Welp

"Smallbear wants a modern Syclone, local Maple Leafs spammer" (smallbear94) 07/05/2016 at 14:00 • Filed to: None

1

29

...it’s a start I guess. This is what I was doing yesterday. Bear in mind this is power at the wheels, not the crank; and it’s virtual dyno, not a real one, so the results aren’t totally reliable. For example, the green run was the last and iirc I feathered the throttle slightly and then got back on somewhere between 5000-5500rpm. Foot jumping ahead of my brain as we were catching up to a truck. Still good for a before and after picture though.

Red is stock, Green is tuned.

I would be happy for some input from Oppo’s mechanical/tuning types though. The guy that did the tuning said he couldn’t understand what the issue was, but there definitely was one. He tuned a truck almost the same as mine on 87 octane, and had the same issues. Knocking all over the place on stock tuning, and a persistent knock at 4300rpm. He started with that as a base tune for me, and even though I ran 89 octane based on his information on the other truck he had on his website, the 4300rpm knock stayed. Everywhere else it took more spark advance, but we ran into knock retard at 4300 every time. As a result, the peaks are pretty much identical to the other truck, but lower down in the rpm range.

Any ideas what could be strangling this thing? The only thing he could think of was the exhaust, on the full size trucks it’s 3" all the way back, in mine it’s 2 3/4" dropping to 2 1/2" after the muffler. The intake side looks OK.

If that’s really all it has to give, well OK. But based on the results he’s gotten with full-size truck 5.3's, I don’t think so. There’s something there that’s killing the potential, and that’s what bugs me.

Anyway, the main thing is it shifts better and actually downshifts and digs in when I want it to instead of torque management coming down with a banhammer and taking 40% of my power.

crowmolly > Smallbear wants a modern Syclone, local Maple Leafs spammer 07/05/2016 at 11:44

1

If you fill with 93, does it go away or lessen?

Smallbear wants a modern Syclone, local Maple Leafs spammer > crowmolly 07/05/2016 at 12:16

0

Don’t know. I just topped up with 89 yesterday when I did the tune. I won’t know anyway because I don’t have the software. I’d imagine it would allow even more advance everywhere else but minimal if any advance at 4300 seeing as going 87-89 didn’t do anything.

But like I said I don’t, and won’t, have any idea. Besides I don’t want to run 91 or 93. 89's my price limit for now, and I’m only going there because it seemed to make up a good deal of the extra cost with MPG gains. What I WANT to do is find the sticking point.

Just one of those things... if that was all the power available, OK. Because I know it isn’t, it bugs me.

crowmolly > Smallbear wants a modern Syclone, local Maple Leafs spammer 07/05/2016 at 12:20

0

I’m trying to determine why you get knock at that specific RPM number and if it could be something false.

If the KR numbers change with octane EXCEPT @ 4300, or the amount of timing pulled always stays the same then I’d wonder if something else is tripping the knock sensor.

Hate to do this, but could you post your mod list?

Smallbear wants a modern Syclone, local Maple Leafs spammer > crowmolly 07/05/2016 at 12:33

0

I’m going by memory here on exact numbers, but basically what he did first was take the stock reading, which was knocking in several places, and then flashed the tune for the guy who was tuned on 87. No knock, because he’d had that tuned out completely. Then he bumped all the timing up a bit, iirc 3deg, and tried again. Net result was 3deg of knock retard. Backing it off 2deg gave 1.5deg of knock retard, and that’s where he left it to concentrate on other details. Basically he said the K/R will keep it from blowing up—he should be right since it’s been knocking much worse on stock tuning—and it’s as close to the edge as he can get it that way. Iirc the numbers he gave it were as high as 24deg under 4300 and 23deg above, but right in that pocket around 4300rpm it wouldn’t take more than 19deg.

As far as mod list goes... NP. I haven’t done much so far, the only things engine/drivetrain related have been a Corvette Servo (no impact), Borla muffler of the same size as stock (I messed up and only measured one side of the pipe, otherwise I’d have caught that the diameter dropped after the muffler. I got a little MPG boost, but nowhere near what I should have got if I stepped up to the proper size), and an AEM Dryflo air filter.

Aaron M - MasoFiST > Smallbear wants a modern Syclone, local Maple Leafs spammer 07/05/2016 at 14:17

3

This is from ZZPerformance, written with a 3800 in mind but it is pretty generic:

“Outlined below is a list of things that can cause false knock.

Sway bar hitting exhaust downpipe – This happens typically with the downpipe of headers because that configuration puts the downpipe in very close proximity to the sway bar much closer than the stock downpipe. The banging noise from the two metal objects hitting may resonate through the frequency band that the PCM detects as knock through the knock sensors. The solution to this is to flip the sway bar over. Because of the curvature of the sway bar near the downpipe, flipping it will allow the sway bar to curve AWAY from the downpipe rather than toward it.

