Racecar Engineering, July 2001 – PCD Saxon, Suzuki

Words: Simon McBeath Photos: Tom Wood/NMM

 

Hillclimbs in the UK are known for being narrow, twisty and short and for being held on private roads with considerably less than pool table levels of smoothness. Nonetheless, maximum speeds of up to 150mph can occur and ultra-soft tyres provide high levels of grip. couple this with remarkably unrestrictive regulations and hillclimbing provides racecar designers with an unrivalled set of technical challenges. 

This is, however, a sport in which creative thought enjoys levels of freedom nowadays unheard of in senior competition categories. The results are stunning. To be able to design a car from scratch, to meet these unique challenges was just part of the motivation for former Lotus Formula 1 chief designer Martin Ogilvie. A big part of the challenge was also to design a car in its entirety at a time when all senior level competition cars are designed by numerous engineers, each working on perhaps one particular sub-assembly of the car. Ogilvie explained: "I've always wanted to do very, very light cars and hillclimbing (and its 'on the flat' counterpart, sprinting) is the only formula where there is no minimum weight limit."

 

To say that Ogilvie's S1100 Suzuki – informally christened 'Saxon' by project partner and driver Rob Barksfield – will shake the sport to its foundations may be an over exaggeration to some, but with around 190bhp in just 280kg including the driver, it is sure to raise some eyebrows.

 

Philosophy 

Through his Prototype Car Design (PCD) concern, Martin Ogilvie began this lightweight single seater project about five years go, since when the design has undergone a few metamorphoses. Then I met Rob Barksfield at the Autosport International Show last year' explains Ogilvie, 'and I told him I was designing a carbon fibre car. He was interested in graduating to (driving) a carbon car so we got talking. I thought it was a lot of money to do the project just for myself which is why it toddled along as a spare-time doodle until I met Rob and it all turned good.' Ogilvie had previously designed a lightweight Lotus 7-type car for himself, and subsequently penned the Westfield FW400 carbon chassis road and track car. But for a lightweight racecar the motorcycle engine format fitted perfectly. "I looked at the motorcycle engined-cars and decided that it didn't look as though people had tackled them in what I considered to be the correct way. They'd simply taken a racing car and put a motorcycle engine in it." He added: "Another interesting thing in doing a very light vehicle is deciding what sort of parts are appropriate. I set a target of 200kg, so you've got to say "what's actually required of this bit and what do you actually need for wheels, or a steering rack." You can also say "it's only going to do x number of miles so we'll do a hollow aluminium rack instead of a steel one." And why take wheels from a 450kg Formula 3 car? You've got to do our own, just bite the bullet and do it."

 

"So that's where I started from. I worked out what all the weights had to be and kept checking as I went along, making sure I was still down to the target. This was meant to be 200kg with the oil-cooled engine variant, which would be a bit lighter with no radiators, and it came out at 208kg with the water-cooled engine." Ogilvie did all the design work and made the patterns for the composite components himself, everything else was sub-contracted. Meanwhile, Rob Barksfield was coordinating the engine weight-reduction and performance development work at Hampshire-based Debben Performance. This work was based on successfully running a Debben-prepared Suzuki GSX-R 1100cc engine previously in a Hi Teck single seater. 

 

This experience dovetailed nicely with Ogilvie's design concept. He said: "The car is designed purely around the Suzuki engine, which is very different from the other engines in that it has side draught carbs. Because I've got the (chassis) structure going over the engine, down draught carbs would be very difficult. It would require a lot of modification to accommodate a Kawasaki or Yamaha engine and it wasn't a primary requirement. Designing it specifically around the Suzuki engine was the only way I could make the car as light." The S1100 was intended to be, and eventually will be a two-pedal car. The third (clutch pedal has been squeezed in for now until a paddle-controlled quick-shift system, complemented by a hand clutch, has been developed.

 

 

Design and Build

Martin Ogilvie's ability to ask fundamental questions and avoid conventional weighty solutions is in evidence throughout the S1100. But an inevitable and important question people have already asked, because of its low weight, is whether or not it will be safe. Ogilvie is reassuring on the this point. "The interesting thing is that the rub is of sturdier construction than early composite-construction Formula 1 cars. Of course F1 cars have come a long way since, but the S1100 is a sort of halfway house." A carbon/honeycomb nose box provides frontal impact absorption and was chosen after Ogilvie expressed concern about the 'bits of bent aluminium stuck on the front' of some older hillclimb cars. The raised nose allows the front lower wishbone pick-ups to be placed under chassis. "I'm paranoid about having the rear leg of the lower wishbone going into the driver's legs. I put them underneath the chassis so, in the case of a shunt, they shear off underneath and the driver stays intact."

