I am occasionally asked to build one of these systems for the N/A motor. I don't have to pass a strict drive-by noise-test so I designed the silencer internals differently from Lotus. When the exhaust valve is 'closed' the gas is routed through a 63.5mm diameter (2.5") straight-thru perforated tube (not a restricted/baffled route like the factory exhaust). 

I use Acoustafil packing material around it to achieve as near as possible OEM decibel levels - certainly won't upset the neighbours at 5am!

The 'interesting' part is when the exhaust valve is 'open'. I use a plain tube - no sound absorption at all - just a straight path to the tailpipes. The exhaust note is pure, howling V6 - not for the shy and retiring.

Feedback has been great but I can always drop the decibel number by placing a Silenced De-Cat Pipe (SDCP) in the old '3rd Catalyser' location.

An electronic exhaust valve control kit is supplied with the exhaust. A very simple fit.

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