Talk with a tuning pro and he’ll list off all the time-honored moves for optimal Harley performance. First, and by far the most cost efficient, is that initial switch to a high-flow air filter and a set of performance pipes. Swapping to more aggressive cam(s) comes next, easily bringing another 10 more horsepower or so to the game. A big-bore kit, opening up that 88 TC to 95 or 97 inches and a 96 to 106 puts even more performance on tap. Then comes the final step, cylinder heads, and coupled with everything else those ported, big-valve heads put that whole combination over the top.
Swapping heads is an easy move and these days it doesn’t have to be an expensive one either, relatively speaking. CNC-ported heads, like the ones offered by S&S as an example, are readily available on an exchange basis. They come completely assembled and ready to bolt on and along with their reshaped, high-flow ports, the package includes brand-new racing-grade oversize valves with matching guides and high-performance valve springs. There’s a lot of bang for the buck here.
“As soon as they became available,” says Jamie Hanson of Speed’s Performance Plus, “We’ve made it a point to keep a good supply of those exchange heads with us all the time. On a stock-displacement motor, they’ll make a noticeable difference, and on top of a big-bore kit they really make a difference!” The cost for this? Right around $1,000, give or take a few bucks. Those high-flow heads are totally compatible with everything else done to this point, starting with the air filter and pipes, and if there’s a big-bore kit in place you’ll now be taking full advantage of that extra displacement. A numbers comparison tells you why.
“There are no worries about adding a little compression to a street engine either, not with innovations like the S&S Easy Start cams available.”
Start with the valves. Stock Harley valves measure 1.805 inches on the intake, 1.575 for the exhaust. That can change to around 1.900 and 1.610, respectively—a significant increase. As for the ports, an OE Harley head will typically flow 215 cfm or thereabouts through its intake and about 190 cfm through the exhaust. Ported heads will bump that to almost 250 cfm and 210 cfm. All this means a bigger charge getting into the cylinders. The new heads will typically have a slightly smaller combustion chamber, too, boosting the compression. Put all that together and the power potential jumps up by 10 more horses or so, on top of everything else already done. Not a bad return on investment. We’re talking about an engine that’s now over the 100 horsepower range.
But hold on, there’s more to be had here, Hanson advises. If you’re willing to take a second look at the performance cams that might already be in the engine, swapping those moderate-lift cams that were compatible with the OE valve springs for something more aggressive, like a 585 in a 88- or 96-inch application and maybe a 625 in those big-bore situations, and bump up the compression just a little more, you can almost count on doubling the horsepower and torque boost those hi-po heads are good for. Now we’re talking about adding 20 or more horsepower, a lot of performance to leave on the table. There are no worries about adding a little compression to a street engine either, not with innovations like the S&S Easy Start cams available. A clever design, they use a centrifugally retracted compression-release lobe milled into the heel of each exhaust lobe that bumps open the exhaust valves slightly during the compression stroke making the engine easy to turn over. Once that engine fires, the lobe swings out of the way allowing the engine to run normally with full compression. Those Easy Start cams are available in all the grinds, 585s and 625s included. Bottom line: without the hassle of compression releases, you can have the performance gains of big cams and high compression and, coupled with the right exhaust system, gain gobs of mid- and top-end performance without sacrificing that all-important bottom end.
“We’ll always make a rider aware of what’s possible with a swap to hi-po heads,” Hanson concludes. And 10 more horsepower or so with the mild cams, or double-plus that with a bit more camshaft and a little bump in compression is tough to pass up. It’s definitely worth thinking about and the guys at Speed’s add this kind of performance all the time. For more info check out its website, and when it’s at an event nearby, stop in have a talk, getting the “heads up” on high-performance heads. HB
Speed’s Performance Plus
(605) 695-1401 – MN | (605) 695-2272 – SD