fa/fb

[subarob]

hey to whom ever was wondering about the fa engine that doesnt already know. not that im special lol but im a subaru technician and in my fb engine training module we discussed direct injection and the fb was already bossed for it, as far as the heads and intake go. so subaru has long since planning this. i had slipped away with toyota for awhile back in 08 and got a very little insight then. but from what i can see the difference in the fa and fb is the fuel managment and compression...and likely cam profiles. however i can tell you my instructor told us that the fb wouldnt really be good for a high boost application...likely nothing stronger rods and pistons would not cure. when we opened this little baby in class i found it to be one of the closest tolerance engines ive ever seen! 15% coolant flow to the block and 85% to the heads with high volume not high pressure oil pump. kinda reminds me of porsche. hot running rotating assembly with nice cool heads. lots of o-rings instead of gaskets. all in all....makes an ej look like an ea82.

[bersh]

sweeet
Have you experienced any problems with these new engines yet?

[ej25ti]

ooooooooooooooo
hmm
sounds good

[Cal]

hey to whom ever was wondering about the fa engine that doesnt already know. not that im special lol but im a subaru technician and in my fb engine training module we discussed direct injection and the fb was already bossed for it, as far as the heads and intake go. so subaru has long since planning this. i had slipped away with toyota for awhile back in 08 and got a very little insight then. but from what i can see the difference in the fa and fb is the fuel managment and compression...and likely cam profiles. however i can tell you my instructor told us that the fb wouldnt really be good for a high boost application...likely nothing stronger rods and pistons would not cure. when we opened this little baby in class i found it to be one of the closest tolerance engines ive ever seen! 15% coolant flow to the block and 85% to the heads with high volume not high pressure oil pump. kinda reminds me of porsche. hot running rotating assembly with nice cool heads. lots of o-rings instead of gaskets. all in all....makes an ej look like an ea82.

Anyone want to break that down for me?

[modifiedMR]

Anyone want to break that down for me?

Basically most of the coolant goes through the head to keep it cool, but NOT through the block. This means the block is meant to stay hot, which helps piston rings seal because the tolerance gets tighter as the heat expands the block (making the circles the pistons fit in, tighter). O-rings vs gaskets really isn't a gain in sealing, but o rings are easier to replace because gaskets have to be properly set when you are putting things together. O-rings usually sit much more easily in place.

What are the tolerances? I work in a machine shop, but we don't do very tight tolerances usually. Typically, between 3 and 5 thousands variance and some tougher stuff in the -1 thousand. Occasionally, I'll see +/- .01 and wonder, who wants something so dang loose?

[G4BROKE]

nice info..i'll have to discuss with my shop.

[hilux guy]

Maybe he means it is a tight tolerance engine as in "interference engine" and it has high compression.
If he is talking about the fact that the engine has tight tolerances as in clearances for bearings and bushings etc... I should hope so... It's brand new, and any engine needs tight tolerances.

[modifiedMR]

Maybe he means it is a tight tolerance engine as in "interference engine" and it has high compression.
If he is talking about the fact that the engine has tight tolerances as in clearances for bearings and bushings etc... I should hope so... It's brand new, and any engine needs tight tolerances.

There are huge differences in what "tight" actually is. I work in a machine shop. Some engines aren't built super tight because they don't need to be and if they are, it is possible if the pistons get hotter than usual for any reason, the engine will lock up. This is why many non-performance engines leave a little more room, so that the engine is less likely to fail from scoring. That and it's easier for them to build them initially too. To put this in perspective, we are talking about splitting hair differences.

[hilux guy]

Nice, what kind of machine shop do you work in?? I am an AME and when we build aircraft engines the tightest I have seen is 2-3 thou, but those were turbine engines....
It makes sense to have extreme cylinder tolerances in higher compression engines for better sealing.

So then the statement very close tolerances is that of saying it is a very high performance engine!!

I am very excited to see this car in person, and I really hope it's realease as a scion will not change the car too much.

[modifiedMR]

Nice, what kind of machine shop do you work in?? I am an AME and when we build aircraft engines the tightest I have seen is 2-3 thou, but those were turbine engines....
It makes sense to have extreme cylinder tolerances in higher compression engines for better sealing.

So then the statement very close tolerances is that of saying it is a very high performance engine!!

I supposed the tighter tolerances is to keep blow-by minimal? Not for sure. I work for a multi-purpose machine shop. We make gears and gear racks mostly, but do some other custom stuff too. Typically for a gear, we'll get 2-3 thou, but some get as tight as 5 tenths. Some of the custom stuff is within 1 thou (usually a -.001 off the print), but most stuff is a +/- 2 to 5 thou range. All depends on what the customer wants really. We don't make a particular part for one or even just a few customers. We make all sorts of stuff. LOL. Crane parts, little plastic gears for who knows what, brass racks and gears, etc. Makes things interesting.

[Cal]

Who wants to explain tolerances to me?

[modifiedMR]

Who wants to explain tolerances to me?

Tolerances are variances allowed in a print. Either they are in a chart, or on each dimension on a print. Think of having a 3D box. You would have one dimension for height, one for depth and another for width. The tolerance is how far you can be off, like saying the box should be .100", but when you machined it, it ended up being .103". If the print says .100 +/- .005 you are cool. If it says .100" -.005 (meaning they only want the box to be between .100 and .995) , the part needs to be cut down (if possible) or is scrap. There is a whole lot that can go wrong in machining and that's why they have tolerances. Tight tolerances mean they are not allowing for much variance, but in each industry, tolerances vary. In the auto industry, tolerances are pretty small to begin with now.

[Turbowned]

When I think of "FA" engine I think "Formula Atlantic", specifically the 4A-GE that so many AE86 fans lust after. Subaru is going to make things awfully confusing...