The Twins Cup homework build
2021 Aprilia RS 660 — Build an RS 660 to the MotoAmerica Twins Cup recipe — not to race yet, but to learn what the class already knows.
We put this build together from what riders recommend — prices verified Sep 2026.
- Akrapovič Racing Line full systemCarbon Racing Line, the version made for this bike — the value full system at about $1,300. Pair it with the fuel controller.$1,300
- Dynojet Power Commander 6Piggyback fuel controller matched to the open exhaust; the stock ECU isn't reflashed, so its map stays for resale day.$530
- K-Tech 25IDS fork cartridge kitSprings for my weight are a separate order. Published Twins Cup settings for this bike exist — start there, not from zero.$1,310
- K-Tech RCU Razor-R rear shockMatches the front. The stock shock is fine for the street and out of ideas on slicks.$910
- Race fiberglass bodywork kitUnpainted, with a race tail that fits over the stock subframe. Sell the pristine street plastics — they fund half of this.$1,000
- Bonamici rearsetsCommon in the class, GP-shift capable, replacement pegs and toe pieces available separately — the crash-economics matter more than the billet.$920
- Woodcraft 3-piece clip-ons3-piece design: crash replacement is a $25 bar tube, not a $160 assembly.$160
- GB Racing engine cover setRequired for race groups by most orgs. The 660 cases sit wide — cover them before the first track day, not after.$420
- Vortex 520 sprockets + EK MVXZ2 chainAlready a 520 chain from the factory — this is gearing and an EK X-ring chain, not a conversion. Carry a spare rear in a second size.$270
- SBS Dual Sinter race pads (per caliper)The race-pad upgrade. Race-only compound — track use only.$180
- Pirelli Diablo Superbike slick setSC1 front / SC1 rear to start; warmers stop being optional at this point. Budget tires as a per-weekend consumable, not a mod.$500
How it came together
The RS 660 became a race platform the day it launched — Twins Cup grids filled with them almost immediately, which means the setup homework is already done and floating around every paddock. This build copies the recipe instead of inventing one: full system, fuel controller, real suspension front and rear, crash-proofing, race bodywork. When the class has already found the fast configuration, originality is just a slower lap time.
The money followed the grid. K-Tech front and rear because that's what a good share of the field runs and there's published settings data for this exact bike; the stock suspension is genuinely decent for the street and clearly soft once you're on slicks. Akrapovič's carbon Racing Line over the pricier titanium systems because the class rewards a value pick — about $1,300 is the least I found for a full system on this bike — and it runs with the fuel controller. What I deliberately kept stock: the rider-aid electronics and the quickshifter. Aprilia's package is legitimately good and the rulebook doesn't reward spending there.
The unglamorous truth is that the bodywork and case covers are the most important parts on the sheet. Race fiberglass and covers are what let you crash on Saturday morning and still ride Saturday afternoon — that's the whole difference between a track hobby and a very expensive single session. And the number plates don't make you fast: my first outing on slicks I was seconds off what this suspension is capable of. The bike is built to the recipe. The rider is still in development.
Shop this build
Boxed links go straight to a product, at the price we saw on the date shown. The rest are retailer searches. Most of these parts are model-specific, so confirm the exact part number for your year, generation and market before you buy.
| Part | Typical price | Where to buy |
|---|---|---|
| Akrapovič Racing Line full systemExhaust | $1,300 | |
| Dynojet Power Commander 6Tune | $530 | |
| K-Tech 25IDS fork cartridge kitSuspension | $1,310 | |
| K-Tech RCU Razor-R rear shockSuspension | $910 | |
| Race fiberglass bodywork kitBodywork | $1,000 | |
| Bonamici rearsetsRearsets | $920 | |
| Woodcraft 3-piece clip-onsClip-ons & Throttle | $160 | |
| GB Racing engine cover setCrash Protection | $420 | |
| Vortex 520 sprockets + EK MVXZ2 chainDrivetrain | $270 | |
| SBS Dual Sinter race pads (per caliper)Brakes | $180 | |
| Pirelli Diablo Superbike slick setTires & Wheels | $500 |
Some links may earn Unstocked a commission at no cost to you. Prices shown are typical street prices — always verify fitment and price at the retailer. Model-specific parts (exhausts, rearsets, bodywork) can run 2–3× between bikes — the sheet shows a typical figure.
Ride your version
Open this parts list in the build composer, swap what you’d change, and share your own link.