Mixing lightning with thunder
Back in 2016, under the direction of partners and owners Todd Gaines and Don O’Shea, Indian Motorcycle of Libertyville (Illinois) began delving into performance enhancements for the iconic Thunder Stroke 111 engine. While this engine is no slouch, these dealership owners have a passion for performance and, since they were an Indian dealer, felt compelled to see just how far they could take the stock design. Looking back, I doubt this duo ever envisioned the end result.
My first encounter with the highly-regarded Thunder Stroke was during its initial unveiling during Daytona Bike Week in the spring of 2013. After months of tantalizing and vague snippets of information from Indian concerning a new powerplant (you could hear it online but not see it), the mystic veil was lifted with a cutaway motor on display at a renovated building on Main Street, Daytona Beach. When I asked engineer and chief designer Eric Fox why they had settled on a 111 cubic inch displacement he replied, “Just to give Harley a nudge. See what they might do next,” in obvious reference to H-D’s 110” CVO models. You could even go over to the Destination Daytona dealership and hear a Thunder Stroke run. A static-mounted engine bolted to a pedestal, it was impressive even without frame or wheels—a throaty exhaust note with classic finned head covers reminiscent of a 1948 Indian Chief flathead. The engine was well received by the Daytona crowd and continues to garner a huge fan base till this day.
When the Libertyville team first began to chase down a few extra horsepower from the Thunder Stroke, they initially settled on conventional approaches—tuning, air intake, cams, free-flowing slip-on mufflers—and achieved a moderate level of success. This was not enough for O’Shea, Gaines and their crew. Next on the laundry list was to modify the stock heads. But even with porting, the installation of larger valves and a new hot cam, the product lacked that fine line of breakthrough performance. Everyone knew what was needed and it was time to call in the pros.
Tapping into a vast resource of motorhead professionals, those providing intellectual commentary varied from Nascar engineers to Baja racers who specialized in air-cooled engines. In the end, the consensus was the same—redesign the combustion chamber. Much R&D followed leading to the establishment of a new company, Indian Performance Solutions, in 2017. Redesigning the stock heads netted promising results but was quite labor (and cost) intensive and suffered in its performance consistency. Finally the decision was made to make the investment in a proprietary casting with the product being finished by CNC machining. It should be noted that the foundry selected to produce the raw cast heads uses a patented process that results in only the highest quality of non-porosity structure.
The new IPS cylinder heads increase the compression ratio from 9.5:1 to 10.5:1 without changing the bore or stroke, and the the stock pistons and rings are maintained. The exhaust valve received a serious overhaul with the backside contour totally different than the OEM valve. The intake port was also modified and the pushrods upgraded. The end results are quite impressive. The stock Thunder Stroke 111 delivers 73 hp and 103 ft/lbs of torque at the rear wheel. With the installation of the IPS heads the numbers jump to 112 hp and 125 ft/lbs of torque when used in conjunction with the hot-rodded cam and the company’s exclusive X-Pipe exhaust system
“People fixate on horsepower but torque is where it’s at,” stated O’Shea. “Our new cam puts us in the middle with good numbers on the top without giving up much on the bottom. Our upgraded valves and springs are provided with the heads and are very similar to the Chevrolet LS valve springs. This is an engineered, manufactured solution for the everyday rider who wants a performance machine. No one has a similar solution and no one gets these results for the Thunder Stroke 111.”
O’Shea went on to explain, “From the day we started looking at performance, changing the exterior iconic look was not an option. Our solution is on the inside. The look of the Thunder Stroke 111 is intact. In every way, shape and form it resembles the stock Indian 111 cubic inch head. Inside the combustion chamber and port redesign makes the solution work.”
The IPS Performance Package is designed to fit all model years of the Thunder Stroke 111. It is being distributed through Indian Motorcycle of Libertyville, 847.984.2542, www.indianmotorcycleoflibertyville.com and is for sale to individuals and independent shops. Once demand increases, the IPS kit will be available through other authorized Indian dealerships.