Competition silencers?

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knutspeed
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Competition silencers?

Post by knutspeed » Tue May 14, 2013 8:11 am

We're running quite simpler (non-across-the-bum) silencers on our race Imps, think they're made for Caterhams or something. Anyway, they are borderline too noisy for Sweden which run 95dB compared to 100 in Norway. I hate the looks of the across-versions, but we may have to go there anyway.

Anyone know of somebody who provides these? Full-race engines.

I'd also like some suggestions if running motorcycle silencers is a good idea? Have seen that on a couple of hillclimb cars.
Matthew Birger Patrick (Knutsen)
Sarpsborg, Norway
FIA App K Historic Racing Imp - Bevan Tribute - www.shag.no
Mike Hanna
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Re: Competition silencers?

Post by Mike Hanna » Tue May 14, 2013 10:21 am

Hi. How is the noise test done? Is your pipe pointing directly backwards in line with the car?. I put a 90 degree turn in the tailpipe to the right side of the car so the noise test is done from the side so less mechanical engine noise is picked up. I also made the bottom of the silencer removable so it can be re-stuffed. Might help to try this. Cheers. Mike (I can send you photos if you can give me your email address)
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knutspeed
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Re: Competition silencers?

Post by knutspeed » Tue May 14, 2013 10:30 am

Hi Mike & thanks!
Yes, the outlet points straight out the back. It does stick out a bit too far as well.

They used to do tests in scrutineering with half max revs, 50cm away from the outlet, 45 deg angle. This year they're trying trackside measuring in Norway which seems much more reasonable. The Imp is noisy at standstill due to the proximity of the engine/exhaust, but quiet on-track, at least compared to a BDA or any of the motorbike-powered cars. The mufflers we use can be re-packed, but it seems we'll need to do this every second race.

Photos would be super - try bk@shag.no
Matthew Birger Patrick (Knutsen)
Sarpsborg, Norway
FIA App K Historic Racing Imp - Bevan Tribute - www.shag.no
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benwick3
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Re: Competition silencers?

Post by benwick3 » Tue May 14, 2013 11:06 am

The advantage of the cross the back silencer is that it moves the measuring point away from the mechanical noise. Another helpful mod is to direct the exhaust down to the ground as this can knock off a couple of decibels.

I tend to agree that trackside measuring is more realistic in respect of Imp engined cars but unfortunately unless you know exactly where the tests are being carried out there's no chance of restricting rev usage by changing up early. Also I've never been able to understand how it's possible to gain a reading for a particular car within a group. I always had trouble with trackside noise measuring at Zolder in Belgium even on the first lap I was picked out from a grid of 30+ cars. I'm sure it was because the Clan was different and stood out and was therefore easy to remember!

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SimonBenoy
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Re: Competition silencers?

Post by SimonBenoy » Tue May 14, 2013 12:36 pm

Bearing in mind that a full race Imp engine revs to 7000rpm max, your noise test should be conducted at 3500 and will not be overly loud. We are allowed 105db at 2/3 or 3/4 max revs measured at 1m. I have an across the back silencer as there isn't really room for a large enough silencer otherwise - the bigger the diameter, the less the noise. Sometimes, dipping the clutch can help a little along with the other suggestions above. Wherever there is drive by testing, I have never had any problems with an Imp engine, but static tests can be difficult - my road going G15 failed at Goodwood when I did a sprint there, but it is a bit noisy.

I have run a Yamaha R1 silencer and it never failed a noise test, my new silencer is a Tech-Craft, quiet and shiny :lol:

Cheers - Simon
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knutspeed
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Re: Competition silencers?

Post by knutspeed » Tue May 14, 2013 12:54 pm

Thanks Simon!
Our current setup is one or two dB plus/minus 100 which usually is ok in Norway, but the Swedes are stricter, and we need to get to 95 at 50 cm, 45 deg angle.

Very helpful forum, got lots of good tips I'll try out!
Matthew Birger Patrick (Knutsen)
Sarpsborg, Norway
FIA App K Historic Racing Imp - Bevan Tribute - www.shag.no
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benwick3
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Re: Competition silencers?

Post by benwick3 » Tue May 14, 2013 1:20 pm

As much as 7000rpm Simon, I thought it was 6500rpm.

Pete Richards
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617sqn
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Re: Competition silencers?

Post by 617sqn » Tue May 14, 2013 1:29 pm

I thought 7000 was fine for road cars 8)

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Mike Hanna
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Re: Competition silencers?

Post by Mike Hanna » Tue May 14, 2013 10:29 pm

OMG. I didn't know they revved that much! No wonder they blow up!!!! :lol:
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knutspeed
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Re: Competition silencers?

Post by knutspeed » Wed May 15, 2013 6:43 am

The scrutineering rev limiter is strong in our cars :)
Matthew Birger Patrick (Knutsen)
Sarpsborg, Norway
FIA App K Historic Racing Imp - Bevan Tribute - www.shag.no
moose
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Re: Competition silencers?

Post by moose » Wed May 15, 2013 8:39 am

a link pipe to move the silencer across the back has benefits, increased tuned length that helps with low end torque, silencer packing material further away from the high temps of the gas at the manifold so it takes longer to burn out and increase noise, the outlet is on the opposite side of the car to the carb induction noise. the larger the diameter of the silencer the quieter you can make the car.

regards mike
Regards Moose
Century Autosport
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