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Guest Message by DevFuse
 

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fuel delivery swap question mpfi vs. spfi.


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6 replies to this topic

#1 Guest_archemitis_*

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Posted 23 July 2003 - 05:54 PM

is there anything inherantly better about the mpfi? like if the spfi didnt have such a bottleneck where the tb is would it make a good efi system or is the mpfi alot more effiscient or someting. i need efi on an ea81, and if mpfi is that much better i will make it work.

#2 Guest_offroadsubaruguy_*

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Posted 23 July 2003 - 09:18 PM

id say to go with the multi point if you can... its just a better system, easier to work with.......

#3 Guest_x silvershad0w x_*

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Posted 24 July 2003 - 07:38 AM

As to which is better, MPFI should yeild you better performance overall.

SPFI is an excellent choice for an EA81 conversion thou, because it is easy, just bolt on the manifold and install the appropriate wiring harness and ecu setup, along with a fuel pump swap, true in either case.

For MPFI'ing a EA81 with EA82 MPFI system, to make it super easy, i would use the EA81T heads, since the injector bungs are in place and ready to go. I know they are hard to get ahold of, but it would make for an easier install. MPFI uses the spider-style intake afaik, and so can't adapt that easily.. I would go for trying to adapt a fit of the MPFI throttle body unit onto the EA81 carb intake manifold, or on a EA81T manifold, because those have a nice casting separation between the water channel and the intake runners.

EA81T throttle bodies use a different TPS, that is a switch, not a variable reistor, like found on SPFI and MPFI TB's. You might be able to adapt the sensor and then use the EA81T throttle body, which could make it easier on you as well.

Hope this helps some, this sounds like a great mod to an EA81. (My favorite 80's powerplant :) )

#4 Guest_OH Noah_*

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Posted 24 July 2003 - 08:55 AM

There were two MPFI systems used on EA82s. The '85-'86 system used the switch only TPS, while the '87+ version is the one that used the potentiometer. My understanding is that the '85-'86 system is almost identical to the EA81T system.

I agree that SPFI is the easiest choice for an EA81. The biggest problem involved in the swap is altering the LED distributor to work on an EA81. I think you'd have to do that to use the '87+ MPFI as well.

For ease of install, my natural suggestion would be to use CIS-E from a VW Fox. On an EA81 without Turbo heads, this would require drilling injector holes into the heads, but that would be true of any MPFI system. I was planning to do this to my hatchback until a EA81T engine fell into my lap. I'm still going to use CIS on it, but it's going to be a whole lot easier now with an engine built for MPFI.

Here's how CIS fit on my EA82 Wagon:
www.fortunecity.com/silve...baru/1/CIS

#5 Guest_archemitis_*

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Posted 24 July 2003 - 10:03 AM

if i was to use the mpfi i was thinking about building a better intake for the standard single intake heads(so i can use junk. with a mini tranny cooler in the middle for the hot heads water supply. say 1 7/8 inch intake runners? but i'll probably go with the weekend install of the spfi, instead of a month long ordeal.:P think my ea81with spfi will run the same hp as the spfiea82 ?

#6 Guest_OH Noah_*

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Posted 25 July 2003 - 06:50 AM

I think an SPFI EA81 would be stronger/smoother than a carbed one, but not as strong as a SPFI EA82. The EA81 has lower compression (8.7:1 vs. 9.5:1) and a pushrod valvetrain.

#7 Guest_archemitis_*

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Posted 25 July 2003 - 12:28 PM

now for the curve ball... turbo. does the mpfi compenate any better for a stock turbo system...




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