I just got done watching the Swedish Rally, and my curiousity was bugging me. So does anyone one know what that chirping noise is that all of the rally cars make?

the chirps are the BOV... the popping (small backfires) is the anti-lag system.

I think you are talking about the anti-lag systems that keep the turbo spooled up during shifts...
Basically an amount of fuel is allowed to pass through the engine off throttle so that when it hits the red-hot exhaust it combusts flowing more gas and therefore spooling the turbo very quickly! Then you have instantaneous boost when back on throttle...
BUT the downside is turbo repair/replacement very often and very harsh on other parts as well!

That is the "jist" of it, there is more info available online about it though...

Brandon is right (I forgot you said chirpinghttp://www.i-club.com/ubb-files/smilies/biggrin.gif) the chirps are probably the blow off valves
but the flames and gun-like repititions are the ALS kicking in...

[This message has been edited by SubaFast (edited April 23, 2001).]

speaking of rally sweden, burns didn't look so friendly when he was yelling at the spectators to help, hehe.

Why does everyone think the chirping is a BOV...if you have a BOV on a car with antilag, they preaty much cancel each other out.

Its the wastegate, not the BOV.

Not untill someone shows me a technical drawing proving otherwise.

well i woundnt be to happy either. i was watcing the last race they showed, (was it monte carlo?) and when the former subie driver that now drives the Focus RS (cant remember his name) broke down on a turn, about 3 people came down to "help". that would bother me too. some of the fans over there are pure itiots. they should stay OUT OF THE ROAD and on the side where they belong. (end vent http://www.i-club.com/ubb-files/smilies/wink.gif)

Well, on a street car, that chirping noise occurs when the blow off valve fails. It is caused by compressor surge, in that when the throttle plate is closed under boost, the pressurized air hits the plate, then the wave ricochets back to the turbine and then back to the t-body, etc. creating pretty much the exact same chirping noise. The noise itself comes from the pressure wave hitting the turbine wheel. You can destroy a turbo this way in not too much time.

Not sure if this is what is going on in the rally car.

Thanks for the clarification on that subject I have been wondering what that sound is as well.
As for Burns yelling at the fans I think that he was just extremely frustrated which you could see by the expression on his face. At least there was a Subie in the top six.

Later Z

You guys are all wrong...


The chirping sound is the back-up squirel drive system. http://www.i-club.com/ubb-files/smilies/smile.gif

I think it is the mechanical thingy that regulates boost pressure when the throttle is closed. Is this a wastegate or a BOV?

Chirping = Blow Off Valve

like WRXRob said, the chirping is due to a compressor surge. Typically race cars do not run a BOV. It's just another place to leak boost and another part to break.

If you are feeling really stupid, and have a MBC installed, you can re-create that chirping by building mad boost with the MBC. It's not that good on the turbo, but sounds really cool.

Suspension is what is causing it

I don't know the answer myself... but I don't think any of you know what it really is.

http://www.i-club.com/ubb-files/smilies/lol.gif

Engine RPM up, car in gear, lift throttle.
Turbo still making pressure but with throttle closed where does the pressure go?
Blow Off Valve.
Leak? Hardly!

--scott

I usually hear a couple different chirping sounds, or sounds that could be described as chirping.

Hardened tranny/suspension/engine mounts? I know those things are noisy as hell on bumpy roads if you don't lube them up.

Its the BOV. All grp WRC, A and N cars use them.

Geez, I can't believe all the misinformation that is being presented here!

The chirping you hear is the cruise control manifold when it is being turned off so the driver can take manual control of the throttle. That's all it is! And I know, so don't bother arguing!!

http://www.i-club.com/ubb-files/smilies/lol.gifhttp://www.i-club.com/ubb-files/smilies/lol.gifhttp://www.i-club.com/ubb-files/smilies/lol.gifhttp://www.i-club.com/ubb-files/smilies/lol.gifhttp://www.i-club.com/ubb-files/smilies/lol.gifhttp://www.i-club.com/ubb-files/smilies/lol.gif

Is this chirping sound the really high pitched whine that you hear inside the cabin?
I noticed that during the outside shots you can't hear the highpitched whine, but inside the cabin the whine is very prominent. I'm wondering what that whine is. Is it the same chirping sound you describe or something different? I'd like to know.

Could it be the chattering of the differentials through the turn?

the whine inside the car is just the turbo and the high strung engines remember that their gears are very short so it revs extremely fast

the chirp sound AFAIK is the blowoff valve going off mixed with the anti lag system, the ALS gives off a series of backfire explosions, coupled with the bov's normal psheeeeeeshhh sound ...

you can hear it all well here, check out how the "chirp" sound goes off when they let off the throttle, so basically it goes off when the antilag and bov go off...
http://www.pr-roadracing.com/22B.mp3


[This message has been edited by ProgWRX (edited April 24, 2001).]

The sound to which the original poster is referring sounds like rabid squirrels on helium. A whole bunch of them. Always at the entrance to corners/lift throttle. Sort of sounds like tires slightly breaking traction but the pitch and rhythm is too consistant for that. chi-chi-chi-chi-chi-chi-chi-chi

<FONT SIZE="+3">It is the Blow Off Valve</FONT>

Sounds like suspension squeaks to me.

Even more specific, it is the HKS Super-Sequential blow-off valve. http://www.i-club.com/ubb-files/smilies/smile.gif

THANK YOU ANDREW!!!!

Someone from the rallying comunity that KNOWS what he is talking about.

Think about it people, what does a BOV do? Regulat boost presure, and bleed excess boost presure.

What does anti-lag do? Keeps the turbo spooled during throttle lifts, reducing turbo lag, and keeping boost levels up.

