Removing auxiliary silencers - Advantage and disadvantage

[arjunior45]

I?m thinking to remove the two ?auxiliary silencers? after the cats, maintaining the rear one.
Is there any problem with that? Is there any mechanical risk, concerning back pressure, turbo liability or any other part?

MoT won?t be a big problem ? I think.

Nick

[pavs]

I have had mine removed for over a year now with no detrimental effects, sounds better anyway :cool:

[Brul(tm)]

Is there any problem with that? Is there any mechanical risk, concerning back pressure, turbo liability or any other part?

Not a problem at all !! Your performance from the turbo spooling gets much better :smoke: At least, that was my experience. But i have only a very small rear sliencer right now and from the cats a 3" pipe in a straight line as much as posible :cheers: Don't have a picture here, will post them tonight.

Greeting,
Marc

[AlfaJack]

Will be fine :) Steve Webb has always suggested this - turbo cars need little silencing :)

[Steve Webb]

Did I hear my name?

Yep, as far as I'm concerned, you can remove pretty much everything downstream of the turbo, 1 silencer is probably a good idea though.
I ran for a few years with just a single rear silencer, its noisier but nothing like the chav's in their Corsas.

Turbos work best with a large pressure differential across the turbine, spool up quicker etc. Which if you take it to extremes means you lag the manifold (to keep the exhaust gas as hot as possible and taking up as much volume as possible therefore at as high a pressure as possible) and run the exit of the turbine housing straight to atmosphere ( short fat straight pipe out to the side of the car)

Of course for the road this is a little extreme, but for high power applications its the thing to do. I believe some drag Integrales use this sort of exhaust setup.

[arjunior45]

ok guys,
the day after tommorow I'm going to remove them and mount a free flow rear one only.
If everything goes probably I'll have my Q4 on the street by the end of next week.

Thanks for the infos.

Nick

[arjunior45]

Not a problem at all !! Your performance from the turbo spooling gets much better :smoke: At least, that was my experience. But i have only a very small rear sliencer right now and from the cats a 3" pipe in a straight line as much as posible :cheers: Don't have a picture here, will post them tonight.

Greeting,
Marc

waiting for any picture although your answer is clear.

Nick

[AlfaJack]

I'll have my Q4 on the street by the end of next week.

Thanks for the infos.

Nick

We want pictures!:cool:

[Brul(tm)]

waiting for any picture although your answer is clear.

sorry, totally forgot it... :doh:
I'll try again tonight :redface:


Greetings,
Marc

[arjunior45]

We want pictures!:cool:

as soon as possible I'll post some pictures.

I went by the 'muffler's service' this morning and the guy there told me that keeping only the rear silencier it won't be a problem with our MoT {as long as the noise is not exessive}. A good quality rear one will do the work.

As for the tube connecting the cats with this 'rear silencier' he told me the followings:
a} for a car up to 270bhp a tube at 63.5mm dia {almost 2,5"} will better than the 3" one.
The 2,5" tube is more 'suitable' for the rev range with no boost {less than 3200 rpm} and it does not restrain the turbo at the 'boost' revs up to the rev limit.
and
b} the 3" tube is the must {'one way'} for cars with more than 270-300 bhp. In a car with less bhp will increase the lag!

Any comments about 3" tube increasing the lag at 'low' rpm {N/A aria}?
You see, we are going to use Q4 as an everyday car, mostly in city traffic and I certainly do NOT like to have more lag at all!

Nick

[Brul(tm)]

Any comments about 3" tube increasing the lag at 'low' rpm {N/A aria}?

My experience is that the turbo spools much quicker..... boost around 3000RPM in stead of the 3500RPM with the original exhaust. Can't notice any increase of turbo lag.... The config I have, works fine and much easier/fun to drive :cool:

Keep in mind that only a rear silencer for a daily driver could be to much..... I don't mind, i like it.

Greetings,
Marc

[arjunior45]

Keep in mind that only a rear silencer for a daily driver could be to much..... I don't mind, i like it.

