BACK Mulsanne's Corner NEWS

Pete Lyons' fantastic Can-Am Cars in Detail:
May/June 2011
Reload to see the latest news

All news content copyright Michael J. Fuller, unless otherwise noted
>>Le Mans 2011<<

Dissecting the protagonists. With a few weeks post-Le Mans 2011 we've been having a think about our post race analysis:

It was pretty clear the Peugeot 908 was running less drag.  We could see this in the slightly higher straight line speeds 
averages as well as the longer fuel stints.  And of course there was the obvious indicator with Peugeot's anti-wicker rear wing flap.  

Audi's top speed wasn't too far off, but more importantly the R18 was clearly carrying more downforce.  

But the differences seemed slightly more fundamental than that.  Peugeot driver Alexander Wurz complained of instability in the car's setup, "With our #7 car we were always on the back foot because our chassis balance was very oversteery."  And while we can't verify, we've been told at least one of the 908's testing accidents was caused by an overly aggressive setup coupled with driver error.  The 908 was noticeably less stable than the R18 through the Porsche Curves though interestingly the 908's straight line braking seemed to belies this, suggesting a slight yaw issue.

The reduction in drag through the elimination of highly cambered rear engine cover trailing edge shapes as well as paring out drag from the wing means there's less stabilizing underfloor draw from these items and it would seem that as downforce was taken off the 908 it has become slightly less stable when compared to the Audi R18.

Without knowing actual power output differences between the two we are speculating, and for arguments sake we're going to assume similar power outputs.  Yes, this isn't accurate. But we'd be surprised if the power difference was more than 5% and at the moment we don't know which way it would swing.  Thus calculating drag from similar power levels shows only about a 5% difference.    

Quicker lap times, nearly same top speed, coupled with more downforce must simply mean the R18 is more aerodynamically efficient than the 908.  And that's reflected in the higher L/D.  A 5% better L/D gives the R18 nearly 500 lbs more downforce at 200 mph than the 908.
>>The ACO is proposing a number of aerodynamic changes for 2012 to further reduce sudden yaw induced flight and is currently shopping this list amongst the manufacturers.  The proposed changes include a longer and taller fin that is integrated into any roof inlet, an increase in the area of the mandatory front fender louvers from 160 cm2 to 200 cm2, mandatory louvers on the rear fenders (100 cm2), and an increase in the height of the domed skid from 20 mm to 30 mm.  For now this is a draft list and nothing is set in stone though these proposals seem to be born out the FIA/ACO meeting held with the manufacturers in early April.

Audi R18, Mike Rockenfeller accident, Le Mans 20116.20.11

Following their two crashes in the 2011 24 Hours of Le Mans, Audi finds itself having to replace the destroyed cars while the winning 3rd car heads to the museum.  Of seven R18 chassis originally built, only five remain and chassis R18-103 and R18-107 have been tapped as the replacements.  Says Audi's Ralf Juttner, "One monocoque has been with us as a spare and was partly built up (fuel cell, looms, pipes etc.). The other car has to be built from a complete new, unprepared one."  The disposition of the damaged monocoques is undetermined, "If the accident tubs can be used for show cars or similar is not yet decided.  For the moment they are undergoing lots of checks and investigations to at least get as much information as possible out of these two 'unintended' crash tests."

>>Mazda recently made some rumblings about possible new directions and Mazda Motorsports North American head John Doonan offers some further details.  "Mazda are assessing all of our options regarding power plants across all of our motorsports activities.  As you know, the challenge with Le Mans is that the ACO regulations require a stock block engine in LMP2, and LMP1 unfortunately requires an investment that is extremely big."  With SpeedSource Racing leading the investigation into possible applications for Mazda's SKYACTIV technology, Doonan clarifies, "SKY has a wide range of applications, architectures, hp and torque levels.  So SpeedSource is looking at all options for us, with SKY-G (gas) and SKY-D (diesel)."  Though Doonan admits, "LMP1 is too rich for our blood."  So don't expect a diesel LMP1 engine out of Mazda.  But given the costs to be competitive in LMP1 it leaves Mazda with little options, "The current Mazda MZR-R prepared by AER is an LMP1 engine for ALMS, it is not a stock block."  

