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COMPETITION AUTOMOBILE DESIGN

 

   

GT2 / GT3 PROJECT

Design and engineering of BMW competition automobiles is the thrust of the company. We have completed a tube frame GT chassis designed specifically for the SCCA's GT3 competition and based it on the earlier 3 series E36 M3 body style. We employed a proven front suspension design which is virtually identical to that which enabled the 1998 GT3 national champion Nissan to break the Mid Ohio lap record at the time for both GT2 and GT3. Our engine development has been handled by Rebello Racing of Pacheco, California - the same manufacturer that builds the Nissan engines that often qualify fastest at the SCCA runoffs and which is currently preparing SPEED Channel touring class engines for race winners Ken Dobson and Marc Kirberg.

Several West Coast designers, of which we are one, are sharing information and are together developing competitive GT cars based on a similar chassis design. After customers purchase a chassis, they will have access to an ongoing stream of information and components that we make available to improve and update the chassis. GT cars lend themselves to being updated rather easily and affordably which means that they remain competitive throughout their useful life when the updates are performed. Manufacturers in Trans-Am chassis do this for their customers all the time. Very often what you see in Trans-Am when you think you are looking at an entirely new car is simply a rebodied chassis that may have had several seasons of racing. This creates the opportunity for serious racers to maintain both the current body style and the competitiveness of their car. It's not possible to make an E46 out of the older E36 that someone may already have spent what amounts to a ton of money on. This can be done affordably with these tube chassis cars by simply replacing the body panels.

DESIGN

Our GT2/GT3 chassis is a square tube framed "Trans-Am" design employing independent front wishbone suspension with coil over shocks. The rear suspension design employs a "full floating" style solid axle housing with removable third member and a pair of coil over shock absorber assemblies. The axle housing can be designed to accept either a Toyota 7" Ford style "third member" or, for GT2 and Grand-Am, the heavier duty Ford 9" assembly. Final drive ratio changes are accomplished in about a half hour by swapping out the third member units. The Ford assembly is slightly more expensive and only a bit heavier but is more appropriate for the six cylinder or V8 engine. They both employ the same axles and floater components. Solid rear axle construction, although not required by SCCA rules, keeps the cost of the chassis affordable and requires little setup time for different tracks. It is, however, the required rear axle design of the NASCAR administered Grand-Am series. We have incorporated a special pivot assembly below the housing that is a key design feature of this chassis. It offers the lowest possible roll center at the rear of the car and the ability to adjust easily for anti dive and anti squat.

TRANSMISSION

The transmission choices vary from the heavy duty Trans-Am favorite Hewland STA five speed gear box to our newest recommendation - the several versions of the Argentina manufactured Saenz gearboxes which include a really nice six speed sequential unit. We initially used the Houseman Autosport "Black Box" which is a straight cut gear, dog ring redesign of the Toyota T50 split case gearbox. This is suitable only for GT3 and lesser horsepower competition, however.

BRAKES

Brakes are a standard four wheel disc design using Wilwood calipers and rotors. Certainly other brakes can be fitted; however, the Wilwood brakes are very effective and quite reasonably priced. The current Wilwood GT3 rear caliper and disc design is probably adequate for all classes including Grand-Am. Our GT2 design will incorporate AP front calipers as an option.

ENGINE

The GT3 powerplant is a normally aspirated, carbureted BMW 318is M42 engine with a displacement of 1.8 litres. This is the engine configuration that was stroked to 2.0 litres by BMW and was used successfully in the various touring car series throughout Europe during the 90's. Development on our 1.8 litre has been performed by Rebello Racing of Pacheco, California. Maximum power with Webber carburetors is currently in the range of 260hp. Fuel injection will be fitted for 2003. Engines are supplied with Carillo or equivalent I beam design alloy connecting rods and custom "touring car" design pistons. The camshafts are computer designed and ground from factory billets. The cam followers are a special solid bucket race component employing shims on the valve stems for adjustment.