Greetings,
Marc

Thanks for the reply Mark.
If you mean the noise from just the rear silencer for the "to much" of yours, won't be a problem at all to my wife and me. My other 'everyday' car is a 'Bertone' step nose w/o air filter at all and just one {the first one} silencer. And my wife drives it too. So, noise is not an issue for the family - hope not for the newborns too, as they 'managed' to have a nap in there.
Greek MoT might be the problem with the noise if it will be more than the legal limits. Do you have such a problem?

Nick

[Steve Webb]

My other 'everyday' car is a 'Bertone' step nose w/o air filter.
Nick

Without an Airfilter? In dusty Athens? :eek:

[arjunior45]

Without an Airfilter? In dusty Athens? :eek:

Yes, I have just the 'horns'! Bought the car {in northen Italy, long time ago} fitted with them and never bother to change them. Fortunately, Greek MoT did not have or find the homologation for this model so I kept them and it is registered with them {and as a 4 seat coupe}. As for the noise, Alfa at that time {'67} gave a +1 db than the nowdays limit and exessive noise is not a problem either.
For the dust? Cann't tell more than I rebuilded the engine eight {8} years ago and still get the 1-1,2 lt/1000Km oil. Strange even to me. Probably due to the American seals mounted.

Any way, in a couple of hours I'll go to the muffler's garage and see what happens {concerning noise and MoT} with just the rear sillencer. Yesterday he told me that if it stays under legal limits they did not care for the number of sillencers!!!?

Nick

[arjunior45]

just return from the 'muffler's shop'.
Finaly I went for the 2,5" {63,5mm} tube and the impressions are:
a} almost no extra noise. Only at idle a barely notice bass rythmic noise. Can pass the MoT test easily.
b} smoother drive up to the 'boost' area
and
c} boost at 3000-3100 rpm. Before it was at 3500 rpm.

pictures before {1st - 2nd} / pictures after {3rd -4th - 5th}

[AlfaJack]

Looking good!

[Brul(tm)]

Looking good, looks very similar to what i have :smile:

This is the original setup with way to many corners and restrictions
http://i115.photobucket.com/albums/n288/BrulTM/EPS%20march%202003/IM002908.jpg

This was removed :eek:
http://i115.photobucket.com/albums/n288/BrulTM/EPS%20march%202003/IM002928.jpg

junction right after the cat's
http://i115.photobucket.com/albums/n288/BrulTM/EPS%20march%202003/IM002930.jpg
http://i115.photobucket.com/albums/n288/BrulTM/EPS%20march%202003/IM002932.jpg

The 3" pipe to the rear silencer
http://i115.photobucket.com/albums/n288/BrulTM/EPS%20march%202003/IM002944.jpg

The rear silencer itself (smallest)
http://i115.photobucket.com/albums/n288/BrulTM/EPS%20march%202003/IM002938.jpg
http://i115.photobucket.com/albums/n288/BrulTM/EPS%20march%202003/IM002953.jpg

Nice and open :cool:
http://i115.photobucket.com/albums/n288/BrulTM/EPS%20march%202003/IM002941.jpg

Nicr straight tot the back
http://i115.photobucket.com/albums/n288/BrulTM/EPS%20march%202003/IM002956.jpg
http://i115.photobucket.com/albums/n288/BrulTM/EPS%20march%202003/IM002957.jpg
And all in stainless steel :tasty:
Sounds great, will post a sound sample soon, if i can find it.

Greetings,
Marc

[arjunior45]

Sounds great, will post a sound sample soon, if i can find it.

Greetings,
Marc

love to hear the sound with the 'open' rear silencer of yours.

The sound with the oem one is 'terrible'. I was expecting to hear something - anything after removing the two auxiliary silencers and I was disapointed. There is less noise than before {with a small hole - 0.6mm dia - on the second after cats silencer}.
Better for the MoT test though!

As for the disadvantages :
I notice a +150 rpm at idle speed. Now idle is at 1200-1250 rpm and need adjustments. I'll do it today and I'll go for the gas emissions test.

