Silencers

[erictharg]

I got a cone with my kit, and it got me through the SVA! Still have it in my spares kit just in case, but prefer not to use it as it must add significant back pressure, especially to a heavily modified engine.

[jonclancy]

I think you both did well with your freebies!

[jonclancy]

I was just bolting my silencer back on today, prior to a windy blast up to the N Wilts / Glos Area meet, and you know what I found in the intermediate pipe?

A perforated cone! Not the same as that pictured on the Yahoo list, but open-bottomed.

Next stop is to re-test my exhaust myself (I have a sound meter), as I have sorted my little misfire out which may have slewed the official test somewhat. I'll test at 4K with a declared redline of 5250 and see what I get.

[jonclancy]

Update from the factory - please look here for details.

http://forum.wscc.co.uk/forum/index.php ... _p__997673

Jon

[erictharg]

I can confirm that my "spiral baffle" made not one bit of difference. Noise tested yesterday at 106! Fortunatley the limit for the Birkett is 107. Think I'm going to have a go at making my own over the winter. Aiming for 115mm diameter round and as long as feasible. Maybe 700mm? Steel ends and perforated centre tube, and an aluminium outer body for weight reasons.

[jonclancy]

I was at the Avenue Drivers' Club meeting last Sunday, and noticed a metalling ringing from my exhaust.

I took the silencer off today, and the perforated cone had migrated from theintermediate pipe into the silencer box.

The cone was easily retrieved and I will probably just reinstall the silencer and noise-test to ensure I'm still under 100dB(A).

Can't think how this small cone should be held in place. Any clues, chaps?

Cheers

Jon

[erictharg]

From memory it just sits there due to a vague interference fit. There's threaded insert so you can screw a bolt into it to pull it out. I guess it you gently "expanded its base again to restore the tight fit it would be OK for a while...

[jonclancy]

Thanks Charles.

I think I will reinstall it tomorrow. Problem is that I actually prefer the lower tone and over-run baritone that the cone produces. The HP or two that are gained are significant percentage-wise, then become irrelevant when on the overrun past a stone wall or when rolling between the lovely old buildings on Tetbury Hill.

[adamwilkinson]

Charles,
How are you finding your thermal velocity wadding?
Does it hold up well?

We're thinking we'll have to go down the 'correct' wadding route as the stuff we use at present blows out after one race.

[erictharg]

As far as I know it held up OK, but the original silencer that it was used in had to be ditched once I put the 649 cam in the engine. It just does not have enough volume to tame the noise. So it didn't get run that long, but from what I recall was no more expensive the the DT stuff and should be better...