Thus it's not an easy decision for Mazda's future program as all paths within LMP indicate a new engine is needed.  The most likely scenario, if Mazda are intent on staying in the prototype category, would see Mazda investigating the utilization of their
SKYACTIV-G (gas) technology for applications within LMP2 considering the ineligibility of diesels in LMP2.


Audi R18, Spa 20116.15.11

udi's Ralf Juttner tells us that the R18 is using "waste air" to cool items in the engine bay.  Recall that we pointed out air being directed from the cockpit through cooling pipes that emerge from the back end of the R18's monocoque (1) and then terminate (2) into the carbon bellhousing.  

Juttner elaborates on the R18's engine bay cooling system, and most interestingly, confirms that the R18 cockpit cooling is not augmented, "...we are not using an A/C system.  All is done with 'normal' ambient air."  Air is directed into the cockpit via the vent intake in the car's nose, used to reduce the cockpit temperatures, and then sent rearward to the engine bay, eliminating the need for additional ducts with the aditional benefit of retasking the "used" cockpit air for additional duties.

We'd be remiss not to inquire with Mr. Juttner about the rear carbon structure, notably the "why" behind it.  Juttner would only say, "About the rear structure I can┤t say anything (but you are - as usual - a skilled viewer)."  Recall that the R18's rear carbon structure has been designed to isolate the gearbox from suspension loading potentially creating a regulatory loophole whereby the gearbox could be replaced in event of a failure. is an online shop for performance parts & accessories, including headlights and tail lights
Porsche LMP16.3.11

he car that never existed.  Mulsanne's Corner devotees will be familiar with the Porsche LMP1 ("LMP2000") story.  And here it is, more than a decade later, and still no official photos of the car exist.  Well, perhaps there's been a cooling in Weissach.  Markus Eberhardt, who obtained these pictures and has graciously passed them along to Mulsanne's Corner, tells us these images were,"...published in an official, but strictly limited, Porsche calender."  Finally an acknowledgment that the car exists?
Porsche LMP1Now, I know there are those within Porsche who regularly visit the website (yes, yes you do).  How?  IP traces (  Surely someone over there at Porsche can get us better images (from the calendar presumably-don't get yourself fired!)?  I know I would appreciate, Markus too I'm sure.

email: is an online shop for performance parts & accessories, including headlights and tail lights
Aston Martin AMR-One, Monza Test, May 31, 20115.31.11

ittle has come out of Aston Martin's PR department since the disaster that was the Le Mans Test Day and Spa withdrawal.  And it would seem the marketing types got a real lesson in, "Any publicity is good publicity," and have since gone silent.  But it's a positive sign to see Prodrive is getting on with it and have been putting in the miles testing.  Here they are today at Monza for day one of what is to be a two-day test.  
Astson Martin AMR-One, Monza Test, May 31, 2011Aston Martin was running with the first chicane removed, identical to how Audi and Peugeot have previously tested at Monza.  Simone relates, "...while I was there, between 2.30 pm and 4.30, the car did a total of something like 25 laps, pace around 1' 36"-37".  For what it's worth, that's considerably slower than what I saw from Peugeot, around 1' 31", and Audi, doing 1' 30" if not under, in earlier tests."

The car's "patina" seems to indicate lots of extended running.
Astson Martin AMR-One, Monza Test, May 31, 2011Simone indicates that rain came in late in the day and that tomorrow's forecast is for more of the same.

The diveplanes have a vertical endfence.  Other than that
there doesn't seem to be any aerodynamic revisions of consequence.  

