Speed’s Spotlight – Performance Heads on a Harley-Davidson Motor
When a big-bore kit and some cams are on the menu, topping that with a set of performance heads is a no-brainer. “On a stock-displacement motor it’ll make a noticeable difference,” Jason Hanson of Speed’s Performance Plus says. “On top of a big-bore kit they really make a difference!”
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On top of a big-bore kit they really make a difference!
Why? Start with the valves, Jason explains. Performance heads will have significantly larger ones, both intake and exhaust, but the ports will have been reconfigured for better flow into combustion chambers optimized for compression and flame travel. All this adds up to a bigger charge making a bigger bang. Put it all together—big-bore, cams, and heads—and the power potential is considerable.
But what about the rider with a newer 103-inch engine or a 110? Generally speaking, bolt-on big-bore kits aren’t tops on their list. How much, after all, are those few extra inches available worth? There’s more than just displacement to this story, though, and we’ll get to that. “Usually, though,” Jason says, “these guys just want more power from that stock displacement.” And most of the action here, he goes on, is with cam swaps. A gear drive and, depending on the rider and how he uses that bike, anything from a 551 or 570 to a 585 or 615. But what about those hi-po heads? Do they have a place in all this? “Absolutely,” Jason says. “You can put ’em on top of stock pistons. But for a little more money you can swap those pistons for something with more compression and deeper valve pockets allowing you to run more cam and get the whole shebang.” This needs some explanation.
“Very rarely will we put a set of performance heads on top of stock pistons,”
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Very rarely will we put a set of performance heads on top of stock pistons
the SPP guys say. Number one, there’s that valve pocket situation. Stock Harley pistons, even in the newest bikes, don’t have a deep enough valve pocket for the clearance needed with oversize valves and higher lift. Sure, you’ll get more flow with better ports, but if you have to restrict that with smaller valves and less cam lift, what’s the point? So since the motor is already cracked open, why not crack open the wallet for a new set of pistons and the barrels to go with them? “With the proper compression,” Jason explains, “and the necessary valve-pocket relief, we can spec in a proper set of cams and then the whole package, cylinder heads on down, will be in sync. Everything performing to its potential.”
In this mix there are a lot of possibilities, everything from budget pistons and middle-of-the-road heads to the really high-end/top-of-the-line stuff, the specially coated and forged pistons matched with welded-up/raised-port heads, custom ported heads with a steeper drop through the ports and considerably more flow velocity. There’s a difference in price, sure, and in the outcome. Depending on the application and displacement that top-of-the-line combination can return up to 20-percent more power and performance. But don’t automatically discount the performance available from those lower-priced cast hi-po heads with their CNC-machined ports. They’ll outperform a ported set of OE heads by a long shot and be head and shoulders above a completely stock set of heads. “And depending on the application and the need, we can use anything from the S&S Super Stock heads to those custom raised-port heads from the most innovative cylinder-head companies worldwide,” Jason says. “We can pick and choose between everything available, making sure that what we end up with is exactly what’s called and hoped for.”
All this can happen faster than you’d think. “People don’t realize we carry all of this with us to the events,” Jason explains. “We can, and do, build complete engines at the rallies
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We can, and do, build complete engines at the rallies
