Turbo Flutter

[Sledgehammer]

I have never owned a car with a turbo so let me know if this is a usual thing. At hw speeds, 60/70 mph, a peculiar thing happens when I push the pedal down half-way. The car will start to spool the tubro (usually the rpms are between 2.5k and 3.4k) what will happen is the engine will variate from pulling hard to nothing and back again quickly. By quick I mean 3 or 4 times a second. During this time I can hear the turbo dumping air through the wastegate and respooling. The sound cooresponds with the engine pull. After 4k rpms it pulls smoothly again. I have been having this trouble for around 5k miles now and it is really bothering me.

On a side note, I hit the car hard in second gear at about 20 mph/>3k rpms and it pulled hard till it got to 5'n change rpms and suddenly the turbo dropped out. It spooled back up again immediately but their was certainly a lack of power. Any idea the causes or is this just a usual thing

[2ndclasscitizen]

Has it just started doing this? If so, it might be worthwhile taking it into your dealer and getting them to plug into their diagnostic equipment and getting a systems check done.

[clutch-monkey]

must...resist..posting.. VL turbo and pigeon pictures..

[2ndclasscitizen]

Post them.

[charged]

Originally Posted by Sledgehammer

I have never owned a car with a turbo so let me know if this is a usual thing. At hw speeds, 60/70 mph, a peculiar thing happens when I push the pedal down half-way. The car will start to spool the tubro (usually the rpms are between 2.5k and 3.4k) what will happen is the engine will variate from pulling hard to nothing and back again quickly. By quick I mean 3 or 4 times a second. During this time I can hear the turbo dumping air through the wastegate and respooling. The sound cooresponds with the engine pull. After 4k rpms it pulls smoothly again. I have been having this trouble for around 5k miles now and it is really bothering me.

On a side note, I hit the car hard in second gear at about 20 mph/>3k rpms and it pulled hard till it got to 5'n change rpms and suddenly the turbo dropped out. It spooled back up again immediately but their was certainly a lack of power. Any idea the causes or is this just a usual thing

Do you run a BOV?, what seems to be happening is when you change gears or back off the boost your making is trying to escape through the turbo as the throttle plate/body is closed and the noise your hearing is the backpressure of boost against the vanes. A BOV will fix this problem , just get a quiet one. Its actually detrimental to the turbo as it puts extra load on the bearings.

[nopassn]

Wastegate issue perhaps. Diaphragm not holding the boost pressure...? That's all I've got. A sound clip should would be helpful.

[QuattroMan]

same thing happen to my Audi about 2 years ago,two days later turbo went-out,goo luck ! dont get stuck on the road like did

[Sledgehammer]

Originally Posted by charged

Do you run a BOV?, what seems to be happening is when you change gears or back off the boost your making is trying to escape through the turbo as the throttle plate/body is closed and the noise your hearing is the backpressure of boost against the vanes. A BOV will fix this problem , just get a quiet one. Its actually detrimental to the turbo as it puts extra load on the bearings.

It only happens when I am accelerating, the sound I hear is when the boost pressure is lost. But no I am not running a BOV, my engine is still stock.

Originally Posted by nopassn

Wastegate issue perhaps. Diaphragm not holding the boost pressure...? That's all I've got. A sound clip should would be helpful.

I will see what I can do.

It doesnt happen all the time either. It just seems to happen when I havent used much gas for a few miles on the hw and in a low gear ratio. It has never happened in 1st gear, once in second, never in 3rd or 4th, only 5th and 6th.

[hightower99]

Originally Posted by Sledgehammer

I have never owned a car with a turbo so let me know if this is a usual thing. At hw speeds, 60/70 mph, a peculiar thing happens when I push the pedal down half-way. The car will start to spool the tubro (usually the rpms are between 2.5k and 3.4k) what will happen is the engine will variate from pulling hard to nothing and back again quickly. By quick I mean 3 or 4 times a second. During this time I can hear the turbo dumping air through the wastegate and respooling. The sound cooresponds with the engine pull. After 4k rpms it pulls smoothly again. I have been having this trouble for around 5k miles now and it is really bothering me.

On a side note, I hit the car hard in second gear at about 20 mph/>3k rpms and it pulled hard till it got to 5'n change rpms and suddenly the turbo dropped out. It spooled back up again immediately but their was certainly a lack of power. Any idea the causes or is this just a usual thing

I am assuming we are talking about your Mazdaspeed 6/MPS...

if it is then it comes from the factory with a BOV (you are hearing air from that, only exhaust goes through the wastegate and you can't hear that).

From what you have described I would say that you are experiencing turbo surge. This is not normal and will eventually destroy the turbo if it continues.

Turbo surge is when the compressor side of the turbo is forced to produce a pressure ratio that is too high for the mass flow going through the turbo. Normally this is remedied by the installation of a BOV (remember you have one on your stock engine). So I would recommend you check yours out ASAP. If you have ever seen a compressor map, the barrier on the left side is the surge line and any operating point that is on the left of this line is where surge occurs.

If you want to read up abit about compressor maps and what turbo surge is then I would recommend you read this: TurboByGarrett.com - Turbo Tech103

Because your car is still stock I would assume that the compressor is not too large. There could be a problem with your BOV and possibly with the wastegate.

