Has anybody added a knock sensor to a NA engine? I have a S4, and the mounting location on the center iron is not drilled or tapped, and I don't think I can get to it with a drill without engine disassembly. Reason I want to add one is I am running a standalone with knock sensor capability, and I plan to add a turbo engine in the near future, so having the knock sensor incorporated into the wiring harness would be a bonus.

 

Knock sensors go into the rotor housings above the trailing plugs on s5 engines, not the center iron

If you plan on rebuilding it, get some s5 housings and save yourself alot of hassle

 

Ok...but what about S4 engines, where the knock sensor is located on the center iron. My NA has the casting for it, but the hole was not drilled or tapped, and it is too close to drill on an assembled engine. I have a S4/5 hybrid turbo engine to eventually go in, that has the center iron S4 knock sensor location and the rotor housing S5 locations. I am re-doing my wiring harness for my standalone and figured I may as well add a knock sensor to my N/A engine, but not sure where I can put it.

 

I don't believe any s4 engine came with knock sensors, out of the US though I'm not sure. On the middle iron wouldn't make sense, knock sensors are supposed to notice knock and pinging, neither of which would be very effective on the center iron, especially since it would be getting it from both rotors, not just one. Sure your not just seeing a random unthreaded hole?

 

Mazda put the knock sensor in the center iron in 86-88, and then moved it to the rotor housing 89+

 

Center makes sense, since the ringing would transmit through the dowel pin area.

IMO I wouldn't bother with a knock sensor, on an N/A you lose power from too much timing before you get into knock, and with a turbo, the combustion chamber shapes are a known quantity and good/safe timing has been worked out a long time ago so there is no need to try to find it yourself.

 

to a point. i think the trouble, which we don't see as much as we used too, is that nobody checks to see if the established timing is indeed safe. the other thing is that the WOT numbers are more established than say the area around 0 psi, the turbo people seem to run much more timing here than we would ever run in an NA.

 

0psi manifold pressure in a turbo engine is less chamber filling than 0psi in a N/A engine, though. So of course they're going to tune them to have more timing and leaner mixtures.

 

Its always nice to have a safeguard though, since it requires little effort to install. I think the purpose of a knock sensor is to protect from getting a bad batch of fuel or something unseen. It is more of a protection from that.

 

I think I will add the knock sensor to this hole on the front iron. You can see in the background the casting where the S4 knock is supposed to go on the center iron. Like said above, it wont be doing anything on the N/A, but I can get it setup in the tuning software, and see what it sounds like on the headphone jack.

 

with the NA you'll find it can knock in the 1500-2500rpm range, depending on mixture and timing. the Rx8's knock in this range, and the big difference is that they run more timing, and have knock control, vs the FC which is tuned not to knock even on crap gas