2007-2011 Acura/HPD ARX-01a, b, c, d, e, & g

Images copyright Acura, Pat Michl, and Michael J. Fuller
Text copyright Michael J. Fuller

Acura ARX-01b, Petit Le Mans 2008In April of 2006 Acura announced their intention to enter the 2007 American Le Mans Series with a new LMP2 challenger. Wind tunnel development commenced in June of that year at the Auto Research Center (ARC) wind tunnel in Indianapolis, Indiana.  The aerodynamics program began by baselining the Courage LC75 in 50% scale.  Honda Performance Development (HPD) had evaluated both Lola and Courage's current offerings, coming to the conclusion to utilize the Lola as the program's chassis-side control with the Courage LC75 as the starting point for car developments.  Applying for a research and development tax credit can save car manufacturers like Honda millions of dollars every year.  All chassis design work would be carried out by UK based Wirth Research headed up by Nick Wirth.  Engine design and development was the responsibility of Honda Performance Development based out of Santa Clarita California and over seen initially by Stephen Eriksen with that responsibility transferring to Yasuhide Sakamoto and then to Trevor Knowles as the primary focus transitioned to the LMP1 engine and the Acura ARX-02a program.

The Courage LC75 evaluation included a full scale wind tunnel test at the Stuggart University in August.  One of the items to come out Stuggart University LC75 wind tunnel test were bodywork modifications necessary to mollify the car's propensity to porpoise.  Says Nick Wirth,  "The Courage test was so memorable because the basic car porpoised so badly it nearly leaped off its mounts and we could have lost it down the tunnel!"  By October of 2006 CFD development was up and running and would parallel the ARC-based scale program.  Ben Wood, aerodynamicist for the LC75, indicated that the Courage only had 10 days of aerodynamic development originally.  Ultimately 80 days of wind tunnel testing would be conducted throughout the ARX-01a program at ARC.  

By January of 2007 the first development items were making it onto the car and the Courage LC75 mule-car was testing new Wirth Research designed suspension while the definitive Acura bodywork was still in development.  
It was this configuration that debuted at the Wheels Down Winter Test.  By early February the "Acura ARX-01a" bodywork was available and pre-Sebring testing of the definitive specification commenced.  A final full scale wind tunnel test was conduced at Stuggart University in February in order to give the Acura-spec bodywork a once-over, confirming the improvements made over the LC75.

According to Nick Wirth, given the number of changes to the Courage chassis, "
The ACO requested the car be rehomologated an ARX-01a as it was so extensively changed from the LC-75, yet the monocoque was still run under the Courage homologation."  The ARX-01a utilized the Courage LC-75 monocoque, front crash structure, and gearbox with a Courage designed Acura engine bellhousing.  Dimensionally, the Acura ARX-01a was on the same wheelbase as the LC75 (as would be the ARX-01b) but the front overhang was increased to the maximum and the rear bodywork shortened (though the wing position stayed the same at the maximum 750 mm rear overhang).  The ARX-01a was also designed to the maximum width and was around 50 mm wider than the LC75.

In 2007 Highcroft and Andretti Green Racing ran the ARX-01a.  At the car's Sebring debut it weighed in some 40 kgs over the 775 minimum, though by the end of the season this number was down significantly.   A surprise Sebring victory was the season's only win for Acura.

Development of the ARX-01b began during the summer of 2007 and was carried out entirely in CFD.  A host of changes over the -01a included; bodywork, front and rear suspension, Wirth Research designed gearbox with integral bellhousing (though same internals as -01a), front crash structure, upgraded monocoque internals, and an Acura steering system.  The new front crash structure required a new crash test for certification and subsequently the monocoque was homologated as an ARX-01b for 2008.  The significance of the use of CFD for this development package might solely be down to the fact that at the time the LMP2 model was more than likely tied up in developing the future Acura ARX-02a LMP1.

The ARX-01b raced successfully in the hands of De Ferran, Highcroft, and Fernandez racing throughout 2008 recording 6 wins and only just missing out to Porsche in the Manufacturer's Championship (213 points vs. 214).  Fernandez Racing continued to field their ARX-01b during the 2009 season while De Ferran and Highcroft stepped up and into the ARX-02a.