Now, why would you run a system to keep boost presure up, only to bleed it all away into the atmosphere and have it do NOTHING for you?

Again Andrew i thank you for providing your profesional oppinion.

As for the high pirched whining sound in the cockpit. Thats from the gear box. The gear box is all straight cut gears, and are cut to VERY close tolerances, so the the transmission is VERY tight. As the gears spin, becuse they are so tight, they make a whining sound.

I just figured the chirping was from all those pesky birds that kept swooping down and pecking at the spectators !

http://www.i-club.com/ubb-files/smilies/biggrin.gif
Brad

Think about it people, what does a BOV do? Regulate boost pressure, and bleed excess boost pressure
Uh...that's what a wastegate does. BOVs are to prevent the surge of air rushing back towards the turbine when the throttle is closed. It doesn't regulate boost pressure one bit, but does bleed off pressure between the throttle body and the turbo when the throttle is closed.
What does anti-lag do? Keeps the turbo spooled during throttle lifts, reducing turbo lag, and keeping boost levels up.

Now, why would you run a system to keep boost presure up, only to bleed it all away into the atmosphere and have it do NOTHING for you?
Even if the air is bled off the turbo is still spining and air is still moving. When the throttle is openned again the air moves into the engine rather than being bled off.

Thank you Strepto. You are correct. Not to take anything away from Andrew, he and the other guys at eurosport definetly know their stuff. And yes WRC cars do have BOVs.

Ill have to dig up some old pictures from Option Japan, they had dyno runs showing how a BOV blead boost presure at high boost levels, and that the "regulation" of boost presure on lifting, actually generated MORE turbo lag, and under long tearm stress tests was ot shown to improve turbo life significantly to warrent having one in a racing set up. Sorry, i got that a little bass awkward. The waste gate controls the pressure of the exaust gases flowing through the impeler housing regulating the amount boost presure. But a BOV will do the same thing. If the boost presure exceeds the limit of the diaphram spring, it will release boost presure in the intake. Which is NOT a good thing. In rally where the turbos are relativly small, and the engines are preaty much always at 90% throttle, and left foot braking is a required driving style, a BOV would prove worthless. I doubt andrew would make a claim like he did, if he didnt know his stuff.
Having laid my hands on a groupe-A EVO-V, and several Groupe-N EVO's, i have never seen a BOV on one. And ive never heard a BOV that chirped as loud as, or even sounded close to a wastegate. Next rally i go to, i WILL take pictures under hoods, and show that there is indeed no BOV.

Again, show me a technical document, or an intake diogram from Mitsu, Subaru, Peugeot, etc that has an BOV. Theres a reason why you cant find one. They dont exsist.

http://www.bensrallypage.com/forsale/mantop_ford6.jpg

This is a cosworth sierra (group N). With a BOV. And yes Buck O I agree with you there are several rally cars out there that do not use BOVs but that doesnt none of them do. Earlier I wasnt implying that Andrew doesnt know what he's talking about, he obviously does, Eurosport has some very innovative and competetive cars.

Is this post over yet?

Brandon

If you don't blow off the high boost pressure it will stall the compressor on lift causing it to have to spool back up when the throttle opens.... which is what BOV's are for in some applications. You have to close and open the throttle fast enough to use this sudden high pressure wave to your advantage (left foot brake).

Now here's my question, to the cars that are running high boost pressures and not using BOV's, isn't there a lot of stress on the turbo? throttle body? There are times where you'll have to lift for a long time, do they just let the pressure stall the turbo while the wastegate opens?

question #2 WRC with ALS.... when the throttle is lifted..... the ALS is trying to spool a stalling turbo, is there a point to this?

question #3 for Buck-O and Andrew, if the wastegate opens what is the point to ALS? all the extra explosions don't go to push the turbine... it goes "wasted"

[This message has been edited by Tralala (edited April 24, 2001).]

EDIT: After listening to the 22B sound clip, yeah its the BOV.

Sounds like a raccoon.

[This message has been edited by Hucker (edited April 24, 2001).]

I'm no turbo expert, but this is what I understand about the wastegate, the BOV and where that chirping noise might be coming from. [If I'm wrong, straighten me out. Please.]

Under heavy throttle, the turbo (along with its motor, together as a system), if left unimpeded or uncontrolled, will run away with itself (feed on itself) and rapidly make too much boost – a recipe for detonation, lean-outs, and subsequent catastrophic engine damage, let alone the issue of unmanageable drivability. Under such conditions the boost level must be controlled or regulated to a certain adjustable setpoint.

That is where the wastegate comes in. As soon as the wastegate senses boost levels beyond its setpoint, it will open up and allow the otherwise tapped (utilized) exhaust to flow around (to bypass, rather than drive) the turbine.

If the wastegate had made noises (chirping or whatever), it would have made them during hard-on throttling. Chances are the roar of the motor and exhaust would've drowned out (mask) such noises.

The BOV, on the other hand, comes into play when the throttle is made to close suddenly (when decelerating or off-throttle shifting). The BOV relieves the sudden (but temporary) buildup of pressure between the throttle valve (or vane if you will) and the intake system (which includes the compressor).

I've been to a few rallies myself; the only time chirping noises take place is when the cars are decelerating or off-throttle gear shifting. Since that is when the BOV active (throttle plate closed), I can only assume that the culprit is the BOV.

Regards,
Ed.

