2.0 Turbo - Wastergate Chatter And Dumpvalves

[Henry Yorke 269 3 Cars]

I have had a few interesting debates on this one with people and it seems there are a few schools of thought on this.

 

The engine concoction in my green skip runs the Motronic MP3.2 system as found in any 2.0 Turbo PSA car along with a brand new standard T25 turbo as found on the XU10J2TE. Boost levels are controlled by the ECU and a boost control solinoid.

 

If I run it without the dump valve, I get a wastegate chatter noise which sounds nice but some think that this is the turbo stalling and starting to spin back on itself. Cybernck disconnected the dumpvalve on his T16 and it made the same noise. Nik also said the 2.0T comes with a recirc dumpvalve as standard. Galv said that by not having one the turbo wears out quicker.

 

However on the other side, some think it is just extra boost escaping and the wastegate doing its job. Also the dump valve is releasing all the pressure, which gives lag as it has to repressurise and the turbo stops spinning.

 

The Cosworth Fords and Audi Quattro UR's have this wastegate chatter (which sounds lovely), but the Subarus etc rely on dump valves (which sound a little chavvy!!)

 

I just thought I would open a healthy debate on this to see if anyone had and actual evidence to prove one way or another. I know the acid test is to get the skip on the rollers and do a run with and without.

[pugrallye 0]

that sound isnt wastegate chatter, its the compressor vanes stalling, similar to WRC cars which do not run dump valves. UR quattros have external wastegates, which chatter, normally on a standard turboed car with a standard recirc dump valve, and chattering starts on overrun, the diaphragm in the DV has split, so in fact is not recircing any boost, behaving in the same manner as removing it. Wanting any proof, I can show its not a good thing!! have 3 or 4 knackered trurbos lying about where the main shaft has snapped through the forces created by this so called 'wastegate chatter'

Edited July 3, 2006 by pugrallye

[TEKNOPUG 3]

I read a really good article detailing all this quite recently. From what I understand, your first point is correct. Ie: that the wastegate chatter is boost hitting the turbine blades. So this is slowing the turbo down whilst keeping the boost pressure up. However, this is causing damage to the turbo and will reduce it's life (not something that Pro-Rally teams worry about). With a dump-valve, the pressure is being released ahead of the turbo. This obviuosly reducing boost pressure (lag) but it is also allowing the turbo to continue spinning. So you sacrifice a little lag in return for less stress and greater longevity of the turbo.

 

I'll try to find that article though as it explained it all a lot better than I just have!

 

Also - the T25 has an internal wastegate and as far as I know, you shouldn't hear any sound from it.

[Jonmurgie 2]

We had a dump valve on our S13 when we got it but the SXOC boys seem divided on whether to have one or not. We've not fitted an induction kit and removed the valve and we get lots of chatter (they call it 'releasing the pigeons' on the SXOC!) which sounds great but to my mind seems to be stupid as it can increase lag between gear changes (or so I've always thought).

 

We're probably going to re-fit a valve to the car and see if it drives better, though I personally thought it drove smoother without the valve... the 200SX don't run with any valve as standard, fitting the induction kit just allows the sound of the stalling turbo to be heard better

[Ryan 99]

I was under the impression that the pigeon noise was caused by air pressure waves in the inlet tract?

[Guest andy309goodwood]

i dont know much about this subject how ever i am attempting to lern before i fit my engine

how ever as far as i know if you have any lenth of of inlet pipe work i would of thought having a bov just before the inlet manifold would do a couple of things one is increase the life of the turbo as there is less stress on the compresser side when you close the throttle as the trapped pressure is released which would help the turbo keep spooled up so decreasing the time taken to spool up and second as your realeasing at the furthest point possable from the turbo your keeping the momentum of the air flow thro the pipe work and charge / intercooler and so helping to prevent the stalling effect of the turbo

dont know if that makes any sence i know what im trying to say just not sure how to say it lol

on the other hand i could be talking compleat bs this is just the way i perseve it at the mo

cheers

andy

[mak 0]

I thought a dump valve reduced lag? Because the turbines continue to spin when the throttle is closed, as opposed to stalling, the turbo spins up quicker to produce boost.

 

Wether it does or not, they do help increase turbo life and with turbos at half a grand a pop, a dv is a worthwile investment in my eyes.

Edited July 3, 2006 by mak

[johnrobertgordon 0]

My friend Craig is building a monster of an s1 rs turbo. He has just taken the car down to silverstone to get the omex ecu fitted and set up. He was looking at having an ecu that incorperated anti lag (for the popping noise allone i think, lol) He also wanted that noise that people refer to as wastegate chatter.

Waste gates dont really chatter, the waste gate allows pressure to be relesed from the exhaust side of the turbo.

The chatter that you get on the wrc cars is when the throttle butterfly closes the air has no where to go and so it heads back and hits the turbo veins. This CAN be harmfull to the turbo as it can destroy the shaft, this is why Craig has a dump valve because he did not want to shell out for a sintered shaft

[pugrallye 0]

If you have anti lag, you have no need for a dump valve, as your compressor is still being turned in correct direction and turbo is permenantly at compression speed

[johnrobertgordon 0]

he aint got anti lag, was just looking into it. thats how he found out he needed a sintered shaft because of the extra force it would take from the air coming back under closed throttle conditions.

[sonofsam 5]

Yeah a dumpvalve is a good idea in my book, however after some reading im finding myself wanting to go the recirculating route, so may do a back to back test at some point and as andy309goodwood states it should be as close to the inlet butterfly valve as possible.

Another rule of thumb is twin piston dump valves for cars with AFM's..single piston for cars without.

[TEKNOPUG 3]

I haven't been able to find the link to the site I mentioned, which is a shame as although it was from an american company, it was very informative about all things turbo and particular tuning turbo engines - from street to track use. Hoepfully I can find it when I get home.

