Jason E

I don't get what the difference is...both are port injection. My Camaro has MPFI (obviously), and the Grand Am has SFI. I'm assuming SFI is better because '94-up 3.1s made 155-160hp, versus 135-140hp for 3.1 MPFIs. How do they vary? Would it be possible to convert a third gen to SFI?

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Jason E
"The Cruiser"
'89 Camaro RS 2.8
Hypertech chip/K&N filters/Accel 8.8 wires, Accel Supercoil/RapidFires
Eclipse CD and 100x4 amp/Boston plates and 6x9s
Alpine Alarm, Keyless Entry
"It's for sale"

"The Driver"
'95 Grand Am SE 3.1 Coupe
No mods yet...

I'm the only third genner who's daily driver is faster than their third gen!

Johnny Ray

Do you mean SEFI?

If you do I will explain SEFI to you.

As we all know the MPFI (Multi Port Fuel Injection) units operate with one throttle body and then the air/fuel mixture is then directed into each individual cylinder through separate ports.

When it comes to SEFI (Sequential Electronic Fuel Injection) the same results (getting a air/fuel ratio into the combustion chamber) is done by another means. SEFI pulses the injectors once per crankshaft revolution. SEFI provides optimum mixture ratios at all stages of combustion. Combined with its immediate response characteristics, it permits the engine to run on the leanest possible air/fuel mixture, which not only gives better performance but also reduces exhaust gas emissions. SEFI is controlled directly by the vehicle's ECM/PCM, which automatically adjusts the air/fuel mixture in accordance with engine load and performance. Because each cylinder is equipped with an injector mounted immediately adjacent to the intake valve, much better control of the air/fuel mixture ratio is possible.

Better control=more performance.

I hope this helps.

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1969 Falcon

1992 Artic White Firebird

1997 Black Firebird

Standard

The main difference between the two is that MPFI uses what's called batch-fire. Basically, it fires all the injectors for one bank of the engine at once. So the injectors are firing at 1 open valve and 2 closed valves.

SFI fires the injectors individually, so they're always firing at an open valve, at least below 3,000 RPM. Above 3,000rpm SFI switches to batch-fire mode. Give slightly better fuel milage and less emissions.

Grim Reaper

I agree with Standard. MPFI uses "batch firing" whereas SFI fires each injector separately.

Also, with "batch fire" the injector pulse width is the amount of time the injectors are open for 1 crank revolution. WIth SFI, the injector pulse width is the amount of time the injector is open per operating cylce (2 revolutions).

Trust me, with my eprom burning, I can very easily lean out my injectors on my "batch fire" L98 350 V8. In fact, that is how I just recently got 27.3 US mpg when I started to experiment with it and I figure I might even hit 29 or 30 US mpgs with my L98.

The biggest advantage of SFI is more precised metering of fuel while the valve is open to give better gas mileage, less emissions and a little extra torque at low rpms. At high rpms, SFI will not develop more HP as the air flow dynamics are so fast, (the pulses travel in waves and to the engine it sees a steady column of air), that there is virtually no advantage to SFI over Batch Fire.

On the PROM Board, we occasionally get people asking about implementing SFI and we always say, "just try burning an eprom" first to find the real limits of your system.

People always want to run, before they can even walk.

TechSmurf

Johnny Ray, corrections...
What you're calling MPFI is TBI.. MPFI systems do have one injector per cyl, just like TPI systems, which are actually just a version of MPFI, just that MPFI/TPI systems fire one bank of injectors (left side/right side) all at once vs. individually... and everyone I know calls SFI SFI, not SEFI.. be kinda like calling TPI TLRMPFI.. you don't need to be so high-horse technical.

The preceeding may or may not be viewed as a flame.. the intent was to correct someone's misconception of how our engines work... well, so maybe the last line was flamage.

