[Mk2] [Turbo] Dump valve chatter

[ilovejapcars]

Need some advice on what dump valve to buy. I want one that chatters, i have one at the moment that just dumps and sounds like a bus

[mrmarc]

i have the standard recirc valve that recircs back into the apexi airfilter.and it 'chatters' a alot.
my mates love it!

[Hellboy]

Dump Valves dont chatter.
There is a common myth in the automotive world about so called "wastegate chatter" or "turbo flutter", a noise created on lifting off the throttle in a turbocharged car. The sound is commonly described as a chipmunk or a rattlesnake and 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 body closing, called compressor surge. However, in some cases, i.e. where the throttle body 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. Diesels 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.

If you have a Revision 1 or 2 with a AFM you wont hear nothing as the AFM flapper will shut whent he throttle is closed and will stop the noise..

[fozzy rev3]

my standard rev3 bov 'chatters' like you wouldnt believe...

Hellboy - nicely put dude

[karammander]

hellboy is right, this gets on my nerves so much. people listen to jeremy clarkson tooo much. dump valves do not chatter nor do wastgates, its just compressed air being cut up by the compressor.

people try to get this noise but in the end its just gonna kill your turbo regardless of type or brand.

if you want a fluttering noise when you come off boost i would recomend the hks ssq with the purple fine and if its one of the early ones set the spring tension quite loose. this will cause the two valves to operate at different pressures therefore a kinda fluttering noise.

sorry for the rant but people should realy use the search function and not listen to much to pub talk about mates cars chattering wastegates.

cheers karam

[C50]

but i remember reading on this forum that you can get a chatter sound from a HKS by cutting off a fin..

I may have a chatty BOV for sale

[mrmarc]

I have read the noise you can hear on my setup is simply the diaphragm design of the BOV/recirc valve.
it becomes alot more noticable because of the air intake system being a single pipe design as apposed to the more complex sound absorbing original.
this of course having no detramentle affect on the turbo.
?

[cantfindausername]

Getting a "chatter" from a BoV is probaly because its only partially venting, so some air is still causing compressor stall.

Look at most cosworths - the most notorious for "wastegate chatter" banter, and non of them run dumpvalves. I have a friend putting 2bar boost through a T38 turbo, and the stall does sound phenomenal, but I'll be interested to see how long his turbo lasts.

[mattcambs]

Also, if you search on the subject you'll find a thread from a few months back that got quite heated about whether a dump valve is actually necessary.....


.....anyhooo, back OT

I don't think the standard bov "chatters" much at standard boost. Mine didn't anyway.

Also, bov and wastegate chatter are surely two different subjects? We know that wastegates don't chatter, but why can't a bov chatter?

[jimGTS]

whatever your asking you dont want this on a cermanic shafted stock turbo.....
could mean bye bye to the turbo and possibly your engine.


i get a little fluttering on partial throttle/boost.....but wot and full boost to blows off as it should..

[Spittinflames]

I love the chattery sound that cossies and the like do but i've yet to get my tubby to do it... and yes i've experimented.

Heres how mine sounds.
http://uk.youtube.com/watch?v=wrIpRZnG0OU

[cantfindausername]

Best example I've heard on an MR2 is MikeJCs in car video from Silverstone on last years time attack. Maybe its something that Garrett turbos are better designed to do over the CT series of Toyota? Look it up on youtube.

[jimGTS]

Best example I've heard on an MR2 is MikeJCs in car video from Silverstone on last years time attack. Maybe its something that Garrett turbos are better designed to do over the CT series of Toyota? Look it up on youtube.

isnt that just because of the external wastegate?
or am i barking up the wrong tree?

[cantfindausername]

Wrong tree Jim. An external wastegate has got bupkiss to do with compressor stall.

The sound heard is the compressed air bouncing back of the throttle body and hitting the compressor blades which are spinning against the air.

[jimGTS]

The sound heard is the compressed air bouncing back of the throttle body and hitting the compressor blades which are spinning against the air.

i know that bit....i just thought it was safer to do because of the EW...
but i asume its safe to do because of the steel shaft more than anything....

[cantfindausername]

I wouldn't say its saver to do as fans aren't designed to have air forced against them in the opposite direction to their natural flow. But they might stand up to the punishment better due to having been made from stronger materials, yes.


Imagine if you will, a kleenex premier league football player represents the CT series turbo, and a rugby player represents a Garrett turbo. And a big stick represents air flowing in the wrong direction.
Both the footballer and rugby player will fall with enough beatings, but the chances are the footballer will fall first.

[RyanRs]

Just to throw yet another stick in the fire, or at a kleenex football player....

BOV's and DV's are different!

The mr2 does not have an oem BOV!! it has an oem DV.

A DV is not adjustable and generally quite xxxx to use on turbos that move a lot of air , such as ours ....as the spring tension in them is too weak and the boost pressure -if high enough - could push it open -letting air escape! They are fine for smaller turbo cars such as R5GTT , Uno Turbo , RST etc. a DV would be something like a Bailey & GGR Piston Type Dump Valve.

A bov is a DV thats adjustable / tunable via usually a 'Hard / Soft' spring -such as the Greddy Type-r , Sard R2D2 etc etc... This allows you to increase / decrease tension on the spring that holds the BOV closed while on boost. this is used to stop it from opening when it shouldnt. If you was to run a bigger turbo/more PSi then you would poss want to increase the spring tension to keep the valve closed.

The reason some BOV's appear to chatter is because where the spring is usually setup to be slightly stiffer than that of a DV, -say the spring is set to 5psi then you would need 6Psi of boost pressure to open the valve. any less than that and the valve will stay shut and surge back through the turbo. obv tho if it opens at 6psi of boost, then the boost pressure will instantly drop as pressure is released..causing surge aswel.

the only way to eliminate surge completly would be to loosen the BOV spring,but then as you reach high boost, it will open / leak boost air. So baically you find a happy medium.

Also i do believe BOV's are designed to remain closed while on tickover, to stop metered air from escaping (for cars with MAF sensor -rev1&2) whereas DV's are open on tickover.

[jimGTS]

the stock DV, it actually called a By Pass Valve....or BPV...


ive seen the above.....
when i got my greddy, it was set to virtually fully soft (or was it hard).....it would fully flutter on any boost at all...i wouldnt get a pptttssshhh AT ALL, just flutter...
cant have been good for the turbo....

ive now set it up so i only get a pttsshh on full boost and no flutter on or after lift off....
i do still get a small flutter on partial throttle and boost tho...i cant do anything bout that....

[mattcambs]

Ryan I thought a blow of valve and dump valve are just two different terms to describe the same thing. So haven't you just described the different types of DV/BOV/whatever you want to call them?

[Chr15py]

Here you go

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

Chris