Milwaukee-Eight 117 Classic vs Custom vs High Output: What Changes
Every 2026 Harley-Davidson cruiser has the same engine on paper: the Milwaukee-Eight 117, a 1,923 cc 45-degree V-twin with a 103.5 mm (4.075 in) bore, a 114.3 mm (4.5 in) stroke and a 10.3:1 compression ratio. Yet the spec sheets list three versions, Classic, Custom and High Output, with claimed outputs from 98 to 114 hp. This guide sets out what is the same, what Harley-Davidson says is different, and what the published numbers tell a mechanic once you put them through the engineering formulas.
Quick answer
- Same bore, stroke, displacement and compression in all three versions.
- 117 Classic (Deadwood, Super Glide, Heritage Classic, Street Bob): 98 hp at 4,600 rpm, 120 lb-ft at 2,500 rpm.
- 117 Custom (Breakout, Fat Boy): 103 hp at 4,800 rpm, 126 lb-ft at 3,000 rpm.
- 117 High Output (Low Rider S, Low Rider ST): 114 hp at 5,000 rpm, 128 lb-ft at 4,000 rpm.
- The difference is breathing, not size. Harley-Davidson describes different intake and exhaust hardware; peak torque barely changes, but where it arrives moves up by 1,500 rpm.
What all three share
The Milwaukee-Eight is a pushrod V-twin with a single camshaft in the crankcase, four valves per cylinder and hydraulic, self-adjusting lifters. The 117 version used in the 2026 cruisers has these figures in common, whichever badge is on the air cleaner:
| Figure | Metric | Imperial |
|---|---|---|
| Displacement | 1,923 cc | 117 cu in |
| Bore | 103.5 mm | 4.075 in |
| Stroke | 114.3 mm | 4.5 in |
| Compression ratio | 10.3:1 | |
| Swept volume per cylinder | 961.6 cc | 58.7 cu in |
| Clearance volume per cylinder (from 10.3:1) | 103.4 cc | 6.31 cu in |
The last two rows are worked out, not published: swept volume is π/4 × bore² × stroke, and clearance volume is swept volume divided by (compression ratio − 1). You can check them in the engine displacement calculator, which opens with these numbers. Some aggregator sites list 1,917 cc; 103.5 × 114.3 mm works out to 1,923 cc, which is the figure Harley-Davidson uses.
The three versions side by side
| 117 Classic | 117 Custom | 117 High Output | |
|---|---|---|---|
| 2026 models | Deadwood, Super Glide, Heritage Classic, Street Bob | Breakout, Fat Boy | Low Rider S, Low Rider ST |
| Claimed power (US) | 98 hp (73 kW) at 4,600 rpm | 103 hp (77 kW) at 4,800 rpm | 114 hp (85 kW) at 5,000 rpm |
| Claimed torque (US) | 120 lb-ft (163 N·m) at 2,500 rpm | 126 lb-ft (171 N·m) at 3,000 rpm | 128 lb-ft (174 N·m) at 4,000 rpm |
| BMEP at peak torque (worked out) | 10.6 bar (154 psi) | 11.2 bar (162 psi) | 11.3 bar (165 psi) |
| Torque at peak-power rpm (worked out) | 112 lb-ft | 113 lb-ft | 120 lb-ft |
| Mean piston speed at peak power (worked out) | 17.5 m/s (3,450 ft/min) | 18.3 m/s (3,600 ft/min) | 19.1 m/s (3,750 ft/min) |
Harley-Davidson’s 2025 cruiser announcement, when the 117 in three tunes arrived across the range, says the Custom version uses a Touring-style intake airbox with 50 percent more volume than the Ventilator and Heavy Breather intakes, and describes a new aluminium intake manifold and a redesigned intake and muffler for the High Output. Camshaft specifications for each version were not published in the sources we found, so we do not guess at them. The same announcement gives 104 hp for the Custom; 2026 spec sheets list 103 hp.
What the numbers say
Peak torque hardly changes; where it arrives does
From Classic to High Output, peak torque rises from 120 to 128 lb-ft, about 7 percent. Peak power rises from 98 to 114 hp, about 16 percent. The difference is rpm: power is torque times engine speed, so the same torque at higher rpm is more power. Put 120 lb-ft and 2,500 rpm into the power from torque calculator and you get 57 hp at that moment; the High Output’s 128 lb-ft at 4,000 rpm is 97 hp. Working back from the claimed peak power, the Classic is still making about 112 lb-ft at 4,600 rpm and the High Output about 120 lb-ft at 5,000 rpm: torque = hp × 5,252 / rpm.
