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Guest Message by DevFuse

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Carb, Elect Carb, SPFI MPFI

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10 replies to this topic

#1 ausubaru92


    Turbo Talker

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Posted 13 January 2005 - 02:20 AM

Does Efi have any benifits over a Carb (other than Efficiency)

A guy who owns a mpfi and carb wagons said that the mpfi dosent yeald any more power than the carb, but the carb will respond quicker in acceleration than mpfi, mpfi is just more efficient

What does the electric feedback carb do?

What has to be done to put spfi on a carb ea82

#2 BobBrumby


    Subaru Nut

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  • Brisbane, Australia

Posted 13 January 2005 - 02:24 AM

spfi and mpfi both came out of the factory with more ponies than the carb version. so efi is more powerfull and more efficient.

the electronic carbs is ment just for emission controlls and was produced for "emmission nazzi" states like California. i have heard you can just disconect the computer and it will still run fine. But in Australia do we get them?

#3 85Sub4WD


    EA82 Junkie

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Posted 13 January 2005 - 07:09 AM

I just converted my EA82 to SPFI. The conversion is relatively strait-forward. You will need to swap the intake manifold, fuel pump, replace rubber fuel lines. If your y-pipe has a hole for an O2 sensor, then you are fine, if not, you will have to swap y-pipes. You will also need the wiring harness off an SPFI car - that is the hardest part - and of course you will need the SPFI ECU. '87 and later SPFI systems are identical as far as their pinouts, but if you have an MT car, you will need an MT wiring harness. (AT has an inhibitor switch) I know a couple of sites you can download an '89 FSM at, and Snowman is/has made a manual on how to do the conversion. I noticed an immediate power increase. One thing is critical is that you must ground the SPFI ECU or else it will die.




#4 archemitis


    guy smiley

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Posted 13 January 2005 - 11:06 AM

spfi has lightning fast throttle response. way faster than any carb i've mashed on.

more hp, prolly debatable, a weber might givemore peak hp, but a spfi will deliver more overall hp.

in my opinion annyway

#5 MorganM


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Posted 13 January 2005 - 11:23 AM


When I'm pointed vertical up a hill and flooring it I don't have to worry about a carb craping out on me. :drunk:

#6 hush777


    More Subarus than Kids!

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Posted 13 January 2005 - 12:39 PM

Snowman did a write-up about the Carb to SPFI conversion, I made it into a PDF file for the USRM, and probably will be posting it there in the next week or so. It includes everything that you need/need to know about doing the conversion.


#7 Snowman


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Posted 13 January 2005 - 04:50 PM

The SPFI conversion is a cakewalk if you know much about cars and electrical stuff. I did it for the first time in less than two days of tinkering.

The biggest advantage injection has is drivability. Carbs can make more power in many cases, but they have issues with weather, altitude, and vehicle inclination that EFI avoids. In my case, I would have to tune my carburetor five or six times along the way on my drive between home and college in order to get maximum performance, whereas my current EFI setup does it for me.

#8 Hank Roberts

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Posted 02 August 2005 - 04:56 PM

What model years did Subaru make the SPFI or MPFI available?
I gather the carb and fuel injection were both available during some if not all years, but which ones?

As I continue looking for a reliable used Subaru ....

#9 Petersubaru


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Posted 02 August 2005 - 05:36 PM

all I know is what I have owned over the years ..I have had 2- 1985's..carb/MPFI,Non-turbo and 3- 1986's/carb/MPFI Turbo/SPFI...the 3 cars I still have...I believe here in Canada that the SPFI came out for the first time sometime around mid '86 which was the end for the carb models ..............

What model years did Subaru make the SPFI or MPFI available?
I gather the carb and fuel injection were both available during some if not all years, but which ones?

As I continue looking for a reliable used Subaru ....

#10 MudisFun


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Posted 02 August 2005 - 11:41 PM

I have finally gotten to the point were I understand the 2bbl. Got her tuned!!! But when I think about, SPFI is the way to go, you may have wire everywhere but you don't have to worry about cut out when you drive on a wall. But the MPFI is just a head-ack, no matter how wonderful it works there is no room to get your hand anywhere. SPFI is the way to go:banana:

#11 NorthWet


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Posted 03 August 2005 - 03:13 PM

What fuel injection can offer is accuracy. A carburetor is always using weird physical effects to try to determine how much fuel needs to be added to how much air in order to get a burnable mixture. The heart(s) of the carburetor, the emulsion tubes, are things that the average person doesn't even know about, let alone do anything about. Until you get into full-on Webers, Solexs, and Dell Ortos, you can't alter the emulsion tubes.

Carburetor mixture depends on float level, main jet, emulsion tube, air jet, venturi size, aux venturi size, discharge nozzle, intake manifold design, how many cylinders the venturi is feeding, engine speed and volumetric efficiency. Too name just a few variables...


Carburetors are black magic, and although a carb'd system seems uncomplicated next to EFI, the carb inself is anything but uncomplicated.

EFI, on the other hand, uses physics to set the mixture. It measures air mass and engine speed/load, and injects the proper amount of fuel to provide the desired mixture. Any physical variations in sensed values are compensated for my the feedback information from the EGO sensor. (If the EGO is giving inaccurate info, then compensating and accuracy go out the window.)

How many professional race cars still use carburetors unless required to do so? That should tell you which gives more power.

Carburetors seem less intimidating, until you have accumulated a small tackle-box full of jets and emulsion tubes. And are cursing that yet ANOTHER brass float has cracked and your oil pan is full of gasoline. :banghead:

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