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    1. Kit: , by (Member) schaumat is offline
      Builder Last Online: Mar 2014 Show Printable Version Email this Page
      Model Scale: 1/8 Rating:  Thanks: 0
      Started: 06-25-12 Build Revisions: Never  
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      [B][U]Porsche 908/03 build report[/U][/B]

      [B]Introduction[/B]
      People and friends following my projects show two types of reaction – they catch fire or they tell me I am nuts. Let me continue being a little ‘nuts’ for now – here’s one of my projects:

      In the last year I became more and more interested in Porsche race cars of the 70ies. It was triggered by my love to automatic-watches and here in specific the Tag Heuer Monaco, a rectangular shaped Chronograph. This watch became famous through Steve Mc Queen wearing it in the movie ‘Le Mans’ driving the famous Porsche 917 (the movie car was driven by the German Porsche race driver Hermann Linge due to insurance issues). Searching more info about this era, I became aware of the 908 series as an extraordinary example of race car engineering.

      The initial Porsche 908 was modified in 2 sequential releases – hence the /01 - /03. For more information, take a look a Wikipedia and other sources, e.g. in the Porsche museum ‘history of cars’ section. Here a summary of what I think you need to know:

      The Porsche 908 raced for just about 2 years. One could say the car was build for two tracks only: The 174 curves of the Nürburgring in Germany, and the Targa Florio, counting 704 curves per round on open streets in Italy.
      The 908 demonstrates the art of gaining competitive performance by weight saving measures instead of blindly adding power to a car. Of it’s last version (the 908/03) only 13 chassis were produced and all of them sBuilt reporttill exist today – either in the Porsche Museum or with Porsche enthusiasts. (A special extreme lightweight version based on the 908 was build for hill-climb races given the model number 909)
      The 908/02 was driven by one of my favorite actors of all times Steve McQueen during the 12 hours of Sebring finishing second with co-driver Pete Revson in 1970:

      But a new FIA rule enforced for the ’72 race season demanded a minimum car weight of 650kg; about 100kg above the racing weight of the Porsches 908, which killed most of the weight-related advantages. Not being able to fully capitalize from their weight benefits Porsche decided to stop racing the 908/03 only two years after the car had done it’s first competition.

      The 03 was the last version of the 908 with maximum weight reduction and -distribution by moving the COG (engine + transmission) towards the front axle. This caused the driver to sit in the very front of the car with his feet reaching in front of the front axle.

      The lightweight alloy tube frame was a piece of art. It’s body was made from very light fiberglass material. To save weight and to maintain a low center of gravity a new air-cooled 8-cylinder 3-litre boxer was developed. The weight of the complete oil cooled engine was about 178 kilograms. It featured a double camshaft, double ignition and produced about 257kw = 350hp without turbo charger. This engine block with the chain driven valve train is the father of all later developed air-cooled ‘flat 6’ boxer engines of the 911 series.

      The final motivation to built a 908/03 RC version kicked in when I found a 1/12 scale RC version had been produced by the German toy company Carrera Structo in the 70ies. The toy-body is of the same years when the original car was raced. Below you find a reference picture of the model in orange, and a picture of the car already painted in Gulf livery.

      Porsche 908-03, Built Report (pics will be uploaded tomorrow)-3361344_1_l-jpgPorsche 908-03, Built Report (pics will be uploaded tomorrow)-p1080905-jpg

      [B]Body modifications:[/B]

      [U]The body[/U]
      The ABS body from the 1972 Carrera Structo RC model had a small crack in the right front fender and was factory painted in orange with black racing stripes. My model did not contain a driver figure as shown in the picture as different versions of this model were released.

      The original decals were water-based and painted over with clear coat Porsche 908-03, Built Report (pics will be uploaded tomorrow) . They stick out slightly higher than the body so I decided to polish them off.

      The fins you see at the rear end of the body were added to the last version of the 908 to increase high-speed stability. But I prefer the sleek and table-like shape of the car so I cut them off and smoothed the tail of the body to resemble the earlier version.
      The body was mounted with 4 screws to the chassis. I had to dremel Porsche 908-03, Built Report (pics will be uploaded tomorrow) off the body stands on the inside to ensure a low enough position on the RC chassis.

      If you look at the right picture (Gulf-version) you will notice the rectangular rear edge of the front wheel arch. The toy body does not have an internal fender, so I added styrene Porsche 908-03, Built Report (pics will be uploaded tomorrow) and shaped the fender edges to suit the real car geometry as close as possible.