WM P88 Peugeot, Le Mans 19885.30.11

t's now been more than 20 years since WM Racing's Project 400.  In 1988 WM set out to be the first to achieve an official radar clocking of 250 mph on the Mulsanne straight.  They were successful in their attempt, but since then very little has ever been written about the technical details of the project, at least in the English speaking press.  And what little has been written is often rife with incorrect details (narrow Michelins for instance).

Three years ago (the 20th anniversary) I exchanged email through WR's PR manager with Gerard Welter, but there simply wasn't enough substance to write a definitive technical dossier on the car or the effort.  And after staring at an unfinished  article now for 3 years, I'm determined to reach drive Roger Dorchy, or any one else who was involved in the project and is interested in discussing their involvement.  

If you have any useful information please contact me,

email: is an online shop for performance parts & accessories, including headlights and tail lights

h yeah, I was interviewed by Tony Castaneira from regarding Le Mans, Audi, Peugeot, and Aston Martin. Check it out.


Acura ARX-01e, Sebring 20115.24.11

hile the statement from Highcroft Racing last week seemed to leave the future of the ARX-01e chassis at the mercy of HPD, according to Nick Wirth, "The ARX-01e is very much a viable customer car, and we have already shown its performance at Sebring.  HPD are very interested in supporting and developing the engine side."  Wirth tells us, "HPD are in advanced discussions with several groups about running ARX-01e's both in Europe and the USA in the near future."

And not all the performance of the -01e was witnessed at Sebring as the definitive Le Mans aero package wasn't (naturally) completely unveiled.  It's a shame Le Mans 2011 is out.

Wirth Resarch continues work on the future LMP coupe, "And now we have seen the 01e's real-world performance, our enthusiasm to build it (the coupe) is higher than ever."

Mazda 787B5.20.11

azda has restored the 1991 24 Hours of Le Mans winning Mazda 787B to running order and will be sending it to the 2011 Le Mans in honor of the car's 20th anniversary win.  According to their press release, "Mazda plans to hold the demonstration of the 787B racecar on the Circuit de la Sarthe at 12:30 p.m. on June 11.  Additionally, the 787B will also take part in the Driver's Parade through the Le Mans city center on Friday June 10."  Nice added bonus for those in attendance!

Mazda has published a number of photos showing the car being restored and running and we have posted them on the Mulsanne's Corner FaceBook page (these are only viewable to FB members).

Here are the Mazda images in a zip file.



he "pre-season" ahead of the 2011 Le Mans has been witness to what has to be the highest pace of development for sports prototypes in history.  Both Peugeot and Audi have gone at it "hammer and tong" and we've lost count of the number of tests.  So it wasn't much surprise when images came out this week of Audi testing, this time at Monza.  What is surprising is that this appears to be another variant of the R18.  Surprising given that one would think that all effort would be going towards preparation for Le Mans, at this point 3 weeks away.
All images copyright Daniele Paglino
The Audi R18 wearing the #2 was testing a new front fender shape.  Instead of having the blunt extrusion that comes up from the splitter that blends to a smooth profile producing the notched shape (left), the new fender's leading edge (right) is now a smooth profile down to the splitter.  This would be a rather large change to execute and would require a new pattern and mold.  Additionally, the headlight would have to be redesigned and remade to accommodate the fender surface changes.  The slight raised section (1) on the inboard bodywork connecting the fender to the nose is larger and the bodywork is slightly shorter in length.  It would also appear Audi have two splitter options as the right hand option is as tested at Le Mans where as the left hand appears as the roll out version.
All images copyright Daniele Paglino
Two different rear wing setups were spied as well.  The mainplanes are different between the two, noted by the outboard upward sweep on the left configuration.  The other item to note is the very different flap position as the right hand configuration is carrying much more flap angle. 
All images copyright Daniele Paglino
Audi R18Simone Recalcati sends these photos that show the rear end differences.  Note on the #2 (below) the inboard rear fender shape is square (compared to the rounded shape on #1) and the "peak" on the centerline of the trailing edge is much lower and with a slight dip prior to heading to the peak.  Looking further, and the changes to the #2's engine cover trailing edge are driven by the much higher overall trailing edge height.
Audi R18Additional detail changes.
>>We've also finally cashed in the bounty for the Audi R18 images  (And if we didn't note it here, we did on the Twitter account, @mulsannescorner, we have in hand images of the Peugeot 908 too).  All these images will be released ahead of Le Mans, the weekend of June 4-5.  

