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04 Subaru STI EJ257 short block

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Hi all,

Anybody know where the best place is to put a second knock sensor on an EJ257 shortblock.

I have a Link Knock block with two sensors; I can replace the first one at the OEM location but I want to find an optimal place to put the second one.

Any tips would be greatly appriciated.


I just stack them on the stock location. I have run two sensors stacked on top of each other into the same ECU, and the signals generated from both will overlay with each other.

Honestly, what a good idea!

I've never thought of that before. Thank you Stephen!

If the goal is to add a secondary monitor in addition to the stock sensor, and retain the stock sensor for the ECU, but be able to monitor the second sensor via knockblock, stacking as Stephen suggested sounds good to me.

Unless I'm misunderstanding though, I was under the impression you're wanting to place one sensor per bank and monitor 2 sensors, both with the knockblock, perhaps in hopes of getting a closer look at bank 1?

Hi Mike,

From experience having both of the knock sensors in the same location, or having them in different locations only changes the amount of gain needed, it doesn't change the signal received. Its more how well the device monitoring the knock sensors gates the signal that determines the effectiveness of the sensors. I have run an EJ20 with 4 knock sensors active, as well as having two of the them stacked, and once the gains are trimmed correctly, you couldn't tell the difference.

Not having the signals gated is why I do not trust devices like the Link Knock lite or similar, especially the ones that have no setup required. All they are doing is saying that there was some noise that triggered an internal threshold, which may or may not have been a knock event.

Especially on a Subaru boxer 4 I absolutely agree. The knock sensor is already relatively centrally located, not far from any cylinder, so having 2 in separate locations doesn't seem helpful.

I'm still trying to understand what JP's goal was in wanting to use 2 new sensors and removing the stock one vs. only using a single sensor in the original location.

If tuning with a stock ECU and wanting to add a second sensor for the aux system, then stacking an aftermarket unit on top of the stock one sounds the right move. JP can you fill us in? What was your thought process and what are you trying to accomplish?

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