 

The carbon-honeycomb chassis construction (with aluminium hard points) reflects Ogilvie's thoughtful approach as he has minimized the number of internal bulkheads. The front of the chassis constitutes the front bulkhead and the dash bulkhead provides the pick-up points for the rear legs of the front wishbones. There is also a small 'mini-bulkhead' under the rear roll hoop stay, and a rear bulkhead right at the back of the chassis. The monocoque is made in upper and lower halves, each half having been done in a one-shot cure in order to preclude the need for extra film adhesive layers. Intriguingly the chassis extends over the top of the engine. Ogilvie says, "I don't know whether it's unique. But the regulations call up quite a study roll hoop and I didn't want a lot of weight high up. So I thought I'd make the roll hoop as small as I reasonably could and take the carbon to it. Then, if the carbon is up that high you might just as well pop it over the top of the relatively low engine and keep the whole frontal area down (by not adding side structures)." The obvious downside of this is that if a spark plug failed it would require engine removal to fix it. The counter-arguement, however, is that the type of plugs used rarely fail, and that most other 'top-end' failures would require raceshop rather than paddock repairs. In any case, engine removal is not really very long job.

 

'Another thing that nobody else seems to have done is to take advantage of the fact that the required fuel capacity is only a few litres. There is no need to accommodate a large fuel cell. So why have a chassis that's bigger than the driver? Once you've gone past the driver's bum, you can then sneak it right back in again. Even so I've got masses of space between his back and the engine. That's why I've got this huge 'NACA duct' down the side to cool the engine, this would have been essential for the oil cooled engine which requires plenty of air cooling. On this one we managed to fit two small radiators but again we've tucked them in very tightly. The carbon/honeycomb rear bulkhead, which carries the rear suspension, the differential mounting and the rear wing needs to be torsionally stiff because, whilst the structure over the engine is torsionally stiff, it requires triangulation back down underneath because it hasn't got any sides.' 

Suspension 

Asymmetric, convergent double wishbones and pushrods are used all round. A monoshock spring damper unit is used at the front, with small coil springs to react against roll. A separate Penske damper controls the roll springs independently of the damper controlling the mains spring's bump and pitch movements. The non-adjustable dampers are actually re-valved Formula Vee units. The rear suspension uses twin coil-over damper units, but there is no rear anti-roll mechanism. Tiny rod-end (1/4 x 5/16in) and spherical (1/4in) bearings have been used throughout the 'Saxon' and pick-ups are small machined steel brackets bolted at hard points to the chassis, or outboard to the fabricated steel uprights. Ogilvie's approach to suspension geometry is refreshingly uncomplicated: "I've basically taken fairly standard suspension geometry and allowed more movement, especially in roll. With a car that's very narrow the suspension pick ups are almost of necessity much further in, which means you can carry long wishbones, and I wasn't very keen on having outboard structures for the top pick ups. So it is fairly basic and conventional. I think if you've got good roll centre control, correct camber change, correct weight distribution and good roll centre heights then it will handle anywhere.

 

Brakes and wheel systems

The small-and-light approach has most definitely been applied here. Whilst the 240mm diameter by 4mm thick nitrided stainless steel discs have been seen previously, the minute Grimeca calipers, as fitted to the rear of Ducati motorcycles, were sourced directly from Italy. The alloy disc 'bells' could scarely be made of less material and master cylinders are also from the Ducati rear system, and the tiny reservoirs are simply clipped to the front bulkhead. The layout of the brakes is interesting, with the discs inboard of the uprights. Ogilvie explains: 'This was done for two reasons. Firstly, if you sandwich the wheel bearings between the disc and the wheel then you have no hub (saving weight). And secondly I anticipated making the wheels out of two spinnings (per wheel) back to back. I then didn't have room for the (outboard) caliper and the disc. 

 

 

The plan for spun wheels fell by the wayside when nobody could economically produce the designs Martin wanted, he finished up with machined-from-solid centres and spun rims. Nevertheless the wheels are extremely lightweight. Another interesting weight saving details worthy of note is the three-bolt fixing that attach the wheels (directly through the Tripode lobes at the rear) to the discs on the other side of the uprights. Tyre choice was a difficult problem. With such a light car the very softest compounds could be selected, but width was not so easy to choose. "The car is so light, why do you need eight and 10-inch wheels? Why not sevens and nines? Any I very nearly went that route" says Ogilvie, "I told Avon the weight of the car and they recommended eight and 10-inch wide wheels because the tyres have been developed. 

 

Aerodynamics 

The S1100 clearly has a very small frontal area, so drag will be similarly modest. The wing set utilises the same profile front and rear, although the front wing chord is extended as a single element device whilst the rear wing is two-element. Both have 1400mm spans. 

 

"We've started off with a fairly basic package but there is a further aerodynamic package coming at a later date. Because we've got no sidepods, and it's a narrow car, we've got a lot of scope along the side and at the back of the car to fit what we like. What you want is to produce downforce with the right distribution. If you start having sidepod diffusers you have to have them quite high for them not to be too sensitive to ride height. Ground effect aerodynamics (and I was at Lotus when it all started off) depend on constant ride height, And you don't want an aerodynamic package which is sensitive to the great variations that you encounter on a hillclimb."

