gcs118

I'm reading up on how the fuel systems of cars work, as I'm no tech expert yet. Just wondering if the 2002 Proteges have multi-port or throttle body fuel injection? If you guys could answer the question, and also maybe elaborate on how to tell just by looking at it? Thanks for your time.

Installshield

Your engine has Mult-port fuel injection. The newest system, available in a few cars and used in racing applications, is Direct fuel injection. There is no valve in the way of the fuel spray, which creates swirling effects, and allows for better injection control...

carguycw

Proteges- and all other modern cars- have multi-port fuel injection (MPFI).

Throttle-body injection (TBI) essentially works like an electronic carburetor. It uses one (or a small group) of injectors that spray fuel into the airstream right after the throttle body; all cylinders are fed off of the same injector(s). Like a carb engine, a TBI engine is "wet flow"- the fuel is mixed with the air BEFORE the air travels through the intake manifold, rather than being injected right at the end like an MPFI system, which is known as "dry flow." MPFI engines are easily spotted because they have individual injectors for each cylinder.

TBI is basically a cheap and dirty way to add EFI to an engine designed for carbs. TBI has better fuel control than a carb, but shares many of a carb's disadvantages- mainly, poor fuel atomization because the fuel tends to seperate from the air while it flows through the intake manifold, particularly during cold starts (fuel atomizes better in hot air). This leads to poor emissions and cold-start drivability. Wet-flow systems also typically have poor mixture distribution from cylinder to cylinder because the air has to follow different paths to reach different cylinders, and it also forces compromises in intake manifold design in order to keep the air (and fuel) moving at low rpm for good idle quality.

TBI was used a lot in the early 1980's because many cars' engines (particularly American ones) dated from the 60's and 70's and were not designed with MPFI in mind. Modern emissions standards and higher buyers expectations for good drivability have forced carmakers to abandon TBI.

Hope this answers your question.

Installshield

I thought some of the newer Mitsubishi's were using Direct Fuel Injection, if not they soon will be...

gcs118

Thanks guys, definitely answered my question completely between the 2 of you.

carguycw

FWIW you can actually buy bolt-on TBI kits for older American cars...

Holley TBI Kit

You can also buy MPFI (or MPI) kits, but they're not quite so bolt-on...

Holley MPFI Kit

The number of parts and comparative price between these two kits helps to demonstrate why many car companies used TBI as a stopgap measure.

leungwingkei

Does some new BMW engines use direct injection also? I think the new Rolls Royce Phantom 6.8L engine developed by BMW uses direct injection and so does the 6.0L in the BMW 760i.

Some Mitsubishi cars use direct injection, it's the GDI system.

gcs118

So let me get this straight...in MPFI the fuel is atomized right in front of the intake valve? And with Direct Injection it is atomized right after the valve? How does this placement affect the performance of the cylinder?

Installshield

They both kind of mix in the cylinder, but the MPFI system sprays fuel right into the back of the valve, which creates different swirl patterns that are not always good, + can make it difficult in higly tuned engines to keep track of the fuel requirements becuase the mixture reaction can become inconsistent. A direct Injection system does not spray fuel into or through any valves, just sprays directly into the chamber. The swirl problems are mostly illiminated, and the fuel/Air burn remains more consistent...

nickkaranikas

yes but know talk about wich system is the most efficient in power
a certain amount of turbulence is needed for the best possible atomization before the valve, and before the intake port altogether!

from monster pro5 with 440hp

Installshield

I don't really understand what you mean, in a MPFI engine (+Direct injection) the fuel and air don't mix until the combustion chamber. Certain amounts of turbelence and swirl is needed for proper air flow through the intake manifold, but not for the fuel and air to mix, at least I thought....The swirling effects of MPFI engines are what cause in some cases poor atomization and incosistent mixture ratios...So I would think the Direct Injection system would be more efficient for power...In both systems the injector does its best to atomize the fuel, by spraying a mist. In short, swirling effects can sometimes 'de' atomize the fuel and create rich and lean Fuel/Air mixtures througout the same combustion chamber, which isn't good...Try to think of a Direct Injection engine making uniform french salad dressing, while a normal MPFI would make Italian salad dressing...

gcs118

Can't say I really follow the salad dressing analogy, but it is creative. I understand about the consistency issues however. Is Direct Injection a lot better than MPFI on turbo, or on NA, specifically? Would there be any significant gains if say a well-tuned NA car switched from MPFI to Direct Injection? A well-tuned FI car?

nickkaranikas

what i mean is a system other than mpi or direct injection
remember that these systems were created to meter the proper amount of fuel that each cylinder receives
to stop the starving cylinder syndrome

in dealing with forced induction i find that longer thinner runners increase velocity and VE in conjunction with a feul injector instead of pointed towrd the intake valve, it would have a 180 degree
about face to the intake runner
alowing the the high flow positive air charge atomize the mixture more efficiently


i wish i had more time
im at luch now sorry

later

carguycw

Direct injection (DFI) is better than TBI or MPFI because the fuel is injected directly into the cylinder, so it can do a lot of things that are impossible with other systems because it's not constrained by the ability to inject fuel only when the intake valves are open. If it's engineered properly, it can use a leaner mixture than other methods, and it can also inject fuel at critical moments to reduce detonation, allowing higher boost and/or ignition advance.

However, let's get something straight first... DFI CANNOT normally be added to an engine designed for another injection system. It requires a fitting IN the combustion chamber for the injector, and also requires much higher fuel pressure- carbs typically use 4-15 psi, normal EFI typically uses 30-80 psi, but DFI uses 10,000+ psi! DFI is cutting-edge technology that's being developed for a new generation of engines. To use computer terminology, it's not backwards compatible.

Also, FWIW nickkaranikas mentions in his mod list (in another thread, forgot where) that his monster turbo Protege has a couple of extra injectors mounted right after the throttle body. This is a somewhat common trick among the turbo crowd that effectively creates a hybrid EFI system- the extra injectors are essentially a piggyback TBI system, meaning that the car has MPFI *and* TBI!

Installshield

That was a stupid analogy and didn't realize it until now...All I meant was that a DFI system would create a more uniform "solution" of Air and Fuel like French dressing, while the MPFI system would create more of a "suspension, like Italian dressing, with unequal concentrations of fuel and air througout the mixture...I know, it sucked...

And as Carguycw said the DFI system is cutting edge technology and offers more control of the fuel system in general than a MPFI sytem...So I would think it would be better for any tuned engine...