Side effects of exhaust modification

[Alex200mph]

Hi gals and girls
I wonder if anybody can help me please. I took my Chimaera off the road for two weeks and took the wadding/packing out of the rear box and put the exhaust sytem back on the car. It sounds really nice at idle too. However when I put my foot down i get a hissing/squelling noise at higher revs, but it doesnt do it at low revs. At first it sounded like the fan belt slipping but now I am not so sure since this was fine before. I noticed that the tube that goes through the inside of the back box has lots of holes, could it be that these are causing this noise when the air goes over/through them? Anybody taken the packing wadding out and experenced similar? If it is this I guess I will have to take the box apart again and put the wadding back in or put some tubes over the perforated ones to stop this like other people have done. anaybody know? Before I take the exhaust system off again!
Thanks
alex

[Simpo One]

Not an expert but from what I've read elsewhere you're supposed to replace the perforated pipe with a straight-through piece. But do check 'cos I'm not 100% sure.

[monaco]

alex

I haven't done this yet but most people that have replace the inner pipes with solid ones, and this seems to be ok.

Did you have to weld the back box together again after you removed the wadding ?? how exactly did you open it in the first place ?

[Alex200mph]

Neil, The reason I went for just taking the wadding out was because i wanted the car to sound a bit more like a yank v8 but and a little louder but not deafening. All that I did to take the packing out was to cut a square hole out of the top of the box and hook all the wadding out and then weild a plate back over the top. However I now have this hissing noise which I am not sure what it is from, perhaps from these perforated tubes I am not sure.
As for a straight through you are suppoesed to slide some metal tubing over the perforated tubes that are already in the box, I have not done this so cant advise exactly how it is done. I think you have to grind the back of the box off rather than cutting a square access hole like I have done to get the wadding out. If you want to know how to get the exhaust off I can advise you on that

>> Edited by Alex200mph on Wednesday 11th September 10:34

>> Edited by Alex200mph on Wednesday 11th September 10:35

>> Edited by Alex200mph on Wednesday 11th September 10:39

[craigalsop]

Are you sure the hissing isn't coming from the intake side of things?
Try checking that the so-called "idle screw" hasn't been adjusted too much anti-clockwise. (Bible says screw it down till it stops & then unscrew 1.5 turns (cat cars) or 2.5 turns (non-cat cars))
Mine hissed a bit till it was adjusted correctly (apparently they can squeal too if really far out)

just a thought,
Craig

[loudpedal]

I have this whistle on mine after having the wadding taken out. It's air coming out the perforated pipes as someone else said, especially under full throttle. Solution is to sleeve the pipes inside the back box, but this will make the car REALLY loud. Mine are half-sleeved which is a compromise, and personally, I quite like the whistley noise... bit like a turbo in a way.

>> Edited by loudpedal on Wednesday 11th September 11:58

[vinny]

wheres the idle screw then, would like to check mines ok. The things I have checked due to this site is never ending, good to compare though. like to keep on top of things, or is that under.

[shadowninja]

I did both modifications on my chimaera... here's what happened...

Just wanted it to be louder/more sporty so had the baffles removed... they (Motorvation) cut a large square out of the top and extracted the lot. Drove about for a couple of weeks and experienced the whistle which I think was down to bits of baffle blocking some of the holes in the perforated pipe... to be honest I didn't really like the sound (ignoring the whistle)... most of the time at around 1500 - 2000 rpm it sounded like I was driving through a tunnel but was a bit too droney/boomy for my liking... at high RPM it sounded good though

So I took it back to motorvation and they cut out the perforated pipes and put in normal pipes... now it doesnt sound so droney at particular rev ranges but sounds really aggressive when cruising, and mental at high rpm! I love it!!

If you live in Surrey I'll happily give a demo...

[jammygit]

mr ninga i'm interested - wanted to do a exhaust conv for some time have 4hc - is that motorvation in dorking? and how much if you don't mind me asking?. i live in croydon area but regularly commute to banstead. send me email if poss.

[Alex200mph]

thanks craig I am going to check the idle screw, even though by look at what people are saying here the noise is from the back box.

Looks like its a case of either living with the hissing noise from the back box as it is, or putting straight through tubes on which will make it louder but will get rid of the hissing noise, or put the wadding back in (still got it in a bag!), or putting straight through tubes over half or 3/4 of the perforated pipes and having a little bit of hissing but not loads.

Not sure which yet
Thanks for everyones help
alex

[apache]

the normal way of doing it is to grind off the back box end, remove the wadding replace the perf pipes with bits of scaffolding, replace the wadding, weld up back box, start up and grin like an idiot....pops and bangs on overrun, howls like a banshee at high revs and sounds like a dragster ticking over £100 to £170 to you sir

only side effects I've noticed are a desire to hurtle through tunnels and keep revs high in town

>> Edited by apache on Wednesday 11th September 18:59

[shadowninja]

quote:
the normal way of doing it is to grind off the back box end, remove the wadding replace the perf pipes with bits of scaffolding, replace the wadding, weld up back box, start up and grin like an idiot....pops and bangs on overrun, howls like a banshee at high revs and sounds like a dragster ticking over £100 to £170 to you sir

only side effects I've noticed are a desire to hurtle through tunnels and keep revs high in town

>> Edited by apache on Wednesday 11th September 18:59

sounds about right. which reminds me... one side effect is a drop in MPG as you tend to stay in the upper revs unnecessarily... like when passing below underpasses on the A3, you slow down to 40mph, drop it down to 2nd, rev it up to 50mph and slowly lift off for maximum effect

[MikeyT]

quote:
the normal way of doing it is to grind off the back box end, remove the wadding replace the perf pipes with bits of scaffolding, replace the wadding, weld up back box, start up and grin like an idiot....pops and bangs on overrun, howls like a banshee at high revs and sounds like a dragster ticking over £100 to £170 to you sir

only side effects I've noticed are a desire to hurtle through tunnels and keep revs high in town

>> Edited by apache on Wednesday 11th September 18:59

Apache

Was this an "Offord Production' and didn't Marshy have the same?

>> Edited by MikeyT on Wednesday 11th September 22:22

[apache]

had mine done by Thames Valley Racing.....Marshy got his done at Offord I think

[Ballistic Banana]

Heard Apaches at Le mans and Duxford and can vouch for it sounded the bees Knees and will be getting mine done at next service or probably sooner.

These are probably required after the Le mans trip though

Simon

[Mark.S]

quote:
Was this an "Offord Production' and didn't Marshy have the same?

I had mine modified by Offord, after hearing Marshy's as it happens. Apparently its a half-way house between regular and deafening which I elected to stick with after hearing one of the full-blown ear bleeder conversions they'd done.

Pops, bangs, fiendish growl at tickover, the works! £120 or so I think.

[MikeyT]

I gotta have this done methinks

[shpub]

You are all big boys but bear in mind that if you want to go and play on a track day, that they have noise limits and these are getting stricter by the year. Some of the mods that have been described areso loud that even with inserts etc, the cars will not make the regs.

If you want to play on a track which is far more thrilling than suffering from premature deafness or perforated ear drums, then think carefully before modding that exhaust.

Steve

[Alex200mph]

apache, I was going to go down the route of what you had done but changed my mind since I though that it would be too loud what with neigbours etc and just took the wadding out. Sounds like I made the wrong choice due to hissing noise from the exhaust passing through the holes in the tubes in the box! will have to rectify it in the next couple of weekends. Under the car again here we come!

[monaco]

Isn't the back box stainless steel, In which case don't you need a special welder to put it all back together again ??