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Supercharged 496 Motor - Long Rod Rat
Build The Ultimate Torque Monster-A Stroked, Supercharged 496.
Jan 30, 2007
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Supercharged 496 Motor - Long Rod Rat
The Long Rod Rat started with a standard-bore four-bolt 454. The block was bored .060-inch, and it was hot tanked, line-bored, decked, and Magnafluxed to ensure optimal strength and straightness.
The machinists at Jim Grubbs Motorsports in Valencia, California, performed the machine work, including a cross-hatch hone designed to help the moly rings seat properly. Note the epoxy urethane primer in the valley, which improves oil flow to the cam and bottom end.
New cam bearings from King High Performance were installed in the block, along with stainless steel pipe fittings to block the galley.
Next, we clearanced the block for the forged Pro Series stroker crank. We used a high-speed dremel with a fluted iron bit to grind a smooth radius into the block skirts between each main cap.
After pre-fitting the main caps and studs, we prepped the block for the crank shaft by installing the main bearings. After pushing in the bearing tang first, give each one a thin coat of 50 weight motor oil.
The Pro Kit includes your choice of a 3.750- or 4.375-inch stroke 4340 forged crankshaft with gun drilled mains and drilled pin arms to reduce rotating mass. We went with a 4.250-inch stroke, which combines with a .060 overbore (4.31-inches overall) for 496 cubic inches.
Forged Lunati pistons are available in a variety of configurations, including dished, flat top, and several domes. Note that by using a longer than stock connecting rod, the wrist pin hole actually intercepts the bottom ring land.
The cornerstone of the Long Rod Rat project are these trick Lunati 4340 forged Pro Mod steel rods, which come from the factory fully balanced, blueprinted, stress relieved, and fitted with ARP 12-point rod bolts. We selected a 6.385-inch long rod, which is a 1 quarter-inch longer than stock 6.135-inch Chevy rods. The long rod gives the piston more dwell time at top dead center, which provides a more complete burn cycle and is said to improve torque.
Lunati includes plasma moly rings with the kit, which are taken into account when the rotating assembly is fully internally balanced. The bottom oil ring includes a flat snap-ring that seals the top of the land off from the wrist-pin bore.
After assembling the pistons and rods with the supplied full-floating wrist-pins and rings, lubricate the cylinder wall and the rings with 30-weight oil. Don't wipe the cylinder walls down with WD40 as some old-time engine builders suggest, it will prevent the rings from seating correctly.
Next, use a ring compressor to tuck the piston into the cylinder, tapping on the top of the piston (valve relief down) until the connecting rod makes contact with the crankshaft.
Lubricate both the crank and the rod bearings with more 30-weight, then install the rod caps and ARP rod bolts. Coat the rod bolts with ARP moly lube to ensure an accurate torque reading.
Since our plans included running several blower pulleys and boost settings on the 496, we decided to step up to Cometic steel laminate head gaskets, which provide an incredible seal that can stand up to high boost levels, without the hassle of o-rings and traditional copper head gaskets.
Four ultra-thin steel layers make up the .040-inch thick gasket. Rivets in the corners (sticking out beyond the block) hold the layers together.
After dropping the gaskets down onto the block dowel pins, the next step is installing the ARP 135-4001 head studs. The studs provide even pressure distribution for maximum strength under pressure.
We decided to stick with a common theme, and selected a pair of Holley aluminum square-port cylinder heads, which come fitted from the factory with 2.25-inch stainless steel intake and 1.88-inch stainless exhaust valves, screw-in studs,and guideplate
We had Mike Slover of Slover's Porting Service in North Hollywood, California, smooth the ports, transitions, ramps, and combustion chambers. He also port-matched the supercharger intake manifold for maximum flow. We're convinced this porting job helped achieve the rat's gargantuan power numbers.
The ARP kit originally came with six-point nuts, but our six-point socket didn't fit into the machined boss in the cylinder head. A phone call to ARP headquarters and a one day wait netted a complete set of 12-point nuts, which allowed us to use a thin-wall socket to do the trick.
Again using a torque wrench, it's extremely important to torque the head studs in the standard Chevrolet pattern using ARP moly lube.
With the cylinder heads torqued down, we installed a Lunati Weiand 02002 supercharger cam, which features 224/234 duration at .050-inch, with .498-/.520-inch gross valve lift and 112-degree lobe centers. The wide lobe centers will work to keep the boosted charge in the combustion chamber for maximum power.
The Lunati double roller billet timing chain features a notched crank gear that allows you to install the cam in several degrees of advance or retardation. We elected to install the cam straight-up at zero advance.
The billet gear and high-quality chain will provide optimum timing and strength, even under harsh dyno test conditions.
In an effort to match the valvetrain with our cam, we used a set of Lunati 1.7:1 billet aluminum needle bearing roller rockers.
Properly tightening the rocker arms involves dropping each arm onto a 7/16-inch stud, then turning the motor to top dead center. Starting with the number one cylinder, turn the engine until you feel air blow out of the spark plug hole. Then tighten then lock with an wrench slowly while wiggling the pushrod. When the rod spins freely but has no play, tighten the wrench a 1/4 turn and tighten the locknut.
We had to notch one rocker arm on each side to clear the Granatelli Motorsports sheetmetal valve covers. Slightly rounding one edge with a bench grinder won't significantly weaken the rocker arm.
The added effort was worth it, the valve covers look killer.
We used a GM Performance Parts harmonic balancer for an internally balanced 454. Note the timing marks.
A Weiand ball bearing high-volume polished aluminum water pump should tackle the rat's cooling demands with ease.
The Weiand 250 MegaBlower provides the cool looks of a Roots-style supercharger with the high efficiency of Teflon-tipped rotors and a compact design. Multiple upper pulleys are provided for several boost levels. The smaller the pulley, the higher the boost.
Holley 0-80573S 750 double pumper is a supercharger-specific carburetor. The power valves reference intake manifold vacuum below the supercharger,allowing the power valve to operate correctly. A power valve provides further enrichment to the main metering system under load (low vacuum) conditions. Without this external referencing, the power valve would be "reading" the supercharger boost pressure, which has no bearing on the engine load.
The lower blower pulley attaches to the harmonic balancer with three grade-five bolts.
Weiand's 250 Megablower breaks down into three basic components: the intake manifold, the supercharger, and the upper carb plate. Here you see the intake bolted to the motor with polished stainless ARP fasteners. A gasket (included with kit) goes between the intake and supercharger.
The 250 is two inches shorter than a 6-71, and is designed to run with a short water pump and use two accessory V-belts. The thick-wall case and CNC-machined rotors are capable of sustaining high rpm, not that we're going to need that with this stump-pulling 496.
A plate opens and releases pent-up pressure in case of a hiccup or backfire, rather than filling the blower with flame and blowing out the power valves (or launching the blower itself).
Weiand's optional linkage and fuel line kit includes pre-bent stainless hard line that meet at an aluminum distribution block with a -6 AN fitting. All you have to do is run a line from the fuel pump, to a pressure regulator, to the metering block, and you're good to go.
It may look tricky, but the pre-engineered linkage system works well and installs in minutes. Aircraft-style rod-ends and billet aluminum brackets give the system strength, and a blower-mounted pivot is perfectly placed to hook up to a standard '60s Chevy throttle linkage.
Finally, after dropping in an MSD billet distributor and a set of 8mm MSD wires, the Long Rod Rat was ready to rock the dyno. It combines old-school muscle, a little modern internal engineering, and lots of cubic inches.
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