The engine uses an externally mounted custom three stage dry sump oil pump with a specially cast dry sump pan. Webber carburetors are fitted to our custom cast intake manifold. Fuel injection has recently been introduced to this class, and we will be using TWM throttle bodies along with our manifolds. The engine runs upright in the chassis rather than on the standard 30 slant as in the street car for packaging considerations. The clutch is a 5" twin disc assembly engaging a custom 102 tooth flywheel fitted in a low height aluminum bellhousing with a tiny rear mount starter. All these components have been provided by Tilton Engineering. The exhaust system employs a beautiful stainless steel header neatly packaged with a Borla stainless steel muffler that helps the car to conform to sound regulations at most US tracks.

An additional engine supplier is Performance Developments of Costa Mesa, California, which is currently undertaking a new development program for the M42 and M50/S50 engines. Neil Harvey, the owner of that company, has worked with BMW on their Formula 1 engine program during their world championship years with Nelson Piquet in the eighties. He is very knowledgeable on a variety of race engines and has some special skills to lend to an engine development program. He has also had some articles published in performance car magazines regarding his BMW engine work. His direct connection to the BMW M GmbH engine staff will provide the program with much needed technical assistance.

The GT2 engine is the US version 3.0 litre M3 S50 engine which design is basically two more cylinders added to the M42 engine. Outside of the front timing case construction, the engines are fundamentally identical. Adaptation to the chassis is handled similarly to the M42 engine and the engine suppliers are the same. SCCA rules now allow free fuel injection and free engine management since the 2002 season. This means that the full potential of all engine configurations can be reached and customers will have total flexibility with the same engine and chassis package to run in SCCA, Grand-Am and BMW CCA events. Engine management will be handled by a Link II system that employs all the stock BMW ignition components save the control unit. It is a sequential system that will also handle vanos; however, we do not use vanos.

A basic four gauge display is offered for engine instrumentation; however, a custom data logging system from Stack may be substituted at additional cost. Switches and wiring are kept simple and efficient. If customers wish to do this installation themselves, wiring diagrams are provided.

BODY

Our E36 body style is identical to that of the E36 M3 GTRs campaigned by Tom Milner's Prototype Technology Group. The panels are supplied by the same company under license to GT Technic. The rear spoiler used in the SCCA GT3 category (pictured in the photo gallery) is substantially different from the PTG adjustable rear wing; however, a customer can always purchase through us the PTG wing for BMWCCA Club Racing. Pricing is in the catalog section. Our new body - for the E46 M3 - is now available and will be widened with the 2001 ALMS winning Schnitzer/PTG flare kit for GT2 and Grand-Am competition. Pricing is not developed for this kit at the present time, but it should be similar to that for the E36.

The body panels are mostly lightweight original body parts made of composite material that are attached to the tube frame by means of a straightforward mounting system. We feel that this individual panel design is more practical than the Trans-Am approach of using one large nose and one large rear body assembly either of which when damaged can be difficult to repair. In addition these large units require special handling for transport to and from race events as spare parts and are especially troublesome to ship by common carrier. Our hood and deck lid are hinged with standard components while the doors are simply skins attached with Camlock fasteners.

DELIVERY

A basic frame takes approximately six weeks from receipt of deposit to final construction. This time period, however, marks only the beginning of the assembly process. Some components are supplied from outside sources and may take longer to arrive at our facility. Preparing a rolling chassis is dependent upon sources beyond our control for which we can make no firm guarantees. Depending upon a customer's options which may require frame additions after the initial fame is complete, it can take several months of additional preparation prior to delivery. Mounting the body to the basic frame requires fabrication of front and rear impact structures and utilizes some specially designed components to assure accurate body panel placement. This task will take two skilled men approximately two weeks to complete. A first class sheet metal interior job can take one man up to a month depending upon the detail required. Riveting panels onto a chassis can be quick, but to make them easily removable with Camloc fasteners or threaded inserts is careful detail work. Should the customer want to do some or all of this him or herself, purchasing many of the precut sheet metal components would reduce a great deal of assembly time and eliminate a lot of hassles in panel fabrication.

There are several time consuming tasks involved in the preparation of a chassis. You may examine the section on the GT3 chassis pricing which refers to the many labor operations involved. Delivery, therefore, is entirely dependent on what configuration is ordered. However, if all suppliers make deliveries to us according to schedule, a basic rolling chassis should take four to five months F.O.B. California.