In 2010 Wirth Research updated the car's aerodynamics resulting in the ARX-01c.  The -01c's front end bodywork was revised; the front fenders were redesigned and new diveplanes and a outboard turning vane were developed.  At the rear, what was essentially the the LMP1 Acura ARX-02a's rear wing was adopted to the -01c.

For 2011 Wirth Research's development of the -01 diverged given the upheaval of the regulations.  Two versions were developed:  the ARX-01d utilizing Honda's new 2.8 liter, twin turbo V6, LMP2 engine, and the LMP1 ARX-01e.  Revisions resulting in the -01d were minimal, new turbo inlets were added to -01c aero specification.  

However the LMP1 version, the ARX-01e, was drastically redeveloped (1, 2, 3).  The formerly-Acura, now "HPD", 3.4 liter LM-V8 engine was retained (but now breathing through larger restrictors given the move up to LMP1) though a new gearcase attached to the rear end.  Changes to the bodywork consisted of completely redesigned front fenders and diveplanes as well as rear bodywork revisions and new rear wing endplates.  Mechanically the car was mostly similar to the LMP2 but for slightly larger front tires (though not in the width range of the ARX-02's "wide" fronts) and the previously mentioned new gearbox.   And the ARX-01e LMP1 equated itself rather well in its one and only race, Sebring 2011.  Unfortunately there were no other buyers and Highcroft shuttered its LMP operation before the planned Le Mans outing.

But Wirth Research wasn't done yet.  In July of 2011 WR announced the ARX-01g,  a cost-capped version of the ARX-01c LMP2.  LMP2 regulations had evolved and heavily favored cars that fell within the ACO's chassis cost cap, thus the non-cost-capped ARX-01d was often finding itself at a disadvantage from a regulations standpoint (more weight, smaller engine inlet restrictors,
smaller fuel flow restrictors).  The ARX-01g's exterior shape and the "hard bits" (engine, gearbox, tub, suspension, uprights, brakes, etc.) are identical to the non-cost capped -01d.  The primary changes to the -01g are cast wheels and a reduced data system.  And a reduced price of course.  The cast wheels are in deference to cost-cap regulations.  But in essence the car has been simplified and the options eliminated.  For example, the standard -01c utilizes two alternators (a primary and a backup) and the -01g will more than likely only have one.  The ARX-01g debuted with Level 5 Racing at Laguna Seca, followed by a second car at Petit.
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ARX-01e LMP1:

2007-2010 Acura ARX-01a/b Specifications
Designer: Courage LC75 originator: Paolo Catone
Completely revised to Acura ARX-01a/01b specification by Wirth Research
Layout: Mid-engine, rear-wheel drive
Monocoque: Carbon fiber and aluminum honeycomb monocoque (Courage LC75 monocoque)
Engine: Acura LM-V8, 3.4 liter normally aspirated V8, 4 valves per cylinder, DOHC
Engine management: Continental/Honda ECU
Horsepower: 550+ hp
Torque: -
Gearbox: 01a: 6-speed Hewland cast magnesium gearbox with Courage aluminum bellhousing and Zytek paddle shift system

6-speed Wirth Reaseach designed, Hewland manufactured, cast magnesium gearbox/bellhousing and Acura/Zytek paddle shift system.
Clutch: Carbon, AP pull type
Steering: KYB electronically assisted power steering (rack and pinion)
Suspension: Front:  01a: All new Acura specification upper and lower A-arms, with revised pushrod to monocoque mounted spring damper.  01b: same, but with revised bell cranks and third spring/damper added

Rear: 01a: All new Acura specification upper and lower A-arms, pushrod to bellhousing mounted spring damper.  01b:  same, but with redesigned rear anti-rollbar system and third spring/damper added.
Brakes: 4-piston Brembo/AP calipers, Brembo/Hitco carbon discs
Uprights: 01a/01b: Wire cut steel, Acura/Wirth Research design, manufactured by Pankel
Wheels: BBS
Front:  12.5" x 18"
Rear:  13.0" x 18"
Tires: Michelin radial
Front: 30/65-18
Rear: 31/71-18
Length: 4617 mm
Width: 2000 mm
Height: 1020 mm
Wheelbase: 2870 mm
Front Overhang: 997 mm
Rear Overhang: 750 mm
Weights: 815+ kgs (Sebring '07)
Tank capacity: 90 liters
ęCopyright 2011, Michael J. Fuller