Anyone measued cylinder walls of fa20 yet?
 

My wife and I are in the market for a fourth car in the near future, and since im part of this forum I think you can guess what we are looking at :)

sooo... being inclined and curious to research engines I have limited experence with I present thoughts of cylinder wall inconsistency from subaru when upgrading to forged pistons down the road.

http://forums.nasioc.com/forums/show...2279165&page=9


as a reference the link above.

thoughts?

You might try asking Crawford Performance about that. They just replaced the pistons and rods in a car they put a turbo on.

Crawford would be the best bet, they're the only group I know of who have done a complete engine teardown. They have posted pics on their facebook page, and unfortunately due to some debacle with the admins here they aren't active on the forum any longer. ...sadface...

They and most others were impressed with the engine, the piston ringlands were beefed over the EJ257's, but if the cylinder walls are in question, do you have plans for huge power with forged internals or are you just worried in general? Accelerated Performance/Visconti is confident with an 11-sec 440hp+ bolt-on-E85-tune to deliver as-is to customers with all stock internals. (After lots of hard drag passes and hard 30min track sessions and they're still improving on it).

I read only a small portion of that thread, and it looked like like an isolated thread grenade. Is this happening with any consistency or just a few individuals with forged bits have had blocks pop and raised questions?

Considering the number of tuned high-boost Subaru engines are out there, if it was a serious problem, I suspect it'd be more common knowledge...

Dave,

I think it was just the STI 2.5ej series but am not sure if it is all subaru flat fours that have inconsistency in bore from cylinder to cylinder.

as for big power, that would not be in the near future more thinking out loud for future adventure (I currently have a stock bottom end 4g63 making 670whp) so im not scared to push the stock bits as far as possible, would just be nice to know what to expect from a machining standpoint the potential for .03 difference from bore to bore could be interesting for a set of forged pistons/gapless rings to make good contact. (sorry if that wasnt a full thought ive been typing this for 20 minutes at work between talking with customers)

Honestly, I think the Frs or Brz will make a great stock block boosted car, at most might run higher strength head studs and head gaskets but otehr than that I've been very impressed with this engine (and by nature as a mitsubishi guy I typically hate anything subaru has touched)

Subaru does stamp the blocks with A and B per cylinder depending on the bore size so there are variances cylinder to cylinder sometimes. Forged pistons require more clearance to account for thermal expansion so you do not need to keep track of whether it should be an A or B sized piston like the stock cast ones. Many have installed off the shelf forged pistons into a EJ257 block and I doubt the FA20 is much different.

assuming I wouldnt run a over bore piston is where the issue rises though, (I know "stock" bore forged pistons are still slightly larger .002 or so) but the point would be to have cylinder walls so new that a simple hone and drop in piston/rod combo is what my concern is. Yes it may work, but it also may have excessive blowby or even worse expansion cracking the walls. Which ofcourse, would suck.