      I opened the air intakes for the engine / gearbox cooling. The former owner of the model glued one body mount in the wrong place and closed one of the fuel tank holes. I opened it up again and made two alloy tank lids.
      The original body has an unusual large tank lid, which must have been added for more realistic appearance – but it is too large and does not exist in reality so I decided to remove it. I filled the whole with styrene Porsche 908-03, Built Report (pics will be uploaded tomorrow) and putty Porsche 908-03, Built Report (pics will be uploaded tomorrow) and smoothed the section behind the right door – just leaving a small opening for the scale fuel-tank lid which I made from alloy. See here the before / after pics:

      Porsche 908-03, Built Report (pics will be uploaded tomorrow)-p1060546-jpgPorsche 908-03, Built Report (pics will be uploaded tomorrow)-p1090087-jpg

      I added a crossbar under the tail of the body, which carries the rear lights. This tube is glued to the engine hood from underneath.
      Shut lines of doors and engine hood are simulated with Kyosho micron tape over the clear coat Porsche 908-03, Built Report (pics will be uploaded tomorrow) .

      [U]The cockpit[/U]
      I had planned to cover the chassis cockpit area with a thin ABS sheet, but then I got the idea to try to keep the complete driver figure rather than just the upper half of the driver.
      This meant to dremel Porsche 908-03, Built Report (pics will be uploaded tomorrow) off a section of the upper chassis rail to create more room for the driver seat. The seat is glued to cockpit floor panel and fire wall. Both are glued to the engine. Once mounted, the cockpit floor sits tight on the flat mounted steering servo. The seat itself is from a 1/10 racing kart kit – I cut the center section to make it smaller.

      Porsche 908-03, Built Report (pics will be uploaded tomorrow)-p1060559-jpg Porsche 908-03, Built Report (pics will be uploaded tomorrow)-p1060620-jpg

      I use speed, rpm and oil temp indicators from my RSR 934 leftover box. I made the steering column and steering wheel to the scale shape and dimensions. (the steering wheel outer ring is a rubber o-ring) The dashboard sun cover is made of styrene Porsche 908-03, Built Report (pics will be uploaded tomorrow) to fit smooth with the curved body opening for the cockpit.

      Porsche 908-03, Built Report (pics will be uploaded tomorrow)-36-jpg

      The original window was glued to the body from underneath. I modified it so that it sits on top of the body and it is kept in place with 7 scale rivets (0,5mm thick).

      Porsche 908-03, Built Report (pics will be uploaded tomorrow)-21-jpg Porsche 908-03, Built Report (pics will be uploaded tomorrow)-32-jpg

      [B]Chassis modifications[/B]
      The shape of the ‘flat’ 908 body requires a low building chassis. I know there are more useful chassis out there (e.g. pan cars) but I went for the ABC Hobby genetic chassis because I had one sitting around. Having modified the same chassis already for another project I felt comfortable working the same chassis again - even if this meant some heavy surgery here and there….

      [U]Wheelbase[/U]
      The original M-size wheelbase is too long. I repositioned the front axle by 20mm and removed enough material on both sides of the base plate to allow free turning of the front wheels.

      [U]Wheels and Tires[/U]
      Next I had to create the wheel-tire combo which is kind of my specialty. I decided for F201 rear rims and wheels on the back because they match the 70ies balloon tires with large sidewalls. On the front I decided for F201 front rims to match rim geometry and I added ABC Hobby genetic tires. This required several modifications to the rims reducing diameter and width. I also added scale alloy valve stems in very nice CNC quality.

      Porsche 908-03, Built Report (pics will be uploaded tomorrow)-p1060610-jpg Porsche 908-03, Built Report (pics will be uploaded tomorrow)-p1060608-jpg

      [U]Axle width[/U]
      I adjusted the axle width with modified (thinner) alloy hexes. The wheel chamber was increased (a positive increase of chamber angle can compensate up to 2 mm offset without looking too x-legged).

      [U]Body fixtures[/U]
      I always mount the body to the chassis before I select the wheel tire combo. I used the original body mount fixtures of the ABC chassis and produced two alloy mount adapters with a 3mm threat for the rear. The body was then drilled to be fixed to the new body mounts with 2 allen-screws sitting level with the surface of the body.
      I use the original body mount of the ABC chassis for the front. I insert a body clip on each side in the air intake keeping the body down and centered. I use red silicone cable tube on the body clips to simulate the tow hook appearance at the front. To avoid major damage to the body by a front crash, I integrated a thin carbon front bumper lip.

      [U]Building height of the front diff[/U]
      I had to keep the high building front differential case - it contains the fixtures for the upper wishbones and for the steering rods.
      I cut off the upper part of the diff housing (the front body mount bridge) - a little unfortunate because the upper wishbone mount is quite importantJ. So I had to reproduce a flat upper wishbone mount which helps to position the body low enough over the tires. To fine-adjust the ride height of the front axle I use the small allen screw in the lower wishbone.

