There’s no replacement for displacement. It’s an adage as old as hot-rodding and one of the set-in-stone truisms. It’s also the thought process behind the ever-increasing popularity of stroker engines. Back in the day, the most popular combo was turning a common 350 small-block into a 383. But today just about any mill can get the stroker treatment. The real gain of any increase in displacement is torque. It’s why a big-block almost always beats a small-block in this department.
If you’re building an engine, and you need to buy a rotating assembly, then going with a stroker makes even more sense because the cost of a stroker crank and rods is only a little more than the stock-sized stuff. For example, Lunati sells their 355ci Sledgehammer rotating assembly for $2,362. But their 383 kit is only $2,404. That’s 28 additional power-producing cubes for a paltry 42 bucks. No other speed part gives you such a return on your performance dollar than a stroker. Well, maybe nitrous, but that’s another story for another time.
Like all good things, you can take the theory too far. Go too big on the bore and you can weaken the cylinder walls to the point of failure. You can also run in to overheating problems. Push the length of the stroke to the ragged edge and you could experience another set of failures: the biggest problem can occur when the piston reaches the bottom of its stroke; this is known as bottom-dead-center (BDC). If too much of the piston extends out of the bottom of the cylinder bore, and the piston isn’t designed for this, the piston can rock, scoring the cylinder walls thus eventually junking up the engine. That’s why it’s always good to check with the manufacturer on what they recommend. We also think a good way to go is with a stroker kit. In a kit the parts are designed to work together in a particular application rather than hobbled together in the hopes they are mechanically compatible.
Lunati and Wiseco have been working together to make sure the stroker kits they offer work. And more importantly, are reliable. The pistons in their LS stroker kits are specifically designed for LS applications. This is critical since every detail matters when you’re pushing the stroke to the ragged edge of what’s possible with a stock-sleeved cylinder.
We’ve been itching to put a bit more power under the hood of our ’68 Camaro, Bad Penny. The LS2 currently in it is running the stock GM short block with a medium-sized COMP cam, FAST 90mm intake, and some sweet AFR 205 heads. It made good power, but for how we use the car, more low and midrange torque would make it quicker—hence more fun.
A Stroker’s Biggest Enemy
Not all pistons are created equally. Wiseco has been working closely with Lunati to ensure that their pistons are designed properly for stroker duty. Toss in a piston that’s not up to the task and the results can get expensive fast. The key is in the design of the skirt taper for LS-based 4- and 4.125-inch strokes. The basic premise is that the piston must still be at full diameter when it reaches bottom-dead-center (BDC) even if a lot of the skirt is hanging out of the bottom of the bore. This way the piston won’t wobble and tear itself apart as it’s forced up the bore, and past the sharp edges at the bottom of the cylinder.
According to Brian Nutter at Wiseco Piston, “LS blocks have varying cylinder lengths ranging from 5.420-inch in the 6.0L block, 5.455 to 5.475-inch in the LS1, 2, 3, and 92 blocks, LSX at 5.575-inch and LS7 at 5.900-inch. Most pistons are tapered approximately .050-inch from bottom to top to accommodate for thermal expansion, but it’s important that a piston skirt be at full diameter at BDC. The necessary taper must be introduced at a point above this. When the piston is at full diameter at BDC, it won’t rock, and the bottom of the cylinder will not dig into the skirt, causing rapid wear. Reducing piston rock also keeps the rings perpendicular to the bore and oil control is much better. To further reduce wear, Wiseco recommends that the bottoms of the cylinders be deburred with a cartridge roll around the circumference. Forged piston manufacturers have different specifications for a piston’s skirt taper depending on the application. It’s important that a customer speaks with them directly to verify proper design.”
In late August we received and interesting invitation: The website www.Later-g.net needed two cars to compete in the Optima Batteries Ultimate Streetcar Invitational. The competition was set to take place November 8th; the Saturday after the SEMA show. The event would consist of a 2.2-mile road course, an autocross, a 0-60-0 competition, and a styling component. It sounded like our kind of event, so we signed on the dotted line. The only problem was that there was a ton of things we wanted to do to the Camaro, and we only had two months to get it all done. So we kicked it into high gear and started Project Bad Penny Track Edition. More proof that hot rod projects are never really done. Step one was more power. After all, can you ever have enough?
The foremost reason for the Wiseco Flow-dome is hitting the target volume necessary to maintain the needed compression ratio while accommodating different valve angles, centerlines, and valve diameters of the different cylinder heads. It also allows bigger cams to be run before running out of piston to valve clearance. The Wiseco Flow-dome mirrors the face of the valves and doesn’t shroud them or create a tall dome that impedes combustion. Incoming charge past the intake valve and outgoing exhaust past the exhaust valves doesn’t get caught in the void underneath the valve and flows smoothly past it. Because the void under the valves is filled around TDC on the exhaust stroke, it clears out the cylinder a bit more as well.