Is turbo "flutter" bad?

[pedrosixfour]

Am I right in thinking then that a turbo with an anti-surge housing the next step in the evolutionary process and limits compressor stall?

[Kirk]

Thats the idea of them. Rather than the air exiting straight through the compressor it goes out through the swiss cheese housing or atleast thats my understanding of it

 

Apparently dude mentioned something about reading a book which convinced him 100% that he needed one. Id love to know what it was that gave him that impression.

[Guest initial_j]

way i look at it, just look at all turbo charged engines used in proper racing, none of them run BOV's.

 

ive personaly never used one, and had no problems. though i admit thats normaly been on smallish nissan engines SR20/RB25 not running silly levels of boost.

 

and compressor stall sounds the tits!

[Homer]

Ask anyone in the motorsport business if one is needed and you'll always get the same answer - No

 

The "flutter" noise you hear is caused by air being pushed back out of the air filter.

 

Turbo stall still happens on completely stock turbocharged cars, it's just you can't hear it due to:

a) Factory cars have recirculating dump valves which put the excess pressure back into the intake

b) The stock air intake filters out nearly all of the noise of the air being pushed back out of the air filter

 

Quoting CW: recirc dump valves are only put in place to reduce "unwanted" noise.

 

Additionally, it's pretty much impossible to stop turbo stall anyway since no number or dump valves will be able to react quickly enough to remove it entirely. Secondly they only work at certain pressures, so if you set one to work optimally at say 1.4 bar, it will not be optimal when boost is much lower. I.e. turbo stall will be reduced at higher boost levels, but increased at lower.

[Westcoaster]

Off topic for Supras, but my other car is a Smart Roadster which has a small KKK turbo with no bov.

 

The flutter "turbo stall" sound happens with every gearchange. I know of someone with a Smart roadster with 140,000 miles on the original engine and turbo. Turbo failures are uncommon and are more related to unsympathetic warming up/cooling down than compressor stall wear on the turbo bearings.

 

Ironically, those who fit bov's and then fail to service them, are the ones who have problems!

[caseys]

I'm a fan of my turbo chatter/flutter

 

http://en.wikipedia.org/wiki/Wastegate

Wastegate chatter myth

 

There is confusion in the automotive world about so called "wastegate chatter" or "turbo flutter". A noise created on lifting off the throttle in a turbocharged car, commonly described as a chipmunk or a rattlesnake, is often stated incorrectly as being a result of the turbo's wastegate closing.

The noise is in fact the air compressed by the turbo passing back through the compressor wheel of the turbo after the airflow is abruptly halted by the throttle plate closing, called compressor surge. However, in some cases, i.e. where the throttle plate doesn't open fast enough or is set up to only react to high boost, some chatter will remain. Surge can occur on diesels when the turbo is attempting to pressurize the air at a higher pressure ratio than the compressor wheel can flow at a given speed. Diesel engines have no use for a blow off valve as they do not have a throttle plate.

The chatter noise is very noticeable on World Rally Cars, where anti-lag is used.

A compressor stall like this can cause excess stress and wear on the turbo's shaft or bearings under higher load applications of the turbo (around 15 psi (1.0 bar) and greater depending on the trim and flow rate of the compressor side).

Actual wastegate flutter occurs instead under partial boost conditions such as partial throttle near the boost threshold. It sounds like FftFftFft not ShuShuShu and is caused by the rapid opening and closing of the wastegate at boost levels near the spring pressure. It is commonly heard more clearly and may be more prominent on cars with modified intake silencers, up-pipes, and or downpipes, and is not harmful.

 

Not that wikipedia is definitive. EDIT : But wastegate flutter OK, compressor *surge* bad.

Edited September 1, 2010 by caseys (see edit history)

[Homer]

I think you're getting things mixed up there Caseys. That article is confusing and very badly worded as it is!

 

Compressor surge is something completely different and is indeed a bad thing.

 

Compressor stall and "wastegate flutter" are the same thing. The noise has nothing to do with the wastegate, it's compressor stall. It's just MUCH more audible on single turbo cars due to the far larger mass of air they shift and larger turbine wheel.

[caseys]

I think you're getting things mixed up there Caseys. That article is confusing and very badly worded as it is!

