Mitsubishi Lancer Evolution - Tech Knowledge

Billet Crankshaft
With the block in new condition, it was time to select the rotating assembly components. The bore was left very close to standard, so a longer-stroke crankshaft was needed to increase displacement. Fortunately, there are many aftermarket crankshafts readily available that offer strokes from 92 mm to 106 mm-a significant increase from the standard 88 mm stroke found in the EVO. The desire for torque resulted in the purchase of a Brian Crower (BC) 102 mm billet crankshaft. The new BC crankshaft will help increase torque and bump displacement up 20 percent to our target 2.4 liters. All Brian Crower crankshafts for Mitsubishi engines are 100-percent machined from new 4340 steel billet and feature large radii on each journal for improved strength and durability. The nicely polished journals were measured with a digital micrometer and found to be the perfect size. The BC crankshaft was installed in the block with ARP main studs and WPC-treated ACL main bearings.

H-Beam Rods
If the standard 150 mm rod was used with the 102 mm BC crankshaft, the rod-to-stroke ratio would become slightly worse than the already marginal OEM ratio. To counter the effects of the longer-stroke crankshaft, Brian Crower 152.4 mm (6-inch) H-beam rods were selected to help restore the rod-to-stoke ratio to near-OEM levels. The improved ratio will help reduce side loading on the pistons and cylinder walls, therefore increasing piston and component life. The BC rods feature high-quality ARP 625+ bolts that require 0.0063-0.0067 inches of stretch for correct preload. Checking rod-bolt stretch is the only way to ensure accurate clamping force between the rod and rod cap, since friction between the threads and bolt head can cause the torque method to vary significantly. In this case, a point micrometer was used to measure the bolt stretch after they were installed with WPC-treated ACL rod bearings.

Custom Designed Pistons
Despite the fact that the rods and crankshaft are available off the shelf, the required piston design is less than ordinary. Fortunately, JE Pistons was able to manufacture custom pistons for this combination in under three weeks. The wrist pin location (the distance between it and the top of the piston known as "compression distance") was changed to properly locate the piston top relative to the deck of the block. The remaining piston features, such as skirt and crown thickness, were adjusted to handle the stresses associated with the longer stroke and increased cylinder pressure. JE also added their "Tuff Skirt" coating to reduce wear on the piston skirts and "diamond-like carbon" coating (DLC) to the wrist pins. JE Pro Seal rings were matched to the pistons to seal combustion pressure and maintain oil control. Once installed, the pistons provided a pump-gas- and E85-friendly 9.0:1 compression ratio.

ATI Crankshaft Damper
One component often overlooked when building a high-performance engine is the crankshaft damper. When the engine is running, the crankshaft is being pushed and pulled in different directions due to the various forces related to the engine's four-stroke cycle. These stresses cause the crankshaft to "twist" and can become problematic if not controlled properly. To resolve this issue, we called ATI Performance and purchased a Super Damper. ATI's dampers significantly reduce torsional crankshaft vibrations (twist), which helps to increase engine and component life. The damper included a press-fit hub that installed easily on the front of our BC crankshaft.

Aluminum Oil Pan
The OEM oil pan works well for street applications, but is not specifically designed for the effects of high-speed corning and extended track time. We picked up the new AMS aluminum oil pan to help keep our engine safe at the track. The oil pan holds an extra 1.5 liters of oil for better cooling, and features a trap door designed to maintain a constant supply of oil to the pickup. The kit even included a crankshaft oil scraper and all the necessary hardware for installation.

Project 4G64 MIVEC
Check back as we progress deeper into our 4G64 build, covering intimate details on porting the cylinder head, addressing the drivetrain, and bolting on some go-fast goodies to propel our soon-to-be daily driven EVO.

By Scott Tsuneishi

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