Those are vacuum actuated, being whatever poundage they are set at they'll activate, but is it a gradual opening for full on? I wonder if that's a direct draw off the motor, which would make sense, or if they came up with some new fangled device just to make it complicated and expensive?

 

Front box was interesting, has the front half ported so they can both expand into the first chamber. The other half was the usual perforated tube but only used steel wool as the lagging. Front box is also double skinned like the rear boxes.

Middle boxes are single skinned, usual perforated tube and used long strand hair like fibreglass as the lagging, also had the plastic wrapping around the lagging. All boxes genuine Jaguar had Jaguar embossed on the outer skins.

 

Would that be the gap between the different diameters in
the pipes of the front part of the box?

Perhaps the plastic around the lagging that you have found
is meant to melt at some temperature after engine startup
and just never did.

The front and middle boxes seem to offer little to impede
exhaust flow if the internal piping is the same diameter
as the rest of the piping.

 

Yes the front box has different diameter tubes in the first chamber, so the exhaust gases can escape and can merge in the first chamber only.

I think the plastic wrap is just to speed construction by keeping all the lagging together on assembly. It maybe heat resistant.

Flow wise they look well made for stock exhaust boxes. By removing them I doubt it will gain much in terms of adding more power. I have used a similar size tube to replace the boxes I removed.

 

I agree that like many head scratchers, the plastic wrap is to speed
assembly. They just picked the wrong plastic.

Thanks for the detail on the front box. Maybe some day I'll crawl under
and drill right through the double wall and pipe on both sides then plug
the double walls with a pipe plug or similar.

You might not hear many in Dorset, but the Mustang GT V8's are the
exhausts I like most and they have a H-pipe at the transmission with
only rear boxes. The boxes are perforated pipe and lagging construction
like the ones available from MagnaFlow.

 

When the F-Type was first released I was parked in my Coach near the local Jag Dealer. I was having a little power nap when I was woken by a pair of mechanics razzing by in a F Type with the exhausts wide open. That's some sound.

They sell the Mustang in the UK now as a RHD model. It's so quiet that when I'm next to one at lights I can't hear it running, and as it drives away it barely makes a sound. EU Noise laws.