so a carbureted setup can typically run more aggressive tunes for the given fuel to generate power without detonation. The 2nd being the decrease in charge temperature results in an increase in density....meaning a carbureted engine typically has a slightly denser air/fuel charge entering the cylinders. NASCAR teams running tests on Cup engines at WOT have found temperatures of the air charge inside the manifold to regularly be more than 20*F below ambient. That means when it's 80*F outside, the induction charge temp in a carb'd setup is 60*F or less.

That cooler and denser charge has another advantage. Fuel won't burn as a liquid, it MUST be a vapor at the time the plug fires or it won't burn. In a carb'd setup, that cooler and denser charge more rapidly absorbs heat energy from the manifold as it begins traveling down the runners(and due to fuel delivery at the throttle, has that opportunity as it travels down the runners), and it gets the fuel closer to it's vaporization/flash points. Because the fuel is substantially more conductive of thermal energy, the fuel itself absorbs most of the heat and causes it to approach it's vaporization point. Unlike an EFI setup where the air charge absorbs heat energy raising the charge temp as a whole, and then introducing the fuel at the last moment, and relying on the compression stroke and whatever heat the fuel can absorb from the air charge to generate the thermal energy needed to get the fuel into a vaporizable/combustible state; a carb'd setup essentially pre-heats the fuel and gets it closer to it's vaporization and combustion point much more easily. That means during the compression stroke, there's more energy available to raise the charge temperature in the chamber closer to it's flash point, rather than expending additional energy trying to vaporize fuel.

Since you start off with a charge that has a lower overall temperature with more readily vaporizable fuel, you end up with a more stable and more efficient combustion process. The thermal efficiency of the engine is slightly higher, and it's less prone to detonating.

Another advantage is in the area of boosters. Booster technology was poor 20-30 years ago, so carburetors didn't always do a good job of mixing and metering fuel. But with modern booster designs(such as annulars), carburetors have another advantage over EFI. It's in the area of atomization. Air/fuel charges burn best with a homogeneous mixture(one where the air and fuel are evenly mixed and distributed throughout the whole of the charge). Modern booster technology sprays the fuel in the carb in a nice even cone. The fuel droplets themselves are small and evenly spread throughout the incoming air charge. That combined with the additional time the air/fuel charge has as it travels down the runner(where varying liquid flow currents and tumbling effects mix the charge further), means that carb'd engines typically have a better QUALITY air/fuel mixture. It's more homogeneous, so it burns better and is more detonation resistant(the better mixture quality means less chance of a lean pocket somewhere within the charge that may try to detonate or pre-ignite).

The better booster technology is also what allows for much greater metering sensitivity. It's why modern carbs have very controlled AFR's, get good mileage and have excellent throttle response and drivability.

On the area of throttle response, that's a matter of booster sensitivity combined with accelerator pump tuning. Even EFI has an accelerator system in the fuel mapping. It's typically called "accel fuel" or something similar within the software, and it basically sprays additional fuel as you open the throttle to prevent transient lean outs as the combustion and airflow conditions rapidly change. A carburetor uses a mechanical pump linkage to squirt fuel into the carb throat. But they both accomplish the same thing, providing extra fuel during throttle transition to prevent a transient lean. On either system when not properly tuned, throttle response is poor. So throttle response comes down to tuning, and not the system. And given the high combustion quality nature of a carb'd setup, it's not uncommon for carb'd cars to have better throttle response when properly tuned, on account of higher quality combustion getting started sooner.

So, the question then is if carbs are so great, why aren't they still used on new cars? 1 answer...government regulations. Primarily emissions. Nearly all the harmful emissions that an engine produces are at idle and low rpm/throttle operation. This is where carb's fall way short of EFI. While the idle circuit on a carb is simple, and can idle on anything, the way it distributes fuel is uneven from cylinder to cylinder. That means to account for the leaner cylinders, you have to idle richer overall. And the idle circuit itself doesn't mix fuel that well when idling, so combustion quality is lower. It'll idle just as well, but it ends up producing far more emissions in the process. Far beyond the current legal allowable levels. The same is true to a lesser extent under cruise conditions. Combustion in all engines at those levels is difficult to control due to the lack of efficiency(engines are most efficient at WOT at peak torque rpm). A modern emissions controlled vehicle needs precisely controlled exhaust gas temps for proper catalytic converter operation. Carb's can't do that. They CAN control things well enough to get the same mileage, but they don't change tune in response to an EGT or a cat temp sensor or an O2 sensor to keep exhaust emissions and temperatures within ideal catalyst operating ranges.

On the matter of drivability, that's a matter of tune and sensitivity for a carburetor. If a carburetor has poor low rpm drivability, then it either lacks booster sensitivity, or it's tuned improperly. Older carbs suffered from drivability issues mainly due to lack of booster sensitivity. They just didn't have enough airflow at part throttle to operate efficiently. That's not true any more when using a modern carburetor. Most drivability issues with a carb though can be traced back to the wrong carb(loo large, wrong metering circuitry etc) resulting in poor efficiency, or improper tuning such as wrong timing, wrong jetting etc.

