SPEEDÕS SPOTLIGHT
WORDS AND PHOTO: JOE KRESS
NEW KITS AND THE M-8
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n the world of Harley-Davidson performance, nothing stands still for long. The aftermarket is constantly coming up with new
parts and packages to better the output and efficiency of a V-twin. Pro tuners and engine builders take those new possibilities and mix and match them to come up with exciting results of their own. And not to be outdone by any of this, the factory itself will jump in with an all-new powerplant, the introduction of the multi-valve Milwaukee-Eight being the latest example of that. The techs, tuners, and engine builders at Speed’s Performance Plus are right in the thick of all this. Paying close attention to what that performance aftermarket puts in front of them, and what new engine platforms the factory develops, they’ve been busy exploring the possibilities of both—new ways of looking at the venerable Twin Cam and pulling more performance from it, exploring the possibilities of the all-new M-8. And in both instances they’ve come up with some interesting results, the first being a new look at a 110-inch big bore kit for those TCs, a bolt-on with performance potential especially in the all-important torque department. “For a while now we’ve had great results with the 106-inch engine kit we’ve developed,” SPP’s Jamie Hanson begins. A bolt-on package made up primarily with big-bore barrels and pistons, new cams with a gear drive, and high-flow cylinder heads, all carefully chosen and joined by a proper exhaust, a free-flow air filter and a custom tune it’s a combination netting nice, all-around street performance for both OE 96- and 103-inch engines. The horsepower goes way up and torque jumps into the 120 pound-feet range. Bringing those engines up to 110 inches promises even more but not without some careful forethought about how it’s all going to go together. “Initially, these new 110-inch packages gave me a little concern,
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primarily because they include domed pistons,” Jamie says. “For years we’ve had great success with flat-top pistons.” Additionally, those domed pistons raise the compression ratio up a little higher than SPP likes to see on a street engine. How high is too high to SPP thinking, at least for an everyday street engine? With domed pistons the compression ratio is 11.2 to 1. “And we like to keep things around 10.8 or even a little lower,” Jamie says. The workaround SPP has come up with centers around the choice of cylinder heads to use here and their gaskets. Substituting heads with a slightly increased combustion chamber volume drops that 11.2 ratio down considerably—too much, in fact. But by using a thinner head gasket things instantly go back into that 10.5 range. “Just a tick lower than we normally shoot for, but with the added flow of those bigger valves and ports the horsepower will be comparable to what we see with the 106s and with that little bit of added displacement the torque gets a nice bump,” Jamie says. How much? “We’re looking for horsepower right around 120, torque at 125-plus.” All this is exemplary of just how important it is to look at any engine modifications as part of a package deal, with a total understanding of how any one change can have a dramatic effect on any number of other changes. Everything has to work together toward a desired goal, and the Speed’s
Performance 110-inch kit certainly does that. “Something else we’re working with right now are performance packages for the new Milwaukee-Eight,” Jamie says. So far there’s not a lot available in the aftermarket for this one, a few new camshaft options, some air filters, and a couple choices in the exhaust department being about it. But even with that the possibilities of the M-8 are apparent. S&S, for example, is claiming 96 hp and something like 114 pound-feet of torque with the 107-inch M-8 using just its .465 lift cam and slip-on mufflers. Substitute a 2-into-1 for those slip-ons and all that’s going to head north big time. “And this is just scratching the surface,” Jamie says. “If a cam swap and the right set of pipes can get horsepower and torque like that, imagine what a big-bore kit would do.” And big-bore kits for the M-8 are the worst-kept secret in the industry. There’s already talk about 130-plus displacements from a bolt-on package. “The potential here is amazing,” Jamie says. “Horsepower of 150-plus is not out of the question.” Like we said, in the world of Harley-Davidson performance, nothing stands still for long. HB SOURCE: SPEED’S PERFORMANCE PLUS speedsperformanceplus.com (605) 695-1401 – MN (605) 695-2272 – SD
