Why Subaru Engines Blow Up!

Mike from MotoIQ here and for this video we're going to talk about why Subaru engines blow up so easy. A lot of people have trouble with their Subaru engines and I kind of tend to agree about that. I think the engines are pretty fragile, at least in turbocharged form. The naturally aspirated models, they can go for a long time and you don't hear about them having too much trouble but the turbocharged variants like the STIs and WRXs, they pop their motors a lot. A lot of it is most almost everybody with a WRX or an STI builds their car and there's all types of people that are qualified to build engines and tune them and probably at least half of them aren't any good. You know when you have an engine that's marginally strong it's really easy to push it over the edge. So let's look inside the Subaru engine and I can tell you the kind of failures we see. Subaru guys are some of our best customers and I think that's because a lot of them break their engines. The main thing we see are broken ring lands. Now this is a Subaru piston. Subarus have short strokes and really big bores. You know that's kind of good for high revs in some ways but in the case of the Subaru, you know like you have a big bore, you have a lot of crevice volume, so for Subaru they want to cut down their hydrocarbon emissions so they could pass the U.S.'s stringent smog requirements. When you have a big bore and you have your crevice volume which is the space between the number one compression ring and the combustion chamber, that's an area where hydrocarbons can hang out and believe it or not that's a significant contributor to hydrocarbon emissions. So Subaru raises their number one compression ring as high as they can the piston to try to help with emissions and this is fine for emissions but it's bad for durability of a turbocharged motor. Now you probably noticed that the dish of the piston is pretty big and it comes way out to the edge here and the ring is really high. What that means is that you have a really fragile ring land. In fact all the rings are pretty high on the piston and they're pretty unsupported and thin so the ring lands are fragile on the Subaru. So any detonation especially with a stock hyper-eutectic piston tends to either pinch the rings kind of bend the ring land down a little causes the ring to stick and you lose compression or worse yet you know like you break your ring land and you totally lose compression. Now this piston here the rings are pretty stuck you know it's subjected to some detonation because you can kind of see it as a sandpaper texture to it so that's a sign of mild detonation. The ring land didn't actually break but the ring is stuck and that's what caused this engine to lose compression. For instance if you want to compare it to an engine that has a reputation for being pretty strong this is a Nissan SR20 and you can see how the rings are a lot lower on the piston than the Subaru so the ring lands on the Nissan piston are a lot stronger. You can see how the bore is a lot smaller and you know there's less room to trap hydrocarbons so Nissan could get away with lowering the ring package you know that's the number one reason. You know with a bigger bore too the flame front takes longer to travel so a Subaru engine has to run more advanced so generally you run a few degrees more advanced especially when you tune them having to run more advanced having a long flame front that's gives the cylinder slightly more propensity to detonate. Detonation is death for these engines. If you look at the cylinder head the cylinder head the combustion chamber geometry is actually not bad. It has a shallow included angle and has generous clench pads. Now shallow included angle has a low surface to volume ratio and the clench pads tend to produce turbulence to kind of squish the fuel air mixture toward the plug and it makes the fuel air mixture in the chamber turbulent as the piston comes to TDC. All of these things are good to prevent detonation. Now you have a good chamber but for some reason Subaru didn't line up any kind of clench pad on the piston with the clench pad on the combustion chamber. I think if they did that like a lot of other engines do you would actually have a more turbulent chamber and less propensity to detonate but for some reason Subaru has a good chamber design but they didn't exploit it as much as they could to reduce possibilities of detonation. I would say that's the main reason why we see Subarus blow up. Now a lot of people have problems with the head gaskets on these engines and you can see here's the engine case like the head gasket is not very well supported like it's a it's an open deck engine but you know there's different open deck engines and the Subaru is probably like the least supportive of the head gasket of you know just about any engine that's turbocharged from the factory. I mean you can see that there isn't very much area for you know the uh to get clamp on the head gasket. I mean like here's the head gasket right here and these black areas are kind of where the clamping pressure is and it's mostly open space. You know that's not too conducive for good seal for a turbo motor. The other thing is that you know everything's pretty flimsy and can flex around like the turbo models most of them have like these buttresses here at least the EJ257 does some of the other ones don't have these buttresses and that kind of keeps the cylinders from moving. The cylinders move they work the head gasket and there's more propensity for