Let me start off by saying I haven't touched the motor. It's been in the car since I bought it and only know what the PO knew. It runs smooth and quietly though. -EJ22T block (Stock bore) -Stock EJ22T pistons -Stock STi rods -Stock crank -EJ25 heads -Stock cams -Stock valvetrain -OEM headgasket Using these numbers.. Cylinder Bore: 96.9mm Stroke: 75mm Head C.C. Volume: 47cc (I couldn't find a definitive answer, so I used something close) Headgasket Bore: 97.5 Headgasket Thickness: .59mm Piston Dish Volume: 28cc Piston Deck Height: 0.016" (Again, I chose to use this because I couldn't find a definitive number) I get a CR of 7.98:1 I couldn't put together a definitive answer as to whether or not STi rods are same length. When doing the math I assumed the rods were the same length and provided approx. the same piston deck height as stock 22T rods would. Is this a realistic number with current setup? I tried to use accurate numbers, but I'm still new to the Subaru game. That's why I'm here asking you. Thanks in advance!
Sti rods are 79mm if I remember correctly. If you are serious about these numbers and you need them for something in particular, then you don't guesstimate. A slight change of a cc or two in the head volume, and a mm or two here and there will have drastic changes to the compression ratio. I know when I had my hybrid 22 I had to have specific head gaskets to keep the CR in the 8.25:1 zone I was shooting for.
Unsure of which heads I have. I'm looking up how to tell right now so I can check tomorrow. Headgasket is genuine Subaru. Unsure if they used one for a 22T or 25. Big ups for catching the stroke difference too!
I'm getting the impression you have the motor already and it is assembled. Where did this motor come from?
Yes, motor came assembled, running in the car when I bought it. PO bought the motor as a longblock. I don't like to guesstimate either. But without tearing it apart and doing it myself I'll have to get as close as possible. Tomorrow I'll check what 25 heads I have.
I would see if you can contact the original owner or at least the person that put that motor in there. There's really no way to just look at the block and tell what the internal components are. If you aren't in a hurry, I can do some research on the components you have listed. I'm guessing the heads are the SOHC 2.5 heads since that was a popular combination for the EJ22T hybrid. Easy way to tell is to look at how the spark plugs are mounted and if they have coil packs. If they are facing an upward angle, located on the top of the head covers, and have wires directly on them (standard plug wires) they are likely the SOHC heads. If the plugs are in the center of the head cover they are DOHC. Also, on the forward facing part of the head, if there is one cam gear or two (duh.) Pistons: (if PO says they are OEM, we'll go with that) Rods: (PO says STi rods...we go with that) Crank: EJ22T Headgasket: OEM? Probably the EJ22T fitment. Though I'm not sure I would have gone with the stock one. I think they are all MLS now though, I guess it depends on when this was assembled and who assembled it. Was the seller a member here? Another thing to keep in mind, if they did all this custom Subaru Lego Builder work, they may have had the block decked, which will change the piston/deck clearance slightly. Remember what I said before, little changes can make a large difference in the compression ratio realm.
100% sure they are DOHC heads. I've also been racking my head about which HG they used.. Like you, I would have used the one for the EJ22T. But, obviously we can't be sure. Changing the stroke to 79mm made a huge change in the result. Closer to 8.3:1 vs the 7.98:1 with a 75mm stroke. Ugh, I hate the guessing game. I am friends with the PO of the car, I'll try to get in contact with the guy who built the motor.
Sti rods length are identical to the stock 22t rods, but just a bit beefier. Now the Sti crank is 79mm vs the stock 22t's crank which is 75mm. so it's still a 22t. best thing to do is tear it down yourself and assemble it back up. that way you'd actually know what's inside of your motor instead of taking someone else's words would definitely help to know which ej25 heads
NVM, for some reason late last night, I confused myself with "EJ25 heads" and started thinking EJ25 rods. Yes, the STi rods are the same length as nearly all other Subaru rods. The EJ25 phase 1 DOHC had the longer rods in it. Which led to the confusion, as I had been down the stroker path back in the day with the 22T and the SOHC phase1 EJ25 combo. Nuke is correct here. Rods should be the same.
Now, everything makes sense. Thanks for the response! I would love to have the luxury of time, space and money to be able to tear it down. But I had to move back to the cities and don't have a garage space anymore. That and it's currently sitting under about 12" of snow and ice. The motor runs great, even with the old Legacy ECU. It's just really slow due to the low compression.
I've been searching all over and can't find a consistent answer. What's the difference in combustion chamber volume between a stock EJ22T head and an N/A EJ25 head? I have numbers from what I deducted, but I'd like to see what you guys come up with. From what I've read, I see two common answers. 1) As long as a stock rotating assembly is used CR will stay the same between EJ22T and EJ25 heads. 2) CR will drop because the 25 has a larger CC volume than the 22T. I willl dig the car out today and see if I can identify what heads are on there.
