I read a BUNCH of old posts about adding aftermarket knock sensors, but couldn't really find a good argument for or against their inclusion in an engine buildup. Is this a case of "by the time they detect knock your engine's already fried; tune it better next time", or do they really help protect a turbo rotary?
Thanks for the input.

 

hey im in the fresno area to.
i drive a turbo first gen and just bought a TII..

Knock sensors suck. you cuold hook one up to a monitor and you may catch it in time to not blow it up but when your driving fast you wont notice it anyways untill something feels wrong normally.

 

So woud one be useful during the tuning stages?

 

Knock sensor tries to separate detonation caused by spark, from pre / post detonation cause by something else. And it's not a matter of when you hear it it's too late... since your hearing isn't precise enough to hear the beginnings of detonation.
The knock sensor is nothing more than a tuned Mic. and it listens for sounds that are not part of combustion. And you as the tuner need to set a threshold. Once the threshold is set, anything that makes more noise, will cause spark / and or fuel cut to prevent the detonation to continue so that you would be able to hear it and the motor would blow a seal.

Someone telling you they're crap either doesn't know how to use them, or set the threshold way to high. so that detonation happened before the KS was able to intervene.

 

the only problem is on a rotary engine specially a high power one there is so much noise the knock sensors often read incorrectly.

many cars have this problem

a pebble hitting the engine can set off a knock sensors.

most tuners use a wideband and or egt to tune cars and monitor whats going on.