Injectors Upgrade: when flow does matter

When building an engine to attain moderate to high HP figures one thing usually needs to be revisited: the injectors. The 2.5RS Impreza comes stock with injectors that flow 280cc. That is well suited for the out of the dealer HP numbers but if you wish to read around 300HP (like the STI!!) then a new fuel pump and a new set of injectors are an absolute must.

I shopped around on the Internet and read various post on the subject. I wanted to keep the price reasonable so I went with a reputable Ebay seller. I found a set that would suffice my HP goal and gives me some room if ever I wanted to go crazy :P I chose a set of 720cc which are on the same base of the Injectors Dynamic ones. I know I went a bit too big and this is perhaps a mistake I made but I confirmed with a tuner in my region that there would be no problem tuning with them.

What you need to perform this installation:
14mm socket
New O-rings
Optional:  Fuel pressure gauge

New 720cc injector with O-rings in original location.

One thing I noticed when I compared the OEM injectors with the high flow I ordered is that the bottom O-ring, the one that fits into the intake manifold, is a little too big. The 720cc injector set what very similar to WRX stock injectors. Although I was assured that these would fits the 2000 Impreza 2.5RS I had some doubts...

After having pulled out the two injectors from the passenger side I installed two high flow in place. First problem, the top two little O-rings did not really seal in the fuel rail.   This was easy to know because the injector was not holding into the fuel rail like the OEM injector.  I decided to remove them and use the OEM injector fat top O-ring  (a little note here, I strongly suggest using new O-ring to get a good seal).  After some inspection I noticed that the bottom O-ring also had issues. It was a bit too wide and was not correctly sealing the injector hole. I swapped it and used the two little ones that wer supposed to go into the fuel rail. With those installed the residual problem was correctly sealing the injector hole. I studied a bit more the stock injector and tried removing an intermediate O-ring in order to fit it to the 720cc injector. To my surprise I was able to slide this O-ring to the mid section of the 720cc injectors.

High flow injectors seated into the intake manifold...

...and from another point of view.

Once this amusing game of swapping O-ring was done I was able to install a duo of 720cc injectors and they seemed to fit not too badly. I have not yet started the car with those but you can be sure that I will be watching closely for any fuel leaks. I still need to install the 720cc on the “pilot” side, then let's fire that baby...eh but I don't want any fire ;)


Last weekend I did my first test to verify that my newly installed 720cc injectors were not leaking fuel.  My first test was to simply turn the key to the ON position.  This will activate the fuel pump and build up some fuel pressure (you might want to put some rags near the bottom of the injectors to absorb any fuel that could leak).   I quickly realized that two of the four injectors were badly inserted into the fuel line since they were leaking from the top.  I had to remove them and insert them better.  You have to make sure they are really hanging to the fuel line, even without the injector clip installed.  To increase my chance of success I generally make them do half turns in both directions while pushing upward on them.  My next check of simply tuning the ignition to 'On' prove that I had done a good job, no leak were present and fuel pressure was about 35psi.

Next step is to crank the engine a few times but not let it start and check again for any fuel leak.  I have a fuel pressure riser with a gauge so it is possible for me to see rapidly that the fuel pressure had built up, no leaks were present.  I disconnected the coil & igniter to make sure the engine would not start and cranked it a few more times.  If no leak are observed at this point then it is safe to try and start the engine

In my next blog I will talk about how I did a basic tune with these 720cc injectors.

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.