I have an MNR exhaust with their stainless repackable silencer on an R1 engine. Has anyone had a similar exhaust measured for noise level for a track day? What does it come out at?

Marc,

I guess you've had one measured for things like total kit car live and the donnington kit car show, as well as for racing.

[Edited on 3-3-2006 by smart51]

hi colin
yep for donnington we tested at 99 db with a decibel killer this came down to 95db on the r1, but we did have the silencer outlet pionting straight to the meter rather than to the ground slightly

best regards

marc

Hi smart 51 if you want it tested we have noise meters. the same as the msa use we are in birmingham.

cheers matt o121 350 3258

just ring if i can help you

Matt, that would be great.

Colin

Colin,

Another thing to consider is noise emmited from other sources not just the exhaust - engine noise ( from under the bonnet ) pannels rattling. intake noise

another point is not everything that sounds noisey has a high DB level the V8 SOUNDS VERY NOISEY but at the SVA was well under the limits ( I think this has a similar can to yours ( ok - well one each side ) .

We have the DB metter that you can buy from maplins think I bought it while it was on special offer. The SVA man kindly checked this on his calibration machine and found it to read slightly out.

Make sure you let us know what it reads as this would be usefull for future queries not all MNR customers use this site.

Manj thanks

Agriv8

I had an R1 can on for SVA. SVA said it was 100dB at 7600 RPM (2/3 max power). The MNR can sounds louder at tickover than the R1 can. Most track days want to test at 3/4 of max revs which is 8800 RPM. I'm concerned that I won't meed the 105dB limit on the most generous tracks. because of the louder can and higher revs. I'll ring procomp in a minute and book a test.

At tracks with drive by noise meters you have to be on the ball, but at others Ive cut down the max rev display on the dash if that's makes any sort of sense ? My old dash you could figure in max revs from 0-16000rpm, I normally set it at 12000 but for noise testing I used too set it at say 8-9k as there pretty cute these days and rather than take your word for it sneak a look at the rev counter for max revs rather than ask, if your dash wont allow this then its of no use too you whatever, personally I wouldn't rely on a DB killer as I've had little or no joy from them, if your at all worried get the noise down by other means.
Get a decent quiet system on, get it set up and leave well alone, whats the point in getting all your fueling and ignition spot on only too mess it all up by fitting a different exhaust for a track day, the one time you would like to be running optimum engine set up ?

That's my take on it anyway.

Jon - what can do your run on you GT1 and is it quiet enough?

Mark - are you till selling your re-packable cans for BEC that Rizla had on his that proved to be really quiet?

Cheers,

Pat...

Marc,

what were you running to get 99dB? Was it similar to mine with a foam filter and no other sound proofing?

[Edited on 28-2-2006 by smart51]

quote:

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Originally posted by Avoneer
Jon - what can do your run on you GT1 and is it quiet enough?

Mark - are you till selling your re-packable cans for BEC that Rizla had on his that proved to be really quiet?

Cheers,

Pat...

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The nice chaps at procomp tested my exhaust noise level today. 107.9 dB at 8900 RPM. I need to lose 3dB or more to get in at loud track days. What's the best way of doing this?

What silencer did you have on when it was tested. I need to decide what to put on mine soon.
Could do with some advice before I spend.

Cheers, Steve.

I am using the repackable stainless steel can suppled by MNR. Marc recons the can should be quieter than this and thinks the noise must be coming from elsewhere.

What's the latest on the noise levels?

I'm thinking of getting a Std R1 can, but will this be any quieter than the MNR special?


Steve.

The MNR silencer is a stainless tube with end plates riveted in. This is so they can be removed for repacking. The gaps were not sealed and were blowing. Also, some of the rivets were blowing through the centre. I have filled all these with clear silicone which seems to have worked.

I have put self adhesive chassis foam around all the bonnet joints to keep the induction noise in.

I was going to measure the noise agian today put it has been raining solidly since first thing so I won't be going out unless it stops.