So for a car with anti-lag, blow-off valve & wastegate - would you want to tap the wastegate control from the inlet manifold after the throttle plate? I'm thinking this would provide boost control when on-throttle & then when off-throttle would provide closed wastegate + open blow-off valve which would optimize the efficiency of the antilag system (by maintaining a flow path thru the turbo but not so much thru the engine)? When off throttle the inlet pressure before the throttle plates should remain at the boost pressure set by the blow-off valve spring until throttle is opened again - then bam, instant boost!

The chirping sound is the blowoff valve also known as the wastegate. The whirring/whining sound heard inside the car comes from the straight-cut gears in the transmission.

The BOV and the waste gate are two different things. "Chirping" is the BOV, the popping backfires accompanied by a small flame from the tail pipe (can be seen easily on night stages) is the anti-lag and the in car noise is the gearbox.

I just wanted to place a vote for the BOV people who are finally starting to win the majority on this thread. It is the BOV that makes that sound, and is a pretty common sort of noise on turbo'd race engines. The older racing Toyota Celicas were notorious for sounding like they were laughing at their competitors when the throttle was lifted (-:

As far as what that whine you hear from the in-cockpit shots is, I'm not sure, but I'd guess it's actually the engine electronics interfering with the communications system the driver and co-pilot are using to communicate, which is where the audio from the interior shots is coming from.

Just had to add a little more speculation to this thread at the end there :-)

-tim

You guys are all wrong, the chirping noise is from all the squirrels that get out of the way.

The whining is from the diff...Kaaz?

Hey everybody,

The noise you are speaking about is in fact the wastegate. The noise is coming from the turbine. Remember, most WRC/Group A cars run with an open wastegate. That is why it is louder than most cars that run the wastegate into the downpipe. You still hear it, but not as much. I know this, because our rally car makes the same noises.

Hope to see you all at STPR, come and introduce yourselves.

Cheers,

Andrew Hadjiminas www.eurosportrally.com (http://www.eurosportrally.com)

To disprove the "suspension creak" theory - go sit in your WRX (you do have one, right?). Start it up. Give it gas and let off. Hear the little chirps? That's the BOV.

Ed

that sound bite was beautiful! do you have the video to go with it?

argh, I've been reading this post and argh is all I can say. BOVs DO NOT BLEED BOOST!! A wastegate bleeds boost, a BOV releases the back pressure when the TB closes. So, a car equipped with an anti-lag system and no BOV would be totally pointless. The turbo would break so damn quick from air hitting the turbine coming from the TB and extra exhaust trying to spool it up.

Err... maybe this helps.
http://bbs.scoobynet.co.uk/Forum9/HTML/001078.html

Wow E'Scubi you really started some ruckus here! I think you guys should all fight. Fight fight fight.... Just kidding. This is kinda interesting.

E'Scubi, can you say anything more specific about the noises you are talking about? Did it happen before a corner? While they were shifting? When the car was dancing a jig?

Here is another (potential) question & theory. Do group N cars use air assisted shifting? If they do maybe he was hearing those noises. It is a chirping noise as well.

C'mon guys and gals. Of all people you should recognize that sound. I do.

It is the trunk monkey hanging on for dear life and cheering on the driver and co driver.

http://www.i-club.com/ubb-files/smilies/biggrin.gifhttp://www.i-club.com/ubb-files/smilies/biggrin.gifhttp://www.i-club.com/ubb-files/smilies/biggrin.gifhttp://www.i-club.com/ubb-files/smilies/biggrin.gif

Dan - Flyin 555

This seems to be painful for most people to understand!

The chirping is the BOV. The throttle plate shuts during gear changes, and off throttle situations. When on full boost this is problematic. A pressure spike can damage the turbine on the compressor. The BOV vents this either to atmosphere, or back into the intake (depending on the MAS system being used)Some BOV's are adjustable, some aren't.
Some are sequential, some aren't. Some make different noises. They basically ALL do the same thing.

The Wastegate controls boost. Period! An MBC will allow boost to be turned up, which effectively means the wastegate stays closed longer! Some boost controllers are manual, some are electronic. They ALL do the same thing.

Antilag systems or bang bang systems usually employ a standalone fule injector that dumps neat fuel onto the exhaust turbine. IT spontaneously ignites because of the heat of the turbine. It keeps the turbo fully spooled althoug the BOV, or Wastegate could be open at the same time. One you get back on it, there is less lag, and spool up is instantaneous!

The whining noise is the straight cut gears in the sequential transmissions. In the swedish rally, In car footage, I think there could also be some electrical interference adding to the whine.

You really do have that bass ackwards. A BOV can't regulate boost. If a BOV were to start releasing pressure, the wastegate would just stay closed longer until it was equalized. If the pressure couldn't equalize, the turbo would eventually shatter its turbine from overrevving and too much centrifugal force.

BOVs can leak, but they are set so they do not. I have seen street guys with BOVs that could take 40psi without a single leak, and the Dodge Ram diesel guys run 40 psi all day long on their Holsets without leaking BOVs.

CART race cars use them.

To not use a BOV if you have ALS would be insane and would probably trash the turbo's bearings in 5 seconds flat with the force of the exhaust gas trying to push the turbo one way, and the reversion wave coming from the throttle trying to push it the other.

The way that a BOV prevents lag is that it allows the turbo to keep at its current speed after the throttle is lifted, and even though it dumps boost pressure, as soon as it closes up, the boost builds near instantaneously because the turbo has continued spinning with the help of the BOV and ALS. Meanwhile, without the BOV, it would have to rebound from having just been smacked down a few thousand rpm by the reversion wave, and would have to spool up all over again, which would take longer, and be more lag.

As far as it being the waste gate goes, I seriously doubt that, because when the throttle is lifted and the BOV opens up, there is not sufficient boost in the pipes to cause it to open.

It has to be the BOV.

