Mercruiser Knock Sensors Thunderbolt 5?

[tank1949]

I may be going to south Florida to examine an older Sea Ray that has been retro-ed with 383 stokers converted from 350 blocks. I believe that he stated that heads are traditional Wedged shaped burn chambers. I was concerned if it would burn 87 octane gas, since that is the cheapest gas. He is not sure of the compression ratio. I believe that 9.5 to 1 is about the highest you can have and still burn 87 octane gas, but I may be incorrect. Owner indicated that he fuels with marina gas, which is usually mid-range octane. He also stated that motors have knock sensors. Do these sensors reduce timing advance if detonation is sensed???? Or, should I reduce initial timing setting if I hear "pinging" while boat is under load?

 

[alldodge]

Knock sensors if working correctly will retard timing IF a knock is picked up by the sensor. There will be no alarm, you will just loose some power from it not being able to get full advance.

With 9.5:1 compression I would run an minimum or 89. A lot has to do with how the motor was built and did they do the heads right