Two Automotive Questions (mild tech content)

They are both restricted and silenced. All Le Mans series cars will become silenced in the next couple of years which is unfortunate.

They also run a very odd secret header layout. They changed the pipe layout and it changed the sound of the engine to that banshee noise rather than just a bundle of high revs. It worked and they stuck with it

Ahhhh....that I need to see!

Well for number 1 its probably mostly to do with the header layout as Jonny69 said, but engine characteristic sound is affacted by (and this isn't all the things that can affect it) losses inside head (flow ability), angle of valves, position of spark plug, matched length inlet/exhausts (gives a very clear set of tones, otherwise known as th engines firing frequencies) the camshaft timing, the type of crank plane (flat or cross) and the angle of the V, obviously number of cylinders also has an effect between engine types. Also god knows what they use as a firing order but that also has an effect, inlet and exhaust runner length, then of course theres the huge effect of the exhaust system itself, not to mention the inlet system (amazing how you can change the sound of a car with some different inlet plumbing)

I won't explain all of that, cos it takes ages, the plane of the crank is interesting though - Ferrari use a cross plane V8 which is why it sounds quite differect to other designs. As for the angle of the V, well think of the different noises made by a standard inline 4, a V4 and a boxer 4 to get the idea! (no really angle of V but it makes the point!)

As for number 2, well...... The DSG is not an automatic, it is a dual layshaft automated manual with 2 viscous clutches (one for odd gears 1,3,5 and one for even 2,4,6 and reverse) controlling the torque transmission and hydrolic valves controlling which gear is selected and which gear is preselected. All of that is controlled by a massive set of equations in the TCU which takes a gazillion inputs from all over the car (suspension, engine, gearbox, wheels, brakes, steering etc etc etc)

As its electronically and hydrolically opperated it can act as an automatic, and I would assume this is the system that is used during the CO2 type approval. Now deisels and petrols produce very different power/torque curves, not least cos the diesel is turbo'd, so the gearboxs ratios and control stratergy will be very different - this is the 1st reason for the difference between petrol and diesel - I.e. diesel worse with DSG, petrol better. The team who did the petrol might well have been a lot better at there job (people always forget that factor!)

The other interesting thing, and this is probably the main reason, is that the diesel will (because its a diesel) produce a lot more torque, so much more infact I'm willing to bet that it is torque restriced in 1st, 2nd and mebbe 3rd gears with a DSG box as the clutches probably can't deal with full torque. The manual box too with be limited, but probably not as much and since the EU drive cycle does a fair amount of low speed driving its probably where the difference comes from - more limiting means less efficiency basically.

At cruising speed I'd assume they've used the same top gear ratio, so the cars should be nearly the same emissions was with the exception of losses in the gearbox - these will be a little higher in the DSG due to pumps and the viscous clutch - though the second point might be wrong as I'd expect them to employ a lock-up system on the new ones which means there shouldn't be any losses across the clutches.

As for the petrol, well it might well not be limited anywhere so the greater ability of the DSG to always be in the most efficient/effective gear means it gives improved efficiency - simple as that I guess.

DSG boxes do tend to be heavier, and this can have an effect on the emissions, and their need for high pressure pumps also saps power. God they can even mess up the packaging enough to cause cooling system issues that mean they have to make the engine run a bit cooler which removes efficency too! Typical engineering, everything has an effect, just some have a much bigger effect and thats all very car/engine/gearbox etc specific. Hopefully that clears a few things uprather than confusing you - which it probably has cos I'm a terrible teacher!

Looks like a 6-2-1 which isn't anything unsual as such, not much restiction though and its very short on the run to the tip. I assume that if it really does sound different must be as much to do with the cam profiles and intake as it is to do with the exhaust. It is lovely though ;D

And being viscous even though they're small they can still take a lot of torque, especially if they're multi-plate. But they do have they're limits and with modern 2 litre diesels making over 400Nm I wouldn't be surprised if thats over the limit! Have to remember the box was originally designed for petrol only, so its probably not optimised for deisel use. I have heard they're working on a dry clutch DSG so save money/weight and make it more efficient again, but there a a lot of problems with that like how to apply torque nicely, torque limit (again) and life span - all very interesting.