Aston V8 Vs Audi V8

[SteveH]

Watched Top Gear last night and they had the V8 Aston on... it sounded superb, why doesn't the V8 of the RS4/RS6 (even with Milltek) sound as good?

[Wolverine]

Well, on the RS6, an inherent part of the problem is the Turbo .... which supresses the sound.

[bogie]

agreed - i test drove a V8 Vantage last week, and with the exhaust fully open it sounded awesome

[Rek]

Aston also said publicly that they spent quite a lot on tuning the exhaust noises of their V12 cars. Maybe the same with the V8.

[bogie]

I think the NA Audi V8 in the new RS4 with a Milltek will sound similar...but the Aston also has a flat plane crank (like TVR AJP V8) which gives it a unique sound

[RSVI]

Didn't know what "Flat plane" was so did a search and here's the info for others to read.

There are two classic types of V8s which differ by crankshaft:

The cross-plane V8 is the typical V8 configuration used in American road cars. Each crank pin (of four) is at a 90° angle from the previous, so that viewed from the end the crankshaft forms a cross. The cross-plane can achieve very good balance but requires heavy counterweights on the crankshaft. This makes the cross-plane V8 a slow-revving engine that cannot speed up or slow down very quickly compared to other designs, because of the greater rotating mass. While the firing of the cross-plane V8 is regular overall, the firing of each bank is LRLLRLRR; this leads to the need to connect exhaust pipes between the two banks to design an optimal exhaust system. This complex and encumbering exhaust system has been a major problem for single-seater racing car designers.


The flat-plane V8 design has crank pins at 180°. They are imperfectly balanced and thus produce vibrations unless balance shafts are used, with a counter rotating pair flanking the crankshaft to counter 2nd order vibration transverse to the crankshaft centerline. As it does not require counterweights, the crankshaft has less mass and thus inertia, allowing higher rpm and quicker acceleration. The design was popularized in modern racing with the Coventry Climax 1.5 L V8 which evolved from a cross-plane to a flat-plane configuration. Flat-plane V8s on road cars come from Ferrari (the Dino), Lotus (the Esprit V8), and TVR (the Speed Eight). This design is popular in racing engines, the most famous example being the Cosworth DFV.

In 1992, Audi left the German DTM racing series after a controversy around the crankshaft design of their V8-powered race cars. After using the road car's cross-plane 90°-crankshaft for several years, they switched to a flat-plane 180° version which they claimed was made by "twisting" a stock part. The scrutineers decided that this would stretch the rules too far.

The cross-plane design was neither obvious nor simple to design. For this reason, most early V8 engines, including those from De Dion-Bouton, Peerless, and Cadillac, were flat-plane designs. In 1915, the cross-plane design was proposed at an automotive engineering conference in the United States, but it took another eight years to bring it to production. Cadillac and Peerless (who had hired an ex-Cadillac mathematician for the job) applied for a patent on the cross-plane design simultaneously, and the two agreed to share the idea. Cadillac introduced their "Compensated Crankshaft" V8 in 1923, with the "Equipoised Eight" from Peerless appearing in November of 1924.

[SteveH]

Cheers all, some good info there... RSVI, your note reminds me of what my old man told me the other day, he worked all his life in the car industry as a technical trainer, teaching dealer mechanics. We were talking about the DRC suspension on the RS6 and RS4, he said "you would have thought that they would have sorted that one by now, after all, Austin used that design in the 1950's"

I wonder what the RS6 would sound like with no cats? Perhaps a little too much!

[BigMo]

we could try decatting one. That usually gives a brilliant V8 track. Failing that, gutting the pre-cats and fitting a hi-flow sports cat (eg Milltek down pipes) might do the job.

[Wolverine]

I'm sure someone here has gutted their precats ?

I know my mates decatted TVR Cerebera 4.5 not only spits out flames, but also snarls and pops .... sounds awesome, and following him down dark country lanes and seeing his exhaust light up is just magic. Always wondered if the RS would do the same ................

[quattrokid1]

by decatting the pre cats on the B5 RS4 or any car for that matter... wont it fail its MOT emissions test then? or do you put in a system whereby you put them back in for the test?
apparently removing the pre cats does make a big difference... is this so?

[Rich_C]

Tweaky has had his stock exhaust pre-cats removed by MRC. You still have the main cat after that which I think is 400 cpsi for emissions purposes so won't fail it's MOT. Audi has to design the exhaust system to cover worldwide emissions tests which can be more stringent than here in the uk. Mix in varying fuel grades world wide most manufacturers will overdesign the systems.

My RS6 has Milltek downpipes & 100 cell cats (there's no pre-cats in the Milltek system) as it bolts straight onto the back end of the turbo's (or so I've been led to believe) and it's just past it's 2nd MOT. Removing the pre-cats is a reasonably cost efficient modification compared to the cost of the Milltek replacement cats ... plus there's the added benefit from the underside of the car Audi is not going to no any difference unless they want to pull the downpipes off and that really is a big chunk of work.

As for differences most of the usual tuning houses report further increases of 15 to 20 bhp when using replacement cats in conjunction with the Milltek cat back and remap on the RS6. Although as you might suspect bhp per £ spent is quite low for the replacement cats - depends if you want to release the full potential of the beast. As an aside you do get a little more acoustic enjoyment from the engine bay area with the cats fitted.

As for removing the cats completely I know of a fellow forum member who is contemplating this mod ... we'll have to wait to see if anything comes of it!!!

As for the AM V8 now that I've seen a few in the flesh they do look rather fetching although I can't decide if the wing mirrors compliment or detract from the design ... if I was spending that kind of money I'd still opt for the Porshce.

I could seriously have a TVR Cerbera as a weekend play car though ... still love the shape of the design even now and the sound of the TVR V8 .

Rich.

[rossybee]

I think the NA Audi V8 in the new RS4 with a Milltek will sound similar...but the Aston also has a flat plane crank (like TVR AJP V8) which gives it a unique sound

Correct ref flat plane crank, like the TVR AJP8 and Ferrari 355/360/430

Should also be noted that modern Astons have a valve in the zorst which remains shut at light throttle to comply with noise regs, but opens & therefore gets more fruity when the taps are fully opened

[bogie]

yup - Ive had mine "de-corked" so the flap is open all the time ...sad to say goodbye to RS6, but Im not using the backseats ...maybe will have another in a couple of years when sprogs arrive !

[BigMo]

jammy get with ear defenders

[SteveH]

Have a test drive booked in an Aston tomorrow, was the cheapest car in the ferrari dealership!!, going to that dealer is bad for you, its practically car-porn!!! Quite helpfull sales people though for a dealer thats well above my affordability radar, went to the Porsche dealer down the road and they were positively rubbish.