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'86 Camaro SC, black /w silver racing stripes
2.8l MPFI/700r4
In search of new v8 engine & transmission
MSD coil, Accel 8mm wires, SplitFire plugs, Gabriel hijackers

TechSmurf

Oh.. uh.. the second question. Uhm.. well, I've looked at a grand am 3.3 before, and it didn't seem to be much the same as ours.. but I wasn't looking at it from a conversion point of view either.. Actually I suppose all you'd really have to do is replace the intake and ecm, rewire everything, burn a custom prom for it, and I'd grab the heads too if you can get your accessories to bolt to them.. make sure its firing order is the same as ours.. actually now that I think about it there's alot more involved than that.. it's probably set up for a distributorless system for the reference pulses to know when to fire the injectors.. so I have know idea how it'd work, and it could prove to be a pain to set up.. so I really can't give a solid answer.. but there's an idea of what you're looking at.

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'86 Camaro SC, black /w silver racing stripes
2.8l MPFI/700r4
In search of new v8 engine & transmission
MSD coil, Accel 8mm wires, SplitFire plugs, Gabriel hijackers

Grim Reaper

TechSmurf, I have also seen SFI referred to as SPFI. But most just refer to it as SFI as the fact of it being sequential already suggests "port" injection.

My beef with SFI over MPFI is that for SFI to REALLY operate to its full potential, you really need an O2 sensor on every exhaust primary. Then the ecm can "trim" each individual injector to its specific needs. Without individual O2 sensors, SFI does not have any real advantages over a "batch fire" system; other than the points mentioned above.

But I suspect cost vs benefit is the biggest reason they don't put individual O2 sensors on every exhaust primary. Imagine the repair headaches too.

TechSmurf

Glenn, my point exactly! The fact that it's injection suggest electronic (I've never heard of mechanical fuel injection, so if it's out there, bleh) .. thank you =P
And also, the bit about the o2 sensors.. maintainance nightmare, yer right.. and in theory I don't see any real advantages without it beyond the fuel/air being atomized and shot into the cyl a tiny bit better.. and that's personally not enough to go changing the top half of my engine. (I can see it now.. *blink*SES*blink* pops code 34 for lean exhaust suggesting a bad o2 sensor.. and you're sitting there going 'which one???' no..)



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'86 Camaro SC, black /w silver racing stripes
2.8l MPFI/700r4
In search of new v8 engine & transmission
MSD coil, Accel 8mm wires, SplitFire plugs, Gabriel hijackers

Jason E

Hey Johnny Ray,

Thanks for the info, but don't get smart about the SEFI vs SFI notation...I'll be more than happy to pop my hood for ya and show you the "3100 SFI" cast into my plenum.

I know it's electronic injection!!! That's all the E stands for...hence why GM doesn't use it. Ever see "MPEFI" cast into a 2.8 plenum??

Thanks to everyone for the explanations!

Grim Reaper

ACTUALLY, a lot of the earlier fuel injection systems prior to the 80s WERE mechanical. Bosche was the leader and tended to be on "high end" european sports cars. But 57-64 Chevies had fuel injection too (the original RamJet) and it was mechanical. Also Pontiacs had it available in the late 50s on their 347 but few know or remember about that one.

The problem with mechanical fuel injection is that without the electronics and microprocessor it is a mechanics nightmare. When the 57 Chevy came out with the Ramjet, it was rated at 283 HP on a 283 c.i. engine. Whereas the 4 bbl was 270 HP.

When the Ramjet was tuned right it was slightly quicker than the 4 bbl. But, on any given day, the 4 bbl was quicker as it was not prone to requiring adjustment for something as simple as a rainy day. Yup, a simple change in the weather could make the Ramjet out of tune.

That is why Chevy abandoned Fuel Injection in 1964 (or 65 ... I forget, as I am old), because of the tuning nightmare and warranty claims. It took the microprocessor before GM tried fuel injection again with their CFI system on the 82 Corvette.

When you get into eprom burning you become amazed of all the things the computer compensates for; air pressure, air temperature, air flow (via MAF or MAP), coolant temperature, Throttle position, etc. And all modifiable (yahoo!).

Also, when you see EFI, it is generally a fancy way of saying TBI.

TomP

Glenn, weren't those mechanical injection units really funky looking, with vertical pieces sticking up out of 'em?

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-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
---Think your car could be pic of the week? Visit http://www.f-body.net for details!

Grim Reaper

Depends which type. The one with the individual velocity stacks tended to be Hilborne IIRC.

One version of the RamJet had the nickname "Dog House" for obvious reasons.