This new forged 3 5/8" bore stroker piston replaces several cast and forged big bore pistons that S&S previously offered. Applications for this piston include 88" (4 1/4" stroke), 93" (4 1/2" stroke), and 96" (4 5/8" stroke) engines with stock 8 1/2" diameter flywheels, and 98" (43/4" stroke) and 103" (5" stroke) engines with 8 1/4" small diameter flywheels. As with the new stock bore stroker piston, the modern metallurgy and advanced skirt profiles allow a relatively close piston fit for low engine noise and long engine life.
S&S will fit these pistons to your existing cylinders (when purchasing new cylinders, pistons can be fit to them as an option).
| S&S® Forged 3 5/8" Bore Piston Sets For 1936-’84 OHV Big Twins |
| Size |
Part Number |
| Standard (35⁄8") |
106-5535 |
| +.010" |
106-5536 |
| +.020" |
106-5537 |
| +.030" |
106-5538 |
| +.060" |
106-5789 |
| Recommended Piston Fit: Close: .003" - .0035" Loose: .004" - .005" |
| Flathead Power® 3 5/8" Bore Forged Piston Application Chart |
| Displacement |
Stroke
|
Flywheel Diameter
|
Compression Ratio |
Cylinder Length |
| SH-Series & P-Series Engines |
KN-Series Engines |
| 88" |
4 1/4" |
8 1⁄2" |
8.5:1 |
5.330" |
– |
| 93" |
4 1⁄2" |
8 1⁄2" |
8.5:1 |
5.405" |
5.625" |
| 93" HC |
4 1⁄2" |
8 1⁄2" |
9.1:1 |
5.363" |
– |
| 96" |
4 5⁄8" |
8 1⁄2" |
9.1:1 |
5.440" |
– |
| 98" |
4 3/4" |
8 1/4" |
8.9:1 |
5.530" |
– |
| 103" |
5” |
8 1/4" |
9.7:1 |
5.630" |
– |
| Note – piston deck height 1.260” |
NOTE: Compression ratios will change when replacing existing pistons in S&S engines with this series of forged pistons. If higher compression is desired, we suggest shortening cylinders, or decking heads to achieve the desired compression ratio. A change of .060” will produce approximately 1 point of change in the compression ratio.
