Twin Cam 96 vs 103 — same top end, what does the displacement buy?
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: 5500 rpm, limited by engine.
Where each one wins
| RPM | 96 | 103 | diff |
|---|---|---|---|
| 2000 | 94 | 100 | +6 |
| 2500 | 101 | 107 | +6 |
| 3000 | 107 | 113 | +7 |
| 3500 | 111 | 118 | +7 |
| 4000 | 111 | 118 | +7 |
| 4500 | 105 | 112 | +7 |
| 5000 | 98 | 105 | +6 |
| 5500 | 92 | 98 | +6 |
Torque, lb-ft, at the rear wheel. Everything except the part named is identical between the two runs.
Every part above the pistons is identical. The only difference is the bore — 3.75" against 3.875" on the same 4-3/8" stroke.
This is the cleanest way to see what displacement is worth on a Twin Cam, because nothing else is allowed to move. The gap is consistent across the range rather than appearing only at the peak, which is what displacement does: it lifts the whole curve.
Worth knowing before you pay for a big bore on an engine whose top end has not been addressed. The same money spent on the cam and heads of the smaller engine is not obviously the worse deal.
The build
| Engine | TC96 (2007–2011) 3.75 × 4.375 |
|---|---|
| Crank / balancer | A motor — non-balanced (Dyna / Touring / CVO) |
| Pistons | Forged flat-top (11cc combustion gain) |
| Head gasket | Cometic .030" — neutral baseline |
| Cylinder heads | STOCK -06 + S&S CNC port service · 1.9/1.575 |
| Porting | Stage 2 CNC port (full) |
| Camshaft | S&S 510 · 238/252 dur · 0.510" lift |
| Valve springs | Stock springs (as fitted to the heads) |
| Rocker arms | Stock rocker arms — 1.625:1 |
| Pushrods | Stock pushrods |
| Lifters | Short-travel hydraulic (Feuling/Andrews) |
| Induction | HPI / SE 55mm 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) |
The other one
| Engine | TC103 (2010 CVO / 2012+) 3.875 × 4.375 |
|---|---|
| Crank / balancer | A motor — non-balanced (Dyna / Touring / CVO) |
| Pistons | Forged flat-top (11cc combustion gain) |
| Head gasket | Cometic .030" — neutral baseline |
| Cylinder heads | STOCK -06 + S&S CNC port service · 1.9/1.575 |
| Porting | Stage 2 CNC port (full) |
| Camshaft | S&S 510 · 238/252 dur · 0.510" lift |
| Valve springs | Stock springs (as fitted to the heads) |
| Rocker arms | Stock rocker arms — 1.625:1 |
| Pushrods | Stock pushrods |
| Lifters | Short-travel hydraulic (Feuling/Andrews) |
| Induction | HPI / SE 55mm 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) |