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Project Subaru EJ25 - Part 2

Rise of the Phoenix, Part 2

Scott Tsuneishi
Apr 17, 2014

Since we last left off with our Subaru build, we repaired and upgraded our EJ25 cylinder heads with a set of Kelford R-199-B (264/260 duration) camshafts and Supertech valvetrain, and got the head massaged with the help of Portflow Design. After months of planning and installing parts, we have finally arrived at building the block. At this point, you may be thinking that this build is overkill for the average street car. We would resoundingly agree, but excessive planning and building is what is going to take us to our promised goal of netting respectable lap times at Buttonwillow Raceway in the near future. With a large portion of our build focused toward improving the reliability of our engine, we haven't forgotten about adding some much needed grunt to our beloved EJ25 engine. Follow along with our buildup process as we meticulously assemble the bottom end using key components.

If you recall, a deadly combination of over boosting 30 psi due to a dislodged wastegate line at the track caused a lean air/fuel condition that melted our Cosworth piston, which in turn caused a nightmare of scenarios that ended with a dramatic engine fire. We were able to salvage the cylinder heads, but the block was decidedly thrown in the garbage and replaced with brand-new case halves we purchased from South Coast Subaru located in Costa Mesa, CA.

WPC Treatment

Project subaru EJ25 WPC treated piston 02 Photo 2/25   |   Project Subaru EJ25 - Part 2

Prior to assembling the Subaru engine, we sent our JE pistons, rods, crankshaft, and bearings to WPC for treatment prior to assembling the EJ25 engine. What is WPC, you ask? Simply stated, WPC is a metal surface treatment that enhances the surface to reduce friction and strengthen engine parts. WPC is not a coating nor is it shot-peening. The treatment is executed by firing ultrafine particles at the part's surface at very high speeds. The ultrafine media of the WPC process, when projected at high velocity toward the product surface, creates compressive stress (the compressive load per unit area of an original cross-section) at the impact points. At the same time, a micro-thermal reaction takes place. It effectively seals minor surface fractures, allowing a condensed surface to form improving surface density due to the compaction. This altered and highly compact surface condition overcomes the problem of brittleness that is usually encountered when metals are hardened. Treatable metals include steel, aluminum, titanium, copper, and brass as well as soft-surfaced bearings. WPC can basically treat any metallic item in an unassembled state, from rotary apex seals to rear differentials.

Project subaru EJ25 WPC treated parts 03 Photo 3/25   |   Project Subaru EJ25 WPC Treated Parts 03

Many of the top motorsports manufacturers, such as HKS, Suzuki Sports, TRD, and Tomei Powered, rely on WPC to treat their high-performance products. The WPC process uses a special ceramic bead composition ranging from 20 microns or larger depending on the application and area being treated, which shot-peening can never duplicate. In comparison to shot-peening, the media being used for the WPC process is 50 times smaller and is applied at a higher velocity, pressure, and impact, creating a higher compressive stress level. The numerous impacts during the WPC process not only increase the residual compressive stress but also cause it to reside a lot closer to the surface. The result is a product that looks dull in appearance (as shown in the image to the right), but has durability unrivaled by conventional peening.

Carrillo Pro H-Beam Connecting Rods

Project subaru EJ25 carrillo pro h bean connecting rods 04 Photo 4/25   |   Project Subaru EJ25 - Part 2

The Carrillo Pro H-beam configuration can handle extreme engine loads. The tapered beam allows for some weight saving on the reciprocation end and gives increased clearance for fully boxed pistons. A side-by-side comparison versus a competitor's rod shows why the name is synonymous within the motorsports world and used by top engine builders around the world with good reason. Some key features in design include ribbed PE strap for increased stiffness/minimum PE distortion and stout H-beam rod shaft design.

Project subaru EJ25 carrillo rod caps 05 Photo 5/25   |   Project Subaru EJ25 - Part 2

Notice the Carrillo rod cap with its lipped relief design versus the competitor's piece? The lip was introduced to promote additional strength.