By the way that 22B sound clip sounds like it's from a game...... and doesn't sound like a 22B AT ALL!! 22B has no sequential gearbox, no anti-lag.

ROFLMAO http://www.i-club.com/ubb-files/smilies/wink.gif

sorry for being so long on this one, i was trying to resist but can no more. http://www.i-club.com/ubb-files/smilies/biggrin.gif

There is an awefull lot of misinformation floating around about dump valves (BOV). Must be the biggest single con by the tuning trade in the history of turbo tuning.
The reason car manufacturers fit BOV's is to prolong the life of the turbo, to allow them to get away with selling cars fitted with 300 degree thrust bearings.

Having a BOV on a turbo engine reduces throttle response, it allows boost that would be there to bleed away.

Removing a BOV from the system will give you better throttle response than having it there. Do this with a standard turbo and you will reduce its life.

If you want to run without a BOV to get better response then a good idea is to use an uprated turbo with a 360 degree thrust bearing. (I have run normal 300 degree bearing turbos without BOV's for over 12 months on track days and road without a problem.)

The only time it becomes esential to use a BOV is when you get to using turbos the size of an RS500 full race T4. Anything smaller than that and you do not have any problem whatsoever without a BOV.

No WRC car runs a BOV, WRC spec anti lag systems wont work with a BOV.

Turbo's of the size we use on our subaru's, cosworth's and WRC cars do not suffer from reverse pulses stalling the turbo, thats a complete fallacy. I have discussed this at length with WRC engine builders and they all agree this is not what happens.

The chatter is the sound of the exhaust gasses passing through the waste gate button in the turbo housing. You need very high exhaust gas speeds to cause the waste gate to chatter, this is something you only start to see when you run high boost. WRC engines run at 34PSI boost at low revs (3000rpm) and this is bled away as the revs rise to stop the air going supersonic as it passes through the 34mm turbo restrictor. This is why the chatter is more noticable at low speed transitions as the revs are lower and the boost is much higher on WRC cars.

The boost curve is far more conventional on my own engine in the westfield, that gives 26PSI boost at 3300rpm and then only drops 3psi till 6000rpm so i get chatter right accross the rev range.

Do i use a BOV? NO
Do i need one? NO
Does my turbo have a 360 degree bearing? Yes

In case you dont know me, i run a full GroupA spec Escort cosworth rally car with ALS, WI etc, i also run one of the fastest westfields in existence on track using the engine from an escort cosworth.

WRC engines are quite unique due to the restrictors on the turbo. they dont produce much power, around 340BHP but they produce huge torque, around 480lb/ft.

Due to the restrictors in the turbo, most work is done in the 3500-6000rpm range, above that the power is being limited as the air tries to go supersonic in the turbo inlet.

it was mentioned earlier that WRC cars use external waste gates, they dont. The last true rally cars that used external waste gates were the GroupB monsters like the RS200, of which i have the pleasure of looking after and driving one. http://www.i-club.com/ubb-files/smilies/biggrin.gif

Hope the above is helpfull.

A blow-off valve is not a wastegate. A blow-off valve prevents compressor surge from a rapidly closed throttle plate... a wastegate controls compressor speed, thereby controlling the amount of boost produced. Your anti-lag sytem works by enrichining the fuel mix during closed throttle & retarding the timing so far that the ultra rich fuel mixture is still burning on it's way out of the chamber and into the turbine, keeping it spinning and keeping boost on tap when you get back into the throttle.

CART's do not have the same BOV's as what know them as... they have a POP-OFF valve..... and the major difference is that it is DOWNSTREAM of the throttle body... so NO it does not blow off when you lift... if merely serves as a boost controller to prevent overboosting. They are merely another way for officials to control racing (just like restrictor plates and so on)

This post is funnie, or am I the only one laughing? Nontheless, informative.

The[1]one

My question #3 remains, if the wastegate opens what is the point to ALS? all the extra explosions don't go to push the turbine... it goes "wasted" no?

uh... you are all wrong, it is just a different breed of trunk monkey making that chirping noise!

Wonder if they are street legal? http://www.i-club.com/ubb-files/smilies/biggrin.gif

John, once i again i bow before your great skils.

*bows*

Thank you for your opening statement about BOV's. That is my biggest beef about them. And i hate driving a car out fitted with one. Especially considering my driving style relies heavily on left foot braking. Nothing worse then heading into a corner, lifting slightly, pushing the brake on a late apex, and start feathering the throttle mid drift only to hear "PHIIISHSSHSHHHHHHHH!!!!!" and the engine grab for power as what WAS a nice drift suddenly becomes an embarassing spin.

John, you are my daddy. http://www.i-club.com/ubb-files/smilies/biggrin.gif

damn Buck-O, now i feel old! http://www.i-club.com/ubb-files/smilies/wink.gif

My question #3 remains, if the wastegate opens what is the point to ALS? all the extra explosions don't go to push the turbine... it goes "wasted" no?

NO.

ALS is a complex system, this is how it works.

