See the cars that are in action on the 750F grid


Postby Steve Boother » Mon Mar 07, 2022 12:37 pm

Designed and built by Dave Robson

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The following is a description / listing of what I did to design & build SDAR/17. It is not a recipe to design your car. However, you may find some of the details to be useful to get you in the right ball park if you are building a
car. As with most designs, if I did it again I would do it differently, and better hopefully.

The design for this car is partly driven by the desire to create a successful race car but also to experiment with new technology.
I wished to try an unconventional approach to the design and construction of a 750 Formula car and use more current engineering tools and techniques.
These included:
Design modelling using CAD, use of FEA for details, laser cutting sheet material, 3D scanning to capture difficult shapes into CAD, 3D printing components and moulds for casting and the use of data logging to refine the car (and the driver's) performance.
All work was carried out by myself apart from precision machining by Frank
…..............this is why it all took so long!

Start Design (and learning CAD) - August 2016
First Race - July 2018
Finally sort out oil supply and carburation problems to get the car to run properly - August 2021

Classic front engine with drive through a propshaft to live rear axle
All enveloping bodywork

Standard FIAT 1108cc engine from Punto 55 - 176 B2 000
Stainless steel backplate with polybush engine mounts - t = 4mm
Engine installation leans from the vertical to raise the inlet side - 10 degrees
Lightened cast flywheel - 3.7kg
Modified sump with minimal baffling
Standard head, skimmed - 48400108
Compression Ratio - 11.0 / 1
Regulation Newman Cam with associated valves / standard timing wheel, dowelled
Head Gasket available in two thicknesses - Payen BP280 at 1.7mm, Payen BP940 at 2.0mm

Standard FIAT water pump is fitted.
Two front-mounted Seicento radiators are mounted on a tubular sub-frame. (cost & packaging reasons) - Radiator x 2
Aluminium expansion tank mounted high with water feed to the bottom water pipe and air bleed feed from the rear of the cylinder head
Aluminium tube and silicone connectors carry coolant. Air bleed is provided where pipes form hump and potential air trap - 32mm diameter
Return ‘cool’ coolant passes through Laminova oil / water heat exchanger

Oil System
Laminova oil to water cooler 160mm length with 32mm water tubes - MOCC43-9078-M32
Accusump 1 quart aluminium 12" x 3.25" feeds into tapping in oil pump casting with no valving - N24-046
Sandwich block takes oil to Laminova via braded pipes - MOCAL
Standard oil filter screws onto the sandwich block. Jubilee clip on filter used to prevent loosening - MahleOC983, Motorcraft 1137362
Oil catch tank for engine & gearbox :- fabricated aluminium container with top breather and bottom drain bolt

Dellorto DHLA (second hand emission type; not the best) - DHLA 40F
Intake trumpet 3D printed in PLA
Dellorto modified to only use one of the twin chokes
Choke size - 32mm
Jetting best set up on rolling road or using logged Lambda data - not given
Comment: Emission carburettor type needs careful adjustment of idle settings; they affect the whole rev range
Cable pull choke system is retained for cold starting
Cast aluminium inlet manifold, cast at home from 3D printed pattern
Inlet manifold has no water heating
Dellorto mounts onto manifold with rubber O Ring gaskets to give a degree of flexibility
Fuel regulator / filter; Filter king 67mm alloy - Pressure 4psi
Original Fuel Tank: Purchased APR aluminium tank - 9.2 litre
Fuel Tank modified: Spill lip added, catch pot added to increase volume and help with fuel pick-up, M10x1.5mm outlet boss - 10.4 litre
Installation of the tank is behind the rear axle so is protected by 'crash' structures and crumple devices

Laser cut stainless steel manifold flange - t = 6mm
Stainless steel tube sections bent to 90 degrees and MIG welded - (1 Stop Direct) 1D radius t = 38mm
Stainless 4 into 1 collector 38mm to 1.5” - Part 2532589 07911
Stainless steel exhaust silencer purchased (50mm inlet, 127mm diameter & 500mm long) - (Every Exhaust Part Ltd) BOX-127-CLAMPON
Welded boss for Lambda sensor after 4 into 1

Electrical components protected by fuse bank with anti-shake foam to firmly locate them - Fuses x 6
Fuel pump: Facet posi-flow (4 to 6 psi flow rate of 32 US gallons per hour) 11 gallons per hour measured - 60106
Battery: Lithium ion (LiFePO4) by Powerlite (9Ah, 1.4kg, 150x87x104mm) - PS-09
Dash instrumentation, apart from AIM logger display includes ignition master switch with cover, momentary starter button, AIM logger power switch, rear LED switch (illuminated) plus choke pull, extinguisher pull and Battery isolation pull
Starter Motor: High torque WOSP starter - WOSP
Jump plug for external battery and charging at RHS side pod

MegaJolt Lite/Jr. electronic ignition controller - Megajolt/E
Coil pack, EDIS unit, SENSOR, plug leads and wiring from scrapyard Ford Escort CVH
Trigger wheel laser cut steel - t = 6.3mm
NGK spark plugs - BCPR7EIX

