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| Starting with a production K24 block, 4Piston installed a set of L.A. Sleeve ductile iron liners to push the bore out to 90 mm (3.54 inches) over the stock 87 mm (3.42 inches).
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| Wilson chose GRP’s aluminum, 6.125-inch-long rods to connect to the Wiseco forged aluminum pistons. For this naturally aspirated, high-rev application, lighter rods are essential.
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| The pistons are Wiseco 2618 alloy forgings with a 90mm bore and only two-ring grooves with ArmorPlating hard-anodized coating on top along with Wiseco’s Armorglide skirt coating to reduce friction. Also note the vertically drilled gas ports that load the top ring.
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| Checking bearing clearances is essential with any race engine and imperative at the speeds this engine will see. 4Piston prefers ACL tri-metal bearings for its K24 stroker.
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| There are those who say Winberg sets the standard for quality in the race crankshaft business and 4Piston would agree, electing to bump up the stroke to 106 mm (3.90 inches) for this engine.
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| Most ring manufacturers insist on a ring expander to install, especially with rings in the 1.0mm-or-thinner range.
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| Thin rings make installing the piston and rod assembly a bit challenging, but it’s easier with a Wiseco tapered ring compressor.
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| Initial torque is backed up by checking the rod bolt stretch to ensure a proper clamp load. High rpm tries to pull the cap right off the rod, so an optimized clamping load is critical.
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| Measuring deck height is another crucial blueprinting spec, so 4Piston uses its own twin-indicator stand to finalize the measurement. Aluminum rods require more clearance to accommodate for the increased linear expansion. 4Piston generates a 0.060-inch piston-to-head clearance using a 0.020-inch deck and a 0.040-inch Cometic head gasket.
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| Now we get to the fun stuff. The CNC-ported head is filled with Ferrea titanium 1.51-/1.181-inch valves and a 4Piston Pro Stock single valvespring kit. The valvetrain consists of aluminum Ferrea rockers that are half the weight of factory steel versions.
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| The CNC porting pushes some truly impressive flow numbers of 400-plus cfm out of this production K24 casting. The port work is near jewel-like.
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| It’s a straight shot from the intake right past the valves to the chamber, which is why the flow numbers are so good.
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| Those are Skunk2 BMFx cams about to work their magic. Wilson won’t comment on duration or the lobe-separation angle, but he did tell us the valve lift is 0.678 inch while the exhaust valves open to 0.615 inch.
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| With the cams slid in place, Intake closing and overlap are essential specs, but the engine builder also has to be aware of valve-to-piston clearance. A minimum valve-to-piston clearance for a high-rpm engine is essential to maintain compression. The intake clears by a scant 0.030 inch while the exhaust is a touch wider at 0.055 inch.
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| Final assembly includes a set of ARP L19 head studs and a Cometic 90.5mm MLS head gasket to ensure a proper seal. Cometic makes these gaskets specifically for 4Piston Racing.
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| With the valves and springs in place with installed heights all equalized, the Ferrea rockers slide right in place.
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| Induction duties fell to Kinsler with its 71.5mm throttle bodies and 1,600cc/min injectors (152 lb/hr). The large injectors are necessary for the VP M5 methanol fuel. 4Piston experimented with inlet tubing length but essentially the shortest will make the best peak horsepower.
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| Wrapping up the install included adding the Dailey dry sump, Moroso oil pan, and the ATI balancer. Myers Competition supplied the stepped headers that end up measuring 2.250 inches on the primary tubes. Motec is responsible for exerting the fuel and spark control.
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| To truly appreciate this power curve, take a look at that nice flat torque curve where this motor delivers no less than 280 lb-ft of torque from 6,800 rpm to horsepower peak at 9,600. That’s an impressive 2,800-rpm powerband. Wilson commented, “That is a big header, and the engine can make a broader powerband with a smaller header and an additional inch or so with a little 2.5” collector. For our application, we are pulling power out in first gear, then the rest of the track is 8,300-10,600 rpm. We are OK giving up some low end in favor of carrying the top another hundred or more rpm.”