Firstly, boost is controlled very acurately by using 2 fuel injectors as air valves, these feed the boost/atmospheric pressure to the waiste gate actuator, allowing minute and very fast acting boost control.
Secondly, the normal method of controlling engine iddle via an idle control valve, that bypasses the throtle butterfly is dispensed with, the static idle is set in the old fashioned way by a locked off bypass screw.
Thirdly, where the idle control valve used to be, a new valve is fitted that has a solenoid controlled valve (looks like an engine inlet valve internally) that can open/close the throttle buterfly bypass orifice very qickly.
Forthly, a miram turbo shaft is used to withstand the massive increase in turbo temperature generated by ALS.
Fifth, there is no dump valve used on an ALS equipped engine, the whole point of ALS is to keep boosting the engine, even on closed throttle.
The way it works is that when you come off the throttle, for example braking hard into a corner, the throttle butterfly closes as per normal, once the boost drops to a certain level, the ECU starts to pulse the Throttle butterfly bypass valve, this has the same effect as you constantly stabbing the throttle on and off very quickly, this means that the engine is being driven by the ECU as though it wants to accelerate again, however this occilation of the throttle bypass valve is happening so fast, it has the effect of allowing the turbo to stay spinning yet produces no additional torque to drive the car forward. The ignition timing is also controlled during this off throttle period to again reduce torque yet maintain boost presure.
The effect of all this is that massive heat is generated in the turbo exhaust side, which ignites all the excess fuel, there is no deliberate overfuelling going on to explode the turbo impellar area.
The most modern of ALS systems on the current world rally cars are far more efficient than a couple of years ago, which is why the ALS banging was less aparent this year on the WRC rallies.
The turbo used in ALS equipped rally cars is smaller than you would see on a race car for two reasons. the first is that the FIA has a mandatory 34mm turbo inlet restrictor that limits air flow into the turbo, this means that it is pointless useing a large inlet turbine unit as the inlet could not flow any more air, secondly the lag would increase due to the inertia of the larger impeller.
The water injection system works by injecting a fine mist of water/air into the inlet plenum chamber when the boost/air charge temp reaches a 42 degrees celcius (switces back off at 38 degrees celcius) below 42 degrees WI actually reduces power.This is not the same thing as intercooler sprays, these cool the external surfaces of the intercooler to help the cooling efficiency of the air/air intercooler.

i should be in bed, goodnight. http://www.i-club.com/ubb-files/smilies/biggrin.gif

Still doesn't really answer my question..... when you said it's the wastegate button going off... this implies it is open... now the ALS works off the extra exhaust gas generated by it's complex system..... if you open the WG to let it all out, how does ALS do it's job?

I thought the BOV's sound something like... Peeeeeewwwwwffff!!! not chirp chirp chirp? Eh?

Read what i wrote, the answer is there.

waste gates dont just sit either open or shut, they are being opened and closed constantly.

Its a very simple device that on WRC cars is controlled by the air injectors. What the air injectors do is meter the airflow from the compresor outlet to the waste gate actuator, when the air injectors are wide open and letting max airflow from the compresor to the actuator, the waste gate gets banged open fully wide. When the ECU is trying to hold a set boost level then as the revs rise reduce the boost all that happens is the air injectors vary the airflow from the compresor to the actuator and thus alter the amount of boost.

Its really quite simple.

You also use a slight amount of preload on the waste gate, this helps to stop it bounce and sets the min boost level your basing the air injector control system to operate in.

usually you use around half an eye of preload on a garret turbo running air injectors, although on my westfield i am using 1 eye preload as i am using an amal valve with 2mm inlet jet size and 3mm exhaust jet size. This gives me a nice 1.7bar peak and 1.5bar sustained boost.

OK, off to bed, i am driving the westie round cadwell park racing circuit tomorow, up in 5 hours!

Do they retard the timing for ALS?

Retarding the timing is what ALS revolves around. Its how the unburnt fuel dumps into the exaust manifold to be ignited by the turbo.

edit: ROTFLMAO!!! I just realzed i said "intake manifold"...DOH!! http://www.i-club.com/ubb-files/smilies/lol.gif

[This message has been edited by Buck-O (edited April 26, 2001).]

It does not get ignited by the turbo. It is moreless simular to pre-ignition. When the timing is retarded in extreme amounts when you lift off the throttle, extra fuel and air is injected via air control valve. The backfire caused is what keeps the turbo spooled up, since it has to exit the exhaust port, manifold , through the turbo and exit the rear of the car. The wastegate only comes into play when you are on full throttle when the boost pressure is to be controlled to whatever set limit. The BOV only comes to play when you lift off the throttle under load (load conditions)

Depending on the type of BOV, either diaphram or piston type, the noise they give off varies.

Ver.III allow me to take the liberty of quoting John...

The effect of all this is that massive heat is generated in the turbo exhaust side, which ignites all the excess fuel, there is no deliberate overfuelling going on to explode the turbo impellar area.

Simply having the excess air and fuel dump into the exaust manifold isnt enough to keep the turbo spooled. Especialy when the engine is at what amounts to idle. Without the combustion of that excess fuel and air, the turbo would actually bog down from having it dumped into turbo manifold like that. And there wouldent be the charicteristic BANG!! and blasting lick of flame out of the exaust if it didnt ignite in the turbo.

I thought the BOV's sound something like... Peeeeeewwwwwffff!!! not chirp chirp chirp? Eh?

They can. They can also sound like a shriek or a chirp, depending on the type of BOV and the amount of boost being bled.

BOV 101 - The BOV sits bewteen the compressor and the intake manifold. When the Engine spins faster, it needs more air from the turbo to produce the same amount of boost, so the turbo spins faster. duh.

If the driver pulls off the throttle during acceleration, the engine needs less air, yet the turbo is already spinning to produce more boost anticipating the accelerating to continue. This causes an excess of boost, which can damage the engine, or more likely, cause the turbocharger to backspin (turbo go boom). The BOV is there to let some of this air out to prevent damage.

Want to hear your BOV go off? Get on the highway, drop to third gear and mash the gas pedal. When you start nearing redline, instead of shifting, just pull completely off the throttle. In the WRX, you'll hear a SKREEEEEEEEEEEEEEAAAAAAOOOoooooo.

