What a 117" Twin Cam build makes
Simulated rear‑wheel horsepower and torque — measured after the primary drive, clutch and transmission, the same way a chassis dyno reads a bike. These are not flywheel numbers, and they are not directly comparable to a manufacturer’s crank rating. Rev ceiling for this combination: 6200 rpm, limited by engine.
A 4.125" bore on the stock stroke — the big-inch Twin Cam that does not need a stroker crank. It requires cases machined for the larger cylinders, which is what separates it from a bolt-in big bore.
This is a genuinely different engine from the one that left the factory. The torque peak has moved up, the pull continues far past where a stock 103 has given up, and the parts list reflects that: aftermarket heads, a spring kit rated well past stock lift, and short-travel lifters.
Compression sits where pump fuel is still sensible. Chasing more with a thinner gasket is possible and is exactly where builds like this start eating pistons — the tune has to be right before the compression goes up.
The build
| Engine | TC117 big bore (4.125 × 4.375) |
|---|---|
| Crank / balancer | A motor — non-balanced (Dyna / Touring / CVO) |
| Pistons | Forged flat-top (11cc combustion gain) |
| Head gasket | Cometic .040" — drops CR ~0.25 |
| Cylinder heads | S&S Super Stock 89cc · 2/1.605 |
| Porting | Stage 2 CNC port (full) |
| Camshaft | S&S 585 · 245/260 dur · 0.585" lift |
| Valve springs | AV&V VSK6500 beehive — .650" max lift |
| Rocker arms | Stock rocker arms — 1.625:1 |
| Pushrods | Stock pushrods |
| Lifters | Short-travel hydraulic (Feuling/Andrews) |
| Induction | HPI / SE 58mm throttle body |
| Exhaust | 2-into-1 stepped (D&D FatCat / E-Series) |
| Air cleaner | Screamin' Eagle / Stage I high-flow |
| Tune | Dyno-tuned (matched to build) |
| Power adder | None (naturally aspirated) |