EJ short block buildup: Choosing the proper parts

One thing is sure when it comes down to building an engine for mild power the most important thing is to choose the proper parts.

I was aiming to get power in the range of the Impreza STI, so about 300HP.  Since my short block was from an STI, I decided to use the OEM piston rods but go with forged pistons.  I could not use the STI pistons mainly because of improper valve clearance with the RS heads.  The pistons I choose were Techworks Engineering pistons.  The service at Techworks is great, they answered all my questions and  gave me good advices.  The pistons are designed to safely withstand 18psi, so no problem there.  They are also over sized to 100mm compare to 99.5mm for the stock pistons.

Bare in mind that this was my first engine rebuild / buildup.  I was reading a lot from various forums and spending quite a lot of time reading books.  I am very far from a professional but I think I gathered enough knowledge to make less mistakes :P

So here is the list of parts I chose:

• Techworks Engineering 2.5RS SOHC Turbo forged pistons & rings
• Added ceramic coating on crowns
• STI OEM connecting rods
• ACL Race crank and rod bearings
• STI Oil and water pump

How it all started...

Why, oh why !

So I decided that my Subaru Impreza 2.5RS MY00 was in need of a new engine that could tolerate some boost.  One of the options available was to proceed with an engine swap.  With the multitude amount of JDM engine reseller currently available one could ask why someone would prefer to rebuild its engine instead of buying a used one.  This is a legitimate question and I have a very simple answer.  Most of the time this is no way to confirm the mileage of actual condition of the JDM engine.  Even with a perfectly honest reseller there are no real guarantee how long the engine will last.

Knowing that the Subaru EJ251 block was not ideal for a turbo or supercharged application, I decided to try to find a used STI short block  Lucky enough, I find one on Ebay with minor damage.  I bought it for about 500$ including shipping.  It included the crank, the pistons and the oil pump.

Let's get to work...

The first thing to do of course is to open up the engine and remove all its internal parts.  This is not very difficult when you have the proper tools.  It is surely handy to have some specialized tools, for example to remove the piston pins, but with some imagination you can do without.

Once the block was bare, I was able to do a basic inspection.  Make sure you look closely to the cylinder wall for any deep scuff, that could be more difficult to repair if too extreme.  Mine has a single cylinder damage but was quite minor, so no worry there.

Another important part to inspect is the crank and where it rest on the block.  Crank damage should be easy to spot since the crank bearing will surely be damaged too.  Generally a crank can be repaired and in most case you will need to fit undersized crank bearing.

Having a good idea of the damage and then went searching for a good shop that could proceed to repair the block and the crank.  Make sure you find a reputable shop because this is the base of your engine, starting with a good base is essential.

In my next blog I will talk about the internal parts I choose and why.