If you don't want the BOV to go off, try this:

Drop to third and mash the gas. at around 5k, pull off the throttle AND depress the clutch. Your engine is no longer being held back by the drivetrain, so it will just rev up to 5500-5700 rpms for a split second to eat up that excess boost.


Back to the topic - Since these rally cars are (obviously) pushing much more boost than a stock WRX, that is going to cause the BOV to emit a higher-pitched shriek. Also, if they're left-foot braking, that would cause even more backed-up pressure when they let up on the gas, as the brake pedal forces the engine to spin even slower with the clutch engaged.

Hence CHIRP - CHIRP - CHIRP as they work the pedals in corners.

<pant>

Sanguine please read the next to last post on page two by John.

WRC, and Groupe-A cars do not run BOV's. Alot of Groupe-N cars, liek teh EVO, do not run BOV's either.

And as John said, BOV are the biggest bunch of tripe in the "tuning" industry today.

I hope EVERYONE gets a chance to read Johns posts, and get educated on turbo setups. The man KNOWS what he is talking about.

For one thing, John is exactly right about the flow restriction at the restrictor plate. For a given diameter, it is easy to calculate the maximum flow rate possible - this is because any compressible fluid flowing through a converging duct can never go supersonic (check any fluids manual). The best it can do is sonic (mach number = 1) so voila, the maximum flow rate possible!

Hey, I finally found one positive use for all my fluids classes!

http://www.i-club.com/ubb-files/smilies/biggrin.gif http://www.i-club.com/ubb-files/smilies/biggrin.gif

John, thanks for the details on the ALS system. This system is completely different than what is commonly used on the street here!

If I'm understanding the ALS right, it doesn't need a BOV to control boost because it uses a much more ingenious way to do it. When the boost in the compressor side gets too high, the air injector (ingenious use here BTW) bleeds a metered amount (I assume based on the boost level) of air to the waste gate actuator. If you have precise control over the duty cycle of the injector, it seems like you can have near exact control of the bleed flowrate. Thus, the metered flow from the compressor opens the wastegate at an amount proportional to the duty cycle, and bleeds a set amount of exhaust gas, thus reducing boost (which is the purpose of all this).

John, if this is the case, why not have the air injectors REPLACE the wastegate. Have the ECU monitor the boost levels and when appropriate, have the ECU duty cycle the exhaust air injectors. UNLESS the airflow needed to be effective just cannot be achieved with the air injectors (since they have such a small orifice that the flow rate is extrememly small).

At this point, the thread is so long it will probably go unseen but I'll ask anyway.


I'm not disagreeing with the fact that the chirping noise is in fact "wastegate" flutter, since quite a few people in the know as well as the SWRT themselves have said this. But...

As was mentioned, the wastegate is constantly being opened and closed to regulate boost, that is obvious. But why then on WOT stretches such as sections of the Safari can you not hear the wastegate fluttering when the cars are flying by. As loud as the chirp is, especially if they do use external wastegates, surely you should be able to hear it chirping then, or anytime the car reaches full boost for that matter.

Why then do you only hear it when it seems the driver lifts the throttle...which brings me to my second question.

The wastegate does in fact stay closed when the turbo is producing anything but full boost, which obviously after that the boost must be regulated to stay there(enter wastegate). So why then is this chirping sound most pronounced when the driver's seem to be completely off the throttle, such as coming into a corner, when the turbo would be producing very little boost if any at all.

Why would there be any exhaust at all passing through the wastegate at this time, since at anything but full boost, the wastegate remains closed?

Because you only really hear the sound when it seems the driver's are lifting the throttle, I can see why many say it's a BOV, or even that it is boost pressure pack-peddling and hitting the compressor wheel after the throttle plate is suddenly closed(especially since I believe a UK guy reproduced the chirping sound after blocking off his BOV, and letting the boost travel backwards to hit the compressor wheel).

Just hoping one Andrew or Buck-o or John or someone else in the know can answer my questions. Again, not disagreeing with anyone, just curious.

Also, can someone explain what this BOV-looking thing is connected to the intercooler pipe on this 98-spec WRC motor is? Not saying it's a BOV, just saying it looks like one, and is in the place where one would be. http://www.iwoc.co.uk/images/rally/wrc99y.jpg

<IMG SRC="http://www.iwoc.co.uk/images/rally/wrc99y.jpg" border=0>

Thanks
(hoping everyone didn't leave this thread by now)

That actually looks more like a recirculation valve, commonly used on Audis and centrifugal supercharged car, such as the S4 and Mustangs with Vortechs instead of a BOV. I had a couple of those on my Thunderbird too, because I didn't like the noise of the BOV that revealed the mods my car had.

You can see a similar system on this Ford 2.3.

<IMG SRC="http://www.modernperformanceinc.com/images/engine2.jpg" border=0>

I'm not sure if that is a recirculation valve on the Scooby there. There are lots of things that could be, but it definitely appears to be a recirc valve.

buck o, i believe you are mistaken. that bov is meant to keep the turbo spooled. when you are on boost in a turbo car and you shift, the turbo conintues to move air. but at points were the throttle body is closed the turbo pushes air up against he closed door, thus putting in air to a length of pipe that will back feed the turbo and slow it down. a BOV prevents that by venting the air and letting the turbo conintue to spool.