it to blow. So if we're building an engine that's going to run you know more than the low 400s for very long like you know if it does track days or road race or time attack we always do a closed deck conversion so this part gets CNC machined out and the close tolerance insert gets pressed in and you know that makes it act like a closed deck. This makes everything a lot more rigid gives a lot more clamp area for the head gasket. Pretty good thing like if you're probably up to you know like 420 430 horsepower you don't need to do it but I mean it almost doesn't hurt. So the head gasket seal is one thing some people put studs in but I'm a not a proponent of putting a stud in a engine that's not going to be completely gone through and we'll get into that in a little little bit. The other thing that causes these engines to mess up a lot is the oil pump pickup. So the stock pickup is really flimsy it's really thin metal it's brazed together with like not much brazing material and not much fillets. So the pump pickup is actually prone to breaking. Now I haven't seen a pump pickup break on a totally street driven EJ motor but people that do track days I've seen several break. Even like kind of casual track days I've seen them break and even if you get a crack developing the pickup will suck air and your engine won't get a good oil supply. Usually like it completely breaks off and that's total destruction of your bottom end. So the pump pickup is not the way to go. So the way to get around the pump pickup breaking IAG and Killer B both make excellent heavy duty pickups. If you're going to be doing any track driving at all or if you do like a lot of spirited driving in general probably recommend one of these. They're not that expensive and the cost of one of these things failing is pretty high. I mean it's not like they all break but I've seen a few break for no reason other than just being at high rpm and the vibrations and everything. So this guy is a cause of a lot of engine failures. The other thing that we see on track driven and cars that are driven when cornering hard is these cars spit a lot of oil out of their breather system and I mean it's possible to spit so much oil like in a track session that your your sump is starting to run low and one of the reasons is that Subaru's have very little crankcase volume. So you have these pistons going up and down and as you can see the crankcase volume is really low compared to like almost any other engine. So they run a lot of crankcase pressure and this tends to blow a lot of oil up through the breather system. You know if you have a stock car and just drive on the street you probably don't have too much of an issue but you know if you have a tune and some bolt-on parts and you drive on the track like probably most of you do you are going to be spitting a lot of oil. And I mean I've seen cars fill up two large catch cans in one session on the track so you know that's probably almost half the crankcase capacity. So a lot of these cars get run low on oil and that causes bearing problems and you know also leads to failure. Now the other reason why they spit a lot of oil is this is a flat motor so on most motors when the oil comes from the top end and everything it just drips straight down to the pan. On these engines like the pans down here here's your crank the oil kind of like is not dropping straight into the pan but it's kind of like making a 90 degree turn in the pan plus if the oil's sloshing around it's real easy to under high g's to slosh up and hit all these rotating parts which causes a lot of windage which causes a lot of oil to get spit out especially when combined with the high crankcase pressure due to the small crankcase volume. Because of this a lot of times the stock pan is inadequate. Now the stock pan is actually not that bad I mean it has a couple of sets of baffles and everything and you know it has a lower baffle that keeps oil around around the pickup and it has an upper one to prevent big slosh but you know if we if you have like a track driven one of these cars and you know you have modified suspension and big sticky R compound tires and things like that we prefer that you run a performance pan like a IAG or a Killer B with the you know the pan baffles the trap doors and the windage tray. We really like the IAG windage tray because it actually has trap doors so the oil can drop down to the pan but it can't get splashed up into the crankcase area but windage tray, baffle pan, higher capacity it's all good stuff. Now the oil pump and all that is generally pretty good and the oil capacity is pretty decent you know it's fine for most use but you know it's just the idiosyncrasies of the flat motor and the crankcase pressure all makes this a perfect combination to puke oil out of the breathers. Puking a lot of oil out of the breathers your sump gets low your pickup sucks air and there goes your bearings. The other thing that's important on these engines is to run a good air oil separator. Now if you have a stock engine you drive on the street I mean it's probably not necessary but if you drive on the track and have sticky tires modified suspension if your engine's built like let's say you have a full bolt-on car in the tune you know I kind of feel like you need an air oil separator. The air oil separator will take the get all your blow by and all that stuff that's getting puked out it'll separate that from the blow by gas and put the oil back into your pan. So I think IAG makes a really good air oil separator so does Killer