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Kieran
27-08-2005, 01:25 AM
Here's a conumdrum for you....

I currently have a standard exhaust apart from a De-cat. It's nice and quiet, but I know from other people's experience that the back box does rein in the engine somewhat; it's certainly not the most free flowing design.

My question is....

How can I increase the flow of the exhaust, BUT not with any major gain in noise? Ariadne is a silent assasin, you see.... :evil2:

bradc
27-08-2005, 06:28 AM
if you change just the back box the car will stay fairly quiet anyway due to the resonators in the system. You can of course get different styles of back boxes which may not be as loud as others.

Kieran
27-08-2005, 12:28 PM
if you change just the back box the car will stay fairly quiet anyway....

Hmm. Not sure on that one - All the ones I've seen where only the rear box has been changed are all noisier than standard by a fair way. :inquisiti

Quail
27-08-2005, 02:42 PM
Yea when I changed just the backbox on my civic (cat & mid-silencer still in place) it turned into a bit of a monster! Im still surprised how loud it is.

I think it may be worth going to a custom fabber and asking for a nice subtle cat back system

Nick VR4
27-08-2005, 03:25 PM
Didnt Sulli get a new back box and could take out part to make it noisy if required ?

Quail
27-08-2005, 03:45 PM
You can get exhausts with baffles, but they sap your power when the baffles in (so i've heard). They look a bit :inquisiti with the baffle in too imo.

http://www.tanabe-usa.com/images/Exhausts/Tuner.jpg

^ Not a good pic, but 2nd exhaust has baffle in.

bernmc
27-08-2005, 04:05 PM
I think you'll inevitably end up with a noisier exhaust if you just change to a free-er flowing backbox. Perhaps add an extra silencer + backbox if you don't want to do a whole cat-back system?

pezza
27-08-2005, 05:03 PM
I have similar thoughts to Kieran about mine too... esp having driven a couple of *standard* cars... I like that silent stealth factor thing...

also cruising past the :-policema at junctions... silence is key :thumbsup:

I have a ralliart back box which is bit echoey and howly... but now have a powerflow silencer where the decat / cat section was. Made world of difference to cruising in the car... and the noise at startup first thing in morning is much better too. its a lost a bit o f edge up near the 7Ks but that does not bother me.

There are a few too many noisy cars driven by yobs locally... I prefer not to be seen as one of em /yes silent yob is much better IMO :evil2:

caishanvr4
27-08-2005, 06:32 PM
I am too looking for a s/s exhaust from cat back but worried about the noise levels too. I dont mind having to resort to sticking a baffle in but does the power sap all through the revs , at the start of revs or the top end of revs /Hmmm

bradc
27-08-2005, 08:51 PM
well how about a different option then.

Buy yourself another standard VR-4 back box and put it on the right hand side of the car. Then get rest of the system changed into larger piping, and have a Y at the rear axle, like what I've recently done to my car and BDA.

You will still keep the noise level low, but you will have a lot less restriction, and your car will look rather unique with 2 exhausts. I'm sure there are lots of standard VR-4 exhausts around that you'll be able to pick up very cheaply.

Kieran
27-08-2005, 09:31 PM
well how about a different option then.

Buy yourself another standard VR-4 back box and put it on the right hand side of the car. Then get rest of the system changed into larger piping, and have a Y at the rear axle, like what I've recently done to my car and BDA.

You will still keep the noise level low, but you will have a lot less restriction, and your car will look rather unique with 2 exhausts. I'm sure there are lots of standard VR-4 exhausts around that you'll be able to pick up very cheaply.

That's more or less exactly the conclusion I had come to Brad! Quieter and less restrictive.... One potential hiccup... Will that Big ol' box fit on the offside?.....

andy43
27-08-2005, 09:38 PM
Didnt Sulli get a new back box and could take out part to make it noisy if required
Yep, that would be my car :smug:
The new exhaust is stainless, from the cat back, with a decat pipe as well.
It was pretty loud, even with the baffle in, so I put the cat back on to try and reduce the noise as well as make the car legal - no difference really to the noise level, couldn't detect any change in power either to be honest, with the cat on or off.
The exhaust came with a removeable baffle, basically a 2 or 3" pipe maybe 8" in length, with a saucer shaped disc welded to it - this slides down into the exhaust tailpipe (which is a good 5" in diameter) and is attached by two allen bolts. I took the baffle out this morning, as the noise the car made on full throttle over about 4,000 revs was literally earsplittingly loud - like a fighter jet - this is due to the baffle - proper 'what the f*ck was that' looks when other traffic catches you up :thumbsup:
I've now lost the whistling 747 sound, and was hoping general noise levels wouldn't be affected - not so - the extra booming with the baffle removed at around 2 to 3,000 rpm really would 'do your head in' on a long journey - it's really too loud for a family car /grr Yes dear /help
One thing I would say, and this is only from maybe 10 miles driving with the baffle removed, is that power (or maybe just pickup/ throttle response) is very much improved - seems more 'revvy' - so the back box is possibly the key to a power increase, rather than the cat?
I've agreed to buy Ritchie rich's Ralliart exhaust from him when he gets his replaced - if that doesn't quieten it down without losing too much power, I'll be going to JP Exhausts in Macclesfield (they did an A1 job on my old TVR - absolute work of art) to see if my current rear box can be toned down a bit. I must be getting old :embarasse

Wodjno
27-08-2005, 10:00 PM
That's more or less exactly the conclusion I had come to Brad! Quieter and less restrictive.... One potential hiccup... Will that Big ol' box fit on the offside?.....