As far as power over rpm ranges...most newer engines aren't making broad power because of EFI, it's because of cam timing. The new Ford 5.0 DOHC for example has independent variable intake and exhaust valve timing. It makes insanely broad torque not because of EFI, but because the vale events are constantly being changed in an attempt to optimize cylinder filling under the given conditions. That's a matter of valvetrain control vs no valvetrain control, not fuel delivery system. If you locked out the valve timing to it's setting for peak hp, it'd lose a ton of mid and low rpm power.

As far as cylinder balance tuning, it depends. Some factory intake designs, like the 5.0 EFI intakes from the 80's through to 2002, were notorious for having cylinders run lean. On Fords usually the front 2 cylinders ran leaner. The only way to have a balanced intake is to either run a tunnel ram, or individual throttle bodies. But any conventional intake with a plenum will by design have flow imbalance. Not necessarily a bad thing, since you can tune different cylinders to have different peaks and broaden the power out over the rpm range.

So again, carburetors aren't the problem. It's the people selecting and tuning them. My carb'd car(still not even tuned right as I wait for more parts) starts fine and runs fine in whether from 0*F up to over 110*F, low altitude to high altitude. I can run my carbureted engine all the way down at 1,200rpm in 5th gear at high altitude and it still generates signal and will accelerate(albeit slowly). None of my parents EFI cars will even operate under those conditions. It gets ~25mpg on the highway still running rich at cruise rpm. Do I have a magic carburetor that defies the laws of physics? No.

EFI is great for better emissions, or for people who either don't know how, or don't want to mess with tuning a carburetor. But EFI isn't some magical device that runs better or makes more power than carburetors. A modern carburetor is easily a match for any modern EFI system.

boeing747arowair

amen brother!

MustangFTW

fancy carbs are nice.

67mustang302

Fancy carbs are nice, and are more expensive than not fancy ones. But still cheaper than EFI, generally speaking(I have over $1,000 into my carb in parts etc, prolly close to $1,500). But, you also have to know what you're doing, or know someone who does, or you can rapidly end up with something that isn't even drivable or damages an engine.

ozarks06

double post

hightower2011

Carb!

ozarks06

At the risk of simply repeating the same old crap I'll quote a couple more mind-bogglingly ignorant people, from 'How to Tune and Modify Engine Management Systems' by Jeff Hartman (Motorbooks Workshop).

Knowledgable racers and hot rodders soon discovered that well-tuned modern programmable EFI systems almost always produce significantly higher horsepower and torque than the same powerplant with carbureted fuel management, especially when the engine is supercharged or turbocharged. This increased performance is in addition to improved drivability, cleaner exhaust emissions, and lower fuel consumption. . . .

Advantages of Individual Port Electronic Fuel Injection

Greater flexibility of dry intake manifold design achieves higher inlet airflow and consistent cylinder-to-cylinder air/fuel distribution, resulting in more power and torque, and better drivabiility.
More efficient higher engine compression ratios are possible without detonation.
Extreme accuracy of fuel delivery by electronic injection at any rpm and load enables the engine to receive full air/fuel mixtures at every cylinder that fall within the tiny window of accuracy required to produce superior horsepower.
Computer-controlled air/fuel mixture accuracy enables all-out engines to safely operate much closer to the hairy edge.
EFI can easily be recalibrated or adapted to future engine modifications as a performance or racing vehicle evolves.
Electronic engine management with port fuel injection is fully compatible with forced induction, resisting detonation with programmable fuel enrichment and spark-timing retard and enabling huge power increases by providing the precisely correct air/fuel mixture at every cylinder.
EFI powerplants have no susceptibility to failure or performance degradations in situations of sudden and shifting gravitational and acceleration forces that might disturb the normal behavior of fuel in a carbureted fuel system.
Electronic injection automatically corrects for changes in altitude and ambient temperature for increased power and efficiency and reduced exhaust emissions. (9, 10)

After explaining how different A/F ratios are needed based on engine load and rpm, even during WOT runs, he summarizes:

The main difference between computer-controlled engines and earlier modes of control is that the computer's internal tables of speed and loading can have virtually any desired degree of granularity and can generate spark advance and fueling that are essentially unrealistic with mechanical systems.

Bottom line, computer-controlled engines eliminate compromises of mechanical fuel delivery and spark control. Multi-port injection eliminates problems with handling wet mixtures in the intake manifold that are associated with carbs, resulting in improved cold running, improved throttle response under all conditions, and improved fuel economy without drivability problems. (22)

Or more of the same old crap, 'Engine Management, Advanced Tuning', Greg Banish (CarTech Books).

The biggest compromise here [carburetors] is that, other than at idle where the mixture screws have enough authority to change things, we are locked to one flow ratio of air to fuel for the primary circuit and one ratio for the secondary circuit, if so equipped. This means tuning a carburetor often boils down to a compromise of desired air/fuel ratios between cruise, light throttle, and wide open throttle. With crude adjustments at best to control transition and no real way to adjust for nonlinear performance across a wide RPM range, there is room for improvement. Additionally, since actual fuel flow is proportional to air velocity in the venturi rather than actual air mass flow, air/fuel ratios can change slightly with changes in ambient conditions. The term 'good enough' works for many racers, but leaves a lot to be desired on a daily driven car expecting good economy and emissions. (19-20)

Apparently there are at least a couple of mind-bogglingly ignorant automotive engineers who are repeating the same old crap.