EJ30 Build Details












Embark with us on about a 2 year journey to make the most custom Subaru engine ever built. Sit back, relax and dive into how truly insane and passionate we are.

As an engineer and engine builder, we wanted to do something nobody has ever done before. We wanted to make the most insane NA Subaru 4 cylinder ever. We tossed around the idea of stroker, high rpm and then eventually started getting serious and actually sitting down and trying to figure out how we can do this. It started with a goal, we wanted to push the limits of displacement in the stock block. The goal was 3.0L of displacement. After a lot of measuring, designing in CAD and thought, we devised a plan on how we would get there. It all started with a rough model of basic dimentions of the case halves we drew up in Solidworks to work out the dimensions of everything and visualize it. After a couple weeks of tinkering with dimensions in CAD, we found a combination we believed would work well to achieve our goal of 3.0L.

We found 104mm bore with custom sleeves was about the max we could safely go and still retain enough block strength for it to live a happy long life.

From there, we worked out we could make a custom 87mm stroker crankshaft, 134.5mm rods, and some very radical pistons with a very small compression height on the piston. (the distance from the center of the wrist pin to the top of the piston.) The piston would also need a very small skirt to not bottom out on the block. 

We worked out all the dimensions in Solidworks and started getting the custom parts made. 

After we worked out all our desired dimensions, Micah at 3MI Racing was kind enough to put together a rough model with a 3D scanned EJ block model he had to see if there were any clearance issues we missed with our measurements and rough model we made. We determined clearancing was necessary, but nothing crazy. Thanks to Micah for these CAD pictures.

Case Halves

The case halves start with a closed deck EJ257 block, they are then sleeved with custom sleeves that do not have wrist pin holes because with the large stroke of the custom crankshaft, the rings go past the wrist pin holes. The end result is a 104.0mm bore size which is 4.5mm larger than standard EJ25. The cases are also machined for 1/2" ARP head studs. The block is clearanced for the stroker crankshaft. The mains bores are pinned to keep the case halves from flexing as well as secured with ARP main bolts. We also ported and smoothed the oil passages inside the block.


We started the pistons with the key dimensions we sorted out in the design phase, and then also had design criteria we wanted to meet to maximize them. This included making them as light as possible, which involved making the skirt design an ultra low profile slipper skirt design and doing a bunch of under head milling to get the crown thickness as thin as possible again to save weight. Another area that had multiple benefits was using.a flat top piston instead of a pistom with a large dome. It allows for a lot better flame travel across the combustion chamber and also allows you to keep the piston light without the extra weight of a large dome. We still managed 13.4:1 compression with flat top pistons thanks to the large displacement and small combustion chambers. The pistons have very light weight H13 tool steel 0.150" wall thickness wrist pins that are DLC coated to minimize friction and galling. The rings are 1.0mm, 1.0mm, and 2.0mm thicknesses and the pistons have lateral gas ports on the top ring to aid in ring seal. The pistons also have Line2Line abrdable skirt and ceramic top coatings. The abradable skirt coating makes sure the skirt profile is perfect to how it needs to be while the engine is running, you build the skirt coating tight and it abrades away until it is the perfect running clearance it needs while running. This greatly reduces pistons rock and improves ring seal. All this coming in at an astounding 312.9 gram weight. Absolutely mind blowingly light at 104mm bore size.

Connecting Rods

We started the rods with the specs we found in the design portion, and then started implementing details specific to the application. The end result is a 4340 forged I beam design steel ultra light rod with 134.5mm center to center length. Which is 4mm more longer than the stock EJ257 rods. The rod has 0.125" chamfers on the big end to clear our radii on the rod journals of our custom crankshaft. The rods weigh in at 481.3 grams. They also have ARP's Custom Aged 625 Plus bolts to withstand the 9000rpm target redline. We chose a 4340 forged rod for longevity reasons as this will be going in a track car and not a drag race car.

Crankshaft Specs:

-4340 steel billet material

-CNC machined on 5 axis

-Large radius journals

-Fully profiled counterweights for reduced windage

-Gun drilled

-Cross Drilled for priority main feeding to the rods

-CNC ground teardrop oiling holes

-Shot peened

-Nitrided (multi step heat treatment)

-Omicron micro polished surface finish

-Cryo treated (promotes the additional transformation of retained austenite into martensite, makes the crankshaft much more resistant to cracking and wear)

-WPC treated (micro shot peening which improves surface hardness and greatly reduces friction)


-87mm stroke (which is 8mm more stroke than EJ25)

Cylinder Heads

The Cylinder Heads start off with a brand new set of EJ205 heads. They are then cnc ported, and machined for clearance for the camshafts, 1/2" head studs, and newen valve job. The valvetrain consists of +1mm diameter valves, stainless intake and inconel exhaust, conical dual valve springs with titanium retainer to withstand the insane camshafts and 9000rpm. Bronze valve guides with stopper are also used for reduced friction on the valve stems, and prevent a guide from dropping. New OEM cam follower buckets, which are DLC coated for reduced friction. The star of the show, the camshafts, are completely custom billet camshafts made for this crazy application, their specs come in at 13mm lift, and 310 duration. They are going to sound absolutely insane at idle and full song.


Based off some calculation and knowledge we have built up over the years building NA race engines, we are shooting for 300whp NA on pump gas and rev to 9000 rpm. Obviously we are extremely deep in uncharted territory, but this is not out of the realm of possibility with a build of this magnitude. That will be 300whp with all wheel drive. 

We might get a little crazy and see what it can do on nitro meth and see if we can come for those Honda boi's, but we will see how it goes as we get it going.

The goal is to track the GC couple that this car is going into, do time attack, hill climb, and tarmac rally. Hopefully be competive with the turbo boi's with our very large power band and throttle response.

EJ30 Shortblock Details Video

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