Errr /Hmmm ?? Nope !! Not unless you can move the AYC to different loation ..

Kieran
27-08-2005, 10:08 PM
Errr /Hmmm ?? Nope !! Not unless you can move the AYC to different loation ..

Arse! I forgot the AYC pump is in the way....

Bah! Stupid AYC pump! /grr /Hissy

Wodjno
27-08-2005, 10:46 PM
I think it's inevitable that Free'er flowing means more noise .. /yes
I would go along with the larger diameter pipe (3in) and then maybe 2 or 3 large resonators down the centre and then either the setup that Physician has with the centr split and 2 small boxes 1 either side at the rear or the setup i have with the feed coming over to the left side of the car and a large box and then the feed coming back out of that box and over to the right side of the car where you have matching tail pipes only and no silencer ( or maybe a small 1). /Hmmm

Dan_G
28-08-2005, 01:16 AM
For all interested I modified the standard rear box.

I have already decided I will be getting a different exhaust in the near future but in the meantime I thought I would try and make the exhaust flow better.

So I cut the back end off the rear silencer to see if I could modify. To my surprise the silencer actually has a flap in it with a spring to increase back pressure Must be for improved torque at low rpm, not good for flow. see the piccy attached.

I took this picture after I had cut/shortened the pipe on the left. this pipe was connected directly to the exhaust system and leads the gases into the baffled section of the silencer, the gasses then go through the baffles then escape from the small hole in the middle (and flap) then eventually down the middle pipe and out the tailpipe. I cut the pipe on the left so gases take the path with the least resistence and go directly out the tail pipe.

NOISE: car is slightly thoatier now but not far of standard.
PERFORMANCE: car pulls stronger at higher rpm.

Note: re welding the silencer was a pain. even on lowest setting the mig kept blowing holes in the thin metal. looked ok once I dressed up the weld and painted.

Quail
28-08-2005, 02:01 AM
^^ wow, nice DIY! Wish i was brave enough for stuff like that

bradc
28-08-2005, 06:31 AM
Kieran, it will be close to the fuel tank, but you could just mount it a little lower than where the normal exhaust sits, and make the stock one a little lower too. I'm sure it will fit. Have a look at my pics in one of my threads.

Andy, my car makes a great noise too, I haven't put my baffles in at all yet, it is 2.5" from the turbos, then 3.5" down the length of the car, then it splits into 2.5" again into straight through mufflers. I find that below about 2300rpm it is very droney and resonates, but from about 2300rpm to 3000rpm it is very quiet, especially bang on 2500rpm, which suits me well because that is 105kmh which is the speed I usually drive at. Above 4000rpm though it is completely insane, I've set off so many car alarms with it, and scared lots of old people too!

andy43
28-08-2005, 09:46 AM
Brad, mines the same - get up to an 80mph/3000rpm cruise - dead quiet - round town thru the gears or at 2500 rpm, drones like hell.
Good case for keeping the speed up :rolleyes4

bradc
28-08-2005, 11:46 AM
I wish we could cruise at 80mph, 130kph. Damned cops in our country! This is a very dumb question, but what is the actual speed limit over there? It is 100kph over here.

Mine starts to get a little bit loud at 3000rpm though.

WODJNO/Kieran, my exhaust is quite far away from the AYC box, I'm not sure how close a larger muffler would sit there though.

Wodjno
28-08-2005, 12:11 PM
I wish we could cruise at 80mph, 130kph. Damned cops in our country! This is a very dumb question, but what is the actual speed limit over there? It is 100kph over here.

Mine starts to get a little bit loud at 3000rpm though.

WODJNO/Kieran, my exhaust is quite far away from the AYC box, I'm not sure how close a larger muffler would sit there though.
Speed Limit is 70mph, soon to be raised to 80mph for Motorways :thumbsup:
My exhaust is the same as in at 80mph it's silent and above it to bad when cruising in 5th.. /yes

You See
28-08-2005, 12:56 PM
Think you'll find whatever you decide, you'll get used to it. If you keep the standard muffler it'll defeat the whole purpose of free flowing pipes as it'll be restricted once it goes into the standard muffler with smaller pipes. Avoid silencers if possible as they will limit the performance of the muffler.
End of the day, more power = more noise.

bradc
28-08-2005, 08:18 PM
I'm so jealous, over here anything over 110kph is a large fine, it sucks. I think that we have a good motorway system and it would be perfectly safe to be able to do 130kph on the motorway.

aaron68nz
29-08-2005, 12:08 AM
To my surprise the silencer actually has a flap in it with a spring to increase back pressure Must be for improved torque at low rpm, not good for flow.

How does back pressure result in improved torque and particularly improved torque at lower rpm?

Dan_G, did you also remove the flap on the spring?. I guess it would make sense to remove it? I think I'll go to the exhaust place down the road and see if they'll do the same thing to my car.

bradc
29-08-2005, 02:49 AM
aaron, I'm not sure exactly how that works either, but it seems to be a common conception that you can over-exhaust a car resulting in reduced low end torque.

ANTHONY
29-08-2005, 09:17 AM
I'm so jealous, over here anything over 110kph is a large fine, it sucks. I think that we have a good motorway system and it would be perfectly safe to be able to do 130kph on the motorway. but you have the nice weather,/yes living down there in nz

bradc
29-08-2005, 10:07 AM
we can swap then ;)

back to the exhaust, kieran, any news on the idea of you running 2x stock back boxes on your car?

Kieran
29-08-2005, 10:18 AM
we can swap then ;)

back to the exhaust, kieran, any news on the idea of you running 2x stock back boxes on your car?

Not been out to measure up and look yet. Might do today.