A Popular And Effective Engine Upgrade

Who said boring is boring? A cylinder getting opened up for one of CP Piston’s 107FT forged pistons.

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.

A Popular And Effective Engine Upgrade Zoom

Up close and personal in the combustion chamber. The Millport produces fast, consistent, and reliable work.

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.

A Popular And Effective Engine Upgrade Polished Engine Zoom

Eric made quick work of getting the engine ready for its new components.

Stock H-D head castings are the castings Rosa’s works with most frequently. They are well made, present the machinist plenty of material to work with, and most importantly, they are plentiful. When heads arrive at the shop, Rosa’s disassembles the stock heads and then mounts the castings in its five-axis Millport machine. They then pick the CNC program (Rosa’s had its own designs digitized) for that engine configuration and let ’er rip. The Millport does what took quite a bit of time to do by hand and it does a great job, over and over again, perfectly and consistently.

Once the head comes off the Millport, the combustion chamber is polished by hand, guides installed, and the valve seats are cut at the Serdi machining station. There is a process involved in cutting the seats and then checking each valve’s seal, it’s not a set-it-and-forget-it machining process, the operator needs skill in knowing just how much pressure to apply to the cutting head—hamfists need not apply. Once the heads have been fully machined, they are CC’d with a burette and mineral spirits to ensure they are consistent to each other and hold the correct volume and then the whole shebang is reassembled using new valves, springs, and keepers. There is a lot of work that goes into a set of custom flowed and ported heads, as you can see.

With one person (Andrew), taking the cylinders and heads through each of the machining, cleaning, and reassembly stages, it ensures that each and every detail has been attended to. There are many steps that need to be taken into account to make sure the job is done correctly, and no corners cut.

Over in the service side of the shop we caught up with Eric (Rosa’s tech) and the Street Glide that had been brought in to get a bump in displacement. Eric handled disassembly and it was a no-muss affair, one of the benefits of working on a new machine. The exhaust was the most tedious piece to remove (as to be expected). All of the pieces and parts were carefully stowed for reassembly; a minute invested in being organized pays dividends down the line.

With the heads and cylinders handed off to Andrew for machining, Eric got busy removing the stock cams and swapping them for a set of chain driven Andrews TW-54 cams. Once the cams were installed, he went around to the other side of the bike and installed an AIM lockup clutch to keep spring/hand pressure modest, while providing the gripping power that will be required when the owner twists the throttle with spirit.

Neatness counts, and makes life a lot easier.
The AIM VP92T lockup clutch will help get a grip on the clutch while also easing the grip on the clutch lever.
The AIM VP92T lockup clutch will help get a grip on the clutch while also easing the grip
A marriage made in heaven, the brand-new CP piston getting fitted with its rings.

When he was finished machining, Andrew gave the cylinders and heads to Eric who had already installed a set of CP 107FT pistons on the connecting rods. Eric placed a fresh O-ring on the bottom of the cylinder and carefully installed the cylinder over the gorgeous piston; a fresh Cometic gasket went on top of the cylinder and next up was installing the head.

A Popular And Effective Engine Upgrade Cometic Gasket Seal Zoom

Cometic gaskets ensure a tight seal.

Using a maintained and calibrated torque wrench is the sign of a pro and Eric had his pricey pride and joy in his hands, making sure the adhesive force holding the cylinder and heads in place was sufficient and up to spec. Then with the heads on and torqued, he began the chore of reinstalling the intake and exhaust system. In many instances the customer’s desire to squeak out the most power out of his/her engine as possible, (no matter cost) dictates the use of one of Rosa’s custom throttle bodies, but in this case, budget and needs didn’t require it, so Eric bolted the stock unit (sufficient by most any measure) back on the machine. When putting the rockers back on, Eric reminded us to make sure to replace the all important sealing O-ring with a new one.

With everything bolted together, cleaned up, and wiped down, the bike was then wheeled into Rosa’s Dyno Hut for its inaugural run in the world of triple-digit displacement. Andrew downloaded the TehnoResearch maps to the ECM and pressed the Start button. We don’t care how many times you’ve heard a new engine fire, but it brings a smile to everyone’s face no matter how salty or green they are.

With the selected map in place the bike was run through its paces and tuned. A few short pulls later, the machine rolled off the dyno with some very healthy and respectable numbers. In its stock trim the 96ci engine made 68.7 hp and 85.4 lb-ft of torque. After the Rosa’s 107ci upgrade and with a set of Rinehart True Duals the Street Glide produced 111.1 hp and 120.1 lb-ft of torque. That equates to a 61.72 percent gain in hp and a 40.63 increase in torque. The bike sounds like a beast, its tractive power is so much more dramatic, new life has been breathed into this machine, upping the fun quotient by a factor of 10x.

If you are considering adding some spice to your 96ci TC, give the 107 configuration as described here consideration; it’s a proven winning combo that has given many folks smiles for miles! B

Eric applying just the right amount of torque to the heads.
Rosa’s offers throttle body options, but for this bike the owner decided to stick with his stock unit.
Rosa’s offers throttle body options, but for this bike the owner decided to stick with his
Missing a minor but important detail like the sealing O-ring can be bad news.

Into the hut, the dyno hut.
The results speak for themselves. The 107 install was a great success that netted a gain of 42.4 hp and 34.7 lb-ft of torque. The Street Glide is a whole new animal!
The results speak for themselves. The 107 install was a great success that netted a gain o