Who said boring is boring? A cylinder getting opened up for one of CP Piston’s 107FT forge
Seventy-Four, 80, 88, 96, 103…the quest for more power from our V-twins has brought us a curious set of iconic numbers that might appear meaningless to most of the population but to V-twin enthusiasts, they are important and this quest for more pulls us steadily up the ladder to bigger displacement.
If you are starting with a stock Twin Cam (TC) engine, there are a number of ways you can get more horsepower and torque, and within each modification strategy there are many variables. If you think about—and if you are considering making changes to your engine, you’d best think about it—you should have a clear idea on what you are trying to achieve and why you are choosing a specific path and the parts necessary to make this vision happen. Having a plan makes sense and since few of us are experienced enough in these matters to formulate a plan for ourselves that will work out of the gate, we need guidance and counsel.
For most of us that have (or had as the case may be) the stock 96ci TC engine compared to H-D’s OEM displacement offerings from the past, the 96 produces improved performance. In an OEM state of tune the engine puts out decent power, spools up easily, is stone reliable, and works well as a package. The stock 96 configuration is strong and it delivers. But what it really presents to those of us who are performance minded is a solid foundation to build upon, so up the ladder we go!
Most gear heads are not in the game for the pedestrian “good manners and reliable delivery,” no-no, we want seat-of-the-pants thrills and plenty of power on tap to keep things interesting and we want reliability. If we have a bagger and travel with gear or passengers, we’ve learned the 96 begins to run out of steam after awhile and we wind up wishing we had more in the way of pull. We want to be able to confidently charge up hills, fully loaded.
Andrew checking the cylinder bore for trueness with his Sunnen gauge.
Good parts make for good work. The cylinder has a perfect crosshatch.
One of many of the OEM cylinder heads that get the five-axis Millport treatment.
Luckily there is a configuration that is available to 96 TC owners as an upgrade, and it delivers just what we’ve been looking for in terms of grunt and pull, it’s a 107ci kit. The parts of the kit we are describing in this article include: pistons, cylinders, cam, heads, lock-up clutch, exhaust, ECM remapping, and dyno tuning. It’s a substantial list of important parts, but all the work happens above the case decks, so the engine doesn’t have to be completely torn down. Yeah, we know, it’s a small solace to the wallet.
Up close and personal in the combustion chamber. The Millport produces fast, consistent, a
Firstly, why a 107? What significance does this number hold? A few things came into play to make the 107 a standard upgrade path. The first was that with machining/boring, this is a realistic number to bump the stock TC cylinders up to. The OEM cylinders on the 96 are strong and beefy enough to allow being hogged out a bit. The second was that there was a piston available to fit this increased bore size.
Andrew Rosa of Rosa Cycles in Huntington, New York, installs and sells (as fully baked kits to shops, dealers, and capable individuals) its 107 kits that are comprised of: in-house bored and honed OEM cylinders, modified OEM castings/CNC ported heads (to Rosa’s own specs), CP pistons, Andrews Cams (in this instance) and all the goodies (valves, spring kits, keepers) that go in the heads from AV&V/Goodson. There are options when it comes to throttle bodies and cams as well as tuning systems and software, but these days Rosa’s recommends using TechnoResearch Flash Tuner software, its own proprietary throttle bodies, and Andrews cams. These are all top shelf, reliable brands that are on point when it comes to product development and customer service. Andrew installs them, he services them, and he stands behind them. A typical 107 kit starts at about $2,500 and goes up from there depending on the components selected and if the shop does some/all of the work. For those that are looking to do the work themselves or have their local shop do the installation, Rosa’s offers a core exchange program. Aside from its 107 kits, Rosa’s offers a wide variety of other performance kits and hop-up parts for older and newer Harleys. During our visit we were able to get a first-hand look at some of Rosa’s machining processes as well as witness the installation and performance results of one of its 107 kits on a 2009 Street Glide.
Rosa’s has a very complete and redundant full-service machine shop on premise. All cylinders are bored on regularly calibrated and maintained boring machines and then honed in a state of the art honing center that does a single set of cylinders at a time. Andrew personally checks the trueness of each cylinder bore himself with his handy Sunnen gauge that itself is regularly calibrated and checked. Once the cylinders have a true bore (no weasely tapers allowed) and a perfect hone, they are cleaned in a soapy hot water bath and cleaned again, and then cleaned again—get the picture? This shop is cleaner than your kitchen! Cylinders are then painted, prepped, and ready to go.
Andrew making sure the valve seats are precisely cut with the Serdi 3.0.
Freshly ported and polished heads ready for reassembly.
Each head is reassembled with high quality parts from AV&V and Goodson.