“It’s pretty easy to get that 97-inch engine up to 100-plus hp with 115 or more lb-ft of torque,” Jamie says. That’s a stout runner. And once again, something totally reliable.
There’s no replacement for displacement. It’s an old saying, and yeah, it’s pretty much true. Now, anyone following along here for the past few months knows that we’ve been taking a step-by-step approach to hopping up a Harley. Tapping into the know-how and experience at Speed’s Performance Plus we’ve outlined the basic Stage 1 mods and then upped the performance potential with a cam swap. And for a lot of riders that’s going to be plenty. An 80- or 85hp bike with almost 100 lb-ft of torque is nothing to sneeze at. But some of us want more, which brings us to the next logical step in getting the most bang for the buck. We’re going big, turning that 88-inch TC motor into a 97 and opening up a factory 96 to a 106. Still keeping it real and relatively affordable, all this is going to be a bolt-on; the engine stays in the frame, the cases remain un-split. The guys at Speed’s routinely install these big-bore kits right at the events.
“But honestly,” SPP’s Jamie Hanson adds, “quite often we’ll end up swapping out the cylinder heads, too, putting everything back together with ported, polished, and big-valve replacements instead of the stock Harley heads.” Now, that extra expense isn’t absolutely necessary—the added displacement and bumped-up compression is going to add plenty. “But with the motor already apart,” Jamie goes on, “and from a time and money standpoint, if a guy knows he’s going to want the extra performance boost of those heads later, let’s do it now.” Something to think about, but first let’s talk displacement.
Most often the SPP guys use S&S hardware to add the inches. Measuring kissin’ close to a 4-inch bore (3.927 inches) those new S&S cylinders are about the biggest that’ll fit into the stock case spigots, and unlike a bored-out Harley cylinder, they’re much stronger. Conceivably, the stock barrels could be overbored to pretty much that same dimension, but from a reliability standpoint, that’s really taking out a lot of meat. It just makes more sense to go all-new, with replacement cylinders designed from the get-go to add the inches yet still fit into the OE cases with no machining required. Those S&S pieces even have room for a clean-up overbore if, somewhere way down the road, a rebuild becomes necessary. And all those intake, exhaust, and camshaft changes already made work great with the new cylinders. Only now the original 88 has become a 97, a factory 96 a 106. Replacement pistons, of course, are part of the package, and with stock heads, the 97’s compression ratio will be 9.7:1, the 106 running at 10.2:1.
What’s all this going to net? Plenty. “It’s pretty easy to get that 97-inch engine up to 100-plus hp with 115 or more lb-ft of torque,” Jamie says. That’s a stout runner, and once again, something totally reliable. For the 106 you can add 10 or so horsepower to that number, with a corresponding jump in torque. Neither of these engines will be the least bit finicky either. They’ll start easily, run smooth and cool, but when the throttle gets cracked, you’ll know something serious is going on down in that engine room.
Now, about that cylinder-head swap: does it pay to make that change now? Depends on what your definition of “pay” is. There’s no denying that bigger, smoother ports and bigger valves are going to pack more punch into those bigger cylinders. That’s just physics. It’s also the next logical step in that quest for performance. And the end result here is a 110- to 120-plus hp motorcycle. Quite a jump from that stock H-D’s 60 to 70-or-so ponies. So, if you know you’re going to want this anyway, someday, like the guys at SPP say, with the engine already apart, why wait? Of course, it’s not an insignificant added expense so consult your banker or your wife for the answer as to whether or not now’s the time to jump. It’s your call. One thing’s a guarantee though: you’re going to love all that horsepower.
Talk with the guys at Speed’s Performance about all of this. They’ll give you the straight scoop. But the bottom line is that there really is no replacement for displacement and a bolt-on big bore kit delivers serious bang for the buck. HB
Speed’s Performance Plus
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