      [U]Front Suspension[/U]
      With the very low profile body of the 908, my real issue was the front suspension, which I did want to maintain fully operational. I thought about a pushrod system but decided to go for a direct suspension link for the lack of space. The dampers underwent loads of modifications: Shorter case, cap and rods, and custom springs to name the major mods…
      The damper mounts are self made from a piece of alloy which is mounted onto the original differential case. This way the suspension remains flat and functional.

      Porsche 908-03, Built Report (pics will be uploaded tomorrow)-front-908-jpg

      [U]Rear Axle[/U]
      The F201 rear rims have a negative offset and rub the c-hubs of the chassis. I cut the horizontal arm and replaced it with my own - much narrower - ‘c-hub stabilizers’ from 3mm steel. I replaced the large diameter dampers with thinner Porsche 908-03, Built Report (pics will be uploaded tomorrow) vintage Kyosho alloy dampers, which fit well after shortening the damper rod and some other minor modifications to spring and housing…

      Porsche 908-03, Built Report (pics will be uploaded tomorrow)-p1060481-jpg Porsche 908-03, Built Report (pics will be uploaded tomorrow)-38-jpg

      Believe it or not the ‘rest’ of the chassis remains unchangedJ
      Porsche 908-03, Built Report (pics will be uploaded tomorrow)-p1060556-jpg

      [B]The flat 8 boxer[/B]
      The engine of the original Carrera Structo model is more simulated than detailed. It is a very rough molded flat chrome plate indicating fuel lines and ignition wires. The only nice detail left are the air intakes and air-boxes:

      Porsche 908-03, Built Report (pics will be uploaded tomorrow)-31-jpg here the original model with engine from Carrera Structo.

      Due to the low profile of the car, the original RC components did not allow for a full sized engine mockup. What’s visible is just the air intake section and the central engine cover which – in reality - guides cooling air to the cylinders.
      With my ABC chassis I have a little more room to built ‘deeper’ - at least I can reconstruct the upper half of the engine heads sitting under the original air intakes.
      For the engine heads I modified 1/8 scale Corvette cylinder heads by cutting them short. They are mounted with 4 short air ducts from styrene Porsche 908-03, Built Report (pics will be uploaded tomorrow) to the air intakes. I transplanted the cooling fan from my static kit left over 934 RSR turbo engine.

      Porsche 908-03, Built Report (pics will be uploaded tomorrow)-p1090052-jpg

      From my 934 spares, I took the distributor case and placed it left to the cooling fan. To fit the ignition cables for the double ignition, I drilled 0,5mm-wide holes in which I inserted 16 single wires from a 540 motor copper wire. The wires are attached to the engine with black cable fasteners (from real fasteners) in the same position as in the original engine. I as well added the generator in front of the left cylinder bank.

      Porsche 908-03, Built Report (pics will be uploaded tomorrow)-p1060470-jpg model eningine in front of picture from a real engine.

      For the fuel system I used 0,8mm scale silicone tube which I fitted into each air box in the correct position, running between the air intakes coming together at the fuel pump sitting right next to the cooling fan housing. The tube fixtures are from styrene Porsche 908-03, Built Report (pics will be uploaded tomorrow) and the outer core of a receiver antenna wire. I added a little screw-on chrome lid, a small 2x1mm chrome plate and an even smaller ‘screw-on’ red lid to the fuel pump and 3 alloy scale hex screws – all for a little more 3D realism.

      Porsche 908-03, Built Report (pics will be uploaded tomorrow)-p1090065-jpg

      These modifications take time, but the push of realism by some real cables, alloy air intakes, scale hex screws and fuel liners is unbeaten:

      Porsche 908-03, Built Report (pics will be uploaded tomorrow)-engine-scale3-jpg Porsche 908-03, Built Report (pics will be uploaded tomorrow)-engine-scale2-jpg

      I reproduced a double firewall from styrene Porsche 908-03, Built Report (pics will be uploaded tomorrow) . The firewall is ‘bent’ as in the original car to ensure sufficient air flow and it holds the driver’s safety belt. I pulled the ABS-plate back and forth over a hard edge of my workbench to stretch and flare the material in this area of the cooling fan.
      The firewall is glued to the engine’s cooling fan duct. A fixture underneath the engine - together with the the firewall sitting tight between the chassis and the body ensure the motor stays in place without specific glue or screws.
      This way I have easy access to the brushless motor. In the left picture you see the flared firewall glued to the fan. You can see the large recess for the original tank cap behind the driver door (rectangle), closed and with small tank opening for the self made scale alloy tank lid for more scale realism in the right picture.

