Mercedes-Benz is preparing to launch a powered-up version of the McLaren-built SLR coupe in a bid to stir sales of the 208-mph supercar.

Caught in these spy photos undergoing testing on public roads prior to a planned unveiling at the Paris motor show in September, the reworked SLR is distinguished from the existing model by subtle styling changes around the front and rear ends—all aimed at improving high-speed stability and creating more efficient underbody airflow.

The interior also gets special attention, with carbon fiber trim and other weight-saving changes that help reduce the SLR’s curb weight by about 90 pounds.

Under the SLR’s long hood goes an even hotter version of AMG’s supercharged 5.4-liter V8. The revised powerplant produces an extra 24 hp, pushing total output to 641 hp. With a corresponding increase in torque and improvements to the five-speed automatic gearbox to shorten shift times, the SLR’s 0-to-62-mph time drops by 0.2 second to just 3.6 seconds—fast enough to undercut competition like the Lamborghini Murciélago and Porsche Carrera GT. The 0-to-124-mph time is also 0.4 second quicker, down to just 10.2 seconds.

Further details remain scarce, but AutoWeek sources suggest no more than 150 of the hotter SLRs will be built before the end of the year at McLaren’s showcase Paragon production site in Woking, England. Once that production is completed, McLaren will turn its attention to an open-top version of the Anglo-German two-seater tentatively set for its public debut at next year’s Geneva motor show.

Source: Autoweek

 

Only 5-speed automatic? Can't believe they're not going with 7-speed

On a more realistic note, how can Murcielago possibly be competition to this car? Price-wise? They have such completely different styles.

 

Umm, it's ugly.

 

Their 5-speed is an absolute beast in terms of torque handling, and is a bit lighter weight, too. Their new 7-speed was never intended for their ultra performance cars - its torque handling is too low, not to mention I can only assume there is a pretty minimal benefit in speed between a 5 and 7 speed automatic when you've got that much power on tap.

 

That i do understand... With the recent craze about number of gears, and the fact that GM was criticized for sticking to 4-speed auto in mainstream cheap vehicles, the fact that this world-class luxury ultra-performance sedan is using "only" 5 is ... well, appears to be escaping media's notice.

It was sort of sarcastic rhetorical question

 

The fastest cars on the track typically use 2-speed glide transmissions. It only makes sense.

 

If I was a spend happy rich guy I would rather see a manual than an auto.

This car is supposedly built with handling in mind. I don't see too many 2-speed powerglide cars on the road courses.

 

I see them all the time at PIR.. They just run a 1/4 mile section of the front straight, turn off the track, then limp around back and shut off for another 2 hours.

 

Right, well how many 5-speed autos do you see running as dedicated drag racing cars? Exactly. So this is a compromise between the two.

There comes a point of diminishing and even negative return based on gear ratios and torque output. Take an extreme example. If you had a road course car with a 10 speed automatic and .15 seconds lock to lock shift time then you've spent about a full second and a half wasted being out of the throttle moving from a stop to top gear, not to mention any shifting done inbetween.

Say a 5-speed automatic with the same shift time... instead you have around 3/4s of a second wasted going through the gears once.

Question is, will that beast of a motor really benefit that much from the gearing advantage to make up 3/4 of a second or more per full run through the gears?

The question is often no, especially when dealing with vehicles that have very high torque ratings ultra-flat power bands (as is the case with these mercedes that are typically torque rated from 1700 to 5500 rpm or so). They just don't benefit THAT much from shifting into the next gear at 4700 RPM vs 4000 RPM because they make just about as much power at either RPM, so then you only get the minor benefit of slightly improved torque multiplication of a slightly shorter gear.

 

Does the exhaust come out under the front fender? Or is that some other sort of vent?

 

It's side exit exhaust if you mean the two pipes exiting at the bottom of the car on the driver's side.

 

Tell that to MT, R&T and C&D as well as any other automovite press entity for criticizing C5's 4-speed auto.

I don't think you got what I said - I don't dispute the efficiency or usefulness of this transmission.

 

Yeah but, can it outrun its own uglyness?

 

Good. The only thing stopping me from buying the McLaren SLR was that it was ridiculously slow.

 

The C5's 4-speed was getting long in the tooth. Stick a 5 or 6 speed auto in there and nobody will complain - and look, they did, and everyone's happy.

The C5's 4-speed was an older, slower-shifting trans thanthat 5-speed Mercedes auto. Not to mention still 1 fewer gear, and the Vette's torque curve is not anywhere remotely as impressive as the SLR's... thus it would have more need for more accurate gearing than the SLR would.

Again, I'm not saying the C5's 4-speed was the end of the world or that the SLR's 5-speed is necessarily optimal, but they are definitely not an apples to apples comparison despite both being sport-oriented vehicles of one sort or another.