Another test you could do that can help diagnose the problem is a standing start in 2nd or higher gear (start with 2nd gear and try 3rd gear).

With the car at rest, dial in betwen 3500-4500RPM, drop the clutch, floor the gas. In a car that is 100% it should bog down alittle due to turbo lag, then take off with none of the symptoms you mention. If there is a problem with the wastegate not opening properly you could be over-running/over-boosting the turbo which could cause surge. If the BOV activates at any time when you have your foot on the throttle then it should be checked. The BOV should only activate when you lift off the throttle.

[Sledgehammer]

Dropping the clutch at 3.5-4.5k rpms in a 4wd car is a smart idea? Especially in 2nd or third??? I have never done such a thing for fear of either problems with the clutch or the transmission.

Is that the only way aside from dealer involvement to test for such things. What if I installed a better or louder BOV, the one in the MPS/Speed6 is barely noticeable and you need to concentrate to hear it.

Also how do you recommend checking a BOV in the engine itself?

What is the difference between turbo surge and turbo choke limit?

[fpv_gtho]

Originally Posted by Sledgehammer

Dropping the clutch at 3.5-4.5k rpms in a 4wd car is a smart idea? Especially in 2nd or third??? I have never done such a thing for fear of either problems with the clutch or the transmission.

Youre probably right to have such fears. Continual high rpm starts with a 4wd will turn your clutch into butter. 3.5-4.5K rpms isnt exactly high rpm, but doing so in a higher gear than 1st will certainly make up for it.

[charged]

Yeah after hearing that sounds like a wastegate. Seeing its a new car I would take it to Mazda.

[hightower99]

Originally Posted by Sledgehammer

Dropping the clutch at 3.5-4.5k rpms in a 4wd car is a smart idea? Especially in 2nd or third??? I have never done such a thing for fear of either problems with the clutch or the transmission.

It is abit hard on the drivetrain (compared to starting properly in 1st) but it will not cause damage unless you constantly start like that for a considerable amount of time. Besides the MPS is effectively FWD until the front wheels slip enough to activate the rear differential and by that time you should be moving. I am not trying to get you to damage your car and I only suggest that you do this once or twice on any given day (due to the fact that it loads the clutch and you might experience clutch slipping if you don't give everything a rest). BTW I would like to say that I am not trying to get you to floor then throttle and dump the clutch somewhere between 3500-4500RPM, you should be able to hold the revs stable somewhere between 3500-4500RPM with partial throttle then let the clutch out as you push the gas pedal down to WOT, it should be a relatively smooth start. The point is to load the turbo hard and fast.

Originally Posted by Sledgehammer

Is that the only way aside from dealer involvement to test for such things. What if I installed a better or louder BOV, the one in the MPS/Speed6 is barely noticeable and you need to concentrate to hear it.

No the hard start method is only one way to test. I would first do a simple visual check of the BOV (it's at the front of the engine on the driver's side. just under the plastic cover). Check if all the pipes are connected properly ect. I would like to point out that louder doesn't mean better. Yes you could replace the factory BOV but we aren't even sure that it is the sole problem.

Originally Posted by Sledgehammer

Also how do you recommend checking a BOV in the engine itself?

The BOV is on the intake manifold after the IC on the drivers side. It should be visible without removing anything. you can visually check that the vacuum line is connected properly to the BOV and to the intake manifold. I believe it is a recirculating system (the vented air is led back to the intake of the turbo), so you might try disconnecting the large air return tube and check if the BOV opens properly (you can do this by having a friend rev the engine in neutral). Every time you lift off the throttle the bov should open quickly then close again fully.

However the BOV may not be the problem. The problem might be with the wastegate activater. You could check the pressure line that goes between the compressor housing and the wastegate activater. I am assuming you bought the car used? maybe the previous owner added a "t" to the line to delay the wastegate opening?

Originally Posted by Sledgehammer

What is the difference between turbo surge and turbo choke limit?

Well on a compressor map the surge line is the barrier that runs north-south along the left side and the choke line is the barrier that runs along the right side. The main difference is this: with turbo surge you are trying to produce too high of a pressure ratio with too little mass-flow, while turbo choke is when you are trying to produce too much mass-flow with too little pressure ratio.

When a turbo chokes, the shaft speed goes way up but the mass-flow doesn't. The pressure ratio will normally drop and this means that the engine will start making less power. This normally occurs in the upper rev ranges and is a sign that the turbo you are using might be too small. Turbo choke doesn't damage the turbo unless you are somehow able to force it so far into the choke area that the turbo over-revs and falls apart.

When a turbo surges it means the shaft speed is already to high and it actually starts slowing down the turbo. The flow going through the turbo becomes highly unstable and can in some cases start going the wrong way through the turbo (you can hear this as a loud bark that comes from the compressor in severe cases). The compressor suddenly has high amounts of pressure forcing it away from the center housing of the turbo, this is what damages the turbo as the thrust bearings aren't that great (unless you have a ball-bearing turbo which I think you are lucky enough to have stock ). This normally happens when you suddenly lift off the throttle because that means you cut the mass-flow through the turbo right down. A BOV solves the problem because it allows the mass-flow rate to ramp down more gradually when you shut the throttle.