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CCC
July 2001
CCC July 2001
The S1100 Saxon is possibly the lightest racecar ever built - and with over 900bhp per tonne from its 190bhp Suzuki bike engine, it's a wild racer.
Simon Mcbeath examines it in detail....
 
Progress is inevitable, but sometimes it catches you unawares. This month's Tech Focus subject, the S1100 Saxon Suzuki hillclimber, makes the 360kg, 130bhp 1100cc class hillclimber I drove some years back look like a Neolithic hearse. The S1100 boasts 190bhp in 208kg. That's over 900bhp per tonne already with the target of 1000bhp/tonne achievable with a little more development.

The S1100 comes from the CAD screen of Norfolk based Prototype Car Designs (PCD), run by ex-Lotus F1 chief designer Martin Ogilvie who also designed the Westfield FW400 carbon sportscar. Driver Rob Barksfield has coordinated engine development in a partnership hatched at a chance meeting at last year's Autosport International Show. That the two should meet when one had designed a carbon hillclimber and the other wanted to graduate to one is spooky. But fate or coincidence, the pair have taken full advantage of the opportunity. CCC got the chance to get under the skin, and into the mind of the designer, of the S1100 Suzuki before it even turned a wheel on a track. The Saxon moniker, by the way, is a sort of unofficial name Rob came up with.

LIGHTWEIGHT TUB

To make a car this light, the chassis also had to be light. To achieve the necessary structural properties required to make the car work and keep the driver safe, Ogilvie chose to use a carbon/honeycomb composite. Although the tub weighs a mere "15 to 16kg", Ogilvie say: "it is in fact of sturdier construction than the early composite construction Formula 1 cars." A possibly unique design feature is that the chassis extends over the top of the engine, connecting the stiff rear bulkhead. Ogilvie wanted to only semi-stress the engine, so some kind of rear chassis structure was needed, but to keep the frontal area of the car small he didn't want structural sides around the engine bay. Furthermore, the roll hoop had to be pretty sturdy to comply with the regulations, and as he didn't want lots of weight high up in the car he decided to make the roll hoop as small as he reasonably could and take the chassis up to it. then, with the carbon chassis at that height, it was a small step to extend it over the top of the fairly low engine.

So, you ask, how do you get the spark plugs out? Answer: you fit good, reliable ones, and hope you don't have to remove them in a hurry. It's a calculated gamble; if you are unlucky enough to encounter a top end problem it's unlikely to be just a plug gremlin, and you'll be taking the car back to the workshop to fix it in any case. That said, it's a quick job to remove the rear end of the car should that prove necessary. For most of the time this is one of those compromises that won't be an issue... hopefully. Ogilvie made four or five wooden chassis mock-ups early in the project to make it as comfortable and small as possible. And the need to only carry a small fuel tank for hillclimbs enabled the chassis to be tapered in behind the driver's backside. As he says: "Why have a chassis that's bigger than the driver?" The chassis taper has been shaped to channel cooling air to where it is needed without adding width to the car. We'll explore details later in the aerodynamics section.

Other safety features include what Ogilvie calls "a proper carbon/honeycomb nose box", and the raised nose has enabled him to locate the lower wishbone mounting underneath the chassis. He says"This is something I've wanted to do on any cars I do myself. I'm paranoid about having the rear leg of the lower wishbone going into the driver's legs, which you can always have if they're going through into the chassis or a bulkhead. I wanted to put then underneath so in a shunt they shear off and the driver stays intact." Ogilvie also says the car will also be suitable for circuit racing because it has the regulation cockpit opening for the driver, the current size roll hoop, the front crash structure - every thing you need for MSA approval for racing. And here's another nugget for you - the S1100 was originally conceived as a two pedal car. The extra (clutch) pedal has been squeezed in for now whilst the car is sorted but a sophisticated paddle-operated gearshift mechanism with hand-operated clutch is under development....

POWER PUNCH
CCC has propounded previously on the benefits of bike engines - lightweight all-alloy units producing high power outputs at high rpm. The Suzuki GSX-R motor, though no longer current, is one of the more popular choices for powering small racecars because of the availability of engines, tuning parts and expertise. And the S1100 was designed specifically around the GSX-R 1100 motor because its carbs are side draught (which fitted with the over the engine chassis concept) most other bike engines having more of a down draught angle. Slight over-boring to 75.9mm with standard 60.0mm stoke give 1086cc swept volume. In current specification it produces around 190bhp at the crank at 10,000rpm. That's pretty respectable 175bhp per litre.

Rob Barksfield's engine is prepared by Ray Debben, at Debben Performance in Ringwood, Hampshire and Ray outlined some of the tuning background: "It's basically about blueprinting and parts selection. We've taken weight out of the crank and pistons and so on, and we've also had the luxury of about 50 dyno runs in which we tried all manners of ideas with carbs, cam timing, ignition curves and so on. With the head the trick is to do surprisingly little - basically we've found what not to do. It's all about removing little bits from the right places to induce tumble rather than high gas speed, then you don't need big carbs." The engine uses flat-slide Keihin 39FCR carbs - "good for mid-range power" - but Ray says that fuel injection is on the development list.