Nick

[Brul(tm)]

The sound with the oem one is 'terrible'. I was expecting to hear something - anything after removing the two auxiliary silencers and I was disapointed. There is less noise than before

The exhaust system i have made, is custom done by a specialist (www.uitlaten.com).

They do only custom exhausts for all kind of cars. The rear silencer is an absorbtion type of silencer, filtering all high frequentie sounds so only the low frequentie sounds are left over. This results in a very very dark an low sound :tasty:

After the exhaust moification, i never had to adjust the idle speed setting. So i think you have a different problem. Do you know when the clearance of your vales where checked for the last time? If there is to much clearance you will also have difficulties to get good result for MoT.

Greetings,
Marc

[arjunior45]

The exhaust system i have made, is custom done by a specialist (www.uitlaten.com).

They do only custom exhausts for all kind of cars. The rear silencer is an absorbtion type of silencer, filtering all high frequentie sounds so only the low frequentie sounds are left over. This results in a very very dark an low sound :tasty:

After the exhaust moification, i never had to adjust the idle speed setting. So i think you have a different problem. Do you know when the clearance of your vales where checked for the last time? If there is to much clearance you will also have difficulties to get good result for MoT.

Greetings,
Marc

Marc,

1200 km ago I've changed all the inlet valves {bended due to a cambelt failure} and I believe they should be o.k even now.
Idle was at 1100 rpm and after the pipe went to 1200-1250 rpm. Adjusted this morning to 950 rpm. I know I have to lower it more, to 800-900 rpm and probably I'll do it after the MoT test.

Emissions {with pipe on} are :
CO : 0,045 / HC : 80 / O2 : 4,80-5,10 {idle and 2500 rpm} / CO2 : 40 {or something like that - can't remember right now.
I can pass the MoT test with no other mod and have the 'registration' {hopefully}. Appointment for the test is next Thursday.

Nick

[pavs]

Good luck for next week Nick

[arjunior45]

Good luck for next week Nick

thanks

Nick

[arjunior45]

Just pass the MoT test!!! By next week I'll have the registration and the traffic plates/numbers!!!

According to them, after half an hour spinning in the highway, the emissions are:
a} Idle :
CO : 0 %, HC : 5 PPm, λ{lambda} : -
b} 2500 rpm:
CO : 0 %, HC : 9 PPm, λ{lambda} : 1,005.

Well, removing the two auxiliary silencers and keeping the OEM cats and the rear silencer, does not affect the gas emissions. That's what I've confirmed this morning.
As for the sound they had nothing to notice.

That's all for now.

Nick.

[Brul(tm)]

Well, removing the two auxiliary silencers and keeping the OEM cats and the rear silencer, does not affect the gas emissions.

Of course ;) This effects only the loudness and "color" of the sound the car will produce :biggrin:

But congratulations with the MoT test :cheers:
Hopefully the registration and plates will processed fast.
Have fun with the first legal test drive next week :cool:

Greetings,
Marc

[pavs]

Great news Nick

[arjunior45]

Thanks guys.



Have fun with the first legal test drive next week :cool:

Greetings,
Marc

Mark,
I'll take it for a 'test drive' this weekend {hopefully} if I'll manage to have the papers {registration} tomorrow morning. It will be a freeze weekend and that's good. But I'll drive it with the '0,6 - 0,7 bar boost / no overboost' map at the moment to see if there are any malfunctions with it. So, it won't be that fun!
My wife must become familiar with the car too and that will be an issue.
Little bit anxious to see how the car reacts in fast corners and in the rain.

So, it will be a busy weekend!

Nick

[pavs]

Nick

the wife will love it

[arjunior45]

Nick

the wife will love it

nope,
she already told me that our 'Junior' {gt1300junior - stepnose} accelerate better from low rpm {1000 - 1200 rpm} up to the rev limiter {7400 rpm} and for the more it is a rear wheel drive! She loves to go sideways all the time!