      Porsche 908-03, Built Report (pics will be uploaded tomorrow)-top-view-2-jpg Porsche 908-03, Built Report (pics will be uploaded tomorrow)-p1090064-jpg
      [B]
      The driver[/B]
      I found a driver figure of the 1/12 static Lotus kit in ebay and painted it in 1970 racing livery. Off course, he underwent heavy surgery. I inserted one threaded rod into the back of the driver which fits onto a whole in the firewall. And his left knee is fixed to the chassis with a screw. So I can remove the whole arrangement (engine, firewall, seat, cockpit floor panel and driver) in one piece and the fixtures are not visible.

      Porsche 908-03, Built Report (pics will be uploaded tomorrow)-p1070217-jpg

      [B]The roll bar[/B]
      True experts of you may already have noticed that my model is wrong. Yes, it has the wrong roll bar as this one is the more rigid one and was used with the version with improved high speed stability and with the rear fins. After I had taken off the fins, I only noticed my mistake after the car was painted, and it would have been too much work to close the 4 openings for the roll bar in the body, so I decided to let it go with this one.
      As the original roll bar is a rough mold from soft plastic, it is not possible to achieve a smooth surface and after several trials with filler and paint I decided to go for a self made chrome version.
      I used 4mm round solid brass rods for the main and the rear legs, and 4mm brass tube for the crossbar. I bent and fitted the components brazed them while being mounted to the (already painted and polished!) body. Yes, no fun working with a 1300° C flame close to the finished body…
      After sanding Porsche 908-03, Built Report (pics will be uploaded tomorrow) the braze residuals, I used a very thin filler to paint the roll bar in black. The chrome effect comes with a very special chrome powder from Japan, which I applied with a brush and then just polished with a soft tissue to a high gloss surface. You see pictures of the two roll bars in the beginning of the ‘flat8 boxer’ section.

      Porsche 908-03, Built Report (pics will be uploaded tomorrow)-p1060618-jpg Porsche 908-03, Built Report (pics will be uploaded tomorrow)-p1090102-jpg

      [B]The decals[/B]
      The decals resemble the Gulf livery of the car with the start number 40. This car was designed to run on the Targa Florio, a 72km long back-country road circuit with 704 curves. The drivers Pedro Rodriguez / Leo Kinnunen came in second with this car just behind an identical 908 in 1970. You see two pictures before and after application of the decals:

      Porsche 908-03, Built Report (pics will be uploaded tomorrow)-p1070232-jpg Porsche 908-03, Built Report (pics will be uploaded tomorrow)-p1080905-jpg

      The decals are self adhesive and made from very flexible full color vinyl supplied by the company modellbau-technik (mtm). The vinyl allows to be stretched without damage.
      I used orange left over decal Porsche 908-03, Built Report (pics will be uploaded tomorrow) foil to cover the air boxes for the same type of orange. I applied the decals after the first layers of clear coat Porsche 908-03, Built Report (pics will be uploaded tomorrow) on the flat and even surface. The clear coat Porsche 908-03, Built Report (pics will be uploaded tomorrow) layers applied afterwards protect the decals and prevent them to peal off in some years from now.

      [B]The paint[/B]
      I guess I learned a lot about color compatibility and airbrush Porsche 908-03, Built Report (pics will be uploaded tomorrow) settings when spraying this car. The kit body was painted orange with water based decals covered under a very light layer of clear coat Porsche 908-03, Built Report (pics will be uploaded tomorrow) . The paint was about 35 years old and I decided to seal it off with filler.

      Before I applied the filler, I had to make the body modifications and I filled all sanded areas with Tamiya Porsche 908-03, Built Report (pics will be uploaded tomorrow) plastic putty Porsche 908-03, Built Report (pics will be uploaded tomorrow) and reproduced a rear mirror from scratch.
      The grey filler from Tamiya Porsche 908-03, Built Report (pics will be uploaded tomorrow) is an excellent stuff and it took 3 or 4 spray + sanding Porsche 908-03, Built Report (pics will be uploaded tomorrow) cycles to get a smooth surface.
      The paint for the Gulf theme looks simple, but if you are going to mix it, it is quite challenging. I think if you worked long enough with paints and especially mixing it yourself, you know what I mean. Some light blue colors just don’t match the orange. I had to adjust my light blue to the orange decals I sourced from CMC, a company selling excellently finished models and kits.

