The Twin Cam Big-Bore Ladder: 88, 95, 103, 107, 117
The Twin Cam was built in three factory sizes — 88, 96, and 103 — and the aftermarket has been boring and stroking it into everything from a 95 to a 124 since 1999. The ladder is well trodden. What is less well documented is what each rung is actually worth at the tire, so this page sticks to the sheets that exist, says where they sit, and is honest about the rungs that have no sheet yet.
The factory rungs: 88 and 103
Stock TC88 (2002 Electra Glide Ultra): 56.31 hp / 71.51 lb-ft. Dynojet, correction not stated. Stock 103 (2014 Softail Deluxe): 70.9 hp. Dynojet.
Fifteen horsepower between the first and last factory Twin Cam, from fifteen cubic inches and every revision Harley made in between — heads, cams, compression, and injection. The 96 sits between them; there is no published stock-96 pull in the set yet, and the simulator's 96 is interpolated from these two. The 96 vs 103 page shows the gap on the same top end.
88 to 95: the classic big bore
Boring an 88 to 95 was the first Twin Cam big bore and is still the cheapest: new cylinders and pistons, the same heads and crank. It is a displacement gain of about eight percent, and it is usually done with a cam and compression at the same time, which is why "a 95 makes 90 horsepower" is both true and misleading — the cam and the compression are most of that. The 95-inch page models the bore alone against the bore with a cam, and the honest answer is that on a stock-cam, stock-compression 88, the bore is worth what eight percent is worth. No published pull for a 95 is in the set yet.
103 to 107 and 110: bore on a late engine
The 103's cylinders bore to 107 (and to 110 on the 4.000" kits), keeping the stock heads and crank. Same math: a few percent of displacement, most of the real gain coming from the cam, springs, and compression that go in at the same time. The 103 vs 107 page is that comparison, and it comes out the way the M8 and the small blocks do — cam first, bore second, because a bolt-in cam on a stock 103 is worth more than a bore job on the stock cam.
117: the Stage IV anchor
2017 Dyna Low Rider S, Screamin' Eagle Stage IV 117 kit — CNC heads, cam, pistons, intake — SE Race Tuner, aftermarket 2-into-1. Dynojet 250i, SAE, January 2019. 111.28 hp @ 5,490 / 117.93 lb-ft @ 4,180. (Laidlaw's Harley-Davidson.)
This is the one big-bore number in the set with the sheet on screen, and it is the top of Harley's own catalog: a heads-and-pistons kit, not a cylinder swap. Read it against the Stage 2 103 at 78.29 / 100.67 (also SAE) and the whole ladder is in view — thirty-three horsepower and seventeen lb-ft from Stage 2 to Stage IV, bought with heads, pistons, compression, a bigger cam, and fourteen cubic inches. The 117 page runs the combination; the simulator's 117 lands within about two horsepower of the sheet.
Two cautions. The sheet is SAE, so a STD reading of the same bike would be a few percent higher. And the site's compression pop-up on big-bore combinations has a known cosmetic bug — it can show a ratio the piston and chamber math do not support. It does not touch the power number, and it is on the fix list.
When the bore is the right move
- Stage 1 first — pipe, air cleaner, tuner. Every rung above assumes it.
- A bolt-in cam second. On a 96 or 103 this is worth more than a bore job on the stock cam, and it goes in without pulling the heads. The Stage 1 and Stage 2 guide has the sheet.
- The bore third, and do it with the cam and compression chosen for the new inches. A 107 on a 103's bolt-in cam is a mild gain; a 107 with a spring-change cam and 10.5:1 is the 100-horsepower engine. The cam guide covers the cam side.
- Heads last, which is what a Stage IV is. That is where the 111 comes from, and it costs what a top end costs.
Build your bike in the calculator, add the cam before the cylinders, then reverse the order. The sheets say the same thing the calculator does.
Run your combination in the simulatorSources: Cycle Solutions — 2002 FLH Ultra TC88 stock (hiXksPbD_MY, Dynojet, correction not stated). Cycle World — 2014 Softail Deluxe 103 stock (Dynojet). Kane's Harley-Davidson — 103 Stage 2 (Tf8IG7IUbTE, Dynojet, SAE). Laidlaw's Harley-Davidson — 117 SE Stage IV (xDBV0QvQ5Ys, Dynojet 250i, SAE). No published pull is yet in the set for a stock 96, a 95, a 107, or a 110; those pages are estimates and say so.