But that won't stop us from describing what we saw.  T
he Audi's rear end is as expected: torsion bars, almost vertical dampers (angled to meet bellcrank which is angled for torsion bars), 3rd spring.  But the most interesting thing is the carbon bellhousing structure.  It's much more intricate than the 908s in that it extends full length and the gearbox cradles inside the open ended structure.  With the gearbox isolated from suspension loading, the gearbox wall proper now doesn't have the be as robust.  So thinner wall and a much simplified casing in general with means less weight.  We hear as much as 10 lbs less weight though possibly more.

All rear suspension pick ups mount to the carbon.  The trailing arm pickups are supported by metallic structures behind them that "stitches" each side of the open ended carbon structure together.  The rear structure that carrys the rear wing mount, exhaust pipe, and rearmost section of the underfloor plugs into the back of the carbon gearbox cradle via mushroom pins.

Lola B98/10, Daytona Test 1999We can confirm that the rear brakes are cooled via the ducts just ahead of the rear wheels.  Attention has been paid to cleaning up engine bay flow through.  And in fact the R18's engine bay has structures ahead of the rear wheels not dissimilar at all to what the Lola B98/10 had way back in 1999. is an online shop for performance parts & accessories, including headlights and tail lights

he ACO has released Technical Bulletin 11-18 that lays out performance balancing ahead of the 24 Hours of Le Mans.  It amounts to fuel flow restrictor diameter increases, weight reductions, and engine inlet restrictor increases for most of the of the gas cars, in addition to a weight decrease for the grand fathered Peugeot 908 HDi Pap (-15 kgs, now at 915 kgs), and fuel flow restrictor diameter decreases for the diesel cars:

Percentage restrictor increase:

Area is only calculated for one restrictor in the cases of two restrictors.

P2 changes are as follows:

Once again the privateers will absorb all costs associated with the performance balance.  From The Horse's Mouth:

"(the)Change (the ACO performance balance) is time and money.  New restrictors to be machined, time/money on the dyno, likely change to gear ratios.  Multiply any change by number of cars and number of spare parts and it's non-trivial.

We firmly believe that Manufacturers have the capacity to absorb change far more easily than Privateers and tried to argue that position with the ACO.  Feels like it fell on deaf ears."



esterday Highcroft racing announced they were withdrawing their 2011 Le Mans entry and parting ways with Honda.  In response to our inquiry, Nick Wirth gave this brief statement:

Highcroft's ARX-01e is owned by HPD (who own the design) and will be returned to them immediately.

All of us at Wirth Research are deeply disappointed to see a car that we specifically designed for best performance at Le Mans not running there this year, and we're very sad to see the end to our great and winning relationship with Highcroft Racing.

That would seem to nix any prospect for a Judd (or Zytek) powered "ARX"-01e... is an online shop for performance parts & accessories, including headlights and tail lights

>>So how much torque are the current generation diesels making?  We'll be using the Peugeot engine as the basis, but ultimately we're generating data for a "generic" diesel.  Stephen Knight, "knighty", suggested this first method (and guided us through the second), simply pro-rata the the torque of the previous 5.5 liter engine to 3.7 liters.  We're going to use the official figures for the 908 HDi FAP's torque, 1200 Nm, though we understand this is about 15% too low.  Reducing that figure by 32.7% (the difference in capacity between the 5.5 and 3.7 L) gives us 807 Nm of torque for the 3.7 liter.  OK, so that's a bit of a ham-fisted way to estimate torque, but it gives us an initial figure.  

