These build journal entries are part of a special series on the development of the S85 CSL Style Carbon Plenum and written in collaboration with the design & engineering at Infinity Design.
What could have been.
What should have been.
What may still be.
The M5 V10 CSL
In 2009, BMW M built a one-off prototype of a BMW M5 CSL based on the E60 M5 V10.
It was famously touted as shaving over 20 seconds of the E60 M5 Nurburgring lap time.
Meant as celebration for the 25 years of the BMW M5, it was unfortunately never released.
- 5.5L S85B55
- Est 600 PS & 400 TQ
- +/- 3,900 lbs
- Alpha N engine management
- 1 Piece Carbon Airbox
- Getrag MDCT
- New oil cooler
- Carbon Roof Panel
- Recaro buckets & rear seat delete
- M6 wheels.
- Revised EDC.
- Painted A pillar side mirrors.
More power & Extra Cooling.
The S85B50 was stroked out to 5.5 liters of displacement by BMW M. It gave the V10 much needed mid range torque and an even crazier top end.
We know how it feels from the hundreds of strokers Troy built from the S85.
The development of the S85B55 eventually led to the S65B44 that was fitted to the E92 M3 GTS.
Looking back, this adds more weight to my outlook of the V10 M5.
It was a test bed that saw various improvements but never unleashed its true potential, unlike its V8 little brother.
Additionally, the fitted a secondary oil cooler right behind the grills and cleverly hacked openings in the front bumper.
This would probably have never made it to production.
The DCT Transmission
The M5 CSL was fitted with the E9X M3 DCT transmission made by Getrag that was released in March 2008. It was made exclusively for BMW under the Product Code 7DCI600. That transmission was rated at 443 ft lbs of torque.
It's unclear whether BMW had to modify the internals to hold the additional torque of the S85B55. From the estimated power figures and experiences on supercharged cars, the DCT can handle the estimated power figures.
The 7DCI600 is a relatively simple mechanical swap to the S85: the bell housing is a direct fit. The crank output shaft needs to be slightly machined to fit with the DCT input shaft.
The main issues are software related.
Unfortunately the MSS65 was not designed to be entirely compatible with the DCT.
The upshifts will work, but the downshift program cannot be managed. This has been the primary hurdle to all DCT conversion attempts.
It remains unclear how BMW did it, and whether the downshifts ever worked in their own prototypes.
I remain hopeful it will happen sooner than later from my discussions with various companies involved in the software development.
The DCT + S85 remains an elusive conversion as of 2022
The M5 CSL wasn't noticeably different than the standard E60 at first glance outside of the livery of questionable taste.
However, as you read the Press Release and paid close attention, you starting noticing a few interesting details.
They were able to achieve an estimated 3,900 lbs rating compared to the 4,150 lbs of the original E60 M5.
Not bad at all when you consider the weight of a fully loaded E90 M3 DCT is around 3,800 lbs.
The Carbon Roof
Most notably, the E60 M5 CSL was fitted with a carbon roof panel. Contrary to BMW M's habit to leave it bare, it was painted.
We can estimate the weight savings to be close to 100 lbs from removing the metal roof with its heavy glass to a carbon roof panel.
This is on my to-do list.
BMW M never released another wheel style for the E60 M5 and retained the 166M multi spoke style throughout the entire production.
It looks great, yet its styling was always leaning more towards luxury than performance aesthetics.
The 166M wheels were cast.
The front 19x8.5 wheels weigh 27.12 lbs while the rear 19x9.5 wheels weigh 29.25 lbs.
They weren't light.
The 167M wheels were forged.
They kept the same widths yet were quite lighter, coming in at 22.3 lbs for the front and 23.6 lbs for the rear.
Reducing unsprung weight is a must on a performance car.
This was an easy off-the-shelf upgrade for the M5 CSL.
Rear Seat Delete
The final piece of the weight reduction puzzle were seats - or the lack thereof.
Acting as the ancestor to the G90 M5 CS, the the E60 M5 CSL decided to make due without rear seats and deleted it in favour of a flat bench.
Personally, that's a bridge too far. That's an M6 CSL to me.
Front Bucket Seats
Zoom in or you'll miss it.
The M5 CSL was fitted with Recaro Pole Position ABE seats with carbon shells.
Bucket seats, non reclinable and quite light at 4.5 kg / 10 lbs per seat.
The OEM seats are 73 lbs each depending on the configuration.
The CSL prototype also featured small design changes that fix some glaring visual problems on the exterior.
Carbon Leather Trims
I long chatted about BMW M's lack of carbon fiber trims in the E60 M5 lifecycle.
They did on the E63, and they sort of did on this CSL E60.
They outfitted the dash and door trims with the E9X M3 coveted carbon leather trims.
A style that remains forever exclusive to the E9X M3 generation.
The mirror holders on the A pillars are now painted black instead of body colored, and the interior trims finally had carbon option.
The mirror itself no longer has the split black & body color design. It flows better and is much more similar to the E9X M3 paint & black plastic combination.
Aesthetic Step Backs
BMW M remains confusing at times - and ever more so on prototypes.
They retained the use of the pre-LCI headlights, yet fitted the rear LCI LED taillights.
Limited time, budget or access to parts might be explanations.
We'll never know.
Just BMW M things.
Another missed opportunity was the iDrive.
The M5 CSL was released in 2009 - the year they introduced the CIC iDrive system.
You notice the previous generation iDrive with the singular silver knob.
Missed opportunity to do a coveted iDrive delete "single hump".
A man can dream.
The Mythical Crown Jewel
1 Piece Carbon Intake.
The previously discussed upgrades were must-have features in the eyes of E60 S85 owners.
Yet, none were as arguably as desired as the entirely revised air intake system.
The S85B55 featured a massive 1 piece carbon plenum with enlarged sealed air boxes breathing from the front bumper ducts.
BMW M never even wanted to show off in official prototype pictures.
It remains mythical to this day.
All we get is this lousy screenshot from a video of the pre-iPhone era.
As of 2022, no aftermarket company ever tried to replicate or enhanced the original BMW M CSL design.
Some tried, but reverted to an internally split box design with smaller intake inlets that fit the OEM air boxes.
Pretty show pieces that made great induction noises - but the fire breathing airbox of the CSL was never experienced by owners of the S85.
This is about to change.
Infinity Design has stepped up to the plate and started the development of a 1 piece carbon plenum and complete air intake system to replicate and enhance the original CSL design.