Horsepower is what it's all about. For the Lunati Super Street-style Chevelle, the company decided to go with a thumpin' nitrous-free, 540ci Rat motor to see how far this very streetable A-body could be pushed into the nine-second-e.t. zone. In this second installment of the Street Heat Chevelle buildup, we'll take an upclose look at the pieces that go into an 840hp, 540ci Rat motor.
Not so long ago, building a normally aspirated big-block with this much power would have been a major effort requiring substantial fabrication and Pro Stock-engine-builder expertise. While serious horsepower has always been an expensive art, today most of the parts required are standard catalog pieces that make building an engine like Lunati's 540 relatively easy. This off-the-shelf theory was the whole idea behind the Lunati 540.
The best place to start when building a 540ci Rat is with a great foundation. While it's possible to use a stock iron 454 block, there are a couple of limitations. The most popular approach for a 540 is with a 0.250-inch-longer stroke using a 4.500-inch bore. This requires the use of the larger-bore Mark IV Bow-Tie block, since 454 blocks are generally limited to a 4.31-inch (0.060-over) bore size. The GM Performance Parts Bow-Tie block is available in two different deck heights of 9.80 and 10.20 inches. Lunati chose the taller-deck block to use 0.400-inch-longer connecting rods, which reduce cylinder wall loading. Other advantages of the Bow-Tie block include thicker cylinder walls to reduce bore distortion, a thicker deck surface for better head gasket sealing, and more clearance around the oil pan rail to clear connecting rods on stroker cranks with up to 4.750-inch strokes.
Since this is a stroker motor, the next major item is one of Lunati's off-the-shelf 4340 steel-alloy Racer Series nontwist crankshafts. The 4340 steel is the same alloy used in all drag- and road-race crankshafts and is forged using a more expensive one-piece die that molds the crank in its basic shape. "Twisted" cranks are forged flat and twisted into the required 90-degree shape. Lunati feels that the nontwisted forging has inherent strength advantages over a twisted crank that make it worth the additional cost.
Added to this killer crank is a set of Lunati Pro Mod 4340 steel connecting rods measuring 6.535 inches. Matched to the crank and rods is a set of Federal-Mogul rod and main bearings along with an off-the-shelf set of Wiseco forged-aluminum nitrous-style pistons using 1/16-, 1/16-, and 3/16-inch Speed-Pro rings. With a rough dome volume of 48 cc, Lunati came up with a 13.7:1 compression ratio.
The secret to horsepower with normally aspirated engines is idealizing the relationship between maximum cylinder-head flow and cam timing. A set of cylinder heads that will flow the most amount of air combined with the proper cam timing will make more power than humans should be allowed to play with. For this 540, Lunati chose a set of "Big Brodie" Brodix rectangle-port aluminum heads that flow very well right out of the box. But Brodix also offers a porting service that will deliver a set of hand- or CNC-ported heads to your door ready to assemble.
The Big Brodie heads feature 2.25/1.88-inch intake and exhaust valves with a standard chamber size of 121 cc and a big 305cc intake port that Brodix takes out to around 325 cc when ported. This large intake port is complemented with an excellent exhaust port to generate a very respectable intake-to-exhaust-port flow relationship that helps make serious power without crutching the combination with an overly-long-duration exhaust lobe.
For the camshaft, Lunati has a significant amount of experience with the Brodix -2 heads and has developed a specific mechanical-roller cam for this application that is closely matched to the flow potential of the Brodix heads. The remainder of the valvetrain is also Lunati, including the valvesprings, lighter titanium retainers to extend the valve float rpm, pushrods, lash caps, and 1.7:1 roller rockers. Lunati also added a Jomar stud girdle to the system to improve valvetrain stability.
Super Street rules dictate the use of an off-the-shelf single-four-barrel intake manifold, so Lunati decided on a fully ported Dart intake to match the Brodix heads. Fuel-mixing duties were assigned to a Barry Grant 1150-cfm Reaction Time Dominator carburetor. The BG Reaction Time carburetor is fully CNC-machined, then each booster is flow tested and balanced to produce equal fuel flow from all four venturis.
After the engine was assembled, Jim Fry at DynoTech in Memphis, Tennessee, bolted the 540 to his SuperFlow 901 dyno.
Once the engine was fired and given a short break-in, Fry performed a series of dyno tests to dial in the rotund rodent. The first pull on the engine, with an educated guess at timing and jetting, netted a respectable 828 horsepower at 7000 rpm and 692 lb-ft of torque at 5250 rpm. By the time Fry finished with timing, jetting, and experimenting with Performance Distributor's 18-volt ignition system, horsepower jumped to 842 at 7250 rpm and torque improved to 705 at 5250 rpm. This example shows the value of tuning the combination rather than just bolting on parts and taking the car to the track.
Now that the engine has been built and tested, the next step for project Street Heat will be the suspension and the driveline, which we'll cover next month. We're getting close to putting the big, bad Chevelle on the track to see what it can do. But it shouldn't take much imagination to determine that 840 horsepower in a 3400-pound Chevelle will be one thrilling ride! Stay tuned, we're only nine seconds away from having too much fun.
