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Old 11-04-2011, 03:40 AM   #1
Kostamojen
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Lightbulb Early proposal: FA20 with a FB25 shortblock, .5l more displacement anyone?

I posted this thread on the FT86 forums, but figured I'd start one here too in order to get more info out of the more knowledgeable Subaru folks...

The basic idea is this: Take the shortblock from an FB25 and use it with with the proposed FA20 motor, which SUPPOSEDLY is a FB20 with heavily modified heads to use the Direct Injection system.

Quick comparo pick from what we've seen so far:



At this point we have NO idea whether or not this will work, or how much the FA20 is different from the FB motors. But from what I can tell so far, they are pretty darn close.

I'm presuming the bolt pattern is the same and nothing on the shortblock side (other than the crank/rod/pistons of course) is different. There might be issues with accessory locations and bolt holes, but again, no idea.

The bigger concerns I have are about the coolant channels and such and hopefully it isn't TOO different, but anyway the idea is pretty simple and has been done a billion times here on NASIOC....

Increase the displacement and compression ratio easily.

Thoughts, opinions, more info???
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Old 11-04-2011, 10:24 AM   #2
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I thought that the FB heads have the blank castings for the DI injectors?
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Old 11-04-2011, 12:02 PM   #3
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You sound alot like that guy in OT who has been restoring this 1970's Subaru for like the last six years and hes always mixing and matching parts and all this crazy shi...

(looks at username)


OH, You !
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Old 11-04-2011, 12:15 PM   #4
V3rtigo
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Isnt the FA supposed to be a higher reving motor? I would think this would lead to some changes in the bottom end.
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Old 11-04-2011, 09:25 PM   #5
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Quote:
Originally Posted by UKscooby View Post
I thought that the FB heads have the blank castings for the DI injectors?
You mean the spots are on the head already?

Quote:
Originally Posted by V3rtigo View Post
Isnt the FA supposed to be a higher reving motor? I would think this would lead to some changes in the bottom end.
The FB20 revs pretty high already.

The FA20 is supposedly a 86 bore by 86 stroke block.
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Old 11-09-2011, 10:15 PM   #6
RallyColtTurbo
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Is the HP fuel pump drive off the heads or the block? That will likely be your answer to a "simple" head swap. If the fuel pump is off the block somehow, the block will need to be retained and bored/sleeved.

However, if all the DI stuff is contained to the heads, I'd lay real money it will be almost as easy as an "old school" hybrid. Subaru always seems to design with the Lego mentality.
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Old 11-16-2011, 01:14 PM   #7
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hard to argue with more displacement if it doesn't hurt your redline at all. The Japanese regulations favoring 2.0 ltr engines need to diaf.
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