So we've previously calculated a power output based on top speed and drag estimates of between 609 and 594 hp for the "908".  Taking an average, 601.5 hp, we can calculate for torque using the formula:

Power (bhp) = (Torque(lb/ft) x RPM) / 5252

multiply by 1.35582 for Nm

Plugging in 601.5, and using an rpm range from 4500-2500 RPM (remember, diesels rev much lower), and solving for torque we get and torque range of between 952 and 1712 Nm.  Obviously it's very RPM dependent.  But more importantly, we're calculating torque at peak power and this isn't accurate.  The torque peak is going to occur a bit below the RPM for peak power, and therefore the power at that RPM is going to be reduced as well.  And obviously power varies with RPM though we're going to keep it constant throughout our 2000 RPM ranges (for all our cases, see below) as we haven't a way to predict the relationship (or, plot the curves) in our fictitious diesel engine.  So we're going to have to make some assumptions.  Let's assume that at peak torque RPM the engine is producing 75 hp less than what it does at peak power RPM.  Therefore we'll use 526.5 hp.  Plugging that back into the same RPM range gives use between 834 and 1500 Nm .  Averaged, that's 1167 Nm.

So now that we have a rough figure for the diesel, what does the opposition generate?

With a calculated 570 hp, the gasoline powered Judd 3.4 liter, using similar methodology (knocking 75 hp off peak power, but using an RPM range from 10000-8000), generates between 353 and 441Nm of torque (397 Nm averaged).  So between 42 and 29% the torque of the diesel.  The high revving nature of the normally aspirated engine simply kills torque production.
So what about a gasoline powered turbo engine?  At the moment we really don't have reliable figures for the Aston Martin in the power department.  But let's just assume a solid 600 hp at peak power for a "generic" gasoline powered turbo.  Using an RPM range between 7000 and 5000 RPM (gas turbos torque peak won't be as low as a diesels) gives us 534 and 748 Nm of torque at 525 hp (641 Nm average).

So it's pretty easy to see that the torque figures for a normally aspirated gasoline power engine are not even in the same ballpark.  The gas powered turbo has a better chance, but there isn't even any overlap if you look at best case (for gas) vs. worst case (for diesel).  Admittedly there is a lot of fudge in our factoring, but there's really not enough to turn a 64% difference into a 5% difference.

With the ACO giddy to add hybrids to the line up, and the manufacturers waiting in the wings having designed their new cars around such systems, the performance balance is simply set to go from poor, to ridiculous.  And the ACO has only shown hesitancy in addressing the issue.

We end with a final word from an anonymous source:

The diesels need to be slowed down. We saw a 4.3% lap time difference between the quickest gas and diesel at the Le Mans Test and the diesels lapped under the 3:30 target in the first year of a supposedly "fixed  for 3 years" set of regulations.  We don't agree that Manufacturers should have a 2% advantage over the rest of the competition (as is implicitly acceptable in the regulations), their strength in depth and resources should be advantage enough.  It is unreasonable to place the burden of any change in terms of costs and workload upon private teams, especially when their cars are performing above the target lap time at Le Mans of 3:30.  Instead, the Manufacturer teams should shoulder the impact of any changes, it is the diesel cars that should be slowed down, not the gas cars that should be changed to go faster.  Halving the size of the diesel car fuel tanks would allow us to play on a level field, that gives the real scale of the difference in performance.  Perhaps the diesels should "drive through" every lap instead of crossing the start/finish line?  If there was true equivalence between the engines, why did both Audi and Peugeot decide to build diesel engines for the new regulations, coincidence, marketing?  Or because there is still a rich vein of performance to be mined from improvements in diesel technology?

ean Lariviere is looking for race programs and posters to purchase. 