Transmission oil stick hitting exhaust crossover pipe – This typically happens with the crossover pipe of headers due to their large size and proximity as opposed to the stock crossover. The banging noise from the two metal objects hitting may resonate through the frequency band that the PCM detects as knock through the knock sensors. The solution to this is to carefully bend the trans oil stick away from the crossover pipe so that the two do not touch.

Anything loose in the engine or outside the engine may cause noises that drift through the frequency range that the PCM detects as KR. Carefully check your engine! This is very vague and is intended to be vague because just about anything loose in or out of your engine that is making noise could cause this. This includes loose or noisy components in your transmission as well.

Loose knock sensors, or knock sensors that are too tight. Double check that your knock sensors are torqued to spec (14 lb-ft).”

If it’s knocking only at 4300rpm, and every other cell below and above that rev range can be tuned out, it’s almost certainly false knock of some sort.

Snuze: Needs another Swede > Smallbear wants a modern Syclone, local Maple Leafs spammer 07/05/2016 at 14:21

0

My dad had a somewhat similar problem like this years ago in a Caprice he used to have. He swapped motors from an anemic 305 to a modified 350 with ported heads, cam, and roller rockers. Torque was amazing but power would fall way off over a certain RPM.

Turns out it was the roller rockers. Above a certain RPM they were developing some kind of vibration or something and the computer was detecting it as knock and pulling timing. They went back to stamped rockers and and the problem went away, at the loss of a few HP.

What engine do you have? 5.3L?

jariten1781 > Smallbear wants a modern Syclone, local Maple Leafs spammer 07/05/2016 at 14:24

1

I was helping a friend chase down false knocks (we were reasonably sure) on an LS1. Replaced all sorts of stuff (don’t even remember everything we tried) but what finally cleared it was going to softer engine mounts and an exhaust that was close to stock dB (I think we left the piping larger). It took weeks of throwing parts at it to figure it out.

crowmolly > Snuze: Needs another Swede 07/05/2016 at 14:32

0

Yeah, that’s why the Gen II LT4 had a different knock module than the Gen II LT1

SidewaysOnDirt still misses Bowie > Smallbear wants a modern Syclone, local Maple Leafs spammer 07/05/2016 at 14:34

0

Is their a vacuum advance?

Snuze: Needs another Swede > crowmolly 07/05/2016 at 14:41

0

Yeah. It just seems odd that smallbear is only having this issue at a specific RPM. The issue my dad was having kind of makes sense, where it falls off after a certain RPM. But I’ve never heard of it pulling timing only at one very specific RPM and then being fine both above and below that RPM.

I was wondering if it could be a mechanical issue like a stuck lifter or something? But I would think that would tend to be more like what happened to my dad’s car where power falls off above that RPM.

Snuze: Needs another Swede > Aaron M - MasoFiST 07/05/2016 at 14:43

1

I think you’re spot on with this. If it occurs at a very specific RPM, you’re hitting something’s resonant frequency and it’s banging into something else. That’s the only way I can think of where you have it working fine both above and below the problem RPM.

Smallbear wants a modern Syclone, local Maple Leafs spammer > Aaron M - MasoFiST 07/05/2016 at 15:01

0

Sounds like it could be it. The other thing I know is, it’s something stock that causes the issue, since it happened on the other truck as well. That rules out the swaybar immediately, since it’s aftermarket, even though the exhaust dumps close to it. That also rules out the muffler even though the way the guy mounted it is (I think) less than perfect.

There is a spot where, instead of re-routing the exhaust, they squished it as it crosses the torsion bar. I wonder if the flow could be turbulent through there at 4300. I’ll have a snout ‘round.

crowmolly > Snuze: Needs another Swede 07/05/2016 at 15:01

0

It’s yanking 5* of timing at that RPM range which seems like a lot to me, although it’s been a while.

Smallbear wants a modern Syclone, local Maple Leafs spammer > jariten1781 07/05/2016 at 15:02

0

Stock dB? This looks very helpful but I don’t understand part of it...

Smallbear wants a modern Syclone, local Maple Leafs spammer > SidewaysOnDirt still misses Bowie 07/05/2016 at 15:05

0

I doubt it... I think LS engines are all electronic, no?

jariten1781 > Smallbear wants a modern Syclone, local Maple Leafs spammer 07/05/2016 at 15:09

1

Loudness. We suspected the extremely loud exhaust he had on might be contributing to false triggers. We did the mounts and exhaust on the same day without logging in between so we’re not sure which cleared it. He’d done a ton of mods prior to getting into the tuning so we were basically walking them back a few at a time until the false knocks cleared. We started with just replacing the knock sensors and harness with no joy then hit up all the other piece parts that were either stock, but old and worn, or that he’d 'upgraded' along the way.