 

Anyway, this should clarify any confusion regarding wastegate "chatter":

 

"Compressor surge is basically a situation where boosted air forces its way back through the compressor housing when the throttle is closed, causing that noise as the blades of the compressor "slip" in the air. Although many people like the sound of compressor surge, it can shorten the life of the turbo depending on its severity. The pulsing air in the inlet can cause excess thrust loads on the bearings, and also shock loads on the compressor blades."

[Guest andy309goodwood]

cool dump valve for me then

cheers

[inferno 1]

wastegate chatter sounds well cool IMO with a straight through zorst. however a straight through on a 8v turbo xu engine without step seal upgrades for the T25 produces smoke on idle when warm...

 

as said DV's stop the turbo stalling by releasing unused boost between turbo and throttle bodie,and on my zx it was noticably quicker and smoother to drive with DV on.

 

recirc valves are normaly used on cars with AFM's ect, as they supply the correct fuel for amount of metered air, so dumping the pressure would result in rich running,piston wash, black smoke, ect. with a map senser you can supply correct fuel at any pressure at any time.

[Sam 4]

I've been researching this alot recently, on various forums etc. The general conclusion I came to was its OK on some turbos at low boost and not on others, the general opinion was higher boost (over ~1bar) needed a BOV. Garrett recommend the use of a BOV with their GT series turbos anyway.

 

Theres no such thing as wastegate chatter. Why would there be, the wastegate only opens when the desired boost level (set by vacuum level or actuator rod length) is met so that any excess exhaust gas can be vented.

 

It's a nice sound indeed, as shown here by an ERST: http://the123design.com/temp/femalerst.mpeg

I just can't help but think its not worth the risk of damaging the shaft within the turbo. I've bought a HKS SSQV for my build, tested it on a friends S40 2.0T and it sounds pretty, not your average baileys.

Edited July 3, 2006 by Sam

[Henry Yorke 269 3 Cars]

Cheers for the comments. My other source of information has also been lurking on the 200SX forums and said the same thing about them being detremental to engine performance. It may be a case of the internet propogating bullsh!t again as so often happens (BMW E30 M3 timing chain is another one).

 

There is a bit of old film of mine "releasing the flock of starlings" (sounds like the morning after a good curry night !) which is here.

 

So I will stick with my twin piston dump valve , but put a stronger spring in it as it weeps at cruising speed on a light throttle when the vaccum is low.

[tom_m 0]

you shouldn't need a twin piston DV Henry, because the skip doesn't have an AFM. bailey developed the twin piston jobbie to stop afm's having a heart attack when the boost is dumped

[TEKNOPUG 3]

Yep. Single piston will be fine if you're running new-fangled engine management.

[benje 0]

Going a bit OT here, but I'm sure I read Anti-lag works by throwing fuel down the exhaust ports (Retarding ignition maybe?!?!?) and then igniting it in the exhaust manifold to keep the turbo spinning, anyone confirm this? Just wondering really, I assume the temperatures involved in burning the fuel so near to the turbo is what kill's it??

 

Ben

[TEKNOPUG 3]

Yeah, that's how anti-lag work basically. That's why you see flames spit out of the exhaust because of the unbrunt fuel.

[markic 0]

Couple of points, IMO there is no point with dv's on standard engines, Peugeot or citreon spent hundreds of thousands, possibly millions, developing this engine. And they didn't see the need. Dump valves are for chavs, like the corsa muppets who hold the clutch in and let their 3 cylinder motors bounce off the rev limiter when driving past a group of 10 yr old girls I admit they do serve a purpose but mostly for show. Becoming very difficult to use anti-lag in competition due to noise regs.

[Sam 4]

Dump valves are for chavs

 

So why do Garrett recommend a BOV with their turbo's then. Rather have a turbo that lasts and doesn't kill itself and wreck the rest of the engine. If you don't like the sound go for recirc. There are quite a few cars that have a BOV as standard.

 

Henry, thats quite quiet, wind the boost up a little

[TEKNOPUG 3]

I think you should fit a BOV/DV to an original NA car which is now turbocharged. It just flips people out when you drive past.

 

"eh? What? A 205 turbo??? Nah, can't be..oh hold on, just gone past me like I was going backwardshmmm.must have been then I guess.cool"

 

[adrian_gti 0]

Couple of points, IMO there is no point with dv's on standard engines, Peugeot or citreon spent hundreds of thousands, possibly millions, developing this engine. And they didn't see the need. Dump valves are for chavs, like the corsa muppets who hold the clutch in and let their 3 cylinder motors bounce off the rev limiter when driving past a group of 10 yr old girls I admit they do serve a purpose but mostly for show. Becoming very difficult to use anti-lag in competition due to noise regs.

 

bit of a daft comment really saying dump valves are for chavs.

[pugrallye 0]

Going a bit OT here, but I'm sure I read Anti-lag works by throwing fuel down the exhaust ports (Retarding ignition maybe?!?!?) and then igniting it in the exhaust manifold to keep the turbo spinning, anyone confirm this? Just wondering really, I assume the temperatures involved in burning the fuel so near to the turbo is what kill's it??

 

Yes that is basically how antilag works, the injectors keep firing, but spark gets cut so unburnt fuel ends up in exhaust turbine where is ignites (obviously more to it than that) but turbo's that run on these systems have uprated shafts and stronger turbines to cope

 

And its only really peugeot/citroen that negated the use of dumpvalves as standard, nearly every other large compressor turbo'd vehicle leftt he factory with one (albeit with a recirc item). BOV's are a bit contraversal, but there is no doubting the benefits of a recirc valve.

Edited July 4, 2006 by pugrallye