hi, need some help, after a period of time away from Subaru's (went through a cosworth stage) i decided to buy myself a 1998 STI RA, i bought the car off Flea bay, now on the way back from London to Newcastle upon tyne the engine went bang (big ends) so my cheap ebay purchase and my first impreza in years have let me down, now ive decided to get the motor rebuilt but i have seen alot of classic shape sti's advertised with 2.5 bottom ends, now i can buy a 2.5 bottom end for £500 and my friend can rebuild it using the parts from my broken engine, my question is will the 2.5 bottom end be a direct replacement for the 2.0sti bottom end and if it is are they any stronger ?
thanks in advance
jim

 

make certain you get the turbo 2.5 (EJ257) not the NA.
new from the states they go for about 1500 quid.
And yes the head fits although the bore is a little bigger.
good for up to 400 bhp depending on other mods.

 

I'd change the pistons to some drop-ins, or If you think you will want to go bigger than 430ish, add some rods now rather than later, and maybe some ACL Race series bearings.

 

I am assuming you mean all the parts except what is in the existing block.

£500 is very cheap, and as above confirm the motor is an EJ257, if so you can use your existing heads and ancillaries, be sure to select the correct head gasket thickness as the CR will be different.

The 2.5 will produce lots more toque than the 2lt and will be a better road car IMO, strength wise your ok running up to 360-370 but any more and i would suggest changing the pistons.

 

You will need slightly thicker head gaskets to keep the compression ratio in check, I'm using cometic 1.3mm gaskets.

 

Thanks peeps for the super quick replies, i want to keep the BHP no more than 300 so basically standard, i am more looking at reliability as the car will mostly be used for track days and the odd week end play, so basically if i get the 2.5 bottom end put all the bits on from my engine i should be OK to go, what is the best head gasket to get and also where can i get it from
thanks
Jim

 

also just to confirm i am getting the correct bottom end will it have the engine code stamped into it ?

 

Yes it will.

 

 

They still just have ej25 on them not ej257 as the wrx ej255 uses the same block.

 

I've often wondered about the difference between the bore of a 2.5 bottom end and 2.0l heads..! Does this not result in problems or at least be detrimental to efficiency..?

Is it possible to get 2.0 heads matched..?

 

So how can i tell if its a 2.5 sti bottom end ? or will a 2.5 wrx block be ok with my sti heads ?

 

Sti Has Semi-closed Deck, and should look like this (this one has forged pistons aswell though)

 

thanks SSCJ, so my next question, the one ive been offered for £500 is a used one on ebay, how much more will i have to pay for a brand new one and where could i buy one from
thanks
jim

 

1200 - 1500

lateral performance
flat4online
APi
ZEN performance
etc etc

ps , mine says ej25

 

OK, i am going to order the short engine on Monday unless any one has one for sale on here ? am i correct in thinking i will need the 2.5 head gaskets also or what would people recommend ?
also another thing will my RA have a closed deck engine as standard and i assume my heads will fit on a semi closed deck ?
if anyones interested i will put a step by step post up on how it all went, along with photos
fingers crossed i will have the car running next week

 

you need the gasket from the 2.5, but like said before thickness will determine your final CR. if using the standard gasket CR will most probably be to high for your wishes.
A lot of people use the 1.3 mm cometic ones.

 

Can anyone tell me where i can get the 1.3 mm cometic gaskets from, also will i need to have the car remapped when the engine installation is complete ?

 

I'd be interested in a general guide to your project. Pointing out the sore points and the results also, what you needed that you didn't think you would, all that kinda stuff.

Yes you will need a remap after changing from 2.0 > 2.5, but you'd be better getting it remapped anyway even if you fit a 2.0 with it going bang just after buying it, theres something not right

Good luck mate, its something I'm planning in the next 18months.

 

I've just done this conversion although I'm running a rotated GT30R.

I'm using a standard EJ257 bottom end with 1.6mm triple steel gaskets to go wth my STI version 5 heads.

will be running 1.4bar flat until i swap the rods and pistn in the spring.

Daz

 

The combustion chambers on a 2 litre cars heads are set-up in terms of chamber volume / CR / squish for a bore size of 92-93mm (2 litre). I personally, wouldnt fit heads from a 2 litre without correctly matching the chamber volume / CR / squish to suit the new 100mm bore. Yes people have done it and it works to some extent but its not the right or best way to do it for longevity or efficiency

 

^^^
This was my concern, as I seem to remember this being mentioned before..!

 

Daz was your block strengthened at all?