Bee. A couple other people make catch cans but I think Subarus tend to puke so much oil that you don't want a catch can you want that oil to get back in your crankcase so I recommend the AOS. Now if your car is purely track driven I think the Killer Bee one is nice and simple and will return the oil to your crankcase quickly because it has like this kind of a funnel shape. Now if you do a lot of short hop driving and if you live where it's cold I think the IAG air oil separator is better because it circulates coolant through the can part of the separator so you don't get that milkshake watery oil going back into your pan. So heavy duty pickup a good pan with baffles and a windage tray will help a lot to prevent your Subaru from blowing up. When you look at the crankshaft this is kind of one part of the Subaru engine I think it's actually not that bad the crankshaft is short it's pretty stiff it has a pretty decent journal overlap the stock crank actually gives very little problems we like to run the post 2006 OEM crank that has like you know it's nitrided so the journals are really hard wears real well you know that's the stock crank is good for like maybe 700 horsepower easy and it hardly ever gives problems so your stock crank is one part of this motor that Subaru did a pretty good job and you shouldn't have issues with. Now the case is a whole nother deal now the cases on the Subaru don't weigh that much there's not that much aluminum not that much reinforcement so you're asking this thin flimsy aluminum thing to handle a lot of pressure and a lot of violence going on in there and it's kind of not up to the snuff now if you're serious about you know doing time attack and you're you're pushing this motor for all it's worth I mean a lot of guys will disagree with me but my opinion is is that you know you go much past the mid 500s you get away from the happy zone of the EJ motor no matter what you do to it I mean sure you can make 800 a thousand horsepower you know but those are more drag racing motors if you try to run that level of power on something like that sees road racing use or track days you're going to be going through some motors now you might not have like a catastrophic dramatic failure but you're going to be going through motors and having to maintenance them a lot and tear down an inspection stuff like that I mean they're going to be more finicky than just about anything else and a lot of it is just this engine wasn't designed to take those kind of power levels I mean there isn't much to it like there isn't much metal and much reinforcement to take all of that so this whole case and everything flexes around I mean you know you could uh close deck it and uh you run studs and uh and all that but still I mean you can only uh you can't make a pig's ear a self purse no matter what you do to it I mean some of the things we do is uh of course I talked about closed decking uh we'll also bore the uh holes out then we'll run 12 millimeter ARP studs um you know like we'll if you're getting much above 500 horsepower we'll actually uh dowel pin the mains here uh that kind of keeps it keeps it from flexing and uh getting misalignment down there while the engine's at full song and killing your bearings um but even doing all that you know the engine's not like bulletproof or anything uh it's not like a Honda K motor where you have like that whole uh bottom end uh girdle deal going on so it's gonna flex you're gonna have bearing problems uh you get too bad bearing problems um you know really bad things happen so I think the important thing is to have realistic goals sure you can make 800 horsepower and have a lot of fun but you're not gonna be doing it for long and like a road racing kind of situation if you want to have your 800 horsepower time attack car uh better bring a couple of motors in the trailer you know before you go cross country to Koda or super lap battle or something um I'm just being realistic and uh you know that's what you you can expect I mean you can make these things so they'll pretty much run at 550 for a good long time but more than that uh gets kind of sketchy I I think like another thing is um these engines are actually fairly difficult to build and that's another reason why they get such a bad reputation um it's not like they're difficult to assemble but there's like a lot of quirks to them that if you're not experienced with Subarus uh you're going to have trouble one of them is is that uh when you bolt the head and you bolt the case halves together there's um everything's so flimsy that there's a lot of distortion um so when you machine these blocks um you have to have a bottom plate and a top torque plate and if you're running studs you actually have to pre-machine it for studs and torque everything to the stud torque spec before you bore the block this is because um you know if you uh if you actually measure one of these things when you bolt it all up with studs I mean you can get a easily get a thousandth and a half distortion in the cylinders um and if you bore it with that without the plates when you unbolt it um you know you'll have all this distortion and you know even if you if you run forged pistons you know that's half your piston to wall clearance is taken up by distortion I mean if you have like a you know if you just like have your own machine shop bore out your block and your case and slap it together and you're running the hyper eutectic pistons that run pretty tight clearances I mean your engine can seize and get wiped out because