Mike, without getting into a whole seperate debate, recirculation valve, blow-off-valve, compressor bypass valve, dump valve, or whatever else someone wants to call it, all do the same thing, relieve built-up pressure in the intake after the throttle plate has been shut. It's just that the vast majority of enthusiasts know them as BOV's.( For instance, if you buy an HKS BOV and plumb it back into the intake because you don't like the sound, it's still a blow-off valve even though it's now of the recirculating type)

Just trying to simplify it for others http://www.i-club.com/ubb-files/smilies/wink.gif

Indeed, I just wanted to point out the difference between that which is more commonly known as the BOV(external release) and the recirc valve, which send the released air back into the compressor. http://www.i-club.com/ubb-files/smilies/smile.gif

OK, think about this for a moment.

When the car is full throttle and boosting say on a long straight like on the Safari, once the boost is at the correct level the waste gate is held open at a set angle to allow the exhaust compressor to be held at the required speed to maintain the boost. There is no fluctuation of the actuator and therefor waste gate, it’s just allowed to bleed a little.

What you also find is that during transitions of full throttle and closed throttle the pressure in the pipework between to compressor outlet and the throttle butterfly peaks very high as the throttle is closed. Now the air that is being controlled via the air injectors to the waste gate gets it source from the compressor outlet. Because you get a rapid rise in the pressure at this point the airflow through the air injectors also peaks at the same time, this causes the waste gate actuator diaphragm to be pushed harder than it would under normal airflow and the waste gate button actually bounces. The chatter you hear is the airflow passing through the waste gate button as it bounces momentarily due to this peak pressure wave.

It is very pronounced on WRC engines at low revs in particular, as the boost is very high at this point in the rev range.

Now on a road car, if you remove the BOV you get these pressure waves in the pipework. This again forces more air than is desired back through the solenoid valve that controls the waste gate and again you get the waste gate button bouncing, so you get a slight chirp, even on relatively low boost road cars. Its no where near as pronounced as a WRC car or my Westfield running 26psi boost for example, but it can be heard.

I hope that makes some sense to you. If it doesn’t I’ll give it another go with some drawings.

On the recirculating/dump to atmosphere BOV's you have to be real carefull what you are doing with these. If you have a MAF sensor in the system on the inlet, you will find a recirculating BOV is used so that the air being metered by the MAF stays within the system by being fed back into the inlet of the compressor after the MAF, so you efectively have a closed loop system. Now if you were to vent this excess air to atmosphere you end up with a rich mixture on lift off and then throtle reaplication, this is a favourite mod of the boy racers as it leads to flame outs from the exhaust as the overich mixture ignites in the turbo due to the heat.

John, if this is the case, why not have the air injectors REPLACE the wastegate.

I think your forgetting what is controling the waste gate. The waste gate is a simple mechanical valve, it is opened and closed by air using a diaphragm device. This is the waste gate actuator.

The waste gate actuator is the device that converts airflow into mechanical movement.

In case you dont know, the air injectors are actually just a pair of fuel injectors run in parallel, they have an inlet from the compresor housing outlet of the turbo, there exhaust feeds the diaphragm of the waste gate actuator, it also has a bleed of which is just a 2mm jet, this jet allows the air from the compresor to bleed away so as not to just force the diaphram to continue to be pumped up till it splits. So to gain the boost you require you need to set this jet size to allow enough air to be retained to control the actuator, the real fine adjustment is carried out by altering the duty cycle of the air injectors. As you may be aware, fuel injectors are a digital device, they are either open or closed, varying the square wave pulse duty cycle alters there flow rate.

I think some of you are missing a fundemental point here also. BOV's dont control boost, the waste gate does that. BOV's just reduce the presure waves in the Inlet piping between the throttle buterfly and compresor outlet on closed throttle, they are there purely to help reduce shock loadings on the turbo's thrust bearing. Mass car manufacturers use 300 degree thrust bearings because they are cheep to manufacture and assemble. Competition turbo's use 360 degree bearings which are harder to build up and therefore cost more but provide far more load carrying capacity.

John stated:

When the car is full throttle and boosting say on a long straight like on the Safari, once the boost is at the correct level the waste gate is held open at a set angle to allow the exhaust compressor to be held at the required speed to maintain the boost. There is no fluctuation of the actuator and therefor waste gate, it’s just allowed to bleed a little.

Very well explained, John! I was never under the assumption that at full boost, the wastegate is held open. For some reason I figured the wastegate actuator was constantly being opened and closed. Your way makes much more sence now that I think about it.

Also very good info concerning the air injectors that do the actual actuating of the wastegate actuator. To be honest, again, I always assumed that the basic boost control was similar to that of the road cars.

Again, excellent info. If you come across any diagrams pertaining to the air injector system, I'd like to check them out.

It's a pleasure Shik, glad its making some sense.

I can go better than diagrams, next time i am working on the Escort Cosworth or RS200 i'll take my digital camera down with me and take some photos of the air injectors for you.

I'll also take some shots of the Amal valve system used on the road going coworths so you can see where the jets and pipes go. Hell, i'll take some shots of the 22B setup i am running this weekend also so we have a good cross section of whats being used in the real world.

It really isnt that complex, the trick stuff is the software in the ECU that takes all the inputs and then controls the various valves, injectors and solenoids.

I find this stuff fascinating, plus i help run a semi-pro rally team as mechanic, specialising on the engine and electrical systems. I also run my own car on track so i spent some time talking with the people at the top to ensure i understood this properly. There is a $50K/anum budget rally team riding on the fact i do understand this stuff.

Where or how can I view the recent Swedish rally??? it doesn't seem to show it on digi cable....

Excellent John. Looking forward to the pics. (especially the 22B set-up, naturally http://www.i-club.com/ubb-files/smilies/wink.gif )

So John, from the way you are explaining it, if you upgrade to a better turbo, one with 360 degree bearings, then you say that you do not need to run a BOV or any kind of valve to alleviate built up air pressure in the intake tract? You will still reduce the life of the turbo with this setup, something the WRC teams needn't worry about, but the average enthusiast, after plunking down $1000+ for an upgraded turbo, would.

Concerning the in-car radio interference noise, it always sounded to me that the noise vaired with RPM, but not speed. Wouldn't that mean the source of the interference was ignition related, and not straight cut gears as someone mentioned earlier? Just a thought ...

About those pesky BOVshttp://www.i-club.com/ubb-files/smilies/smile.gif ... I'm just now learning about those air injectors, do they not only feed air into the intake tract (behind the throttle body), but do they also allieveate the pressure wave? In other words, do they allow enough air to pass by the closed throttle body to keep the pressure wave from hitting the still spinning turbocharger? Or do most WRC level drivers just keep their right foot in the firewall all of the time and have no need for such a device?

WRXRob, I don’t know how you think bearings work? Bearings such as the 360 degree bearing in an uprated turbo don’t run metal on metal, they use oil to lubricate, the thrust pressure from the reverse pulses force the turbo shaft onto the oil film of the bearing, not the bearing itself.

The reason 300 degree bearings cant sustain the load is down to the fact there is a 60 degree air gap, when high forces are applied against this type of bearing the shaft tries to ride up at an angle into the air gap and the turbine starts to machine the housing away. This angular load also leads to a break down in the oil locally as the load is now concentrated on a very small area, causing bearing pickup and then failure.

The most important thing to protect a turbo is to use quality oil, replace it more regularly than service intervals if driving very hard and always allow the turbo to cool properly before switching the engine off. The most common reason for failure is burned oil in the bearings due to it crystallising on engine switch off.

You don’t need a BOV on a turbo with a 360 degree bearing unless it is huge, such as a full race T4 that is used on 500BHP plus engines in road car apps. The RS200 I help look after is 575BHP, uses a T4 and doesn’t use a BOV.

My own personal experiences of running road cars without BOV's is quite extensive. My last cosworth used a T34B hybrid turbo with a 360-degree bearing and 7-degree cutback exhaust blades. I used this turbo setup, running 26PSI boost every day for 18 months, I racked up over 30,000 miles in that time, I did on average one track day every month. I never had one single problem. I know of hundreds of cars running this spec with the same results.

My current track day car runs a T3 turbo, 360-degree bearing and 7 degree cutback blade on the exhaust turbine. I have had one failure on this car. I had to switch off the engine when the turbo was glowing white at the nurburgring, as an oil pipe failed. This cooked the oil so the next time I ran the car on boost, the resulting damage caused the shaft to go out of balance, it then threw an exhaust blade, this sent it more out of balance and destroyed the whole turbo. This took about half a second as the turbo was spinning at around 80,000 rpm at the time on full boost. The failure was down to damage due to misuse, i.e. switching the engine off when it was very hot.

As to Our GroupA rally car. That uses a Miram shafted, T35 based Hybrid, 34mm restrictor on the inlet as per regs, 360 degree bearing. This runs 34psi boost, full GroupA spec Anti-Lag and water injection on a 9.1:1 high compression WRC spec engine. We do on average 12 forest rallies a year plus 6 test days. During these rallies the car is full boost/throttle for an average 60 miles plus 120 road section miles. We always carry a spare turbo, the turbo on the car is fitted with quick release couplings, it takes 3 minutes to swap over. At the end of every season we buy a new turbo, use our current turbo as next seasons spare and sell the spare on. We have run full GroupA 4x4 cars for 5 years. We have never had a single turbo failure in that time. We know what we are doing with these cars; we carry out the required maintenance that ensures they stay reliable and competitive.

We compete in one of the most competitive of Forest rally championships you could. We are up against cars such as ex Kankunen, McRae and Burns WRC cars that cost in excess of $250,000. We led this championship for 6 months in 1999 running our home built car on a relative shoestring. We were the top team running on the less competitive Dunlop tyres at the end of the year. We eventually finished in 5th overall, after a gearbox failure and a broken wheel scuppered our championship. The only way we can compete against these kind of cars and this kind of money is to know what we are doing better than our competitors, we don’t have the funds to buy the active transmission systems or the $40,000 engines. We do have a team of enthusiasts who use their brains to extract the maximum plus a damn good driver and co-driver.

I am not giving you guys theoretical info here, this is real world, proven information. It’s up to you whether you want to take this on board as factual.

I believe the previous post is a textbook example of some who knows what the hell he is doing.

Wow, John, I'm extremely impressed. Can you provide a few details of the setup you are running on your Westfield, and how one would setup a street WRX for the best performance?

Great info indeed.

I believe the previous post is a textbook example of some who knows what the hell he is doing.

Amen brother. http://www.i-club.com/ubb-files/smilies/biggrin.gif

Nice post John, again you have completely wowed me from your technical knowledge.

May BOV's burn in hell.http://www.i-club.com/ubb-files/smilies/lildevil.gif

Just got back from 3 days driving the 22B, such a great car. http://www.i-club.com/ubb-files/smilies/biggrin.gif Used it to take my mate to his wedding, how cool is that! http://www.i-club.com/ubb-files/smilies/biggrin.gif LOL

I dont really want to get into tuning tips for the WRX in here as thats really for the powertrain forum.

I think i covered the engine spec earlier for the westie, its a 330BHP escort cosworth turbo, its driving through a 2wd T5 box to a quaife LSD, the car weighs 700Kg so has a power/weight of 470BHP/tonne. Pretty quick. http://www.i-club.com/ubb-files/smilies/biggrin.gif

You guys are SOOO off-base. All rally cars carry a small bird in the inner fender. This tradition dates back to the late 1800's.

Duh!