The exhaust doesn't crackle so much on overrun now but I don't know if it is much quiteter. -3dB is only a modest change in perceved volume to the human ear. -10dB is half volume at 3kHz so I wouldn't expect to be able to tell.

More news when it stops raining.

quote:

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Originally posted by smart51
-10dB is half volume at 3kHz so I wouldn't expect to be able to tell.

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No. Acually, -10 dB is half the volume as percieved by the human ear.

You seem to be thinking of POWER levels. -3dB represents half power on the logarithmic scale and -10 dB represents on tenth power on the logarithmic scale.

I am talking about sound levels not noise power levels.

Let me know how you get on.

Cheers
Steve.

When the rain stopped I went out to a quiet carpark near some woods. the background noise reading was 41 dB(A)

I set the sound meter to slow averaging max hold mode on a tripod 500mm away from the exhaust at 45°, at a height of 450mm (the lowest the tripod would go)

at idle it read 89.9 dB
at 7500 (sva speed) it read104 dB
at 9000 (track day speed) it read 106.7

with the tripod raised to 550mm (hand height) those dropped by 0.5 dB

I moved the car to a different parts of the car park and read 108.2 and 108.9 dB

to gauge what difference the bonnet foam made, I took the bonnet off completely. the reading went up to 109.6 compared with 108.2 - a miserable 1.4dB.

at about 7000 or 8000, there is a lot of low frequency exhaust noise - like wind noise on an outdoor microphone but pulsing. by the time 9000 is reached the engine noise seems louder than the exhaust.

There is panel vibration audible at 6000 - 7000 RPM but this is drowned out at higher speeds. this is despite me puting silcone everywhere.

The MNR can was noticably louder than the R1 can when I swapped them after SVA, yet Marc reckons that their can should be quiet. How can you tell that there is wadding in the can without drilling the rivets off?

quote:

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Originally posted by smart51
I am talking about sound levels not noise power levels.

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I didn't intend to sound at all angry, it was just that my tea was ready and I wanted to type quickly before logging off

I'd hoped that all that silicone and foam would have made more difference. Interesting that removing the bonnet had so little effect. Either most ofl the noise is from the exhaust or the GRP is almost transparent to sound.

One test I intended to do but forgot was to measure the sound level from the other side of the car at the same position.

I fitted the R1 can today. noticably quieter but it messed up the midrange fueling. I leaned off the needles by 1 groove which mostly sorted it. It is now slightly hesitant at full throttle.

The noise:

idle 87 dB
7600 RPM 100.4 dB (same as SVA)
8000 RPM 101.2
9000 RPM 101.6
10000 RPM 102.4

I measured from the same place on the non-exhaust side of the car just for fun

8000 RPM 97.6 dB
9000 RPM 97.6 dB
10000 RPM 102.4

It seems that my statement yesterday that at high revs the engine noise is louder than the exhaust was right.

Now the down side. Whilst the power delivery is smoother from 4000 - 5000, that is because it no longer jumps up at 5000 It now just rises smoothly but bot as far. It feels slower all all engine speeds from 5000 up. I guess that's why I had to tweak the fueling.

What I want is something half way between the two, slightly more punch than the R1 can with only slightly more noise. any ideas?

[Edited on 14-3-2006 by smart51]

I would guess that the fueling is not correct for the R1 can, even though you have played with the needles you may have to go down a jet size.

On my old MK Indy I originally had a modified R1 can and it needed 144 jets (I think). It made 138bhp at the wheels. Your car shouldn't feel flat at higher revs.

I subsequently changed the R1 can for a custom 61/2" x 28" can to reduce noise and help improve power a bit. It needed 150 needles with this free flowing can. Although the car seemed to rev out slightly more urgently, I wouldn't say the move from one can to the other was a great difference. If your car feels that flat with the R1 can I would suspect fuelling before anything else.

If I were you I'd pick the can you want to use and then get the fuelling optimised on a RR.

Hope that helps.

Paul

quote:

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Originally posted by progers
If I were you I'd pick the can you want to use and then get the fuelling optimised on a RR.