His list is:

Daytona 24 Hours programs: 1964, 1963, 1988, 2009
Sebring 12 Hours 
programs: 1953, 1954, 1957, 1960
IMSA Yearbooks:  1975,  1972, 1987, 1994, 1996
Daytona posters from 1966 to 1985 except 1981

Jean can be contacted via:

Let him know you saw this on Mulsanne's Corner. is an online shop for performance parts & accessories, including headlights and tail lights

>>Yesterday brought a bevy of interesting emails into our inbox.  Seems a few of you have been reading our series that is stepping through the methodology of predicting engine power outputs.  Now, power is one thing, and as we've been showing, the outputs between the gasoline powered cars and the diesels aren't too dissimilar.  At least it seems to be much closer than in years past.  So how can the large performance deficit between the two "categories" be explained?  Simple, torque.  As one of our Industry Experts let's on, "I have done a lot of simulation work for Le Mans...torque is way more relevant than anything else.  By a big bunch."  Le Mans has what amounts to five long straights; from Tertre Rouge to the first chicane, from the L'Arche Chicane (first chicane) to the La Florandiere Chicane (second chicane), from the La Florandiere Chicane to Mulsanne Corner, from Mulsanne to Indianapolis, and from Arnage to the Porsche Curves.  Think of these as five drag strips.  What's more important on the drag strip, power or acceleration from torque?  So check this out, our Expert tells us a 10% increase in torque can amount to, wait for it...upwards of a 3.7 second decrease in lap time.  A similar percentage increase in power only drops lap times at Le Mans by around 2.6 seconds.  Furthermore, a 10% increase in downforce is only good for a 1 second drop in lap time.  So of course the manufacturers have gone the technical route that leads to the easiest way to decrease lap time.  They aren't stupid after all and they have a lot of Boffins running the numbers.  Says said Expert, "Two mph faster out of the chicanes is 10-12 mph faster at the end of the straight--even gas turbos can't make up for the 22 to 26:1 compression ratio of a diesel.  All that BMEP just shoves the car down the track, out of each corner."  And it does that five times with consequences each lap.  Stephen Knight, "knighty" on the 10-10ths forum, relevantly relays, "I remember Peter Elleray once said that during the Bentley LMP900 development they actually realized, via many track simulations, that torque was of more importance than power at Le Mans...hence they increased the 3.6 liter Audi engine to 4.0 liters, the net result being slightly less power but a lot more torque, which gave them a significant acceleration advantage, much like the diesels have..."

So what amount of torque are the diesels producing?  What about the Judd?   More this weekend...
Rebellion Lola Toyota B11/60>>Rebellion's Bart Hayden was good enough to speak with us about the team's upgraded Lola.

Mulsanne's Corner:  Who commissioned Lola to develop the new Rebellion Lola update kit?  Can Lola customers purchase this kit or is it exclusive to Rebellion?  Who owns the tooling? 

Bart Hayden:  The update was requested by Rebellion Racing but it was decided to allow the kit to be available to other LMP1 Lola customers (not that there are any other than Rebellion at the moment). This means that Lola own the design and tooling.

MC:  Can you describe all the changes to the car?

BH:  In broad terms a new nose/diffuser, "bullets" (the forward sidepods that the nose connects to), front floor, front suspension and rear wing. The car has a longer wheelbase, but shorter rear overhang as a result of the changes.

MC: Did the switch to wide fronts require new uprights?  Revised suspension geometry?

BH:  The uprights stayed the same, but the wishbones and steering arms changed.

MC:  How were the aero changes developed, wind tunnel or CFD?  Did Rebellion have any input?

BH:  Predominantly wind tunnel, but with CFD for some of the smaller details, that's Lola's standard modus operandi.  Rebellion's input was to provide a list of requirements (such as wanting less drag, improving the lights, updating the appearance), but we gave a fairly free hand to Lola because we didn't want to place too many constraints on the design.

Rebellion Lola Toyota B11/60MC:  What's the primary gain of the alternate nose?
BH:  The alternate nose is higher downforce, so is there as an option for balancing the aero at higher downforce tracks.  Quite possible that it would be used at Petit.

MC:  What is the net effect on car performance from the update?