Smallbear wants a modern Syclone, local Maple Leafs spammer > Snuze: Needs another Swede 07/05/2016 at 15:11

0

Yeah, Gen IV 5.3L, engine code LH9.

It’s stock, and since the 5.3's aren’t known for being difficult to drag power out of, I doubt it’s anything in the actual engine. That said, I don’t know exactly what GM did differently in the LH9 version besides an aluminium block. I’m leaning towards the exhaust, personally, as the guys on the forums with modded trucks don’t seem to have issues and all have aftermarket exhaust systems. That said, there’s so many things that could vibrate. Heck, it could even be the fan clutch, though I doubt it, since often the first thing people do is ditch it for an electric fan.

SidewaysOnDirt still misses Bowie > Smallbear wants a modern Syclone, local Maple Leafs spammer 07/05/2016 at 15:13

1

You’d think they’d have overhead cams by now too.... Does your LS have VVT?

Snuze: Needs another Swede > Smallbear wants a modern Syclone, local Maple Leafs spammer 07/05/2016 at 15:15

1

Hmm, I dunno what to say. It’s just strange that the advance curve is normal but it only pulls timing at that one specific RPM. It really makes me think something is rattling that’s causing a false knock to be detected. Like 4300rpm is the resonance frequency of something in that truck and that’s what it’s seeing as a knock.

Smallbear wants a modern Syclone, local Maple Leafs spammer > jariten1781 07/05/2016 at 15:15

0

Oh, decibel... *facepalm*

The thing is, I’ve only done a muffler, and it isn’t much louder than stock. The other guy’s truck did the same thing and was totally stock. Sounds like a path to chase, but I don’t expect to see the identical solution.

I wonder if I could fine the resonation frequency at 4300 rpm, and play that noise near all along the exhaust, if it would give itself away the way a guitar with some loose component does...

Smallbear wants a modern Syclone, local Maple Leafs spammer > Snuze: Needs another Swede 07/05/2016 at 15:18

0

It could be doing it further up as well, but since the knock sensor feeds the spark back in slowly it could just be running out of rev range before it gets back on it’s feet.

But looking at the dyno, I don’t think it is. There’s a dip, then it picks up again before finally petering out. More likely the “false knock” suggested by others.

Smallbear wants a modern Syclone, local Maple Leafs spammer > crowmolly 07/05/2016 at 15:20

0

It’s just pulling 1.5, but it’s already set low. Set 2 degrees higher it puller 3deg.

Smallbear wants a modern Syclone, local Maple Leafs spammer > Snuze: Needs another Swede 07/05/2016 at 15:21

0

I think you’re right, and I think everyone else does too.

I have two choices. Look for the knock, or proceed with my gradual upgrade process and hope something fixes it.

I think I’ll go with the second.

Smallbear wants a modern Syclone, local Maple Leafs spammer > SidewaysOnDirt still misses Bowie 07/05/2016 at 15:22

0

Fuck that noise :)

And yes it does.

Snuze: Needs another Swede > Smallbear wants a modern Syclone, local Maple Leafs spammer 07/05/2016 at 15:24

1

That’s not the worst idea I’ve ever heard...

You got a bass guitar and an amp? 4300 rpm equals 71.6 Hz. A normal guitar only goes down to 82Hz, so you need a bass. For reference, the 3rd string on a 4 string bass is 55 Hz, and the 2nd string is 73.4 Hz. C# (3rd string 4th Fret) is 69. 3 Hz. So you’re going to need to play with tuning a bit to get close to 71.6 Hz.

But you get some hearing protection, and tune that base a bit, and have someone blast that note over and over again while you get under the truck and see what rattles.

Smallbear wants a modern Syclone, local Maple Leafs spammer > Snuze: Needs another Swede 07/05/2016 at 15:26

0

I’ve got a friend with one. I could give it a shot.

SidewaysOnDirt still misses Bowie > Smallbear wants a modern Syclone, local Maple Leafs spammer 07/05/2016 at 15:29

1

It looks like generally the exhaust cam is at a zero position at 4300 and past on the LSs with VVT. The cam gear changing there could be conspiring with your exhaust restriction.

Snuze: Needs another Swede > Smallbear wants a modern Syclone, local Maple Leafs spammer 07/05/2016 at 16:22

1

If your friend is willing to help it seems like a cheap, relatively easy way to attempt to make a diagnosis. Worst case, you don’t find anything, but at least you’re not out hundreds of dollars playing the “throw parts at it ‘til it’s fixed” game.

Smallbear wants a modern Syclone, local Maple Leafs spammer > SidewaysOnDirt still misses Bowie 07/05/2016 at 17:19

0

Interesting. In that case I’ll see if it’s gone when I eventually do a cam.