DISPLACEMENT OF EVOLUTION ENGINES:
STROKE |
BORE |
3.498 | 3.625 | 3.780 |
| Stock 80” | S & S | Sputhe | ||
| 3.812 | Sportster | 73.268 | 78.685 | 85.557 |
| 4.250 | Stock 80” | 81.686 | 87.725 | 95.388 |
| 4.625 | 88.894 | 95.466 | 103.805 |
CALCULATING THE DISPLACEMENT OF A TWO CYLINDER ENGINE:
Displacement can be determined by the formula: D = B X B X S X 1.5708
| Where: | D = Displacement |
| B = Bore | |
| S = Stroke |
CALCULATING COMPRESSION RATIO:
Compression ratio can be determined by the formula:
| C = D + Vd + Vs + Vc |
| Vd + Vs + Vc |
| Where: | C = Compression ratio |
| D = Displacement of one cylinder | |
| Vd = Volume of dish (+) or dome (-) on piston | |
| Vs = Volume of squish clearance | |
| Vc = Volume of combustion chamber |
To calculate the compression ratio of an engine using Sputhe cylinders the following values may be used.
| D = 782cc for the 95.4” kit | D = 850cc for the 103.8” kit |
| Vd = 16cc for dish top pistons | Vd = 0cc for the flat top pistons |
| Vs = 11cc @ .060” clearance | |
| Vc = 78cc for pre 1990 heads | Vc = 87cc for 1990 & up heads |
Example: 1989 engine using a 95.4 ci kit with dish top pistons:
| C = | D+Vd+Vs+Vc= | 782cc+16cc+11cc+80cc= | 897cc = | 8.54 |
| Vd+Vs+Vc | 166cc+11cc+80cc | 105cc | 1 |
FORMULAS FOR CALCULATING TORQUE & HORSEPOWER:
| T = | Hp X 5252 | Hp = | T X rpm |
| Rpm | 5252 |
TABLE OF EQUIVALENTS:
| 1 inch = 25.4 mm | 1 cubic inch = 16.387cc |
| 1 mm = 0.039371 inch | 1 liter (1000cc) = 61.024 cubic inch |
MECHANICAL COMPRESSION RATIOS
OF SPUTHE BIG BORE CYLINDERS
95 cu inch – Compression Ratios
| CHAMBER | FLAT TOP PISTONS | DISH TOP PISTONS |
| 90cc | 8.7:1 | 7.7:1 |
| 86cc | 9.0:1 | 7.9:1 |
| 80cc | 9.6:1 | 8.3:1 |
| 76cc | 10.0:1 | 8.6:1 |
| 72cc | 10.4:1 | 8.9:1 |
104 cu inch – Compression Ratios
| CHAMBER | FLAT TOP PISTONS | DISH TOP PISTONS |
| 90cc | 9.4:1 | 8.3:1 |
| 86cc | 9.8:1 | 8.5:1 |
| 80cc | 10.3:1 | 8.9:1 |
| 76cc | 10.8:1 | 9.3:1 |
| 72cc | 11.3:1 | 9.6:1 |
Piston Balance Weights
| 95 cu inch – 3.780 Standard bore | Flat Top Pistons – 1057 grams |
| Dish Top Pistons – 1061 grams |
| 104 cu inch – 3.780 Standard bore | Flat Top Pistons – 1042 grams |
| Dish Top Pistons – 1039 grams |
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