Engine swap.
 

Hello,
looking for some tips. I have a 98 classic impreza. 1 year ago I placed a v4 jdm sti engine in it. It runs 330 hp at 1.4 bar. But when i'm idling and i rev it till 3000rpm i start hearing a slight knok... I think a bearing is looking for an escape. The strange thing is when on boost you hear nothing.
Now the thing is I have an engine ej20gn full closed from a v1 wrx. I'm thinking of putting the heads of mine on the short block. But do i need to put the connection rods in the short block. Because i know mine are forged. Any other tips are welcome. Also do i need to swap over thr pistons? I dont want chocolate pistons... All other tips are welcome.
what is the oem height of the head gasket. It goes from 0.6 to 1,6 mm

thanks...

how long has it been knocking? Does the knocking increase with rpm?

No. Its hard to explain. I will try to make a video of it . When the engine is hot, its almost non excististing. The noise is only there until you reach 2500 rpm. And when it did the oil change i found tiny pieces of metal in the oil when i placed my finger in the sumps remaining oil.

sounds like bottom end, why did you have to swap the engine previous ?

Because it was overheating. At that point i knew an STI for low money with rebuild engine but crappy body. So i swapped the internals an bought a ESL board to go along with it.
So now 1year later again engine trouble. I decided now to build my own engine because you can never know if they did it on a tight budget.
So i will need some help on the parts. I have my V4 sti heads. And i have the full closed deck engine from a WRX V1. What internals should i go with? And what bearings to go with? Acl or kings?

Etc..

piston slap.

https://vimeo.com/204861590 Video of the noise

Well I've had the big end go on me a couple of times before and it sounded just like that only it did it all the time, especially more noticeable at idle but yours seems limited to a particular rev range. Seems odd to me.

​​​​

yes its only in this rev zone. At idle nothing and higher then 3000 rpm nothing. Thats why i ask for other opinions.

My first thought if it goes away when warm - do a search, very common on the cars of 97/98 vintage.

Although if you're finding metal in the old oil, maybe not.

Have a look at the timing belt tensioner and check its functionality, just a hunch but nice easy fix if it's that

Piston slap

too loud for piston slap surely?
I get piston slap when cold on my forged 2.0 with Cossie pistons which are notorious for being noisy and its way quieter than that and happens at idle right through the rev range until warm.
Would be great for the OP if it is just piston slap, so I hope I'm wrong lol

I am not so familiar with car engines, as mostly worked on bikes of around 1000cc, but having heard similar rattles on bikes, I would say that noise is typical of big end or small end bearing play.

It knocks as the engine builds load. Once revs rise and piston load is higher, the knocking tends to abate.

These Subaru engines seem quite similar construction to bike engines, so given the lowish note, I would plump for big end (but it's engine out either way).

thats piston slap. had it on 98 uk turbo, sounded exactly like that.

I will see if it gets any worse then this. I also hope for the piston slap but it was not doing this 6 months ago so i'm fearing the bad news.

Any got a good adress for me to send a short block to relocate the main bearing?

Sounds like rod knock/bearing failure to me,and metal in oil so very unlikely to be simple piston slap,could also be Pistons cracked as mine had a similar noise,cosworth pistons all had fracture lines and one eventually exploded.
For block work alyn at ASPerformance would be a very good option.
Ring or drop him an email.