 

Compressor surge is something completely different and is indeed a bad thing.

 

Compressor stall and "wastegate flutter" are the same thing. The noise has nothing to do with the wastegate, it's compressor stall. It's just MUCH more audible on single turbo cars due to the far larger mass of air they shift and larger turbine wheel.

 

I sit corrected

 

As I said, many things on wikipedia are to be taken with a pinch of salt. Seems a lot of sites stating no such thing as wastegate chatter / flutter and that it's surge, rather than stall.

 

Seems a lot of forums get the surge and the stall mixed up. Stall will only occur on close of throttle?

 

Ironically and also confusing if you search for compressor surge, guess what google and wiki partners in crime come up with this page

 

http://en.wikipedia.org/wiki/Compressor_stall

 

With this paragraph

 

Axi-symmetric stall or compressor surge

Axi-symmetric stall, more commonly known as compressor surge; or pressure surge, is a complete breakdown in compression resulting in a reversal of flow and the violent expulsion of previously compressed air out through the engine intake, due to the compressor's inability to continue working against the already-compressed air behind it. The compressor either experiences conditions which exceed the limit of its pressure rise capabilities or is highly loaded such that it does not have the capacity to absorb a momentary disturbance, creating a rotational stall which can propagate in less than a second to include the entire compressor.

The compressor will recover to normal flow once the engine pressure ratio reduces to a level at which the compressor is capable of sustaining stable airflow. If, however, the conditions that induced the stall remain, the return of stable airflow will reproduce the conditions at the time of surge and the process will repeat.[1] Such a "locked-in" or self-reproducing stall is particularly dangerous, with very high levels of vibration causing accelerated engine wear and possible damage, even the total destruction of the engine.

 

Maybe we should get CW or some of the hardened tech section people to become wiki editors

 

Again I am only quoting here for digest/discussion, rather than stating any fact myself!

[Bailey.]

I ran chatter on my Evo 6 for the whole time I owned it, I removed the turbosmart dump valve and fitted a standard recirc back to front, works a treat, I'm not gettin involved in the technical speal but always thought it was turbo stall!!

[Chris Wilson]

People who think a BOV reduces turbo lag on gear changes are also misguided, they don't. The first production BOV's (Bosch on Saab 99 turbos, maybe on BMW 2002 turbos, as well) were designed to stop "funny noises" and complaints to service and warranty departments from owners wondering what the funny squeaking noises were. That is still there purpose on production cars.

[Homer]

Lol at those wiki articles, they are utter bollocks It looks like they were written by a 14 year old! Have a read of the supra one, just goes to show how accurate the information on wikipedia can be

[caseys]

Lol at those wiki articles, they are utter bollocks It looks like they were written by a 14 year old! Have you ever read the supra one, just goes to show how accurate the information on wikipedia can be

 

After it seems wiki and google became inexplicably linked it went downhill. Or possibly the other way around.

 

I must say google is dumbing down people searching and questioning info and instead taking googles first hit, which is what those two quoted articles are.

 

Seems many forums, s13, gtr and scooby clubs have had the same discussion and numerous times people state one or the other is a complete myth.

 

Maybe we should get back to discussing airplanes and treadmills.

[Swampy442]

Just something to note, compressor stall and surge, theyre 2 different things but ar eboth linked, stall is the point just before the surge when the compressor loses efficiency, al related to the vanes angle of attack relative to the airflow, and surge is the total reversal of airflow across the compressor wheel. In the axial flow engines you see on airliner wings surge can be catastrophic, on centrifugal compressors its pretty harmless.

From someone with 18 years experience on gas turbines

IMO though it depends on the style and age of turbo, dont expect your 10 year old stock turbos with journal bearings to react well to surging while a new dbb turbo will take more abuse. As I understand it theres less lag with no dump valve as the pressure is still locked in the pipework but the turbo speed is reduced faster.

[Dash Rendar]

Personally, I can't get enough of this noise!

[davej705]

My Subaru was running a hks ssbv and still had wastegate chatter running at 1.9bar boost,the bov just couldn't get rid of the pressure fast enough,sounded like a rally car so I didn't care to much,not sure if it was damaging or not though...

Edited September 1, 2010 by davej705 (see edit history)