Megasquirt knock sensors settings

[Map63Vette]

As the title suggests, anyone out there running a Megasquirt setup with the internal knock module? Finally found someone making a drop in replacement since DIYAutotune has been out of stock on them for the past 2+ years and took the chance on them. Will be a while before they show up, but I've at least got my sensors prewired and ready to go, just need to update the settings to use them. I know you can set thresholds and stuff like that in the tune and was curious what others might be running. Engine is a 2006 5.7 with a cam, otherwise basically stock. Hoping to maybe push my tuning skills a little further with the safety blanket of the knock sensors, but don't want to go crazy as I know the pistons don't take it very well at all. Just feels like I might be leaving a lot on the table based on what I'm seeing on old 5.7 dyno videos I've been watching.

 

[67Dart273]

Sorry. All I can say is that there is a lot of info at DIY and Megasquirt but some of that is REALLY buried. Just be really careful on hemi advance numbers.

 

[DNasty777]

The 5.7 hemi has a bore size of 94.49mm, so the knock frequency should be around 6-6.1kHz. As far as sensitivity, that's something you'll have to find out on your own. If the sensitivity is too high, you'll have false positives. Too low and you'll have knock and no retard. If you find you're picking up too much non-knock noise in the frequency range of an actual knock you can instead use second or third order harmonics (2nd=12-12.2kHz, 3rd=18-18.3kHz) to kinda isolate the knock, but you'll need to tune the sensitivity again for that.

 

[Map63Vette]

Sorry. All I can say is that there is a lot of info at DIY and Megasquirt but some of that is REALLY buried. Just be really careful on hemi advance numbers.

Yeah, I started doing a little bit of digging and reading and watching videos yesterday, though there is plenty more to do. I have my WOT timing set reasonably conservative still at only 20 degrees at the very top end and 21 a bit before that. It certainly feels spunky enough, but after watching some old dyno videos and car show episodes dealing with the old 5.7s I'm thinking there might be quite a lot still in there. A bone stock engine out of a truck put down nearly 400 hp on one dyno, albeit with headers and no accessories running (electric water pump and no alternator). I wouldn't have thought manifolds and accessories would be worth 50 hp though, so kinda unsure on that one. It did have a FAST TBI system and an MSD ignition running the show, but I was never very impressed with the MSD setup back when I was running it. The way you tuned it with curves instead of a table seemed odd and less capable to me. It was basically like an old distributor in a way with a mechanical (RPM based) advance curve and a vacuum advance curve. Found someone else that managed nearly 400 whp with a cam and headers, which is basically what I'm running. The only time I ever had the car on a dyno though it only made around 270 whp, so ~300 crank maybe. I was running an MS2 setup for the fuel with the MSD for the spark at the time, but wasn't really trying to push anything as it was my first experience with tuning and it was just a dyno day thing, not a tuning session. Couldn't tell you what timing curves I might have had in it though, it was quite a while ago. Upgraded to an MS3x setup a while back so I could get all of the tuning in a single program and have started playing around with the other features like traction/launch control for fun as well. Had some issues getting the car to run on the highway with the original tables I put in it though. I made them based off of a computer dump someone did, but there is way more to the factory computer it seems as my car was just not happy with them. It would shake horribly in 6th gear and could barely maintain 70 mph. Ended up having to add quite a bit of timing to make it happy at cruise. I really like how it runs now as far as being smooth, but would still like to see if I can optimize with the knock sensors to get a little more performance and possibly economy as well.

The 5.7 hemi has a bore size of 94.49mm, so the knock frequency should be around 6-6.1kHz. As far as sensitivity, that's something you'll have to find out on your own. If the sensitivity is too high, you'll have false positives. Too low and you'll have knock and no retard. If you find you're picking up too much non-knock noise in the frequency range of an actual knock you can instead use second or third order harmonics (2nd=12-12.2kHz, 3rd=18-18.3kHz) to kinda isolate the knock, but you'll need to tune the sensitivity again for that.

That's what I gathered from the videos and reading I've done so far. Was hoping someone might have some values for the stock sensors I could use as a starting point, but even then I knew I'd have to take anything with a grain of salt and likely tweak and tune in the long run. I'm actually not even sure my stock sensors still work, they were just there when I bought the engine and I've left them installed, but never had anything to hook them up to until now. Looking forward to playing with them though once the module shows up. I think I hooked them up to my little pocket oscilloscope when I first did the wiring and thought I recall seeing some kind of signal out of them, but it's been long enough ago I really can't remember what if anything I saw.

 

[Map63Vette]

Well, against all odds this seem to be one of the few times things just sort of "worked" for me. I was all ready to do a bunch of logging and testing and whatnot to try to figure things out and I pretty much just plugged everything in and it seems like it was good with the nearly default settings. All of my gains are still at 1, though I might still see about tweaking those a little in the future. I can't think of an easy way to test per cylinder knock with the windowing setup the system uses. The "redneck" way would be to tap the side of each cylinder with a hammer and check the readouts to see what you get, but you would have to tap in the same relative location with the same force each time, and I'm not even sure if it would register since you set up a bandpass frequency filter. Anywho, set the timing retard on knock to 0 and the threshold all the way to 100% and drove around while logging to get some data to look at. To my surprise, with the default gain value of 1 for each cylinder everything was still nicely in range on the log. Mostly runs between 5-15% while cruising and maybe around 40% on a hard throttle hit and higher rpm. Saw what I think were two lean knock events, one right after I left off the throttle near redline and another when I went full throttle in 6th gear at maybe 1200 rpm or so. Seemed to show a noticeable spike above 60%, so that's where I set my thresholds for now.

Curious to see what I can do with it now that I've got them. I might try adding a degree or two of timing on the top end and doing some pulls to see if the logs look any different. I'm not necessarily looking to run on the ragged edge and I'm just running regular 87 octane fuel anyway, but might be fun to build a premium tune I could swap to for the novelty of it. I know the ring lands are pretty fragile though, so trying not to get carried away.