 

Engine and transmission

The Suzuki GSX-R 1100cc engine is a popular racing option, not least because of the availability of donor engines, tuning parts and relevant tuning expertise. As Ogilvie explained the car was designed around the oil-cooled version with minimum weight in mind. However, he was persuaded that the performance potential of the water-cooled variant made that a better route, despite the weight penalty. An all alloy unit, this particular engine has a bore of 75.9mm by stoke 60.0mm, giving a swept volume of 1086cc and produces, in current specification, around 190bhp at the crankshaft at 10,000rpm.

 

The engine here is semi-stressed, and is connected to the chassis directly by its original mountings. At the front of the engine block two lugs bolt to a triangular section carbon/honeycomb structure which forms an extension to the rear of the car's monocoque. At the rear, four lugs on the transmission casing connect to the bulkhead. The machined-from-solid alloy sump connects to the rear bulkhead and to the base of the triangular carbon moulding ahead of the engine.

 

Ray Debben of Debben Performance described the process of tuning the engine: "It's basically about blueprinting and careful parts section. Weight has been taken out of the major reciprocating masses but we've also had the luxury of doing about 50 dyno development runs. That subsequently allowed us to try all manner of ideas on carburettors, cam timing, ignition curves and so forth. With the cylinder head the trick seems to be to do surprisingly little work. With development we've found what NOT to do, and it's about removing little bits of material from the right paces to indue tumble (swirl). Fuel injection is the next development but the set-up work will be very expensive. There has been so much set-up work done with carburettors that we know what to do with. But the mapped ignition system from MBE Systems (with very supportive input from Mistral Engineering who supplied the base map) has helped a lot on this latest engine." 

 

The engine is lubricated by a wet sump system, and in theory would release more power on a dry sump system. But Ray Debben asserts that the windage losses with such a small sump and small oil volume are not serious compared to the significant weight penalty of a dry sump. Notable weight saving were made in and around the engine by lightening the crankshaft, the sump, the electrics and the ceramic-coated 30 thou (0.76mm) wall thickness mild steel exhaust. Furthermore the alternator, starter and the unnecessary starter gears adjacent to the clutch assembly, have been dispensed with. The engine and transmission unit, bereft of carburettors and exhaust, therefore weighs 62kg. The uprated clutch assembly drives a six-speed racing gear set so that, via the short chain, power is fed to the differential which is also unique in this application. Ogilvie said: "I had to do my own diff. I decided early on that I didn't want a conventional diff with a sprocket grafted onto the side and then CV joints – it would be a toto ally inefficient use of weight. And I found the Fiat diff system that has got the CV joints as the diff sun gears.

 

"I was originally going to do it around a Cinquecento diff. The Cinquecento is only 600cc but if you look up its weight, stick it in first gear, and work out the actual load, the torque that goes through the diff is about the same as we get. But Rob started talking about more horsepower so we've actually gone up to a bigger Fiat spec with an LSD. It's a very compact unit. And I've used that same CV outer in the centre of the upright. Also it's unusual in the proximity of the two sprockets – it's a very short chain. You'd get a bit of cushioning from a longer chain, so that might put a bit more impulse load into it. We'll have to wait and see. You don't know until you try".

 

Martin Ogilvie  

After graduating with a mechanical engineering degree from Birmingham University, England, Martin Ogilvie's first job was at Girling designing racing brakes for such teams as Brabham, Tyrell and Lotus. Then he moved to Lotus and stayed there for 13 years, starting on the Lotus 72 and finishing with the 100, being chief designer from the type 81 onwards. He left Team Lotus in 1990 and spent 18 months as chief designer (advance composites) at Lotus Engineering prior to joining Racing Technology Norfolk (RTN), which was then TOMS, where he designed a Formula 3 car and 'did a bit of Touring Car work'. He then did an abortive F3 car for Tedy Pilette, an outboard suspension car with the suspension inside the wheel. After that he returned to TOMS to do the GT1 Elise for the FIA and Le Mans series. After a couple of years he went back to RTN and then started work with Prodrive 18 months ago to help on the Mondeo Touring Car. Now he's working on a GT project with them.

 

 

S110 'Saxon' Suzuki

Specifications

Marque S1100 'Saxon' Suzuki

Motorsports Category  UK Hillclimbs

Producer Prototype Car Designs

Specification date  March 30 2001

Dimensions

Weight excl. driver 208kg (458lb)

Wheelbase  2150mm (84.6in)

Front track  1400mm (55.1in)

Rear track  1350mm (53.1in)

Overall length  3550mm (139.8in)

Overall width  1645mm

Components types and locations

Chassis  Carbon fibre composite monocoque

Engine Normally aspirated, water cooled straight-four, twin-camshaft, four valves per cylinder, transverse mid-mounted

Gearbox Six-speed, manual,sequential

Clutch Multi-plate wet

Chain DID X-ring type

Differential Modified Fiat, limited slip

Dampers Gas pressurised monotube

Wheels Bespoke three piece

Wheel sizes  8 x 13in front, 10 x 13in rear

Brake calipers Two-piston alloy

Brake discs  Nitrided stainless steel, 240mm x 4mm solid

Brake pads  Asbestos-free conventional 

Bodywork and wings Carbon fibre composite

 

Feature reproduced with permission from Racecar Engineering Magazine