"There's a lot of expensive set up work to do though. With carbs there's about 100 years of experience available, and I've got over 30 years myself, so we know what to do with them." But he says he wants to get into fuel injection and reckons the MBE ignition management system, new on the engine this year, has helped boost performance from 6000rpm and upwards. The engine is wet sumped, partly because of the extra weight of a dry sump system. Ray reckons that the engine runs so little oil in its shallow sump that the windage losses are small enough not to worry about. Weight was the over-riding issue, and with other savings made from lightening (knife-edging and polishing) the crank, not running a starter or the attendant gears and starter ring, or an alternator, and using a lighter electrical loom, the weight of the engine and transmission less carbs and exhaust is just 62kg, The exhaust is made in 30thou (0.76mm) wall thickness ceramic-coated mild steel so it isn't exactly heavy either.

CCC July 2001 SUSPENSION AND WHEEL SYSTEMS

Suspension is by double wishbones and pushrods all round, with a 'monoshock' at the front and dual spring/dampers at the rear. The front spring/damper system isn't really a monoshock because within the small anti-roll coil springs there is a separate damper to control them, as well as the usual one within the larger bump/pitch spring. There is no separate anti-roll mechanism at the rear. The dampers are re-valved Formula Vee units and are non-adjustable. On suspension design Ogilvie says:"I've basically gone for fairly standard geometry and I've allowed more movement, especially in roll." The narrowness of the car means that the inboard suspension pick-ups are on a narrow base, which means the wishbones are pretty long. Longer wishbones give less wheel camber change for a given amount of wheel movement, keeping the tyres flat on the road. Ogilvie reckons: "If you've got good roll centre control, correct camber change, correct weight distribution and good roll centre heights the car will handle anywhere." There is a modicum of anti-dive at the front and (adjustable) anti-squat at the rear built into the geometry. Ogilvie's not a fan of too much of either parameter because they deaden feel and have other adverse effects but he acknowledges that some can be advantageous. There is also Ackerman angle built into the steering (to steer the inner wheel on a tighter radius), beneficial where there are tight corners.

Weight-saving ideas abound on this car, but are more visually obvious in the brakes and wheels. The brakes basically come from the rear of the legendary Italian Ducati bike marque, though the diminutive two-pistons alloy calipers are sourced direct from Italian manufacturer Grimeca. The drilled discs are in nitrided stainless steel, held on by the slightest of alloy disc bells. Even the hydraulic components are minuscule, again from the rear of the Ducati. If all this seems under-engineered, remember the car weighs little more than a bike, yet uses four brakes and four sticky tyres to stop. Ogilvie says there were two reasons for the unusual location of the discs, inboard of the uprights. "Firstly, if you sandwich the wheel bearing directly between the discs and the wheel then you don't need a hub [which saves weight]. And secondly I had anticipated making the wheels out of two symmetrical spinnings bolted back to back, and that didn't allow room for the usual positioning of the caliper and disc. But nobody could make the necessary spinnings economically so I decided on machined-from-solid wheel centres." The rims are spun and with those minimalist centres they still make for extremely lightweight wheels.

The suspension components are attached by 1/4-inch bore x 5/16-inch shank rod end bearing or 1/4-inch bore spherical bearings connected to almost dainty-looking machined steel brackets. Again it all looks small than we're used to seeing. Ogilvie agrees: "That's right. You've got to re-train your engineering eye and say 'hang on a minute, it's less than half the weight of an F3 car, so it has to take less than half the loads.' There's a lot of sayings I go back to Colin Chapman for, such as ' a quarter inch bolt will lift a double-decker bus!' We don't have a double-decker bus so we don't even need a quarter inch bolt!"

The choice of tyre size was one area where Ogilvie succumbed to convention. Avon recommended 8-inch wide front and 10-inch rear tyres because they are well developed. Ogilvie says: "F3 sizes look right, but I would like to try them smaller (and lighter)." The tyres were designed for a 450kg F3 car and do seem disproportionately heavy for such a light car. But with the three-piece wheels, some different rims could be spun to allow narrower tyre to be tried if required. The steering was definitely not compromised, a hard-anodised hollow aluminium steering rack being made by Tian to save a chunk of weight compared to the usual steel bit.

LITHE BODY

As long as driver of single seater have to sit at least slightly upright, there will be a practical minimum frontal area. The S1100 chassis/body is just about down to that minimum, which together with the sleek shape should ensure minimal drag. As mentioned earlier, the radiators are tucked in almost behind the driver's backside. The car was originally going to use the oil-cooled Suzuki engine, which needs plenty of air to cool it too, hence the scalloped sides to direct air at the engine block. Following the decision to use the water-cooled engine, those scallops enabled twin radiators to be used without adding much to the car's frontal area.

Low drag from the body is significant when it comes to how much wing the car can carry. Front wings do not add significant drag but rear wings do and the low body drag allows a reasonably powerful two-element rear wing without undue concern over the induced drag. This will obviously provide a fair bit of downforce. To balance that, the front wing, slung under the nose via a shapely carbon moulding, is a fairly large single element device.

