Screamer pipe

[garagestmarien]

Hi,

Hopefully this question / comment will be good for discussion.

I have read that a screamer pipe on a turbo is a good way to go in squeezing out some extra horses. But because of the sheer noise, the conversion wouldn't work on the street.

So, my idea:

What is wrong with building a screamer pipe with it's own small silencer.
Is this a mad / stupid idea or what?

John

 

[billyo]

Sounds good to me although the silencer would surely need to be pretty big as it makes such a high pitched sound.:???:

 

[garagestmarien]

I think the silencer could be kept small, if it was a baffle type, rather than a straight through. Perhaps, also a couple of bends along the pipe to break the noise.

 

[HDi fun]

What's a screamer pipe, please?

Rgds,

Paul.

 

[pgarner]

i does the same job as blow off valve / diverter valve

but it dumps the air straight from the wastegate to an exhaust pipe so very loud

http://www.torquecars.com/tuning/screamer-pipes.php

 

[garagestmarien]

Thinking more on the subject.
I don't think silencing for the main exhaust is really needed, because the turbine wheel is braking the exhaust pulse up, but when the wastegate opens, then pulsed exhaust is going down the pipe also.
So I think a straight through system for the turbo is okay, to please the authorities and a small silenced pipe for the wastegate.

Doesn't this sound like a way to free up power.

 

[HDi fun]

I think it'd be louder than you think. An open ended turbo screams very loudly indeed, and chucks out the odd flame or two on lift off.

It might be a good way to inimidate the VoSA lot that do roadside emissions tests though. They'd need kevlar suits and asbestos gauntlets

"Just rev it up gently please sir whilst I attend to the lambda probe attached to the tailpipe."

 

[old-git]

OK, this has me baffled (no pun intended)

The wastegate on the turbo allows excess gases to bypass the exhaust turbine once a certain (user defined) pressure is reached. These gases are re-directed back into the car's exhaust system - correct?

A BOV serves no f*****g purpose apart from making a stupid noise every time you change gear - correct? (IMHO - not required on a properly set up system)

So, what the hell does a screamer pipe do that is any different to a wastegate or BOV? I am obviously missing something here.

Sounds to me just a very efficient way to get tugged

 

[HDi fun]

I'm with O.G on this. I can't see the need to vent excess exhaust gas volume given my understanding. The wastegate does that as standard.

Or, is it that the screamer vents compressed air from the induction side that is not required because the throttle valve is shut (diesels don't have a throttle valve so it won't apply to those / again, I'll ignore diesels here).

O.G - is it because the throttle has been snapped shut suddenly, the turbo(s) is (are) still spinning and there's a build up of air mass (therefore pressure, assuming that the intake manifold geometric volume remains constant!). THis could stall the turbo's or perhaps even send it/them into reverse?

But, given the extremely low mass of a turbocharger's rotating turbine assembly, therefore it's low moment of angular inertia surely it would not take very much to bring it to a halt pretty swiftly. Or, have I missed the point - that being that anything spinning at 200,000rpm plus is going to take quite a lot of stopping.

Therefore maybe that's why there's a need to discharge excess intake (engine side) pressure.

But I'm still not sure, why not just fit a damping mechanism to the throttle in the first place? Thus avoiding all the complication and associated noise.

Anybody out there that can advise?

Kind regards,

Paul.

 

[old-git]

Good old Wiki:

http://en.wikipedia.org/wiki/Turbocharger gives a pretty good explanation of the theory and workings of a turbo system, with no mention of a screamer pipe

Looks like some sort of pressure relief valve MAY be needed (still not convinced) in the induction tract, but released gases are better fed back into the exhaust side in order to help keep turbo spinning so as to reduce lag. This means more plumbing and much less noise but what are you after, show or go?

 

[HDi fun]

Yep, Steve, that's a fair point. recirculate the stuff rather than vent it. I think that I emanate from a more gentle era where less more.

As far as noise goes, I always thought that the objective was to make as little [noise] as possible but to get useable, driveable performance maximised.

So, screamer pipes have no place in road cars? That's my position.

As for emissions, I cannot comment - I'm lacking a degree in biochemistry, and also lacking one in green ecology!!

The only thing I can see as a problem (I'm not qualified to comment on this either) is that over zealous EGR can increase combustion chamber temperatures and increase NOx emissions.

Perhaps we should all drive 0.8 litre three cylinder cars which attract £0.00 VED.

 

[old-git]

Ah, Paul, now you ARE showing your age It appears to me that the tuning mantra for today's younger enthusiasts is more noise the better even if it means, usually. less performance You only have to look at the tail pipe sizes to realise that most of then haven't the slightest idea what they are doing! If they are only interested in 'style over function' then I have no problem with that, but they shouldn't confuse style with performance.

For example, my project will be using, probably, a 75mm ID exhaust pipe with a 90mm tailpipe. This will be sufficient for the 500 odd horses galloping out of the back. The final sizes will be determined on the dyno.

What were we talking about? Oh, yeah, screamer pipes. Seems to me that their only functions are as a fashion accessory and blue meanie magnet But, then I am 55 so what do I know? BUT, once a boy racer, always a boy racer (at heart).

 

[claymore]

OK, this has me baffled (no pun intended)

The wastegate on the turbo allows excess gases to bypass the exhaust turbine once a certain (user defined) pressure is reached. These gases are re-directed back into the car's exhaust system - correct?

A BOV serves no f*****g purpose apart from making a stupid noise every time you change gear - correct? (IMHO - not required on a properly set up system)

So, what the hell does a screamer pipe do that is any different to a wastegate or BOV? I am obviously missing something here.

Sounds to me just a very efficient way to get tugged

a waste gate and bov serve completely different purposes, the waistgate stops the turbo from delivering to much boost, the bov or recirc valve let off presure on throttle shut situation, to stop the back pressure in the inlet damaging the tirbine in the turbo, as for screamer pipe I'v got no idea what the advantage of one of them would be

 

[garagestmarien]

Hi

I've already got another post on this subject.
But a few comments they may help.
(I am commenting on an external wastegate)
On my set up, the wastegate pipe goes into the exhaust just after the turbo and at right angles.
Now to me, the wastegate is pushing in pressurized exhaust pulses into the flow from the turbo.
I would think that moving the entry of the wastegate pipe well away would help increase performance, by not disrupting the turbo exhaust flow.
So I would think a screamer pipe would be a good idea and don't see why it couldn't have it's own silencer to control the noise.
I don't know if this would upset the lambda sensor readings, but on my project, it doesn't have one.

 

[garagestmarien]

OOPS!
Sorry, this is my post.
So another question.
Wrapping the exhaust manifold and turbo (exhaust side) to keep the heat up and therefore allow the exhaust gas to go faster.
Is there any noticable gain doing this.
There are kits on the market and quite expensive at that.
Any ideas
John

 

[pgarner]

ok like o.g i search for screamer pipe on wikpedia and this came under wastegate

A "divorced" wastegate dumps the gases directly into the atmosphere, instead of returning them with the rest of an engine's exhaust. This is done to prevent turbulence to the exhaust flow and reduce total back pressure in the exhaust system. Divorced wastegate dumper pipes are commonly referred to as "screamer pipes" due to the unmuffled waste exhaust gasses and the associated loud noises they produce.

so would i be right by saying rather than the wastegate sending the exhaust gas down the exhaust . it sends it down a dedicated exhaust pipe

and whats wrong with having a little 1ltr car with a 4" pipe and 6" tail pipe it gives me 15bhp then i get another 10 from the induction kit

your right thou too many people go along with the more noisy the faster it goes





wrapping the exhaust is supposed to lower the under bonnet temperatures

 

[old-git]

a waste gate and bov serve completely different purposes, the waistgate stops the turbo from delivering to much boost, the bov or recirc valve let off presure on throttle shut situation, to stop the back pressure in the inlet damaging the tirbine in the turbo, as for screamer pipe I'v got no idea what the advantage of one of them would be

Yup, I know that

Probably serves the same purpose as aftermarket BOVs - Lots of noise. Another case of A.F.A.N.S.

 

[garagestmarien]

Yup, I know that

Probably serves the same purpose as aftermarket BOVs - Lots of noise. Another case of A.F.A.N.S.

I agree that after market BOV'S make noise, but like on my engine CX25 GTi Turbo2, the factory recirculating type caused disrupted airflow to the intake. The standard airflow meter is Bosch with the flapper door and when testing the standard dump valve, you could actually see the door being pushed closed for a split second. With a twin piston dump to atmosphere this has been stopped.
However, the new build engine is having a complete new fuel management system, so this won't be a problem.
As for Wiki, it proves my point that more performance can be had by giving the waste gate it's own pipe and I still don't see why, with a good silencer this can't be done and still be quiet.

 

[pgarner]

Yup, I know that

Probably serves the same purpose as aftermarket BOVs - Lots of noise. Another case of A.F.A.N.S.

AFANS???

if the exhaust gases are going down a separate pipe then they would fail emissions due to there being no cat. if you added the cat then there would be no point as the cat would increase the back pressure.

in newer VAG cars 1.8t and 2.0TFSI if a BOV is fitted the cars should overfuel as they are looking for the pressurised air being flowed back into the intake from the DV

 

[HDi fun]

I like the sound of the CX - one of my favourite cars of all time. I've never driven the turbo but do recall the completely over the top brake response on the more modest 2400cc ones.

Brean fun though, in a quirky kind of way.

 

[HDi fun]

ok like o.g i search for screamer pipe on wikpedia and this came under wastegate



so would i be right by saying rather than the wastegate sending the exhaust gas down the exhaust . it sends it down a dedicated exhaust pipe

and whats wrong with having a little 1ltr car with a 4" pipe and 6" tail pipe it gives me 15bhp then i get another 10 from the induction kit

your right thou too many people go along with the more noisy the faster it goes





wrapping the exhaust is supposed to lower the under bonnet temperatures

You can't just keep adding up the suggested bhp increases from sucessive modifications as you imply. Thanks, Paul, for clarifying this. The set of equations is nowhere near linear.

BR's take note, noise and performance are totally unrelated.

 

[obi_waynne]

BR's take note, noise and performance are totally unrelated.

This applies to mopeds as well as cars.

The Ferrari F40 (or maybe the F50) - I am led to believe has a screamer pipe- which is the third exhaust hole at the rear.

 

[garagestmarien]

This applies to mopeds as well as cars.

The Ferrari F40 (or maybe the F50) - I am led to believe has a screamer pipe- which is the third exhaust hole at the rear.

Correct, that is the F40.

John

 

[HDi fun]

Come on - let's keep it in perspective. The F40 is producing something appraoching 500bhp, probably using four turbos to assist. There's a lot of opportunity for high back pressure in such an engine.

 

[old-git]

AFANS???

A.F.A.N.S = All Fart And No Sh*t

 

[pgarner]

Ahh

 

[obi_waynne]

You wish you hadn't asked now!

 

[pgarner]

no i was thining

Another fin something something something

 

[SLEEPER]

A screamer pipe gives absolutely no benefit other than a noise to frighten old ladies etc

It is on the "exhaust" side of the turbos - The exhaust which is diverted through the wastegate to drive the tubo vanes (and thus produce the boost) has to go somewhere . There are only two choices -Either back into the exhaust or not . The latter is called a screamer pipe .
One side effect of not using a screamer pipe is that with a straight though exhaust in the car it can actually be noticably quieter as soon as the turbos come in . A properly tuned exhaust will also take this into account.
Lastly there is absolutely no point in putting a silencer on a screamer pipe cos the only reason for having it is the noise it makes.

A screamer pipe also has absolutely nothing to do with blow off valves which are on the "inlet" side of the turbos .
These are used because the turbos are driven by the exhaust gas pressure to push extra fuel into the engine.
When you change gear and the revs go down (even momentarily) the vanes simply cant slow down this quickly and would continue to spin at the same speed without the BOV , This would mean overfuelling on a big scale as the boost level ( and therefore the fuel level) would be far too high for the lower revs.
The BOV (or BOVS on a twin turbo) reduce(s) the pressure and therefore stops the overfuelling.
An altenative to a BOV is to have a recirculatory valve that sends the "surplus" gases back to the "inlet" side of the turbo. This works fine and is the set up on nearly all standard cars where the boost is running at fairly low presssue.

