FB25 shortblock FA20 heads - Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community

REVZILLA · 12-10-2022, 12:30 PM

Has anyone ever successfully installed a FB25 short block on fa20 heads?

Saw some discussion where the starter needs to be moved to other side transmission, fa 20 piston domes have a (bigger?) dish in them for direct injection, and possibly the combustion chamber on the head possibly needed milled.

https://www.ft86club.com/forums/show...t=45926&page=4

Looks to me like the transmission could possibly be milled out to have a left side starter without an adapter plate, and one only one bolt appears it would need left out of bellhousing. But unsure of other issues, thoughts?

PulsarBeeerz · 12-10-2022, 12:47 PM

Nah, Subi engine families don't lego like Hondas.

REVZILLA · 12-10-2022, 12:58 PM

Not sure if accurate but I think Jet86 (post#70) on this thread said the heads would bolt on the block

https://www.ft86club.com/forums/show...?t=2158&page=5

Just wanting to know what the exact issue with it was- if it was just not worth the trouble or not possible

NoHaveMSG · 12-10-2022, 04:23 PM

Not to mention thinner and smaller in diameter rod journals. No thanks.

https://www.ft86club.com/forums/show...3&postcount=66

Ultramaroon · 12-11-2022, 04:02 PM

Quote:

Originally Posted by NoHaveMSG

Not to mention thinner and smaller in diameter rod journals. No thanks.

https://www.ft86club.com/forums/show...3&postcount=66

Is there evidence that this change makes it less robust? I see a stiffer crankshaft swinging less mass at the rod ends. The smaller diameter also results in lower speed between bearing and journal but that probably wasn't the main goal. I'm sure the decision to give up some bearing surface for a stiffer crank involved considerable R&D.

NoHaveMSG · 12-12-2022, 11:34 AM

Quote:

Originally Posted by Ultramaroon

Is there evidence that this change makes it less robust? I see a stiffer crankshaft swinging less mass at the rod ends. The smaller diameter also results in lower speed between bearing and journal but that probably wasn't the main goal. I'm sure the decision to give up some bearing surface for a stiffer crank involved considerable R&D.

No, but you know my monkey brain just looks at it and goes "smaller bad."

I know it was discussed in that dudes NA build thread but I don't remember the outcome. I think he went with the FA20 crank and a custom rod/piston. If I get a chance I should reread the thread even though it is like 49 pages and 1/3 of it not even involving the build.

https://www.ft86club.com/forums/showthread.php?t=63901

Ultramaroon · 12-12-2022, 11:52 AM

Quote:

Originally Posted by NoHaveMSG

No, but you know my monkey brain just looks at it and goes "smaller bad."

I know it was discussed in that dudes NA build thread but I don't remember the outcome. I think he went with the FA20 crank and a custom rod/piston. If I get a chance I should reread the thread even though it is like 49 pages and 1/3 of it not even involving the build.

https://www.ft86club.com/forums/showthread.php?t=63901

Oh, I hear you. I'm sure there was quite a bit of hand-wringing during the whole development cycle. Maybe they trimmed out some capacity for boosting. We'll see as they start popping down the road.

D K · 12-15-2022, 03:05 PM

Why???

DarkPira7e · 12-15-2022, 03:08 PM

Quote:

Originally Posted by D K

Why???

FA20 heads from our engine are ported nicely from factory, I imagine that is the angle here

Ultramaroon · 12-15-2022, 03:28 PM

-5 missed gif

D K · 12-15-2022, 04:40 PM

never mind about converting from belt to chain

Seriously, why not swap instead??

Quote:

Originally Posted by DarkPira7e

FA20 heads from our engine are ported nicely from factory, I imagine that is the angle here

Ultramaroon · 12-15-2022, 06:33 PM

Quote:

Originally Posted by D K

never mind about converting from belt to chain

Seriously, why not swap instead??

If doable, I might consider it over back-converting all the sensors. Isn't that a thing too?

edit: Wait, no. I'm dumb. Already have to do that. Actually, I can't think of a good reason.

Ultramaroon · 12-15-2022, 06:38 PM

Quote:

Originally Posted by DarkPira7e

FA20 heads from our engine are ported nicely from factory, I imagine that is the angle here

Are they not for the FB?

DarkPira7e · 12-15-2022, 06:39 PM

Quote:

Originally Posted by Ultramaroon

Are they not for the FB?

I haven't seen an FB. But the FA20DIT heads are far less ported than ours so I can only assume ours were quite generous compared to their normal offering

12-10-2022, 12:30 PM	#1
REVZILLA Junior Member Join Date: Dec 2022 Drives: 2013 brz Location: kansas Posts: 2 Thanks: 0 Thanked 0 Times in 0 Posts Mentioned: 0 Post(s) Tagged: 0 Thread(s)	FB25 shortblock FA20 heads Has anyone ever successfully installed a FB25 short block on fa20 heads? Saw some discussion where the starter needs to be moved to other side transmission, fa 20 piston domes have a (bigger?) dish in them for direct injection, and possibly the combustion chamber on the head possibly needed milled. https://www.ft86club.com/forums/show...t=45926&page=4 Looks to me like the transmission could possibly be milled out to have a left side starter without an adapter plate, and one only one bolt appears it would need left out of bellhousing. But unsure of other issues, thoughts?

12-15-2022, 03:28 PM	#10
Ultramaroon 義理チョコ Join Date: Sep 2014 Drives: a 13 e8h frs Location: vantucky, wa Posts: 31,868 Thanks: 52,132 Thanked 36,519 Times in 18,920 Posts Mentioned: 1106 Post(s) Tagged: 9 Thread(s)	-5 missed gif __________________ service manuals

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PulsarBeeerz Senior Member Join Date: Mar 2017 Drives: JRSC BRZ SOLD Location: Ohio Posts: 934 Thanks: 676 Thanked 739 Times in 396 Posts Mentioned: 3 Post(s) Tagged: 0 Thread(s)	Nah, Subi engine families don't lego like Hondas.

12-10-2022, 12:58 PM	#3
REVZILLA Junior Member Join Date: Dec 2022 Drives: 2013 brz Location: kansas Posts: 2 Thanks: 0 Thanked 0 Times in 0 Posts Mentioned: 0 Post(s) Tagged: 0 Thread(s)	Not sure if accurate but I think Jet86 (post#70) on this thread said the heads would bolt on the block https://www.ft86club.com/forums/show...?t=2158&page=5 Just wanting to know what the exact issue with it was- if it was just not worth the trouble or not possible

12-15-2022, 03:05 PM	#8
D K Stig's dark passenger Join Date: Dec 2013 Drives: FR-S Location: I work abroad Posts: 724 Thanks: 60 Thanked 316 Times in 186 Posts Mentioned: 20 Post(s) Tagged: 1 Thread(s)	Why???

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