Harmonic sound from turbo?

linewarbr · **Posted:** Tue Jun 30, 2009 1:29 pm

I got the GDE tune last week, and since getting it back, I've noticed a sound that I didn't hear before. I can't pinpoint exactly under what conditions it does it, but I hear a . . . harmonic sound from the general vicinity of my turbo now. I tried replicating it while parked beside another vehicle, revving the engine in park, but it didn't do it. Seems that it has to be under load?

The best description I can think of for the sound is to compare it to when I was a kid, I had a toy truck that if you tried to turn the wheels real fast, they would vibrate on their axles rather than turn smoothly. In this case however, there is no sense of vibration, just the sound. It doesn't do it all the time, just sometimes - and it seems to occur just prior to shifting, so it is most likely at or above 2500 rpm, and I don’t notice it at WOT, only when accelerating normally. There is no issue with drivability, I just want to address the sound if it indicates a problem.

I've always heard and enjoyed the sucking sound from the turbo, but I never noticed this before. Is it possibly banging off the "rev limiter" of the turbo? Any thoughts or suggestions are appreciated. The only other modification I've done recently was to remove the engine cover for better cooling. It may have always done this; I just never noticed it until now.

vegiH · **Posted:** Tue Jun 30, 2009 2:47 pm

Does the boost pressure flux up and down?Does the GDE increase boost?Is your Maf disconnected? And last when was the last time you checked hoses?It sounds to me to either be loss of constant boost pressure or "overboost"(this usaully comes with a cel).When I overboost in my X, it makes that sound,but I really have to stand on it......................Maybe a loose/cracked turbo tube messing with your boost .Is it like a wurr,wurr,wurr at like 2,300 RPMs?.....................H

chrispitude · **Posted:** Tue Jun 30, 2009 3:03 pm

Our turbo made the sound you describe (toy truck wheels going too fast) awhile back. I could reproduce it at will at about half throttle. It also felt like it was more laggy than normal. The dealer tech heard it pretty easily during a quick drive, and they ended up replacing the turbocharger under warranty. The noise went away and the responsiveness came back. That was on the Inmotion tune.

On the steep hill coming into my development, the engine would occasionally make a similar noise, but much quieter, and only on that hill and at very specific certain throttle condition. I since sold it to Fred. He heard the same faint noise once or twice, but has not heard it since the EGR threw some codes and the EGR was replaced, and the GDE tune was applied (within a day of each other). I think this fainter noise was the EGR stuck partway open, or perhaps some sort of intake resonance that only happened at certain boost pressures/intake velocities.

- Chris

linewarbr · **Posted:** Tue Jun 30, 2009 3:24 pm

vegiH wrote:

Does the boost pressure flux up and down?

Not that I can tell - it is very linear.

vegiH wrote:

Does the GDE increase boost?Is your Maf disconnected? And last when was the last time you checked hoses?

Yes, the GDE increases boost but is supposed to maintain it within the parameters of what the hardware can handle. My MAF is now plugged back in since I have the GDE tune. I replaced my OEM hoses with Samco's about a month ago.

vegiH wrote:

It sounds to me to either be loss of constant boost pressure or "overboost"(this usaully comes with a cel).When I overboost in my X, it makes that sound,but I really have to stand on it......................Maybe a loose/cracked turbo tube messing with your boost .Is it like a wurr,wurr,wurr at like 2,300 RPMs?.....................H

The boost delivery seems to be fine, like I said it is very linear, and it is not a constant noise. It is. . .harmonic, that is the only way I know to describe it. I emailed Green Diesel and asked about it, and this was their (quick, as always - great customer support) response:

Darren,

The sound you hear is normal with the tune, there is nothing wrong with the turbo. We raised the boost pressure in most conditions as one avenue for gaining fuel economy and since the EGR is no longer robbing air flow from the engine the amount of flow rate through the turbo has increased substantially. You are hearing a harmonic zone that the air system passes through. This is related to the velocity of air and the geometric dimensions of the intake tube as well as the turbo tube going to the charge air cooler. Most manufacturers install resonators in the air inlet tube or CAC tube to dampen the harmonics and keep the system quiet. This would have required much R&D to accomplish for an aftermarket kit. The increase in air system noise just lets you know that the vehicle has a turbo that really makes a difference. I would rather it was quiet, but some customers really enjoy the sound. You don’t have any mechanical issues and glad to hear you are enjoying the drive ability improvements.

Thanks,

GDE

nursecosmo · **Posted:** Tue Jun 30, 2009 5:05 pm

linewarbr wrote:

I've always heard and enjoyed the sucking sound from the turbo, but I never noticed this before. Is it possibly banging off the "rev limiter" of the turbo? Any thoughts or suggestions are appreciated. The only other modification I've done recently was to remove the engine cover for better cooling. It may have always done this; I just never noticed it until now.

What "rev limiter" are you talking about?
Ever since removing my kitty cat I get a resonant sound from my turbo right at 1400 RPM under partial throttle. It sounds as though the turbo vanes are spinning at just the right speed and angle to allow the exhaust pulses to flow straight through the turbo charger with very little muffling. I can also really make it very noticeable by disconnecting the vacuum hose to the boost controller.

linewarbr · **Posted:** Tue Jun 30, 2009 5:18 pm

nursecosmo wrote:

linewarbr wrote:

I've always heard and enjoyed the sucking sound from the turbo, but I never noticed this before. Is it possibly banging off the "rev limiter" of the turbo? Any thoughts or suggestions are appreciated. The only other modification I've done recently was to remove the engine cover for better cooling. It may have always done this; I just never noticed it until now.