Revco Precision Machining/Balancing

Project subaru EJ25 revco precision machining 06 Photo 6/25   |   Project Subaru EJ25 - Part 2

When it came down to matching and balancing our EJ25 engine assembly, we contacted Larry Revis of Revco Precision, located in Long Beach, CA. Revco does everything from polishing, balancing, and knife edging to straightening, strengthening, and machining. They do it all within a reasonable price.

Project subaru EJ25 OEM crankshaft 07 Photo 7/25   |   Project Subaru EJ25 - Part 2

We picked up a brand-new OEM crankshaft from South Coast Subaru. The crank came heat treated from the Subaru factory.

Project subaru EJ25 connecting rod balance scale 08 Photo 8/25   |   Project Subaru EJ25 - Part 2

Using a connecting rod balance scale, Revis carefully weighed each rod. This specialized scale is accurate up to 4,000 grams and has the ability to check weight on both big and small ends of the rod. Weighing a connecting rod using this type of scale will determine how much weight to remove and from what side of the rod. A perfectly balanced rod is a key component inside an engine that is spinning 8,000 rpm.

Project subaru EJ25 crankshaft straightness check 09 Photo 9/25   |   Project Subaru EJ25 - Part 2

Revco Precision checks for crankshaft straightness, performing a simple technique of stress relieving the metal while straightening out the crankshaft to allowable tolerance. "A lot of guys won't do the stress relief, and they wonder why their crankshafts crack prematurely," Revis says. In performance applications like our EJ205, the crank was balanced to within 0.1 thousandths of a gram. Too often we hear the horror stories of improperly balanced factory and aftermarket crankshafts breaking into pieces and ruining a perfectly good engine.

Project subaru EJ25 flywheel 10 Photo 10/25   |   Project Subaru EJ25 - Part 2

Revco removed material from our flywheel to balance our assembly before we hauled our parts to be assembled.

Performance Tolerances

Project subaru EJ25 crankcase 11 Photo 11/25   |   Project Subaru EJ25 - Part 2
Project subaru EJ25 cosworth rod bearing 12 Photo 12/25   |   Project Subaru EJ25 - Part 2

Katsu Hibino, formerly of Cosworth USA, machined the block to accept the new JE pistons as well as measuring the rod and main bearings for proper clearances. We finalized our Cosworth rod bearings at .0019 clearance, a bit on the looser side but sufficient enough for our plans when we track the car on the weekends.

Project subaru EJ25 thrust clearance measurement 13 Photo 13/25   |   Project Subaru EJ25 - Part 2
Project subaru EJ25 thrust clearance measurement 14 Photo 14/25   |   Project Subaru EJ25 - Part 2

Another overlooked area when building an engine is to measure thrust clearance. Even with a new set of bearings this should always be checked.

Engine Assembly

Project subaru EJ25 piston ring gap measurement 15 Photo 15/25   |   Project Subaru EJ25 - Part 2

Shingo Yugami of Bluemoon Performance, located in Costa Mesa, CA, carefully took measurements of each cylinder/ring to achieve proper piston ring gap before using an electric grinder. The type of driving and power output you plan to put your engine through will determine your ring gap. Consult your piston manufacturer for proper gap specs.

Royal Purple and ARP Fastener Assembly Lube

Project subaru EJ25 royal purple max tuff 16 Photo 16/25   |   Project Subaru EJ25 - Part 2
Project subaru EJ25 ARP fastener assembly lube 17 Photo 17/25   |   Project Subaru EJ25 - Part 2

Assembly lubes like Royal Purple Max-Tuff prepares potential wear surface and prevents metal contact before adequate lubrication can be supplied. Because of frictional inconsistencies with oil, moly, and other lubricants, it takes multiple cycles of torquing the bolt, loosening it, and tightening it again to obtain the required preload or stretch, causing inconsistent values. ARP Ultra Torque assembly lubricant is marketed as a lubricant for bolts that needs to only be torqued once to get within 5 percent of ideal preload, and it remains consistent through all subsequent cycles (from race-prep machining through final assembly).

ARP Stretch Gauge

Project subaru EJ25 ARP stretch gauge 18 Photo 18/25   |   Project Subaru EJ25 - Part 2

Using a stretch gauge delivers the most precise and accurate way to determine the proper preload, or torque, on a connecting rod bolt. Our ARP rod bolt stretch gauge allows you to accurately measure bolt stretch as opposed to a torque wrench that relies on "friction" at its highest value when the fastener is first tightened. The torque wrench method is often found to be inaccurate and inconsistent when using an improperly calibrated wrench.