      Unfortunately it took me three trials to get there…. First, I mixed acrylic Porsche 908-03, Built Report (pics will be uploaded tomorrow) brush paints (blue and white) to get the light blue, and thinned the mix with water, which normally has never been a problem.
      But when I sprayed the paint onto the body, it created small points like if you would sprinkle water onto a fresh oil paint surface. The second trial with different thickness was not any better, so I decided to completely remove the paint and start from scratch.

      With the AutoAir form Createx I had no issue to mix and paint the model. I finished the blue paint with a very light sanding Porsche 908-03, Built Report (pics will be uploaded tomorrow) using a 1800 grid diamond sanding Porsche 908-03, Built Report (pics will be uploaded tomorrow) product which is the best I have ever used. I kept it like that because I wanted the surface to be a little ‘rough’ to better take the clear coat Porsche 908-03, Built Report (pics will be uploaded tomorrow) .

      For the clear coat Porsche 908-03, Built Report (pics will be uploaded tomorrow) , I used ‘MIPA’ 2-component paint system with these mixing ratios:
      2 EA clear coat Porsche 908-03, Built Report (pics will be uploaded tomorrow) , 1 EA hardener, 10% thinner Porsche 908-03, Built Report (pics will be uploaded tomorrow) and 15% elastifier

      I use a 0,5mm nozzle and about 30 – 45 psi to apply the clear coat Porsche 908-03, Built Report (pics will be uploaded tomorrow) . Yes, the nozzle is a little small, but I can live with that.
      The initial ‘dry’ layer I applied with one pass so that the surface appeared ‘flat’ with very small clear coat Porsche 908-03, Built Report (pics will be uploaded tomorrow) pearls covering the body. I let the paint settle for about 5 minutes. After this first layer, I applied two thick ‘wet’ layers of clear coat Porsche 908-03, Built Report (pics will be uploaded tomorrow) with each a 5 minute curing Porsche 908-03, Built Report (pics will be uploaded tomorrow) time. Then it let the paint dry for about 3 days.
      For the next cycle, I sanded the body with a 2800 grid, just enough to ‘open’ the surface of the clear coat Porsche 908-03, Built Report (pics will be uploaded tomorrow) for better adhesion. I did not sand Porsche 908-03, Built Report (pics will be uploaded tomorrow) away any irregularities because one layer of paint only bares too much risk of damaging the embedded decals by the sand Porsche 908-03, Built Report (pics will be uploaded tomorrow) paper.

      The second round I just repeated the above, with the result that now the irregularities and small holes are nearly all filled and the surface created is already very smooth.

      I wet-sanded the remaining irregularities away using 2800 grid and apply a third round of coat. I let this dry again for more than three days before the final polishing can begin.

      For the polish, I use the pink series from 3M: polishing liquid, polishing wax and final sealing wax, three products used together in the automotive repair industries.

      Porsche 908-03, Built Report (pics will be uploaded tomorrow)-p1090021-jpg Porsche 908-03, Built Report (pics will be uploaded tomorrow)-p1090026-jpg Porsche 908-03, Built Report (pics will be uploaded tomorrow)-p1090027-jpg Porsche 908-03, Built Report (pics will be uploaded tomorrow)-p1090100-jpg Porsche 908-03, Built Report (pics will be uploaded tomorrow)-p1090104-jpg
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  1. schaumat's Avatar Member
    Name
    Matthias
    Join Date
    Aug 2010
    Posts
    6
    Hello,

    I finally managed to add the photos to this built threat. Hope you like it. Still missing a picture with finished and mounted mirror....
    But the car is a stunner on my shelf.


    Porsche 908-03, Built Report (pics will be uploaded tomorrow)
    QUOTE QUOTE #2

  2. JunkGTZ's Avatar VIP/Sponsor
    Name
    Larry
    Join Date
    Dec 2012
    Posts
    342
    Great looking work. I look forward to seeing the finished car pics. Now, while you're at it can you finish the Corvette? I've been looking forward to seeing the finished vette too! Keep up the great work.
    QUOTE QUOTE #3

  3. schaumat's Avatar Member
    Name
    Matthias
    Join Date
    Aug 2010
    Posts
    6
    Hello JunkGTZ,

    the Vette has been asleep for several years now as I was busy with made to order paint jobs. I might finish her off this year,I already received some period looking rims....

    I would really like to get some of my own projects finished but house-upgrades and family kept me away from the basement last year. This summer it will happen. Stay tuned and thank you for patience....

    As for the finshed pics, I have a friend who can better handle appertures and backlight screens....


    Porsche 908-03, Built Report (pics will be uploaded tomorrow)
    QUOTE QUOTE #4

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