The 254R Rotating Assembly is made for the Tillotson R-Series Blocks bored to 76mm.
The 254cc kit is made of a 76mm hypereutectic piston(same material as the 72mm Tillotson Racing Piston), EC's Pinnacle Forged Connecting Rod, and 58mm Wildcat Ductile Iron Crankshaft.
In the world of automotive and motorcycle engine engineering, 250cc is a common denominator for performance engines. The bore and stroke are very common among a single cylinder, 2-cylinder, three-cylinder, and 4-cycle motorcycles. The increased bore sizes don't just add more displacement but increase compression and vacuum, allowing larger valves, ports, and camshafts with less adverse side effects, I.e., low-speed torque and responsiveness.
Whether in karting, motorcycle, or automotive performance, making 1hp per cubic inch is a respectable engine, 1.5hp per ci is often expert level, and 2hp ci is exceptional by the few elite builders. All dynos are different and may reflect higher power per ci; however, you can divide your current power level by your displacement and then multiply by 15.5, which is the ci of the 254R kit for estimated theoretical power output.
For comparison, we should look at the differences in displacement among other small block engines.
212 70mm x 55mm = 211.67cc (12.92ci) difference 42.37cc(2.58ci) 20%
223/224 70mm x 58mm = 223.21cc(13.62ci) difference 30.83cc(1.88ci) 14%
225 72mm x 55mm = 223.93cc(13.67ci) difference 30.11cc(1.83ci) 14%
228 72mm x 56mm = 228cc. (13.91ci) difference 26.04cc(1.59ci) 11%
236 72mm x 58mm = 236.15cc(14.41ci) difference 17.89cc(1.09ci) 8%
254 76mm x 56mm = 254.04cc(15.5ci)
263 76mm x 58mm = 263.12cc(16.05ci) difference 9.085cc(0.55ci) +4%
The difference between the 263R and 254R is the 2mm in strokes. The shorter stroke will provide more clearance for bigger cams and give more options for cylinder heads to manage compression ratio. While you may lose 9cc or .55ci, we highly recommend the 254 for less experienced builders.s.
The 76mm piston is very lightweight, which can help with the "balance" of the rotating assembly, improved acceleration, and increased durability. The piston journal's improved strength is that it is wider than the Tillotson 72mm piston and uses a longer 13mm wrist pin.
We measure the weight of common stock pistons assemblies (piston, rings, wrist pin, and clips) and a couple of market pistons of similar sizes to see how they compare to the 76mm piston assembly. The 76mm piston assembly weighs 195g.
68mm Clone Dish Piston(Lightweight) - 207g
70mm Predator Hemi Flat Top Piston - 203g
72mm Tillotson Racing Piston - 172g
2.8335 Wiseco Single Ring Piston - 192g
2.985 Wiseco Single Ring Piston - 208g
The New 76mm piston is 8mm larger than the 68mm piston and 6mm more than the typical flat top 212/223/224 piston that comes in the 196cc clone, but the 76mm assembly weighs 10-12g less. The 2.8335 Wiseco is 4mm smaller and only weighs 3g less, and the nearly equal-sized 2.985 piston weighs 13g more.
You will also gain inc compression, which can impact what fuel you run or possibly the camshaft and cylinder head you choose.
22cc Combustion Chamber
w/.045 Head Gasket & Zero Deck - 10.33:1
w/.035 Head Gasket & Zero Deck - 10.74:1
20cc Combustion Chamber
w/.045 Head Gasket & Zero Deck - 11.06:1
w/.035 Head Gasket & Zero Deck - 11.54:1
18cc Combustion Chamber
w/.045 Head Gasket & Zero Deck - 11.91:1
w/.035 Head Gasket & Zero Deck - 12.48:1
16cc Combustion Chamber
w/.045 Head Gasket & Zero Deck - 12.92:1
w/.035 Head Gasket & Zero Deck - 13.6:1
14cc Combustion Chamber
w/.045 Head Gasket & Zero Deck - 14.25:1
w/.035 Head Gasket & Zero Deck - 15.1:1
Best of all the features is the price. Compared to all billet assemblies that cost nearly 2.5 times as much, the 254R rotating assembly is only $260, which may not be much more than a bored Tillotson Block.