:  Difficult to tell without a direct head-to-head comparison (and there's been no time for that), but the aero figures, especially in terms of efficiency are a step in the right direction.  We're not talking about quantum gains, but the improved light package and ability to use 2011 tires give additional benefits.
>>Yesterday Lola announced:
Toyota will make additional LMP1 engines available exclusively to Lola for 2012.  This increase will enable 4 cars to be run in the 2012 ILMC in addition to either the ALMS or LMS series.
When asked for a clarification ("Just to be clear, so no other chassis manufacturers can run [or will run] Toyota engines next year?"), Lola's Sam Smith said, "Yes, it is an exclusive agreement for 2011 and 2012."
Audi R18, Spa 2011>>More details are coming out about the Audi R18's rear composite structure/bellhousing.  In this photo we can see how the rear suspension mounts to structural carbon "fingers" (1) that extend rearwards from bellhousing and that the traditional metallic-walled gearbox slides (2) in between them. is an online shop for performance parts & accessories, including headlights and tail lights

>>Another consideration regarding our power calculations; we've always assumed a very liberal 10% drive train loss.   But when calculating for power, we're always solving for power at the wheels.  Thus the drive train loss can simply be calculated afterwards to achieve the "dyno" figure.  Therefore it's easy to recalculate for less drive train loss using different figures.  It wouldn't be surprising to know that the top flight outfits at Peugeot and Audi are running very high drive train efficiencies in the 92-94% range.

Recalculated for 94% efficiency:

Peugeot 908:  569-
Oak Racing Pescarolo 01 Judd:  546 (just over 1% of Judd claim)
Aston Martin AMR-One: 445-

Choose the efficiency number of your choice.  We're hearing 92% might be even more appropriate.  Though note the base hp figure we have calculated is power at the wheels.



>>Last month we produced power estimates for the 2011 Peugeot 908 using estimates from the 2010 908 Hdi FAP as the bench mark.  We concluded the 908 was producing upwards of 600 hp based on trap speeds from Paul Ricard.

This was the thought process:

First we calculated the drag level it would take to achieve 324 km/h assuming 700 hp and 1.8 m^2 of frontal area.  With that in hand, we immediately knocked 150 hp keeping drag constant.  That showed a 298.9 km/h terminal velocity.  But 2011 cars have undergone extensive development and the 908 has most certainly lost drag over last year.  So taking the average of the numbers, we matched drag to that trap speed.  A 24%  reduction in drag got us the 327.5 km/h cited in the dailysportscar article.  But that's a huge amount of drag to peel out of a car with that has essentially the same frontal area compared to last year.  In fact the number simply isn't believable.  So we calculated for a 100 hp reduction over 2010 and a 10% reduction in drag over the guesstimated 2010 numbers.  That netted 318.8 km/h.  Closer, but still not 325-330 km/h.  Finally, with a further 7% reduction in drag we were able to achieve 327.5 km/h.  With a bit more tweaking my guess would be that the 908 has more than 600 at the flywheel and drag actually approaching 1000 lbs.  Naturally all of this is guess work, and it expounds from a guesstimate of the 908 HDi-FAP's drag level for Paul Ricard last year.  So it could get pretty ragged as it relates to the 2011 908, but it should give one an idea of what's involved even when we've decanted the problem into only a few simple variables.

In the mean time we calculated drag at Le Mans based upon the estimated power output and the measured trap speed.  This past week we shopped those figures around to see if industry experts agreed if we were even in the ballpark and if there was any fundamental flaw in the methodology.  Based on that response we revised our drag figure for the Le Mans configuration and recalculated for power.

As can be seen, our original drag estimations were actually quite reasonable.  The resulting revised power estimation actually straddles the initial guess.  We've calculated high side drag and low side and now say the Peugeot 908 is putting out between 594 and 609 hp.  The Paul Ricard figures are used for reference and show 10% higher drag.  This seems to coincide with what we know about the setup for Ricard compared to Le Mans; slightly more downforce is used at Paul Ricard thus it can be expected to have "slightly" more drag.  10% seems to be "slightly" more.

