What does Stage 1 actually add on a Twin Cam?

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

Torque, lb-ft, at the rear wheel. Everything except the part named is identical between the two runs.

Stage 1 is the package almost every Twin Cam gets first: a high-flow air cleaner, mufflers without the catalyst, and a tune to match. No engine is opened.

The gain is real but modest, and it is worth understanding where it comes from. Most of it is the tune. The intake and exhaust changes let the engine breathe slightly better at the top; the calibration is what lets it use the fuel and timing to do so.

Notice the two curves have the same shape. Stage 1 lifts the line — it does not move the peak or extend the range, because the camshaft did not change. That is the honest ceiling on bolt-ons, and it is why the next step is always a cam.

The build

The other one

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