Walkers World - Ssshut it!

Author: Words by Geoff Walker Photos by Alex Hodgkinson

Noise is in danger of killing the sport we all love but with a little common sense we can all keep it down a bit. In the first of a two part special, our tip top tech takes a look at the role noise testing plays...

Here is a cold, hard fact - noise is killing our right to enjoy the sport we all love. With more tracks coming under the scrutiny of tree huggers and local authorities we really are getting ourselves in the brown, smelly stuff.
The problem we all face is partly to do with the four-stroke revolution. The irony is that four-poppers have made a comeback because their lower emissions are better for the environment - but the way the noise of a four-stroke carries (ie further) is seen as environmentally unfriendly. And it's also a lot more noticeable.
Now I'm not on an anti four-stroke trip but something has to be done to prevent the noise factor becoming even more of an issue.
The manufacturers have made an effort and a step in the right direction this year to get the European bikes down to 96db from 98db. This is a good step but there are so many imported bikes from the other side of the Atlantic here in the UK and most of these are still fitted with a 98db silencer. This noise measurement is taken from a very low rev (4500rpm on a 450 and 5000rpm on a 250 thumper) and the real problem occurs when the puppies are at full rip.
This level must be reduced much further to keep our sport from going downhill. The aftermarket pipe manufacturers will work to this tolerance at the test level but as soon as the bike is at speed the noise seems unrestricted.
If you go to any practice track in the UK you are likely to get your eardrums thoroughly punished by a four-stroke which has burnt its packing and would probably test at around 110db. This is pretty unacceptable and at some tracks there is an 'enduro only' ruling in force where only 94db pipes are allowed. This makes a massive difference and if everyone has to run a quiet pipe then there is no performance disadvantage for that day at that track.
The noise problem is being recognized at the very top level and every effort is being made to manage the noise problem at GP and Brit championship level. I caught up with the noise test crew last month to see just what steps are being taken to keep the problem under control...
Here in the UK we have a good bunch of guys who carry out testing at all the national events. These guys do a great job even if a couple of them are past their sell-by date (joke)!
Andy Summers has been around the world of MX for ever (he was responsible for putting the two bikes through technical control before they went onto the Ark). I had many run-ins with him and the noise test team in my days on the spanners - especially at the UK Supercross series where I used to make some naughty tail pipes for the Kawis...
The FIM have been so impressed by the efforts to control noise levels here in the UK that they have given Andy a place on the team that travels to the GPs to oversee the noise testing and take noise readings...
I caught up with Andy to hear what he had to say about the noise issue in the sport.

DBR: So Andy, how did you get this gig with the FIM?
AS: "The FIM approached me about the noise testing for '06 and, of course, I accepted their offer."
DBR: Overall, what are your thoughts on the noise problems that have arrived with the four-stroke revolution?
AS: "The noise from the four-stroke bikes at test level is less than that of a two-stroke of a few years ago at world level but with the four-stroke the noise does tend to travel a bit further. We are working really hard to get these levels down with what we call 'dynamic testing' - this is a noise test carried out around the track where the bikes are coming under full power."
DBR: That sounds like a crackin' plan. Can you see and hear an improvement on the track?
AS: "Definitely and the proof is in the readings. The dynamic tests last year with the 98db static test level pipes fitted on a 250F were an ear bending 114db and with all the hard work that the teams and pipe manufacturers are putting in that level is now a more acceptable 106db on the dynamic testing."
DBR: How does that level compare to, say, an absolutely stock 250F?
AS: "A standard bike with stock 96db silencer from new will test at around 103db on the track."
DBR: That sounds like it is all going in the right direction.
AS: "I think that within the next couple of years the noise level will become more acceptable and that is a good thing for the sport."

So there it is, the guys at the very top level of the sport are making an effort to keep the noise in check. I realise it's easier for the big teams to keep the noise level under control as they all have pipe sponsors who will recondition and re-pack the pipes to keep the levels correct but we all have a responsibility to make sure our bikes are running with correctly packed exhausts.
The packing in a four-stroke silencer can burn out in well under 10 hours and this is where the problem occurs. The noise difference between a newly packed silencer and an empty burnt out one is massive. As well as making a hideous amount of noise, the burnt out silencer will cause a power loss in your motor and ultimately lead to excessive wear in the engine department.
It really is important to try to get this noise issue under control and I personally think that with a little less noise on the tracks of the UK we should all get to enjoy ourselves without any grief. Who knows, we could maybe even start to get something positive going with some of the local authorities who seem to listen to the do gooders and generally fail to listen to our side of the issue?
Look out next month for a step-by-step walk-through on the dos and don'ts of silencer packing and a list of types of quiet level silencers available on the market for your precious metal...

Testing Times How it works...

The static noise test, as taken at pretty much all race meetings these days, requires a few pieces of equipment.
¥ A noise meter, which must be calibrated regularly
¥ An RPM reader
¥ The correct length and angle measure to keep a consistent 45û angle and 60cm distance to hold the noise meter in position while taking the reading
¥ Two human beings and a quiet bit of open space

The test rpm levels for each class bike in MX are...
¥ 450F 4500rpm
¥ 250F 5000rpm
¥ Two-stroke 7000rpm
¥ 85cc two-stroke 8000rpm

The process for the test is simple.
1 Start and warm the bike up.
2 Human #1 will then place the RPM reader on the motor and find the correct RPM for the type of bike being tested. There are digital readers and mechanical readers. The digital readers affix to the HT lead and the mechanical reader works on a vibrating metal protrusion which stops vibrating at the correct rev limit.
3 Human #2 will be standing at 45û to the outside of the rear of the bike, holding the noise meter at a distance of 60cm on a level plane from the height of the silencer.
4 When the correct RPM is reached human #1 will signal to human #2 who will take the reading and proceed to give you the good or, indeed, bad news.