CCC July 2001
Ogilvie says they've started with a basic aero package but developments will continue. "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 to put what we like. You want to produce downforce and the right distribution (front to rear). That's where we require a bit more research. Ground effect aerodynamics depend on constant ride height, and you don't want an aerodynamic package which is sensitive to the variations of ride height you have on a hillclimb.

But as Ogilvie was a part of the team at Lotus, with Colin Chapman and Peter Wright, who first properly exploited ground effect on a single seater (on the Lotus 78), expect him to come up with something effective.

CHAIN GANG

Some purists do not like the idea but chain-driven, bike-engined racecars are quick and are therefore here to stay until a faster alternative appears. It is possible to connect a bike to a conventional gearbox or transaxle but it's a lot heavier than using the integral transmission and chain drive. Thus the uprated GSX-R multi-plate wet clutch drives the output sprocket, and via the short DID X-ring chain, power is transferred to the alloy final drive sprocket. So far, pretty conventional.

The diff however is a bit special. Martin says he didn't want a conventional diff with a spocket grafted onto the side feeding out to CV joints. His solution comes of a Fiat unit which CV inner flanges also serve as the diff sun gears, an elegant weight-saving design which fitted Ogilvie's requirements. It's actually an X1/9 diff with an LSD. The steel outer case is a bespoke machined item, shaved to the minimum (and to be replaced by an aluminium case later). It's a neat looking solution, though Ogilvie admits to some apprehension about the loads imposed by dummy starts and sticky tyres even with a lightweight car. As he says, you don't know until you try...

CCC July 2001 SPARTAN OFFICE

The moulded cockpit is so full of impressive composites detail work that you don't notice the lack of instruments beyond the Alpha steering wheel. Who needs 'em? Not Rob Barksfield, or several other hillclimbers these days. Apart from checking the engines warm and setting revs at the start-line, hillclimb drivers rarely look at the instruments, and probably never during an actual run. So that's a few hundred grams more weight saved.

To assist the timing of gear changes Rob has a bleeping earpiece in his crash helmet, an aural shaft light if you will, that tells him when he arrives at shift rpm. It's less distracting than a system which relies on vision - particularly in a demanding competitive environment like hill climb events when drivers have little time to peer down at the instrument panel. Currently a lever and cable on the left side of the cockpit operate the six-speed sequential manual gearshift.

Rob is to get a custom-moulded carbon seat soon so the car is going to feel like it's a part of him. All single seaters are like that but the low weight and compact dimensions of the Saxon makes may others seem like pantechnicons [one for the dictionary lovers there - Ed].

 
PERFORMANCE AND COST

The S1100 has yet to turn a wheel under its own power as I write, so performance can only be guessed at. But its power to weight ratio without driver is almost in the same ball park as the unlimited capacity hillclimb single seaters like the ex-F1 V8-powered Goulds and Pilbeams, and well ahead of even the lightest 2-litre-powered hillclimbers. In the 1100cc class the lightest competitor is maybe 40kg heavier, giving the Saxon a driver-aboard power to weight ratio advantage of 14 per cent, assuming similar power. Providing grip, handling and reliability are adequate, performance should be highly competitive. If it grips and handles well, watch it fly.

As for cost, Ogilvie reckons the first S1100 rolling chassis stands him in at £28,000 including parts, pattern and moulds but not including labour. So you could reckon on paying somewhat more than that if you wanted a replica. He aims to get the first car developed into a competitive and reliable package first, though he is considering the possibility of making more.

With the S1100 taking on the already developed and rapid Force (which is also running in the 1600cc hillclimb class and in Monoposto on the circuits, and with another carbon-chassis racer still to come from DJ Racecars, hillclimbing is a fascinating hotbed of technical ingenuity at the moment.

TECH SPEC
S1100 Suzuki Saxon hillclimber

Chassis: Carbon fibre composite monocoque

Weight: 208kg

Engine: Suzuki GSX-R, transverse mid-mounted, prepared by Debben Performance. 1.1-litre straight four, four valve per cylinder, DOHC, 190bhp at 10,000rpm, Keihin carbs, MBE ignition management, Suzuki/Rob Barker/Electron Beam Processes crankshaft, Carillo conrods, Wiseco pistons, Yoshimura cams, APE valve gear, Tony Green exhaust, wet sump lubrication system

Transmission: RWD, Suzuki/APE/Goodrick wet clutch, Suzuki/Graham Dyson/Nova Racing Transmissions six speed, manual, sequential gear set, B&C Express DID X-ring chain, Fiat LSD, Titan driveshafts, GKN Tripodes

Suspension: Front: double wishbones, monoshock spring damper with separate anti-roll springs and damper. Rear: double wishbones, dual springs and dampers. Penske dampers

Brakes: Grimeca two-piston calipers, 240mm x 4mm nitrided stainless drilled discs, cockpit adjustable bias.

Wheels: Alloy three-piece by PCD/Mike Barnby Engineering, 8 x 13in front, 10 x 13in rear

Tyres: Avon soft compound, 7.2/20.0-13 front, 9.2/22.0-13 rear

Fuel tank: 1.3-litres

 
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