In plain terms, the Classic is tuned to pull hardest just above idle, where a cruiser spends most of its time, while the High Output keeps pulling higher up the rev range. Neither is “better” without knowing how the bike will be ridden.
BMEP: how hard each cylinder works
Brake mean effective pressure is torque per unit of displacement, expressed as an average pressure on the piston. Because all three versions have the same displacement, BMEP rises in step with peak torque: 10.6, 11.2 and 11.3 bar. Those are moderate figures for a modern air- and oil-cooled engine on pump fuel. The BMEP calculator shows the working: BMEP = 4π × torque / displacement for a four-stroke.
Piston speed: the long stroke sets the ceiling
A 4.5-inch stroke means the pistons travel far on every revolution. Mean piston speed is 2 × stroke × rpm: about 17.5 m/s for the Classic at its 4,600 rpm power peak and 19.1 m/s for the High Output at 5,000 rpm. That is part of why big-twin power peaks sit around 5,000 rpm rather than at sport-bike engine speeds. The mean piston speed calculator explains the typical limits.
US and other markets list different figures
The same engine is listed with different outputs in different markets because they are measured to different standards. Harley-Davidson’s Asia-Pacific site, for example, lists 91 hp and 156 N·m for the 117 Classic, against 98 hp and 120 lb-ft (163 N·m) in the US. EU figures for the Breakout’s 117 Custom give 168 N·m against the US 126 lb-ft (171 N·m). When you compare bikes, compare figures from the same market and method. All figures on MotoWild’s Harley-Davidson pages are US figures unless stated.
For mechanics: what to check before changing anything
- Know which 117 you are working on. The model tells you: the table above lists which 2026 model has which version. Intake and exhaust parts differ between versions.
- Compression matters with any cam or kit change. A cam that closes the intake valve later lowers the dynamic compression ratio; a big bore raises the static ratio. The dynamic compression calculator opens with the 117’s figures; add the rod length and the intake closing point from the cam card.
- Emissions and tuning rules apply. Intake, exhaust and cam changes usually need a matching fuel and ignition calibration, and many are not legal for road use in some US states and other countries. Check before you fit.
FAQ
Is the Milwaukee-Eight 117 High Output a bigger engine?
No. It has the same 1,923 cc, the same 103.5 × 114.3 mm bore and stroke and the same 10.3:1 compression ratio as the Classic and Custom. Harley-Davidson attributes the extra power to intake and exhaust hardware and tuning.
Which 2026 Harley-Davidson cruisers have the 117 High Output?
The Low Rider S and the Low Rider ST.
Why is the 117 Classic rated at 98 hp in the US and 91 hp elsewhere?
Different markets measure power to different standards. Compare figures measured the same way.
What is the clearance volume of a Milwaukee-Eight 117?
Worked out from the published 10.3:1 compression ratio, about 103 cc per cylinder: 961.6 cc of swept volume divided by 9.3. Measure the heads and pistons if you need the real figure for a build.
Does the 117 Custom make more torque than the Classic?
Harley-Davidson claims 126 lb-ft at 3,000 rpm for the Custom against 120 lb-ft at 2,500 rpm for the Classic.
Sources
- Harley-Davidson Media, 2025 cruiser motorcycles (three Milwaukee-Eight 117 versions, intake hardware): h-dmediakit.com
- Total Motorcycle, Milwaukee-Eight 117 H.O. engine: totalmotorcycle.com
- Motorcycle.com, 2026 Breakout specs (bore, stroke, compression, US and EU torque): motorcycle.com
- Motorcycle.com, 2026 Heritage Classic specs (117 Classic, regional figures): motorcycle.com
- Total Motorcycle, 2026 Low Rider S (117 High Output figures): totalmotorcycle.com
- Wikipedia, Harley-Davidson Milwaukee-Eight engine (layout): wikipedia.org
- Heywood, J. B., Internal Combustion Engine Fundamentals (BMEP, piston speed).
