S&S introduces four new forged pistons, two for 74" engine and two for 80" engines. Both 74" and 80" pistons are available in 8:1 and 9:1 compression ratios.
The modern alloys used in these pistons, coupled with the advanced skirt profiles, result in low engine noise and long engine life – in the past, this could only be achieved with cast pistons. The 80" pistons may be used together with 41/4" flywheels to build mild stroker engines for 1936-’78 big twins. However these pistons are only available in 3 1/2" bore, so 74" cylinders will need to be bored to 80" standard bore of 3 1/2".
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 80" PISTONS |
| Size |
8:1 compression |
9:1 compression |
| Standard (3 1⁄2") |
106-5511 |
106-5519 |
| +.010" |
106-5512 |
106-5520 |
| +.020" |
106-5513 |
106-5521 |
| +.030" |
106-5514 |
106-5522 |
Notes: Since many older motorcycles have been modified, be sure to confirm that your engine is still stock before ordering replacement pistons.
Using 80” pistons with 74” (3 31/32” stroke) flywheels will result in very low compression and poor performance. Using 74” pistons with 80” (4 1/4” stroke) flywheels will result in contact
between piston and cylinder head, and potential engine damage.