What "rev limiter" are you talking about?
Ever since removing my kitty cat I get a resonant sound from my turbo right at 1400 RPM under partial throttle. It sounds as though the turbo vanes are spinning at just the right speed and angle to allow the exhaust pulses to flow straight through the turbo charger with very little muffling. I can also really make it very noticeable by disconnecting the vacuum hose to the boost controller.

GDE claims that their tune limits RPM of the turbo to a max of 200,000, and aims to keep it in the 140,000 - 160,000 range. I do not know if the stock ECU tune has something of this nature or not.

I still have my cat, though a cat gut and straight pipe is definitely in the future.

nursecosmo · **Posted:** Tue Jun 30, 2009 5:38 pm

The so-called rev limiter is electronically based on boost pressure vs engine RPM and provides a rough gestimate of turbo speed which will vary with altitude and other factors. It is not any kind of physical apparatus that the turbo vanes could bump against.

linewarbr · **Posted:** Thu Jul 02, 2009 12:34 pm

Yesterday I had a chance to really pay attention to what RPM I heard the sound at. between 2300 rpm and 3000 rpm, though not constant all the way through that range. It is most noticeable at 2300 RPM shifting from second to third and third to fourth. It only happens at part-throttle. If I get on it WOT, I don't hear it, and if I have it in park and rev it without the engine under load, I don't hear it.

I wonder if opening up the exhaust would help. It is not very loud, but I can't help but worry, you know?

gmctd · **Posted:** Thu Jul 02, 2009 3:54 pm

Replace your huge heavy pinched-off muffler with a thru-flow type where the inlet diameter matches the internal diameter matches the outlet diameter, and yer good to go....fer starters................

linewarbr · **Posted:** Fri Jul 03, 2009 7:56 am

gmctd wrote:

Replace your huge heavy pinched-off muffler with a thru-flow type where the inlet diameter matches the internal diameter matches the outlet diameter, and yer good to go....fer starters................

Thx gmctd. Much respect for your opinions.

CRDMiller · **Posted:** Fri Jul 03, 2009 9:09 am

I wonder how they can state the rpm of the turbo when it's very nature is variable.

Boost pressure and engine rpm have very little to do with the rpm of the turbo's compressor.

I'm hoping they have some kind of information the rest of us don't.

I've looked around for this type of information in the past and found nothing.

linewarbr · **Posted:** Fri Jul 03, 2009 11:05 am

CRDMiller wrote:

I wonder how they can state the rpm of the turbo when it's very nature is variable.

Boost pressure and engine rpm have very little to do with the rpm of the turbo's compressor.

I'm hoping they have some kind of information the rest of us don't.

I've looked around for this type of information in the past and found nothing.

If I understand correctly, it is the the vanes on the exhaust side of the turbo that are variable. The RPM of the turbo is variable, of course, based on how much exhaust energy is applied to the turbo before the energy is either vented off or the vanes compress to modulate the amount of energy applied to the rpm of the compressor wheel, which creates the boost pressure.

If you are using boost psi to determine operating efficiency, you are measuring something that affects the intake system as a whole - compressor housing, CAC, CAC hoses, and the engine intake. If that is the only measurable variable, then turbo rpm can only be guessed at, and a certain amount of extrapolation goes into determining the operating limits of that one particular piece of hardware. That would mean that, if GDE has found a way or if the ECM has a way of measuring turbo rpm, then it is a more reliable measure of the hardware's optimum operating efficiency, since it is the rpm of the turbo that creates the boost. In their explanation to me (which I posted in "Linewarbr's GDE Experience") they never mentioned boost, only turbo rpm.

Does anyone out there know if the ECU measures only Manifold Absolute Pressure to determine

Joe Romas · **Posted:** Fri Jul 03, 2009 12:41 pm

All that would be necessary to monitor turbo rpms would be to mount a small hall effect sensor in the aluminum housing close to the intake side impeller. Then knowing the number of blades you would divide the total number of "blips" by the number of vanes and you would have you rpm's

linewarbr · **Posted:** Fri Jul 03, 2009 1:27 pm

Engine rpm's are monitored by the crank position sensor, correct? Is there something similar that is/ can be installed in the turbo?"

nursecosmo · **Posted:** Fri Jul 03, 2009 2:01 pm

Joe Romas wrote:

All that would be necessary to monitor turbo rpms would be to mount a small hall effect sensor in the aluminum housing close to the intake side impeller. Then knowing the number of blades you would divide the total number of "blips" by the number of vanes and you would have you rpm's

That might work if we had steel or ferrous blades in the compressor, but there will be very little to no hall effect with the alloy in the vanes.

nursecosmo · **Posted:** Fri Jul 03, 2009 2:38 pm

CRDMiller wrote:

I wonder how they can state the rpm of the turbo when it's very nature is variable.

Boost pressure and engine rpm have very little to do with the rpm of the turbo's compressor.

I'm hoping they have some kind of information the rest of us don't.

I've looked around for this type of information in the past and found nothing.

Actually engine RPM and boost pressure have everything to do with turbo RPM. The mas of air consumed during one rpm of the engine is a known factor at any given pressure. At sea level atmospheric, it is 1.4 liters at n~lbs . At 30#s of boost it is still 1.4 liters but at 2xn~lbs, etc. All turbos are mapped out by the manufacturer as to compressor rpm-laminar flow-boost pressure. also included in the map are atmospheric pressure and temperature. any simple computer can extrapolate from the map how fast the compressor "should" be turning at X-engine rpm, X-boost, X-altitude, X-actuator vane angle, etc..

Harmonic sound from turbo?

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