Forum » General Engine Building Discussion » EJ25 STI


General Engine Building Discussion

Talk about engine building here. New products, tricky questions or showcase your work - If it's engine building related it's welcome here.

Page 1

I'm building a Subru EJ25 STI for range of 500-600 whp with upgread sleeves but my qustion is what is the main + ROD bearings clearance I'm looking for and what oil number should I run , I'm in very hot country :)


Subaru call for 0.0009 to 0.0019 for the rods if i remeber right. On 500+ plus motor you might want to go a little looser.

Manley, who's rods im using recommend between 0.002 and 0.003.

I friend of mine with a 550 whp subaru has told me he likes atleast 0.0025 on high power subaru rods. And uses thick oil too, like 5w-50 or similar.

Mains i think he likes to use OEM recommended clearances.

I would recommend you ask the manufacturer first.

For that sort of power level I like to build the engine on the loose side of Subaru's recommendations. I'd be targeting 0.002" for the rods. You need to be a little careful with your target for the mains as the alloy blocks grow as they come up to operating temp and this results in the clearances opening up from what you'd measure at room temp. On the mains I'd be looking for about 0.0015".

Your oil choice is a bit tricky to define as it will depend on whether you're running variable cam control. This sort of engine requires a thinner oil which is often at odds with the requirements of a high power engine build. We've run a 10W40 Motul 300V in our FA20 with success (albeit a very high cold oil pressure), but for non cam control I'd tend to be in the 15W50 vicinity.

Great Andre

Thats what I'm looking for thanks bro

And thanks for all guys reply me

Regards ,


Reading your response and now you have me a little bit worried with my build. I was told by my engine machine shop guy that he likes 0.0025 with thick oil. And that was the response he specifically gave me when i asked him in regards to my engine. He personally has a 550hp targa GC car with 2.5L which seams to be doing well. And i have based my clearances off of his advice now.

But, my setup isnt a typical EJ25. There are a few things different about it which my have made him suggest that.

For one. My engine will have no AVCS at all. It is being disabled.

And the crankshaft is an aftermarket 2L crank going into a 2.5L engine. (Manley), which has 2 oil galleries per rod bearing. And each rod bearing is oiled from 2 different main bearings. And each crank oil gallery is straight line gun-drilled. Instead of the 3 way drilling Subaru use.

What are your thoughts about that? I currently have exactly 0.0025 set for my clearances after polishing the crank. And that is using +0.001 bearings. I could go to a standard or even -0.001 bearing to close the gap up if it is a bad move to run 0.0025.

And will also have a dry sump oil pump with adjustable relief.

There's nothing specifically to say that 0.0025" won't work on your mains. The point that's easy to overlook is that a cold clearance like that will grow when the block is at operating temp. You may end up at 0.003" or even 0.0035" but of course it's impossible to measure to be certain.

That sort of clearance is definitely more suited to a thick oil grade which obviously would be problematic if you had retained the AVCS. If your machinist is having success with these clearances in his own engine then that's probably sufficient to have confidence to run with it. The FA20 we're dealing with seems to be much more sensitive to oil pressure issues than the EJ and I know that clearances above 0.002" result in close to no oil pressure at idle when hot.

Thanks for the reply. Sorry. Just to clarify. He has said 0.0025 for the rods. And to target within the OEM tolerance for the mains.

Oh right, sorry. 0.0025" is a little looser than I'd run on the BE but not crazy loose.

Ok. Not crazy loose. Haha.

Another thing that is making me paranoid, is when i took the case to the other engine shop to get the line hone (discussed in the other thread). We got to talking about my engine and when I mentioned that i was going to use 0.0025 on the rods. His facial expression went straight to "eeek, thats a bit excessive". I could tell straight away. He did say its as loose as he would want it. So now im questioning it. Ive got one engine builder telling me to go with that. And a couple of guys saying its a bit looser than they would use. But not crazy loose.