Knock sensor accuracy

[9c1vs]

I'm just wondering about how accurate the knock counts are for a mild 355? I have an NVRAM chip with a hsv knock board and knock sensor.

I have been told they are not necessarily reliable for a modified engine. My engine only has a small cam (Crane 276) but it is high in compression and knock limited to around 21 degrees total ignition advance, so it does ping earlier than usual.

But I have noticed I am getting a lot of knock counts even when I wouldnt expect it. I dropped the retard value to zero degrees and have noticed it is recording knock when I cant hear it by ear. I realise that the microphone picks up knock earlier than by ear, but just wondering what everyones experience is and how much I should be relying in the knock counts vs by ear?

[vlad01]

In my experience, they are completely unreliable for anything other than a stock new engine and even then are hit and miss.

For any sort of decent tuning you must disable it and use proper knock ears. aka knock detection/ audio processing with headphones to make sure you tune to a safe limit if there happens to be any.

[MAGP]

They are ok for what they were designed for but I have to aggree with Vlad and say you shouldn't tune without some sort of knock detection equipment. Knock can damage an engine if it goes undetected and while you are not hearing it it is either not happening or it is happening and you are not hearing it.

[9c1vs]

Thanks for the feedback. Unfortunately without putting in a larger cam or forking out for octane booster everytime I fill up, I am just going to have to put up with the engine being suseptable to knock.

I have done a couple of things to help prevent it from happening: the tune runs pretty rich in transient throttle which is where it seems to happen. I have been using the monitors to ensure my wideband reads the same or richer than my target. I run a fair bit of AE which seems to help. I have also got a set of bosch spark plugs a heat range colder than the factory ngk ones. I also have the coolant and air temp ignition offsets active, pulling a couple of degrees out each underload when the temp reaches 92 degrees and air temp is at 104 degrees.

I might turn the ignition retard back on but limit it to only pulling out a total of 2 degrees just to be on the safe side.

[Dylan]

On those spark plugs. Just double check the heat range. As a Bosch seven is equivalent to a NGK 6. They aren't equivalent across the brand's. They used to have a chart on the NGK website.

[9c1vs]

Yeah I used a chart, I have had them for a while but I remeber the numbers go in reverse for each brand as well just to make things more confusing! I got the bosch ones as ngk didnt make a cooler resistors type plug for efi. I have also used iridium plugs in the past which seemed to do a good job too.