What prompted this reevaluation was some head scratching when we were trying to determine drag levels for Oak Racing's Pescarolo 01 LMP using trap speeds from the LM test.  
The power quoted didn't resolve well to a realistic drag level.  To achieve 325.9 km/h with 540 hp, about 486 at the wheels, meant a .cd of .4665.  That seemed to be so low as to be unachievable for an open top LMP.  So playing with power output, and assuming an output more along the lines of 570 hp (that's only about 5% more than Judd's quoted 540 for the engine), to achieve 325.9 km/h we needed a .cd of .489 (about 921 lbs drag @ 200 mph with a 1.71 m2 frontal area). This is still seemed low.  Lower than what our understanding was for the Le Mans drag coefficient for an "average" open top LMP by about 15%.  But our references were to non-2011 optimized open top LMPs.

Thus the inquiry to industry sources helped revise our drag estimates downward.  But not quite as low as the .4665.  The .489 is more reasonable (let's say it's a low side drag estimate for an open top LMP), but it would also seem that the Judd engine is producing more than the quoted 540 hp as that's the only way to bridge the gap to the 325.9 km/h.  Naturally you can never believe the power output numbers the manufacturers provide.  If Judd's saying 540 and it really is 570, 5% more than their claim, then the 570 is within the realms of believability.  Looking at it another way, 540 hp is within 2% of the target the ACO set for everyone and is a convenient number for Judd to claim.  But we still feel the drag is on the low side, and if that's the case, power is simply higher than we've stated (at .51 we need 531 hp at tthe wheels, around 590 hp @ 90% efficiency).

With a better idea of drag for an open top LMP we decided to revise the figures for the Aston Martin LMP.  Recall that 
Race Car Engineering Magazine was reporting that the Aston Martin AMR-One was barely putting out 300 hp at the Le Mans Test in order to keep the engine alive.  But the 300 hp quoted just didn't pass the sniff test and simple calculations for hp absorbed given the top speed achieved by the AMR-One required an unrealistically low drag coefficient to achieve the 301 km/h mph trap speed the AMR-One set in the first practice session.  Thus we recalculated using .57 and .59 for low and high side drag and produced a power estimate of between 520 and 540 hp.  And reducing drag to between .51 and .55 produced a revised power estimate for the AMR-One of between 465 and 502 hp:

Naturally we're assuming the AMR-One is draggier than the Pescarolo, the assumption being that the Pescarolo is well developed package at this point while the AMR-One is less mature.

We're sure some will be unimpressed that we're suggesting the Judd has power closer to the diesels, but
of course power is only part of the story.  And of course we've simplified the issue into  four statistics:  power, frontal area, drag, and top speed.  We should also stress that we're beholden to the accuracy of the trap speeds.  In lieu of that being within our control, we've attempted to be as accurate as possible with our aerodynamic drag estimates.  Therefore the absolutes aren't necessarily spot-on, but the trends should be.  What trend is that?  Simply, the power difference between diesels and gasoline powered cars aren't as far off as in recent years.  However, there's still a huge performance gap...
Aerodynamicist and automotive enthusiast Paul T. Glessner presents "The Secrets & Basics of Vehicle Aerodynamics" Seminars.  See why more cars are going faster and doing it more safely and in style.  Paul has been asked to speak at venues like Bob Bondurant School of High Performance Driving, Society of Automotive Engineers (SAE), Specialty Equipment Marketing Assoc. (SEMA), and Performance Racing Industry (PRI).  Paul's seminars both educate and entertain.  The day long seminar can be held at your club, organization and/or company location with the organizer paying only $100. Click on the above banner (click event date in site) to read about Paul's extensive background and testimonials from enthusiasts like Jay Leno.  Schedule your seminar at!
"While I am not an engineer or a major technical type, I enjoy the discipline of aerodynamics and was pleased at how Paul was able to explain its intricacies to individuals like me." - Jay Leno, Tonight Show Host

ęCopyright 2011, Michael J. Fuller