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Hi if you want to try it we have the latest stuff that we are using on all of our more noisey racers. but like we said before there is no real way that a straight throgh stainless silencer of that size is ever gonna work . usually the minimum required for trackday use is 28'' long by 6'' dia and ally will always be quieter than stainless.

cheers matt

The short answer is that you can't make the MNR quieter as it is limited by its size (unless you start playing around with internal baffles that can play havoc with power if not carefully done).

For a straight through can the only way you can make it quieter is by increasing the size. As mentioned above you'll need at least 6" width and as long as you can make it. You can use stainless end caps but using an ally shroud is usually quieter. Guys I've known with busa's have often had to resort to 7" x 30" cans to get the noise down enough. Are you running an airbox? That will certainly help reduce noise as induction noise is a big contributor too. I've also found that wadding in cans often needs replacing/topping up to keep the can quiet, if you have been running a rich mixture is can cause some interesting scorching inside the can :-)

I just managed to squeak past the Donington 98dB driveby limit with a big can and keeping the air filter under the standard MK bonnet (no air scoop).

Most of the tracks that are not critical with noise e.g Snetterton, Cadwell, Anglesey etc where 105db is the nominal limit I have never seen them use a noise meter. Its only the Donigton, Castle combe where they will actively test.

- Paul

How much is a larger silencer going to cost me then. I could pick up an R1 can off eBay but if a larger straight through can will give me the same noise reduction with less power loss then this seems to be the way to go.

quote:

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usually the minimum required for trackday use is 28'' long by 6'' dia and ally will always be quieter than stainless.

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quote:

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Originally posted by smart51
How much is a larger silencer going to cost me then. I could pick up an R1 can off eBay but if a larger straight through can will give me the same noise reduction with less power loss then this seems to be the way to go.

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Simpson can

I have phoned them already. They were quite expensive at £250 + VAT.

How much larger do I need to go to reduce the noise by 3dB?

Which is better, larger diameter (6" instead of 5" or larger length (upto 30£ instead of 24"?

I did a simple test today. I took a piece of 0.5mm thick aly and bent it over the rolled edge of the tail pipe on my car so that it blocked off half oif the area. It reduced the noise by 4dB which is what I wanted. A short drive showed that it was a little less clean starting but drove normally at full throttle upto 9000 RPM. After that it hit a bit of a wall in terms of power output. A better outcome than the R1 can that I tried, on balance, but still not good. Perhaps a proper dB killer would be slightly better. OK in an emergency perhaps.

Under bonnet padding had no effect at all.

So I guess I need a new can.. How much bigger than 24" x 5" should I go for?

Smart51,

Far from up and running yet, but have a Supertrapp, Yoshi can and R1 can that will all bolt on and currently working on a homemade 6" x 40" straight through ali can to overcome all these problems.

Have you got a sound meter?

Pat...

Yeah, I bought the one from Maplins. I guess it might not be too accurate but I expect it to be repeatable, so If I measure a 3dB change, it will be correct, even if both readings are 2 dB out.

My new silencer from the kit car workshop arrived today. The 750mm can was actually only 660mm. Had words with Martin from TKCW who said try it anyway and see how it is. It is a whole 5dB quieter than my old can at 102dB. I am now legal for track days.

Marc from MNR measured my exhaust noise at Total Kit Car Live last week at 101dB so perhaps I didn't need a new can afterall. I have been taking my measurements with the meter on max hold mode and he just read the screen. Maybe that means my new can would get me in at donnington.

I'm still not happy with TKCW though. They supplied the silencer with a tailpipe that extended so low that it would have touched the floor, despite me telling them not to. I have cut it off but am not happy with a sawn edge. Is there any way I can trim a tail pipe that wont melt / fall off / look like a tarted up saxo?

colinn i have some preformed rolled edge tubes the will fit over the 2 inch outlet that you can tack / ivet on if thats any good ????

best regards

marc

Hi colin if you need any bits welding stainless or ali just pop in . bet you cant wait to get it on track can you.

cheers matt