the distortion can be the entire piston to wall clearance um the other thing is when you stud everything and torque it down it distorts the bottom end so um you know like a lot of guys might slap studs in there torque everything down and then the crank doesn't turn anymore because it's so distorted that the crank is actually getting pinched um that's why like some other YouTube channels that have tried to build Subaru engines have blown them up like in short order it's not like they don't know what they're doing they're probably just don't know the idiosyncrasies of a Subaru so when um you know we machine the Subaru we do all the boring and in the fixture that simulates the whole engine being bolted together if we're going to run studs we put the studs in and run at the torque that the studs are going to be at so all the distortion gets in there then we do all our bore machining and then you know when the engine's together you'll have nice straight round bores the other thing is if you're running studs we always align bore the cases so that's shaving a little bit off and then running a uh like a line hone through there and um these things require a line boring more than any engine I've ever seen actually so if you're running studs like a hundred percent you're going to need to align bore it and for sure you need the fixturing uh you know that's a big idiosyncrasy and that's probably why a lot of you've probably heard don't try to build your Subaru engine just get a factory long block because the factory is the only one that knows how to build the engines and um that's not exactly true but if you've you know like machine everything properly your chances of success uh go way up so I would say improper machining is the biggest cause for belt engine failure um you know if this is all intimidating um you know make sure your cases get machined by a Subaru specialist you can buy pre-machined cases from like IAG their cases are good or Outfront Motorsports uh they have pre-machined cases you can get them with the uh stud holes all machined and uh closed deck conversion and uh your bore and your line bore all ready to go uh the other thing that happens is that Subarus have a lot of deck surfaces so in your regular engine you know if you're uh going through it and you want to clean up the deck of your head and clean up the deck of your block you need to take maybe five thousandths cut on both and um so your your engine gets about ten thousandths shorter so your cam timing only gets off maybe a little bit but on your Subaru you know you have your case if you align board you know like you take some off of here you take some off of here you you deck the case you take some off of here on on both sides take some off of both heads so what happens is the all those tolerances stack up and your far cylinder uh your cam timing can be really off by the time you get there so when you're assembling a uh Subaru that you've built and everything's fresh it's imperative that you you actually degree in your cams and actually see where your cam timing's at because your far cylinder head there's a good chance that it's actually running pretty retarded in the cam timing now they make uh adjustable timing gears they also make offset keys especially for Subarus so you can compensate from for some of that machining change but you know just don't slap your Subaru engine together measure every single thing um you know degree in your cam with a degree wheel you know make sure that especially the far cylinder your your cam timing isn't like super retarded um and you'll be fine we also get like guys that want us to build like a uh naturally aspirated Subaru that'll rev to nine grand and they think they'll compete with Honda K motors or something but uh that's not gonna happen and there's a few reasons for that uh the number one thing is the Subaru head doesn't flow anywhere near a Honda K series like the intake ports are pretty decent pretty good geometry pretty good short side radius pretty good shot into the cylinder but when you go to the exhaust side the whole exhaust flange is offset so that means that the front cylinder the exhaust port goes through a big dog leg which really kills the flow to that cylinder and it's really hard to get both cylinders to flow equally across the lift curve in fact it's impossible so even the finest cnc heads aren't gonna aren't gonna flow anywhere near a K motor um the other thing is the Subaru has a shim and bucket valve train so that's kind of good because it's light doesn't have mass so you can get away with you know not running as heavy spring and not getting valve float but the problem is is that if you put a radical cam grind with a lot of area under the curve the lobe will run off the edge of the follower so you i mean you can notch the the head to make some clearance but you can only get so radical with the cam before the the lobe runs off the edge and if that happens uh you know it wipes everything out or everything wears super quick so you're limited in what kind of valve events you can have also the Honda uses finger followers and with the finger follower and the roller um you can get well not roller but with a finger follower uh the leverage ratios and everything allow you to have uh valve events that you can't get on the direct acting um what you call like a shim and bucket so uh like the Honda you get you can get way more area under the lift curve and way more radical valve events so you know like we always tell people don't try to build the 9000 rpm ej because you're