Project subaru EJ25 piston head cleaning 19 Photo 19/25   |   Project Subaru EJ25 - Part 2

Always clean any parts prior to assembly. We recommend using a 4-to-1-ratio mixture of warm water and Simple Green cleaner. Using a soft bristled brush, lightly scrub the surface, paying close attention to bristle the piston ring and oil groove channels. Finish it off by blowing it dry using an air compressor.

Project subaru EJ25 seals 20 Photo 20/25   |   Project Subaru EJ25 - Part 2

Rebuilding an engine isn't cheap but you should never cheap out on your build by reusing seals. It is imperative to use new seals regardless of how new or clean they appear.

Project subaru EJ25 silicone sealant 21 Photo 21/25   |   Project Subaru EJ25 - Part 2

Too much silicone sealant can become more harmful than good for your engine. Why? When too much silicone sealer is used, the excess portions will ooze out and can block oil and cooling passages as shown in our image, which leads to overheating. We used a small brush to evenly apply the silicone.

Cosworth Oil Pump

Project subaru EJ25 cosworth oil pump 22 Photo 22/25   |   Project Subaru EJ25 - Part 2

The Cosworth blueprinted high volume and pressure oil pump helps increase the oil volume to help prevent bearing damage and engine failure. This unit is important when the engine is sustained at high rpm, which has been known to cause oil starvation at the rod and main bearings.

JE FSR Pistons

Project subaru EJ25 JE FSR pistons 23 Photo 23/25   |   Project Subaru EJ25 JE FSR Pistons 23

Forged pistons are a must for Subaru motors producing more than 400 hp. The heat and stress high-boost applications produce can destroy a stock Subaru cast piston over time. JE 2618 alloy forged pistons offer superior strength and durability-far more resilient than stock cast pistons. We used a set of +. 25mm 99.75mm pistons with an 8.5:1 compression ratio. When it came to installing these bad boys, we looked no further than ARP. Companies like ARP offer an alternative and much smarter approach when installing pistons with their tapered ring compressors. These hard-anodized aluminum sleeves have a smooth radius that tapers down to the specific bore size. The design allows compression of the piston rings without damage and can be installed with a simple push of your fingers.

ARP Head Studs and Cosworth Head Gaskets

Project subaru EJ25 ARP head studs and cosworth  head gaskets 24 Photo 24/25   |   Project Subaru EJ25 - Part 2

ARP Custom Age +625 head studs offer superior yield and tensile strength (260,000-280,000 psi) over previous ARP model L19 studs to eliminate blown head gaskets from high boost. We combined the +625 head studs with a set of Cosworth high-performance MLS head gaskets.

ATI Damper

Project subaru EJ25 ATI damper 25 Photo 25/25   |   Project Subaru EJ25 - Part 2

Unlike undamped underdrive pulleys, which offer no protection to high-performance engines, the ATI Super Damper provides balanced damping of torsional crankshaft vibrations at all rpm levels. The OEM crank pulley has an elastomer (rubber ring) sandwiched between a central hub and an outer metal ring. This torsional damper type dampens vibrations and should never be replaced by non-damped units. All ATI Super Dampers exceed SFI 18.1 Safety Certification and are approved for competition use.

Stay tuned as we finalize our build in the next issue with some go-fast goodies including a Full-Race turbo kit and UK-manufactured adjustable cam gears that are sure to give this engine some serious boost in performance.


Automotive Racing Products
Ventura , CA 93003
Royal Purple
Porter, TX 77365
Torrance, CA 90505
ATI Performance Products
Baltimore, MD 21207
WPC Treatment
Torrance, CA 90503
JE Pistons
Huntington Beach, CA 92649
Irvine, CA
King Engine Bearings
Cedar Grove, NJ 07009
Bluemoon Performance
Costa Mesa, CA 92626
Revco Precision
Long Beach, CA 90805
By Scott Tsuneishi
247 Articles



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