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Author: Subject: Failed IVA retest - noise
martyn_16v

posted on 16/11/10 at 06:00 PM Reply With Quote
Failed IVA retest - noise

Poop. Took my car in for it's retest this morning, was quite fun taking for a drive for the first time (it went on a trailer for the first test), but my god it was cold

Failure list from the first time around was fairly short...
Speedo miles out (sensor was on one rear driveshaft, and the two rear wheels were spinning at visibly different speeds on the rollers. I've moved the sensor to the prop now and it works lovely)
No telltale for the sidelights (doh)
Wobbly rear brake line bracket
No low brake fluid warning (faulty sender in reservoir cap, replaced)
Noise

We whizzed through all of the list, no problems anywhere, until we came to the noise. On the first IVA test it had measured 104.8dB, so not even close. I had a diddy little Robin Hood/GBS/Whateverthey'recalledthisweek silencer on at the time. This has now been changed for the biggest silencer CBS do (7", as you can see from the pic it's a monster sat next to the dinky one that was there.

exhausts
exhausts


You'd think this would make quite a difference? No. It's down to 'only' 104dB Even at idle it's reading 82dB, I don't know if that's fairly normal or not, certainly doesn't sound excessive until you rev it up.

I'm not 100% sure where to look for all this noise. I'll check the packing in the silencer, but to be honest unless it's missing completely I wouldn't know if there's too much or little in there. I guess a fair amount of the noise could be induction noise, as the engine is running bike throttles with just an air filter in front of them. I also imagine it doesn't help at all that the engine isn't entirely smooth at 4000rpm yet, there is the odd stumble and sputter that will probably be louder than usual.

I did also have an interesting conversation with one of the testers. He's thinking about going freelance as it were, and offering to come out to your car to give it a pre-IVA going over for a small fee, and was asking whether I thought it was something that people would be interested in.

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Bluemoon

posted on 16/11/10 at 06:08 PM Reply With Quote
907 has done a lot of measurements/experiments with his silencers might be worth a U2U. Induction noise many-be? Maplin do a db meter buy they way if the re-test is getting expensive..
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Tiger Super Six

posted on 16/11/10 at 06:27 PM Reply With Quote
I might be wrong but cant you buy a cap that goes over the end of the exhaust which muffles it even more? I though people had mentioned these from Track days.

HTH.





Mark

Tiger Avon

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martyn_16v

posted on 16/11/10 at 06:30 PM Reply With Quote
I've got a feeling there's a proper noise meter somewhere at work, I'm going to try and track it down and borrow it for a while. I tried the decibel app on an iphone but it's so far out (99dB at idle when the proper one was saying 82) that I don't think it's any use at all.

I think my first port of call is going to be to jam a load of wire wool up the tailpipe and see what difference it makes, that'll at least tell me whether I need to be looking at the exhaust or elsewhere (probably both). I might see if the GBS silencer can be chopped up and made to fit as a middle box, I don't know if there's quite enough space.

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RichardK

posted on 16/11/10 at 06:56 PM Reply With Quote
What rev are you testing at mate?
Cheers

Rich





Gallery updated 11/01/2011

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martyn_16v

posted on 16/11/10 at 07:19 PM Reply With Quote
4000rpm
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matt_gsxr

posted on 16/11/10 at 08:58 PM Reply With Quote
Something sounds strange here.

Perhaps give cbs a ring and ask them. A big silencer (with the proper wadding) like that should make a huge difference.

There have been cases where the sound meter is incorrectly calibrated, but I don't know how you dispute that with them.

Matt


p.s. I had the same problem on the rollers with the wheels running at different speeds, they took the car for a drive around the carpark following a fiesta (all very amusing to watch!). It passed.

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adithorp

posted on 16/11/10 at 09:09 PM Reply With Quote
104 sounds a lot with a silencer that size. A lot of that is probably induction.

Decibel-killer in the end will give you a couple of db off. If you put wire wool up the end make sure it can't escape; I've heard of one glowing red wire wool rat shooting across the test centre! Air box would reduce induction noise. I've heard of people lining the bonnet with sound insulation to gain a bit of a reduction.





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Paul W

posted on 16/11/10 at 09:11 PM Reply With Quote
I have a RH Zero with a RH exhaust, for IVA I reduced it from 106db to 97.5db by
rolling some stainless scourers in chicken wire and stuffing it in long pipe of silencer.

checked it after 200 miles and it had all blew out,

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martyn_16v

posted on 7/12/10 at 01:04 PM Reply With Quote
Passed, yay! My god it was cold this morning, last time was a pleasant drive in comparison.

Got it down to 91.2dB in the end. The silencer hadn't been very well packed by CBS, so I redid that, and also knocked up an airbox from aluminium. The biggest change though was sorting out the misfire. It turns out that what I'd assumed was just a lean misfire because I hadn't been able to do any tuning, was actually the VR sensor going ape poopy over 3000rpm, and the spark timing going all over the place as a result. It took a fair bit of head scratching and a few tweaks to the VR input circuit on my MS to get it all running happily.

Forms are all in with DVLA, they will contact me 'shortly' apparently...

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stevegough

posted on 7/12/10 at 08:27 PM Reply With Quote
Nice one, Martyn well done - DVLA gestapo your only barrier to road legal now ! hope they don't take too long !

Noise - I have a 5" silencer from CBS on mine, and it was right on the nail last thursday 99dBA ! phew! After trimming the revs back to the calculated 4275 - not easy! (it was 99.3 initially - but that was at 4500rpm).

Regards, Steve

- ps keep us informed on the registration front - I'm not far behind!





Luego Locost C20XE.
Build start: October 6th 2008.
IVA passed Jan 28th 2011.
First drive Feb 10th 2011.
First show: Stoneleigh 1st/2nd May 2011.
'Used up' first engine may 3rd 2011!
Back on the road with 2nd engine may 24th
First PASA mad drive 26/7/11
Sold to Mike in Methyr Tydvil 19/03/14

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bob

posted on 8/12/10 at 02:45 PM Reply With Quote
Well done martyn

Was the test at Yeading ?






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martyn_16v

posted on 11/12/10 at 08:38 PM Reply With Quote
Ta

Test was at Yeading. Malcolm there is a top bloke, I'd recommend him to anyone. It was really quiet that morning, so I also had pretty much every tester in the station over a some point to have a chat.

DVLA so far are being surprisingly not terrible I didn't get a reg-while-u-wait like some people have managed, but I handed all the stuff in on Tuesday, got a call back on Friday to give me an appointment for inspection this Thursday. So fingers crossed I'll be on the road at the end of the week. This is at Theale btw.

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