Tall Deck Aluminum Chevy Clone Engine - Grunt!

Perhaps the ultimate bolt-on, the stroker crankshaft and rotating assembly absolutely requires an engine teardown to facilitate--a stark contrast between this power adder and the popular external units that include the supercharger, turbocharger, and nitrous oxide. On the other hand, those in search of the biggest bang from this terrible troika would also do well to prepare the engine with forged low-compression pistons and connecting rods, and perhaps by replacing the ordinary cylinder-head bolts with a stud system to sandwich the gasket between an O-ringed cylinder head or block surface.

But in this segment, we're talking about torque, plain and simple. It, not horsepower, is the stuff we drive every day. And nothing produces torque like big cubes and a long arm. The stroker crank offers a definite advantage over the other three in that it never runs out, doesn't need adjustment or maintenance or spool-up time, and is always there whenever the right foot demands it. In this sense, the stroker crankshaft isn't added on; it's always waiting to be evoked right there inside the engine. For purpose of illustration, the combination in question is a 632ci Lunati rotating assembly inside a tall-deck (10.200-inch) aluminum cylinder case. Admittedly not your everyday engine, but it's suitable for this illustration.

Here are the major ways that stroking manufactures torque:

1. An increase in cubic inches creates more displacement, and more displacement means more torque.

2. A longer stroke is like a lever acting on the crankshaft; in practical terms it's like using a breaker bar instead of a ratchet handle.

3. More displacement facilitates a higher compression ratio without resorting to outlandish piston domes that disturb flame travel.

4. A longer stroke creates faster piston speed, so the piston can create more of a pressure drop to fill the cylinder more completely at low rpm. 5. It is thought by some that increasing stroke without increasing the length of the connecting rod builds torque because piston-speed dynamics and the rod ratio create more cylinder pressure at maximum rod angularity, at which point the rod has the greatest mechanical advantage over the crank. In a street engine, lengthening the stroke without changing anything else usually favors low-end torque, not high-rpm horsepower.

Some of the critical things to consider with a stroker crank include block deck height, bore, stroke, rod length, piston compression height, and piston deck clearance. Block deck height is the distance from the centerline of the crankshaft to the flat of the deck surface. To service rotating assemblies with large dimensions, iron and alloy aftermarket blocks are available in various deck heights. Enlarging the diameter of the cylinders increases displacement but is not necessarily a requisite for the stroker crank.

The stroke is the distance that the piston travels from BDC to TDC and is calculated by the diameter of the circle traveled by the connecting-rod journals as the crankshaft makes one rotation. Lengthening the stroke increases the swept volume of the cylinders. Remember that the crank throw equals half the stroke dimension. As for rod length, it's the distance from the center of the piston-pin hole to the center of the rod-journal hole. Calculate the total stroke as twice the distance from the centerline of the crank to the centerline of a rod journal.

Put another way, piston compression height could be demonstrated as the distance from the center of the piston pin to the flat of the piston face. Longer connecting rods require less piston compression height to hold the piston within the limits of the block's deck height. Also analogous to this is piston deck clearance, or the distance of the flat of the piston face to the deck surface of the block.

Other portions of the block are likely to feel the sting of the grinder. Bottoms of cylinder bores and the oil pan rail are likely to interfere with a stroker crank's counterweights. This obstruction is easy to remove and usually requires a notch in the skirt or inner portion of the pan rail. Piston-pin bosses and piston bottoms can kiss counterweights. The connecting rods might contact the camshaft, too, but diminished bolt heads on the big ends, a cam with a smaller base circle, or an aftermarket block with a raised camshaft galley can save the day.

You also want the longest connecting rods that will fit the application, but you must first determine how much room you have to work with within the limits of the block deck height. In the case of our study engine, the constants are 10.200 (deck height) - 2.375 (stroke/2) + 6.700 (rod length) + 1.105 (piston compression height). Adding the piston compression height to the rod length and half the stroke gives you the actual deck clearance. Use this formula: (deck height - stroke/2) - (piston compression height + rod length) = deck clearance. (10.200 - 2.375) - (1.105 + 6.700) = 0.020

In a 3,200-pound envelope, 750 lb-ft feels like a mountain coming down. Scary, mates, scary. Considering the size of the engine, some will scoff at the low specific output of 750 hp, even though it's at a manageable 5,800 rpm; rounded off, this computes to 1.2 hp/ci. Not too impressive on the face of it, but the first time you crack the throttle bores halfway open, you realize how awesome 750 grunts really are. You realize that street tires (P285/40ZR17) are as ineffectual as if they were riding on marbles.

When you goose the throttle at 80, the tires haze and lay down 20 or 30 feet of rubber. The back end of the car shudders like you're coming off the line on a wrinkle-wall slick. It feels like a driveshaft vibe or a tire gone dead soft. A hundred yards beyond the traction failure, you whiff acrid rubber stench. Luckily, the Camaro tracks true, but at lesser speeds, you better be on top of things. Opening the throttle all at once skews the back end of the car immediately and severely to the right (as in a complete 360).

For all its ferocity, the big stroker engine runs smooth and idles right at 1,000 rpm despite its 0.700-inch lift and 258/272-degree-duration solid-roller camshaft. All it takes is judicious use of the throttle and dry pavement. But people get harebrained when they keep seeing those unintentional 20-foot stripes as the car leaves every traffic light. The tires make no noise when they spin. But when you've got open road in front of you and the hour is late, pressing the loud pedal rudely shoves you back in the seat. You are enveloped by the wail of the engine, and the noise and rapidly disappearing tarmac become absolutely hypnotic.

The idea, of course, is not to build a 600ci engine for everyday street use. Mileage is nil and maintenance is forever, but you can't beat the bragging rights.