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GT-R35 road race project (code name NGT-R)

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Discussion starter · #22 · (Edited by Moderator)
Chassis and roll cage.

There are many ways and materials used to build chassis and roll cages. I would not say one is wrong and another is right but I was taught to use a particular set of practices that I will strictly follow in each and every project.

In parallel with exterior design work was going on chassis side. In order to make things faster bent/notched tubes where ordered from Custom cages UK. My thoughts was - this is exactly same roll cage that is used in Nismo/JRM FIA GT3 car and it should be here very soon because they have the design ready. I ordered it in BS4 T45 steel - one of preferable type of steel because of its excellent strength properties (stronger than 4130), high elongation at brake (good for absorbing impact energy) and no need for post weld heat stress relief when TIG welding is used. It turned out that I had to wait longer than expected.

Before welding in the cage one would want to seam weld the chassis. Spot welding used for production vehicles doesn't provide sufficient integrity of separate stampings used by factory to construct chassis. Properly seam welded chassis would gain from around 80% to 110% in torsional stiffness which is absolutely vital for handling. Most highly stressed areas (such as areas around suspension subframes, lower sides seals etc.) are welded with continuous welds and less important areas with "stitch" welding (~25mm weld, 25mm gap, 25mm weld and so on). There's one very important thing - excessive heat would deteriorate steel properties. Proper technique is to weld a stitch of 10-12mm (short enough so metal is not overheated) than leave a ~ 100mm gap than apply next short weld. After placing say 10-15 "stitches" with large gaps between them on left side welder would move to right side of the car and repeat the process there while left side is cooling. Than get back on left side and place a weld in the middle of each gap and move to the right side and repeat it there and so on until one continuous weld is achieved where needed. Doing it this way is a lot more labor intensive and time consuming but it pays dividends in terms of end result - strong and stiff chassis which could be used as a base to build a proper race car.

Seam welding was done and tubes finally arrived. I made a 3D model of Custom cages roll cage to integrate it in standard chassis 3d scan and than analyze it using FEA and some common sense.



When one looks at English cage it's evident that they where mostly concerned with weight saving. That's to be expected because gtr is not famous for ultra light weight and in GT3 class power output would be restricted to near standard numbers. Also there's large restrictions in terms of how much of original chassis must remain intact and unchanged. Because of that (imho) - there's little rear suspension support and front suspension support is non existent. (I'm not trying to say they did it wrong, in contrary I think they did the best they could with given tech. regulation constraints)

On the above image red arrow shows direction of primary forces acting on upper rear damper mounts. It's evident that there's nothing to resist deflection in this direction. (In order to understand how chassis would resist forces imagine that its members/tubes are connected not by welds but only pinned together. For example a triangle will be stiff even if tubes are only pinned together and rectangle would not)

Regarding front part of chassis - here's a couple of screenshots taken from video of JRM testing GTR GT3 in spring 2013.





One can see that there's no roll cage extensions supporting front suspension. But if we look at FIA GT1 version (as well JRM) than there's entirely different situation:





There we can see front upper damper mounts stiffly tied to mid part of chassis (Red arrows). Four tubes form 4 triangles that effectively resist deflections in vertical and lateral directions. Similar solutions are used in Georg Plaza BMW 134 Judd, Australian V8 supercars etc.

I decided to go in similar direction and added front extensions to 3d model of English roll cage:





Than added rear part that stiffly tied rear dampers and subframe mounting points with rest of the roll cage and main standard chassis beams/members.





As a result we have a well triangulated tubular space frame integrated into seam welded factory chassis. This renders a lot of chassis parts useless and adding nothing but weight and it allowed to plan some careful but extensive cutting and saving weight as a result.

Than it was time to leave the CAD station and carry design over and into reality. That's how it looked than:













Every tube connection/node was sanded to clean metal, etched and every weld was made with meticulous attention to every minor detail.

Thanks
Ted
 
Discussion starter · #26 ·
Than time came to paint the chassis. There also was lots of cutting of excess metal but I can't find those images.
Here's painted chassis assembled with subframes, suspension, flat floor and front/rear diffusers.













Thanks
Ted
 
Discussion starter · #32 · (Edited by Moderator)
Cooling system

In the case of factory standard GTR there is conventional road car cooling scheme - water radiator is placed vertically, just in front of engine. Two intercoolers are stacked right in front of radiator. In terms of efficient cooling this arrangement is less than ideal. For effective heat exchange one needs to let cool ambient air come to radiator (this is done) but not less important is extracting hot air out of radiator. Higher amount of air pumped through radiator = higher rate of heat exchange/cooling. If there's no sufficient exit for flow coming through radiator than it becomes problematic. In case of factory GTR problem is amplified by intercoolers - air that gets to radiator is already preheated. This setup works fairly well in normal street conditions with standard power but in case of increased power output (= increased heat generation) and race track conditions it proved to be less than adequate.

In a race car one would always want to design cooling system that will allow air flow entering radiator and will take care about evacuating it out of there. With front engined cars most common place for radiator outlet is upper surface of engine hood. This work well because usually we have a lower pressure zone on that surface (one would always want to take air from higher pressure zone and evacuate it into lower pressure zone as this would allow for highest possible flow volume) and high pressure zone on bumper front face. This has another side benefit in reducing lift on front axle (or increasing downforce if you're so lucky). Air doesn't really like to make sharp turns but hood surface and bumper front surface are positioned approximately at 90%. So one would try to arrange inlet and outlet ducting so the air travels at around 45 degrees (relative to horizontal). Radiator is positioned at 45 degrees as well (but in opposite quadrant) which places it at 90 degrees relative to flow direction. This also has some side benefits - allowing to package taller radiator and slightly lowering its COG. All the above is over simplified but that should make it easier to read.

Our cooling package was designed according to above considerations. Radiator was ordered from Ron Davis - I gave him necessary data (power output and packaging constraints) and they calculated what would work. Same way with intercoolers (ordered from Bell).

Last Saturday we did a mockup installation of front cooling ducts and took some photo's:





Radiators and intercoolers are placed so that they do not shadow each other. On the above images it's easy to see outlet ducting - radiator in the center and intercooler exit ducts on its sides.





Below - couple of images of radiator/intercooler inlet ducting.





Grill is a mockup part so far (it's way too rough and ugly) - final grill is still in production and it will also have two inlets to feed intake air filters.

That's how it looks (so far) when assembled together. Grill is fixed to front bumper by hot glue (it was a trial fit as I mentioned earlier) which is visible in the gaps but that's OK for now
Image










Also this arrangement allowed to make intercooler piping shorter and straighter which in turn should improve throttle response.

Thanks
Ted
 
Discussion starter · #39 ·
We use vacuum infusion process and than post cure in the oven at elelvated temperatures. Without a clave with prepreg there will be usually slightly worse surface quality (because of very high viscosity resin used in prepregs).
All the cad design of parts, than master models/plugs, moulds and finally parts where made inhouse. As well as all the chassis, suspension etc. work. We're a small 4 people team and budjet is restricted. It took longer than I'm used to when working with race teams with large budgets. However now, when all the tooling is in place I can reproduce this car to turn key race ready in about 6 months. It can be done faster but it would be more expensive because I would need to hire more people.

Thanks
Ted
 
#40 ·
What kind of resin systems are you using, are your laminates balanced symmetric, what are your tools made out of? When initially designing the car did you start off using a tire and then building your geometry around that or did you aim for a general change in camber/caster/toe? What were your initial static corner loads for the car? I might have missed it but does this car retain the stock car's awd system?
 
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