going to be disappointed um you know the other thing is um there's not as much na development done in ej's so they don't have like cams that have been researched out as much and even if somebody did try you're limited by the basic design of the so i don't know in our opinion don't try to build the killer na ej um you know a lot of people have asked this too but you know i always tell them you're going to spend a lot of money and you're going to be disappointed uh the other thing is uh when you go na you go high revs and big power the power band gets more and more narrow and higher so if you have your stock wide ratio transmission um you're going to be falling out of your power band in between shifts and that's going to suck so i don't know my opinion for big power this engine wasn't meant to be na it's uh best boosted but it's fragile under boost so you know tailor your expectations um sure there's a lot of guys making 800 horsepower but you know they're either uh hooning on the street with the occasional blast down the freeway and occasional pull on the drag strip uh that's not like doing the track day like let's say let's say you just do a fun track day uh not competitive you know like you let's say you do three sessions i mean you're on it for 20 minutes at a time you know that's i don't even know how many quarter mile passes that is or how many freeway pulls but in one session you'll probably drive your car harder than a lot of these 800 horsepower guys driving a whole year so tailor your expect um your expectations and uh don't overdo things now um i think relief is coming though like ieg is currently developing a fairly affordable case now like there's billet cases for these engines but a lot of times i feel like a billet case isn't necessarily that great for the street most of it is because a billet case is pure solid aluminum billet and the area around your main bearings kind of grows with heat in that respect and it's kind of often it's hard for the stock oiling system to maintain oil pressure at low rpm for instance because your main clearances grow with heat so you might have really low idling oil pressure if you have a dry sump that cures everything you know like a full race motor um but you got to be careful about those full billet blocks they're strong but sometimes you have to consider things like that but ieg is coming out with a um a new uh cast case that's going to be super heavy duty so it's going to have a lot thicker of a deck it's going to have thicker cylinders um it's going to be closed deck it's going to have a lot more beef around the main area and a lot more support around the crank it's also going to have priority mains so that means that the oil pump is going to feed the main bearings first and then the uh surplus oil is going to go to the top end so your mains are have a better chance of getting good solid oil all the time um the most important thing is it's going to have cast in uh steel inserts around all the main bearings um you know just like an oem block and this will control the expansion uh around the main so you don't have the growth and you don't have your um clearances opening up with heat so it's going to be like a stock block but um you know it's going to be way stronger they're addressing all the weak points of the the stock suru it's going to have 12 millimeter studs um you know it's going to not be a elaborate cnc billet piece so the price will probably be like half of what a billet case is um so stay tuned i think ieg is going to come out with that probably in the next six months i could be wrong but i know they're deep into the development process and i think that's going to be a game changer for for the subaru people um you know that way you'll you'll be able to make 800 horsepower and have the engine live and um you know everything will be happy but uh that's coming in the future uh these are the reasons why i think super engines kind of suck but um you know you keep it stock it'll probably be happy but you start playing with it things are going to happen um the last thing before i uh stop is when you mod these engines uh there's a lot of like local shops or whatever that um maybe they don't know subarus really well or they're um one pull hero kind of tuners so they do one pull on the dyno and uh send you on your way um you know you don't want to do that with a subaru you want to be conservative tune conservatively keep your air fuel ratio slightly rich keep your timing um slightly retarded keep your boost slightly lower when you're going on the track run a few gallons of race gas um you know tune for your worst case uh make sure that you have good cooling watch our last video on three ways not to have your engine blow up and then do do that and i think uh you'll be a happy subaru owner now the rest of the car is pretty good you just got to watch that engine so you know follow our advice manage your expectations and uh you'll have fun with your ej so until next time um check us out at moto iq.com we have a ton of subaru build articles um you know check our youtube channel subscribe we have a lot of subaru content there um if you want to build your subaru check out our web store uh we have like most of the parts we talk about um if you want to get some cool merch like uh we have hoodies we have t-shirts if you don't like the giant moto iq um emblem we have some other cool ones too um you know support us uh and they'll help us come out with more content so until next time uh you know have fun out there and don't blow your stuff up