Hi there,

we are debating in our french forum about:

1 • the fact KS -beside its basic function- can move the timing to get benefit of higher octane level, meaning it tries to push ingnition until it starts to knock...

2 • using higher octane level can and will loose power as the combustion speed get slower and torque is no more applied on main shaft at the right time... (beside the fact the fuel can be cleaner, with additives etc... and no pinging of course)

For me answers are 1• No and 2• Yes... Am I wrong?

Matthieu

 

uhm, what's "KS" ?

 

Knock Sensor.

I don't think it does a whole lot, practically speaking.

Early on in the FD world J&S made a more sensitive knock sensor, theory being that you might actually catch knock earlier and help prevent engine damage. I don't think it made much difference, which is why you don't hear about that mod anymore.

 

1. Correct, There is no active tuning based on feedback from the knock sensor in the FD.

2. Correct, particularly with N/A rotaries. The long shape of the combustion chamber appreciates the more volatile fuel. You will make more power by using the lowest octane gasoline that you need to suppress knock.

 

chuck from the pfc tuning notes really stresses PFC users to monitor knock. I don't think it's much of a tuning issue but more of a catch things early before they get worse issue.

 

So on the PFC, and it's been a 1.5 years since my FD ran so I can't remember for sure, but isnt the knock sensor read out on the commander done with a horizontal slide bar that fills in as it starts detecting knock? I remember mine hitting 3/4 full bar at times if I am remember everything correctly.

 

According to the Mazda documentation I've seen (Service Highlights manual), the stock ECU will retard timing if it detects knock. Unlike most modern ECU's, I don't think the 93-95 RX-7 will attempt to advance timing until knock is detected.

I wonder if the RX-8 does this or not, since rotaries don't tolerate detonation as well as piston engines.

 

Yes, you are correct.

I have stopped paying attention to mine, I think the sensor is hosed, because the bar is always all over the place, regardless of what the engine is doing and there was really no logic to it at all. I'm still holding compression between 8.6 and 9.0 on all faces, so thinking everything is working properly...

 

I don't think the slide bar on the PFC is useful at all, I usually just keep it in peak display mode and reset after each wot run after glancing at temps and knock level.

 

thats correct. it only pulls 5 degrees of timing total, and its only below a certain rpm (4000ish?)

so its not like a eurocar, where it advances until it finds knock and backs off