However if you raise the boost ( to get extra power) using the recirculating valve method is not always safe because the boost level becomes far more critical and the recirc valves cant always handle the higher pressures.
It is safer to vent the extra gas pressure into the atmosphere direct.
Bovs can be adjusted to make more or less noise. On my car they are only noticeable on full boost and are absolutely silent the rest of the time.
Depends if you want "go" or "show"

Hope this helps .

 

[obi_waynne]

Very informative Sleeper - thank you.

 

[garagestmarien]

Don't want to cause an argument here but I'm afraid your wrong Sleeper.

BOV's or dump valves whether recirculating or to atmosphere are there to protect the turbo.

Without one, when you close the throttle there is nowhere for the gas to go, but the turbo is still spinning and trying to make boost. So what happens is that the turbo stalls. Apart from this causing turbo lag on gear changes (the turbo has to spool up again) the inlet vane is pushed hard against the bearing and will cause premature wear.
So the BOV allows the turbo to keep spinning without pressure, so that a quicker response is gained between gear changes.

Again with the screamer pipe (I think people are getting confused because of it's name - so lets call it a waste gate pipe), as I stated in an earlier post, I am referring to an external waste gate and with this set up the waste gate exhaust enters the main exhaust at right angles and therefore must disrupt the exhaust flow. Don't forget, we don't want any back pressure on the turbo exhaust.
Also as I stated before, the fuel system on my car doesn't have a lambda sensor, therefore using a "waste gate" pipe will not have any effect on the fueling.
Perhaps on an internal waste gate turbo and on systems using lambda sensors the previous points posted are a good argument.

So once again (depending on engine set up) I think a separate pipe for the waste gate would increase power and again with it's own silencer.
I'm not interested in noise but power.

John

 

[SLEEPER]

I dont think either of us is wrong wrong I think we are both right.
With the screamer pipe, you are referring to a system wihere the angle is 90 degrees and would cause back pressure on the turbo . My post only refers to a custom designed one off straight through exhaust ( which I have)
Yes of course bovd & recircs protect the turbo but they also must control the mixture as well .

 

[garagestmarien]

Okay,

The BOV doesn't have any effect on the mixture for injection, perhaps it does on carb's but I've never had anything to do with them.
On the injection, the fuel is calculated before the turbo and only on the amount of air entering.
On mine using a recirculating BOV (factory Bosch) and a race twin piston dump to air type, there is no different reading on the mixture.
Well not entirely true, my mixture with the race BOV is more stable because of the airflow meter not being disrupted.

Your exhaust system.
Is there any noticeable noise increase using the straight through system and is it stainless or mild steel.
I am contemplating building a straight through in stainless using middle and end silencers, system size from the turbo approx 75mm and mandrel bent tubes, so only joints are the silencers.
I was wondering about the turbo whistle though.
AND I AM GOING TO BUILD A SEPARATE WASTE GATE PIPE WITH SILENCER, BECAUSE I THINK IT CAN ONLY HELP MY SYSTEM.

John

 

[SLEEPER]

your set up is different to mine and i am sure this means different rules apply and you are far more likely to know whats right for your car than I am
On mine the exhaust sytem is stainless and has been designed from the mainfold back . It is 80mm and virtually straight back to the rear box because on my car ( a Nissan stagea with a RB26dett engine) thats the natural shape of the pipework. Because it is large and straight through ( to the rear box) and the turbos waste gases join at a better angle than 90 degrees I dont think I have back pressure issues.
Whilst I am not running silly boost it is above standard level and I was advised the recirc valve should be replaced with twin BOVs ,

Re noise Yes it is loud, Infact it is probably too loud up to 3500rpm when the turbos come in . It then gets quieter because the exhaust is directed through the turbos and then re enters the exhaust in a different way. I cannott explain why but it really does make a noticeable difference and is weird the first time you experience it.