Hi Boucher . . .
Technically speaking the SST-802 is too fast/high-freq for a 6 cylinder application. But that is not to say it is entirely unusable.
Transistorized tachometers are not very complicated gizmos in principle – essentially they ‘count’ ignition pulses – and display that count on a ‘scaled’ sweep-face. The SST-802 sweeps 0 – 8000 RPM assuming 8 cylinders.
Think about a 4-cycle engine in operation. With 8 cylinders a 4-cycle engine will produce 8000 TDC events at 1000 RPM – 4000 of those will be spark events. This is what a transistorized tach is counting. So your SST-802 Tach head will display 1000 RPM when it detects 4000 sparks per minute and will sweep to the max at 32000 sparks.
But a 6 cylinder engine has two less plugs. So 1000 RRM is just 3000 spark events. If you attach that SST-802 to your 250 it will read 750 RPM when you are actually turning 1000. You could get a new decal for the sweep face that reads 0 – 10000 and the tach would read essentially true . . . but half the dial would go unused on a 250 – and it would be hard to read the difference between 1200 and 1500 on the face.
A 6 cylinder tach head is designed and scaled for lower frequency of spark events – typically sweeping 0 – 5000 or 6000 RPM - from 15 to 18000 spark events.
Regards,
stock49
