Its a bit of speculation / deduction / wishful-thinking on the part of people. But there is supposed to be work looking at reducing the noise of 68s - Modern Railways said so (cannot remember the exact article but it was referred to a few pages ago).
Allegedly there is a "empty box" within a "hole" downstream of the 68s engine exhaust ports with enough space for some sort of silencer.
Almost sounds (excuse the pun) as if space for a silencer was left there but the device omitted for some reason ?
I could suggest a reason ??? 68s are really 'universal' locos and maybe spec'ed to give as much hp as possible. Silencing - all silencing no matter what it is - exerts a back pressure on the cylinders and reduces power output. If your power rating is 3000 hp in your spotting book, that value is /after/ the effect of silencing has been taken into account.
The only loss value I know of is with the Soviet M62 type locomotives where it costs around 50 hp on a nominal 2000 hp diesel engine. (And those things are deafening without silencers).
It might be - and I am speculating here - 68s could be fitted with some form of silencer - but at a hp cost - given that they are nominally 3750 hp to lose even 100 hp would hardly be missed on 5 coach Mk5 passenger timings. That 100 hp would be a big loss at the top end of heavy freight working, but not for this type passenger work.
The other key to this is the significant numbers of DMU that could be cascaded from Chiltern to other TOC; 168/1 168/2 168/3 might be non standard cabs Turbostars but nonetheless they are Turbostars and would be welcomed by other TOC.
www.modernrailways.com
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