Not 100% certain, but I think the valve reliefs on the tops of the pistons may not be in the right place for the FA20 heads either, from looking at the pics...

Although I know machining the combustion chamber in the cylinder heads is the best way to ensure the proper compression ratio, I have looked into a alternatives that MIGHT work.

So on the old ej20/25 fourms there were obviously different ways people went about doing it. Some people machined the heads, some used different pistons (probably what EMS tuning did), others said “fuck it” and just slapped the heads on the 25 block and probably had to run super conservative tunes. One thing I thought was an interesting idea was using a thicker head gasket. Grimmspeed currently sells a 1.45mm thick head gasket, which is over twice the thickness of the oem head gasket. My question is if someone were to reach out to grimmspeed about making a fa24 head gasket in that thickness, would it be enough to make the fa20/24 build viable without machining the combustion chamber?

Depending how the head work goes by op this way or way not be worth looking into further.

That is a really good point, I don’t think it is. That actually reminds me of a list I made awhile ago comparing part numbers for parts used on the fa24 and seeing similar to the fa20. In that list it actually states the camshaft position sensors are different from 17+. I think I’ll go ahead and order the correct timing cover to not cause issues on my part.

Here is the list I made;

Fa24 vs fa20 part differences

Different parts
Cylinder head (housing)
Camshafts
Valves
Valve spring
Head gasket
Pistons, rings and pin (obviously)
Con rods and bolts
Crankshaft, bolts, and trust washer
Water pump
Timing cover
Oil pan (upper and lower)
Oil pick up tube
Crankshaft pulley and bolt
Engine bearings
Accessory drive belt idle pulley (on crankshaft)
Crankshaft position sensor
Ac compressor
Alternator
Pcv valve and hose
Valve covers
Flywheel

Same parts
Valve guides
Head bolts
Camshaft followers
Rocker arms (14+)
Valve spring retainer and keeper
Valve stem seal
Valve shim
Vvt solenoid
Camshaft position sensor (17+)
Thermostat
Cam gear sprockets and plates
Timing chain, tensioner and guides
Accessory drive belt idle pulley (independent)

Something to consider is that just because the part number is different doesn’t mean the part is actually different and won’t fit. Changes in part numbers can be caused by small revision changes, change in manufacture, material. PN coding has a lot to do with QC. Honda does this to me all the time.

That’s a good point. I was looking more into the timing cover and I think that’s exactly what’s going on. Hopefully they improved the oil pump but otherwise everything else looks the same.

Saw this on FB a while ago.


https://www.facebook.com/Goldentreer...2770626180789/

Yes, that's the EMS Tuning project mentioned above...

https://www.ft86club.com/forums/pict...ictureid=12825


The FA24 timing cover looks like a winner, Subaru probably made some other improvements inside.

Does this pic show that you resealed your FA20 2017+ timing cover with a FA24 timing cover?

Nah, just snapped a pic of a 2nd gen at the shop that was in for an oil change.


https://www.ft86club.com/forums/pict...ictureid=12826


The oil pickup tube looks improved as well, made from some kind of composite material. Grabbed this pic from a Japanese website...aftermarket baffle plate.

Wow that is a completely different design. Strange how it has that small opening and then it gets bigger (maybe there is a filter in there) and then seems to neck back in.

I don't like it. It's probably just fine but there's a reason breakaway tabs are skinniest where they're supposed to break.

Bumping this. Not sure if anyone else saw this but it was on FB group. Shop in Thailand was able to do a fa20 heads w/ fa24 shortblock. ~260 whp w/ ecutek on racerom on e75
https://www.facebook.com/permalink.p...97121510449973

Reminds me of the k series Frankenstein builds but damn that’s cool. If the new short block can solve the fa20 oil issues on track this would be a serious contender. One down side is it’s got to be pretty expensive with a boxer, two of everything with head work.