We will see this weekend.

Nick

[AlfaJack]

Cool wife you have! My missus hates the Q4!

[wrinx]

My missus hates the Q4!

Really...why? :confused:

wrinx

[cuore_sportivo_155]

the car gets more attention than her?

[Brul(tm)]

My missus hates the Q4!

I don't have that problem :smoke:
She loves Alfa's, she has a 155 1.8 TS herself :bowdown:

Greetings,
Marc

[AlfaJack]

Really...why? :confused:

wrinx

Hate might be a bit strong. Cars are just A-B mobility things for her that should always work and never need fettling. She might be slowly coming round to my way of thinking when I bang on about dealer prices and depreciation etc :eek:

[wrinx]

Cars are just A-B mobility things for her...

That's just wrong...and you want to spend the r....ahh, done that one already :doh:

wrinx

[AlfaJack]

That's just wrong...and you want to spend the r....ahh, done that one already :doh:

wrinx

:tongue2::tongue2::tongue2::smile:

[wrinx]

:cheers:

wrinx

[Ditlev]

just return from the 'muffler's shop'.
Finaly I went for the 2,5" {63,5mm} tube and the impressions are:
a} almost no extra noise. Only at idle a barely notice bass rythmic noise. Can pass the MoT test easily.
b} smoother drive up to the 'boost' area
and
c} boost at 3000-3100 rpm. Before it was at 3500 rpm.

pictures before {1st - 2nd} / pictures after {3rd -4th - 5th}

This looks great, I am looking to do something similar since my silencers are broke.

Those tubes you got, where can i get them? Maybe they have a catalogue number or something I can use to get some like them?

[arjunior45]

This looks great, I am looking to do something similar since my silencers are broke.

Those tubes you got, where can i get them? Maybe they have a catalogue number or something I can use to get some like them?


the tubes are not something special. Ordinary iron tubes {like the oem tubes in the exhaust system} were bended to the shape shown in the picture. I believe that you can find these tubes in any 'muffler's shop-garage'. The question is if they will spend the time to bend them.

If you want something to last for ever you can go for inox tubes and angles. It will be easier to have the shape like that.

Nick

[Q4Jan]

My car had the same adjustment as Brul at the same shop. (A little earlier i believe, not sure anymore.)

http://www.uitlaten.com/imagesb/1038.jpg

http://www.uitlaten.com/imagesb/1037.jpg

Still very happy. Not to much noise, but i had the biggest end silencer placed that could be fitted. I believe Brul has one a little smaller, and louder. :cool:

[Brul(tm)]

I believe Brul has one a little smaller, and louder. :cool:

I have the smallest :cool: It definitely makes a bit more sound, it's more darker and has a bit more "body" or volume i guess :smoke:
And i did the down pipe last year, it's been slightly modified and removed the first catalyc converter.

Greetings,
Marc

[Steve Webb]

How does the rear pipe fix onto the cat's? And did they make the pipe up on the car or fo they have a template :confused:

Looks like it gives more clearance under the car than my current setup.

[Brul(tm)]

How does the rear pipe fix onto the cat's? And did they make the pipe up on the car or fo they have a template :confused:

Looks like it gives more clearance under the car than my current setup.

It's all custom build, so no template here (from memory). If you look under my Q4 and the one from Jan, you will notice that the design of the exhaust is slightly different.
The fixing points for the exhaust are also customized. And yes, the exhaust is a bit higher or closer fixed to the car.

If you take a look at page 1 of this topic, you will find a view pictures :tongue2:
The cats are fitted the same way as the OEM sollution.

Greetings,
Marc

[ecl]

since you passed the mot, its time to get rid of the cats:) 2,5" straight from the turbo, works great,and grat sound. not so sure about the emissions though:D

[Q4Jan]

@brul
Did removing the first cat change the outcome on the (apk)mot?
I believe the first cat only works when the engin is cold but as you got a working example. Is this true?

My car still has all three cats present and is extremely clean.:biggrin: