GTR Exhaust News (modified SBC)

GTR Exhaust News (modified SBC)

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Discussion

T-Rev

Original Poster:

109 posts

277 months

Sunday 3rd June 2012
quotequote all
Hi everyone, I know this is a hot topic, but do hope it may be of use to some of you...
In 2011, I installed a pair of Edelbrock Sound Deflection Technology Mufflers on the basis of trying to seek a solution to noise issues that did not involve 'packed' silencers which tend to burn out quite quickly, especially on modified engines! Having installed these silencers I realised the car seemed noisier than on the old 'burnt out' silencers? So I conducted a noise test as follows...

2011-06-02 Noise Test Results
2/3 Max RPM 4000rpm 120dB(A)
3/4 Max RPM 4500rpm 123dB(A)

Considering these results were based on 6000 max rpm (peak power achieved at 4900 rpm) there was little point testing based on 7200 actual max rpm (current rev limit chip – though it will rev to 8000 rpm with the appropriate chip)… so this is what we had to start with from last year!!!

Since then, other than driving the GTR, I have done very little to it! But now the weather seems to have been improving, up until today at least, I thought I’d better get my act together and start sorting things out. Now we're already into June, a service is needed, then an MOT and then all the extra jobs I’ve been putting off for so long… not least of which the exhaust? Service parts ordered, I thought I’d pop down to Goodwood yesterday, Saturday 02 June (150 mile round trip in the sun) – GRRC Trackday - to blag a noise test as I’m a member, just to confirm what I’ve got to deal with…

2012-06-02 Noise Test Results
3/4 Max RPM 4500rpm 109dB(A)

So, exactly a year later and on the same Edelbrock Sound Deflection Technology Mufflers (see www.trevorwillardracing.co.uk TWR GTR 2011 for details), which I had previously thought were a complete waste of money (even though it sounded great)… they now seem to be coming into their own – I take back anything bad I’ve said about these silencers and maybe patience is a virtue after all! It would appear that 1100 miles in a year has built up enough carbon/soot to help with noise reduction – which I guess that does make some sense? I now only have to achieve a 4 dB(A) reduction and already have a couple of options available to do that, so watch this space! I can feel the tracks beckoning at last!!!

Also the guy's at Goodwood said they had to turn away a GTR that morning for failing the noise test - was that anyone on the forum? If so, my sympathies are with you, I know how frustrating this can be? All the best, Trevor.

P.S. My battery is now playing up!

Edited by T-Rev on Sunday 3rd June 23:33


Edited by T-Rev on Sunday 3rd June 23:35

ROWDYRENAULT

1,270 posts

213 months

Monday 4th June 2012
quotequote all
That close to your noise goal I would consider an X pipe. You should get a bit more torque and perhaps a little less Db. Lee

spatz

1,783 posts

185 months

Monday 4th June 2012
quotequote all
i am sorry but 12db less is most likeley a mistake in measurement. 123db is very loud and I assume this test was not done right. however it tells you that while passing one test you may fail somewhere else without having altered anything.

Life Saab Itch

37,068 posts

187 months

Monday 4th June 2012
quotequote all
I don't know where they do the noise test at Goodwood, but when I tested my formula ford at Castle combe I failed by 3db, then I turned the car around 180 degrees so the exhaust was pointing away from the wall of the scrutineering building and was 2db under.

spatz

1,783 posts

185 months

Monday 4th June 2012
quotequote all
that could easily be the case, the distance of measurement makes a huge difference, usually acoustic measurements are done 1 m from the sound source (e.g. loutspeakers). Then there is usually a weighting factor, lots of possibilities to have completeley different values.

MarkWebb

983 posts

216 months

Monday 4th June 2012
quotequote all
I was measuring similar levels with the very expensive Borla pipes that I shipped from the USA. I now have no problem with a Chris Tullet System at 103db. I have to concur with Ewe though 12db reduction with no mods seems unrealistic however having done extensive testing on my Radical an open space is a must!

Life Saab Itch

37,068 posts

187 months

Monday 4th June 2012
quotequote all
spatz said:
that could easily be the case, the distance of measurement makes a huge difference, usually acoustic measurements are done 1 m from the sound source (e.g. loutspeakers). Then there is usually a weighting factor, lots of possibilities to have completeley different values.
It's fairly standard at UK race venues for the measurement to be 1M away at an angle of 45 degrees.

An Ultima has two big pipes fairly close together. You won't get a reading without some interference.

Storer

5,024 posts

214 months

Monday 4th June 2012
quotequote all
The mechanical noise from the engine bay through the rear vent doesn't help either.

I hope to be down to 100db with my LS7



Paul

T-Rev

Original Poster:

109 posts

277 months

Tuesday 15th April 2014
quotequote all
Sorry it's been a while gents! Thanks for your previous comments and valid points, just to clarify ref. noise testing at UK circuits (2014 MSA Blue Book)... Sound Test Requirements (Chart 5.18)
5.18.1. Measurements will be made at 0.5m from the end of the exhaust pipe with the microphone at an
angle of 45° with the exhaust outlet and at a height of 0.5 to 1.0m above the ground.
5.18.2. Where more than one exhaust outlet is present, the test will be repeated for each exhaust and the highest reading will be used. In circumstances where the exhaust outlet is not immediately accessible, the test may be conducted at 2.0m from the centre line of the vehicle at 90° to the centre line of the vehicle, with the microphone 1.2m above the ground.
5.18.3. Measurements should be made outdoors with no large reflecting objects (e.g. walls etc.) within
3.0m (in the 0.5m test) or within 10.0m (in the 2.0m test).
5.18.4. Background sound levels should be at least 10dB(A) below the measured level.
5.18.5. Where possible measurements should be taken as close as possible to the vehicle, at the defined distances, to avoid background noise.
There is a chart in the MSA Blue Book explaining the requirements for motorsport categories, but trackday requirements may vary on some circuits e.g. Goodwood - so be carefull! Should you experience any problems, you can of course politely request that the organisor meets the above MSA standards for conducting a noise test?
Following my original post below and the previous noise at Goodwood;
2012-06-02 Noise Test Results (Goodwood) 3/4 Max RPM 4500rpm 109dB(A)
I have since installed additional Moroso spiral flow silencers in mild steel and painted black (shaped like cherry bombs). They claim to reduce noise by 5 dB(A) without any restriction on flow (also rated at 800cfm)? I had to shorten them a little to get them to fit and whilst they may not look too special, they do appear to have worked. I braved the potholes and traffic to drive down to Goodwood on Saturday for yet another official noise test;
2014-04-12 Noise Test Results (Goodwood) 3/4 Max RPM 4500rpm 103dB(A) - actual with no allowance for mechanical noise (Goodwood would allow 2-3dB(A) for mid engines cars). Though the noise test is only valid for the day it is conducted, I am confident mine will pass again in the future.
So some good news at long last, I now finally have a system that does not rely on packing, but uses sound deflection/spiral flow to reduce noise without restricting flow, each silencer is rated at 800cfm. I can finally use my car on track (105dB(A) or higher limits)! Which is just as well seing as I've entered the GRRC Spring Sprint at Goodwood in May. Here's what they look like;


Best wishes to all,
Trevor.