Blayton

Ok, so I rebuilt my engine in December 2017 due to a bent rod. I noticed a slight knocking/ticking noise when it first started, but everyone said not to worry about it because it was probably lifters/valvetrain. I felt like it was getting worse (maybe psychological), and couldn't take it anymore, so I disassembled the motor, thinking the machine shop clearanced something wrong and ordered the wrong bearings. Everything was still completely in spec, but I ordered some new ACL rod bearings just to be safe. These are for sure in spec, I had them check the clearances more than once. It still made the noise when I put it back in. At this point I was sure it was in the head somewhere (and still think it may).

The other day, I decided to check the timing again. Put it on fixed timing at 10 degrees, and it was spot on. I revved it up a little, and realized that the knock was basically nonexistant now. Put it back on the timing table, and it came back. This makes no sense to me because this is the same map I used on my stock higher compression motor with no issue. The car has always been filled up with 93 octane gas, so I don't think it is detonation. I honestly don't know what it could be anymore, and that's why I'm here. I've supplied a video to hear the sound, and also two datalogs of revving the motor with 10 degrees, and the timing table. You can see that the knock in is higher on the map using the timing map.

The car only seems to make the knocking noise in low load situations. For example, revving while sitting still, or cruising around 2700-4500 rpm. Seems like it's more noticeable when slowing down while still on the throttle.

Any help is appreciated. If I'm missing something stupid, feel free to call me out on it. Thanks guys

Video:
https://photos.app.goo.gl/iqoo6TgeyB8O2LtL2

Erat

iTrader: (5)

I always wondered if our engines could be affected by low speed pre ignition. I would have to imagine there would need to be a higher load for that.

Mudflap

That doesn't sound like det/knock to me. I can instantly create detonation by hitting the loud pedal while in too low a gear - so called "lugging" the engine. But you are in a zero load situation when out of gear like that. You've got something rattling around in there.

Blayton

Why would decreasing the timing stop the noise then? Not saying you're wrong, I just don't understand. Maybe more vibration?

Mudflap

Someone better at this can comment on what else it could be. But that does not sound like it. It sounds more like rattling rocks in a can - a little electric like static even.

This filtered version provides the general expected sound. But unfortunately it is filtered and doesn't really sound this clear.

This is pretty good:

Blayton

Yea, it doesn't sound like spark knock or detonation, but I just don't understand why it goes away at when at 10 degrees. I am so lost as to what this could be.

Erat

iTrader: (5)

Silly question, but what spark plugs and what gap?
A knock my car was making at one point in time:

Blayton

The ol' NGK BKR7E, can't remember gap off the top of my head. You think it's worth a shot changing the plugs? Or was your noise actually an interior rattle?

Erat

iTrader: (5)

I have no idea what that rattle came from, i searched and searched for like 2 years and never found it. One day it just went away.

Spark plugs are so cheap, it may be worth. You may have accidentally broken an electrode or bent something at some point. I'd say they're worth looking at and gapping at least. Start with the easy stuff first.

Another thing to note, my super tech 9.5:1(i think) pistons (terrible CR, should have went either more or less) slap pretty good when cold. But i see you're up to 200F, so i don't think that's it.

Blayton

Just checked the spark plugs. They all look fine to me, maybe a little on the whiter side. No broken pieces or chips. They are all gapped to .030, maybe a little more, but less than .035.

They are in order from (rear) 4 - 3 - 2 -1 (front)

Erat

iTrader: (5)

Looks hot IMO. Some other people may have some input.

Full_Tilt_Boogie

iTrader: (1)

I dont hear anything that sounds like knock, I also think its impossible or very, very unlikely to get knock when free-reving an engine.

As for why would ignition advance affect it? Well the advance affects how the engine runs, so its not surprising. If you go from 10 degrees to 20 degrees when doing your free rev test, the combustion is happening differently and it may be causing the engine to vibrate and harmonize in a different way. So with 20 degrees of advance you could have something rattling in the bay and not rattling when running 10 degrees.

Blayton

Does anyone think this is something I should fix before driving the car again? Or is it okay to drive with it?

18psi

iTrader: (76)

1st, You'll need to richen it up.
2nd, it's impossible for the car to knock on decel, since no actual combustion is happening (unless you disabled overrun fuel cut)
3rd, my guess why it gets smoother/quiets down with fixed timing is cause you're retarding it so much at 10* that you're literally finishing the combustion process in your exhaust system.

I only glanced at the screenshots/map. Oh and midway into your boosted rows, on pump gas, on 9:1 compression, that's too much timing IMO

icantlearn

Yea you are running way lean. Good plugs look kinda brown. Not black. Like a grey/brownish color.

shlammed

iTrader: (8)

have you checked your timing sync to see if the engine is seeing the timing your commanding? otherwise agree with above.

FWIW, what injectors are you running? the ID725's I had in my Miata were audible through the hood from 25 feet away...louder than my 3" exhaust when standing outside of the car. kind of the sound a Direct Injection car makes for some reason... could it be that and when your under load your exhaust just washes the noise out?

Blayton

I'm running FlowForce 650cc injectors. I highly doubt it's injector noise. If it was, you'd be able to hear it across the RPM range, and the noise is deeper and louder than the injector tick sounds I've heard. Also, my car is pretty quiet. It has the MKTurbo exhaust with the big Magnaflow muffler. As far as I can tell, it doesn't make that noise at WOT.

Blayton

I've thought about that, but my AFRs are actually on the richer side. Is it possible that my WBO2 sensor is bad? I took it out of my downpipe, and calibrated it not too long ago. I would assume if it was bad, it would give me an error instead of just richer AFR numbers.

Blayton

I gave it a more fuel in the lower rpm, low load area. And also retarded the timing where it was knocking. The noise is much quieter now, but I think that is due to the timing. It is still noticeable, especially while revving at idle.

If it is the fuel, then my wideband must be messed up. Cruising on the highway with this map, my AFRs go as low as 13.5, then I believe EGO correction kicks in and brings it in to the 14s. Boosting AFRs are in the low 11s. I'll pull a spark plug an check again to see if they are any darker looking now.

icantlearn