Knock monitoring on turbocharged oil boiler

[rider384]

Hi all, wondering how people are monitoring for knock on their oil boilers. I was running 13 pounds on the stock engine and just checking the plugs for signs of detonation, but now that I've tossed an intercooler in and built the engine I'm both ready to start pushing the system and feeling a bit more protective of the engine now that I've spent so much time on it. 

How are people here generally setting/monitoring for knock? Acoustically or digitally? In either case, how are you doing it? Where is the sensor mounted? How are you isolating the knock signal from the inherent NVH of the engine?

Sorry if these are super basic questions, I've done quite a bit of tuning before but I've never set up a knock monitoring system from scratch. Any advice is appreciated. 

[Gixer1460]

They aren't basic questions - they are pretty deep and generally unexplored as most people don't monitor knock, as to get right is quite difficult. You need to find a substantially thick part in the block to mount sensor then determine what you are hearing is knock or general noise. Mounts in the head are too noisy to be useful. Then you have to have a method of acting on it - with autos, the OEM's write the profiles for adjustment into software,we generally can't.

[Arttu]

Like said above not very basic questions...

I'm having a knock sensor on my own bike connected to the ECU with all appropriate bells and whistles like signal band pass filtering and timing windowing. And for dyno tuning all random bikes I have an earphone setup with mic on alligator clip that can be clamped on some part of the engine. By this far I haven't detected knock any single time by either of these. On the other hand I haven't had any clear knock case which I had missed when using these tools. That's mainly because I always try to avoid knock as well as I can...

With the sensor I can see that signal from the sensor gets higher when I push more boost in but still I have no idea how much higher it would read in case of knock. So I can't really do any knock control by that. I guess one main problem is my sensor placement which is probably almost worst possible, at cam chain tensioner on air cooled cylinder block. Since the sensor has been kind of secondary addition in my setup I haven't bothered to make a proper mounting point for it. But I guess even with better sensor placement it wouldn't be too straightforward to interpret the readings.

Earphone setup works usually quite well from low to mid rpm. You can hear pretty clearly what is going on in the engine, valvetrain and all. So I think knock would be quite clearly noticeable. But at high rpm and full power it gets more fuzzy. Mechanical noise through the earphones gets so high that it's difficult to detect anything in the middle of that. And ambient noise from the dyno room doesn't make it any easier. So I'm not too confident that I could really spot knocking at full power...

[rider384]

Thanks for the replies guys! Given the difficulty in getting a knock system set up on an oil cooled motor, what's the standard MO on tuning high load/high RPM situations? Just checking the plugs for signs of detonation after a while or are these engines generally not knock-limited in terms of spark advance?

[Arttu]

Well, I think there are few different typical methods for ignition timing:

• Just use something that you have heard elsewhere or what you have used earlier. Hope for the best. Turn it down a bit if the engine melts.
• As above but try reading plugs and listening the engine before meltdown.
• Use dyno to find optimal power timing. If there seems to be wider window without significant change in power use lower end of the window. Otherwise as above.

Being knock limited can vary a lot depending on compression, boost, fuel and other variables. But based on my experience turbo bikes are surprisingly rarely knock limited if they have been built even somewhat sensibly and if you don't push the boost too far. So if possible I try to stay at "comfort zone" and then just use dyno to find optimal timing.