Speeds Secrets February 2008
Specialty Engines—Beyond Big Bore
For H-D owners in search of a big-bore kit, the Speed’s Performance Plus top-end conversion of an 88-inch Harley to a 95, or boosting a 96-incher up to 103, is a notable change. As we stated in the December 2007 column, the performance increase is dramatic. Yet some riders always want more. So when, and in what conditions, does the step up to a full-on SPP “Specialty Engine” begin to make sense?
“With those 100- to 110-horsepower big-bore bolt-ons,” Speed’s Wayne Hanson says, “most guys can be reasonably assured of a good, long engine life. But when a rider is a hard charger routinely pouring on the power from a dead stop, it’s time to dig a little deeper. Besides just power, that guy needs strength.” Speed’s Performance can deliver it, building what they call their “Specialty Engine.” Assembled from the bare cases up, this is time consuming, meticulous work mostly done during the off-season at their shops in Knoxville (Tennessee), Sturgis (South Dakota) or Elk River (Minnesota).
“A ‘Specialty Engine,’ “ Wayne goes on, “is best suited to someone running a big, sticky rear tire, maybe doing some drag racing, or at the very least always launching hard, even on the street. To stand up to that, the engine has to be extra tough.” To get there, a Specialty Engine from SPP starts at the bottom and includes practically everything on the parts menu.
It begins with custom case machining for a Timken bearing conversion for the crankshaft, which is much better than the factory roller. That’s followed with a precise align boring of the cases and a dynamically balanced crankshaft assembly that’s set to virtually zero run-out. It all makes for a robust bottom end built to handle serious power. These engines include every trick in the book, including hand assembly of the best of everything. The pistons are Teflon coated, the cams are Speed’s own grind with a gear drive, and the cylinder heads receive custom porting with 1.800-inch intake runners. Everything’s built bulletproof, as dependable as it can be. It’s important to note that these are all street engines, too. Definitely powerful, they’re meant for day-in/day-out use. While any one of these SPP engines could produce wild horsepower and torque numbers to compete in a dyno shootout, that isn’t the intent. Quick throttle response and gobs of mid-range power are the goals.
A number of displacements are possible, starting at 114 inches based on a 4” stroke and 4 1/4” bore. Even the low compression/mild-cam version makes about 120 horsepower and 128 ft.-lbs. of torque. Bump up the compression and cam and the 114 can produce up to 135 ft.-lbs. of torque with 130 horsepower. Serious stuff. Speed’s 117-inch engine, with a longer 4 3/8;” stroke and a 4” bore, pumps out 135 horsepower and 138-plus ft.-lbs. of torque. A 124-inch Specialty Engine also has a 4 3/8;” stroke, this time coupled with a 4 1/2;” bore netting 131 cubic inches. Take note of the stroke dimensions here. They offer an insight into Wayne Hanson’s street-engine building technique.
Run down the spec sheet for most 124-inch engines and you’ll see they get that displacement with a 4 1/2” stroke and 4” bore. Most 131s have a whopping 4 5/8” stroke. Reversing that, SPP tends to go as short as possible with the stroke and as large as possible with the bore. The result, Wayne feels, is an engine that’s quicker revving, more responsive to the throttle and offers better durability for longer life.
“And my favorite of them all,” Wayne says, “is that 114.” With its 4” stroke and 4 1/2” bore this engine will rev as quickly as any hopped-up 95-inch engine, but it adds big-inch horsepower and torque. “It’s a great combination,” Wayne says, and SPP has built lots of them. “And when I go to a little higher compression, about 10.8:1, and with a 625 cam, we’re making 130 horsepower and 135 pounds of torque. With a 114! That’s a pretty mean motor, as fast and as powerful as most 124s.” Swap the pistons for a lower 10.1 or 10.3 ratio and use a milder 615 cam and it’s still 120 horsepower and 128 ft.-lbs. of torque, plenty for any street bike. “That motor is also cooler running,” Wayne says. “It’s a great all-around street engine.”
So, want to have the baddest motor scooter on the block this riding season? It can happen, and now’s the time of year to do it, during the winter when the SPP team is home and in the shop.
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