Helix competition clutch cover assy - 184mm x 1 cera 155 LBFT
Helix clutch plate - 184mm ORG RIG 1 x 23T-7.2mm
Concentric slave release bearing Saab 9002.0i design; Borg & Beck - BCS 164
Clutch Master Cylinder: Girling with integral reservoir - 0.625"

Heavily modified FIAT Punto bellhousing
Transition between bellhousing and gearbox uses two aluminium plates suitably drilled and tapped - 12mm & 19mm plates

Quaife dog box in alloy case, 4 speed, H pattern (second hand) - QBE9ZSTC-Alloy
Gear ratios:- 2.04, 1.54, 1.21, 1.0
Input spline: 1" diameter x 23 splines
Output spline: 1" diameter x 25 spline.
Modifications to tail shaft and lid
Remote gear change to move gear lever forward uses carbon tube & rose joint pivot

One-off from Bailey-Morris Ltd, 1140 Standard / lightened 40mm tube with 2mm wall - Part No. 14C9/6
Propshaft length between centre of U/Js - 405mm
Maximum angle of U/J 13.4 degrees (17 degrees is acceptable)

Rear Axle
Morris Minor axle with LHS shortened by 3" to take Sprite half shaft; Brackets for dampers, links etc are laser cut from 1.6mm steel sheet
Axle located by 4 x leading links (600mm long) and PHR 829mm long at 151mm above ground level)
Leading link anti-squat geometry - 5 degrees
Double bearing aluminium hubs with 4"PCD 3/8" studs; Wheel nut torque:- 35 lbft
Rebuilt Morris Minor differential - 4.22
Short halfshaft from Austin Healey Sprite (later, stronger design with groove through splines) - BTA 806 EN17
Long half shaft from Morris Minor - ATA 7057

Front Axle
Beam axle design from 2" x 2" tube. Located by 4 x trailing links (600mm long) and PHR (824 mm long) at 95mm above ground level)
Brackets for dampers, links etc laser cut from 1.6mm steel sheet. Bottom spherical bearing holder machined from solid
Trailing link anti-dive geometry - 6 degrees
Steering Wheel with quick release hub - 250mm diameter
Steering rack and sliding steering column from FIAT Seicento. Rack mounted directly on beam axle
Stub axles; Triumph Herald
Front uprights: Original cast aluminium versions failed, now machined from solid aluminium
Front Hubs: Cast aluminium with 4" PCD 3/8" studs; Wheel nut torque:- 35 lbft
Bottom Spherical Bearing: 38mm OD / 16mm bore in axial thrust - MSTQ16
Top upright bearing: Rose joint with 1/2" shank and 3/8" bore - RMC6FU

Front Wheel Geometry
Negative camber - -2.2 degrees
Caster - 4.4 degrees
King Pin Inclination - 9.5 degrees
Maximum wheel angle at full lock - 20 degrees
Toe in - 0.5 degrees
Wheel offset to tyre centre at ground level - 30mm
Wheel camber of outside wheel on 20 degree lock - -3.1 degrees
Wheel camber of inside wheel on 20 degree lock - 0.0 degrees
Bump steer - Nil

Front Suspension
SPAX Dampers, single adjustable , 300mm / 246mm (to rubber) - CSX C90/120, 3:1
Dampers fitted at 886mm centres and at 6 degrees to the vertical
Coil springs: 7" static length & 1.9" diameter - 180 lb/in
Anti roll bar: 19.05mm tube with 2mm wall and 132mm levers at 132mm centres
Vertical bounce frequency - 2.7 Hz

Rear Suspension
SPAX Dampers, single adjustable , 300mm / 246mm (to rubber) - CSX C90/120, 2:1
Dampers fitted at 963mm centres and at 6 degrees to the vertical
Coil springs: 7" static length & 1.9" diameter - 220 lb/in
Anti roll bar - none
Vertical bounce frequency - 3.0 Hz

Wheels & Tyres
Rimstock cast alloy wheels: ProRace 1.2: Front (for slicks & wets) - 7.0x13 e35 4x4"
Rimstock cast alloy wheels: ProRace 1.2: Rear (for slicks & wets) - 7.0x13 e15 4x4"
Tyres: Slick are the mandatory Yokohama radials; 160/520/R13, Tyres: Wets are Yokohama radials: 160/520/R13 with block tread pattern - N2669, N2701

Wilwood Dynalite Calipers, four pot, front, 1.75 x 0.38 - 120-6818
Wilwood Dynalite Calipers, four pot, rear, 1.38 x 0.38 - 120-6808
Brake Disc, Front: Vauxhall Firenza type, 255mm diameter, 9.6mm thick - EBC D533
Brake Disc, Rear: Triumph Herald, machined, 232mm diameter, 5.5mm thick - BM309 / BDS4017
Brake Master Cylinder, Front: Girling with integral reservoir - 0.625"
Brake Master Cylinder, Rear: Girling with integral reservoir - 0.7"
Brake balance bar with remote knob adjustment
Braided hose brake pipes with some copper pipes

The chassis is a semi-monocoque with a top-mounted ring frame to carry the major loads from rollbar, engine mounts and suspension. The lower part is a folded & riveted single skin aluminium 'tub'
Steel tube top frame: 38 x 19 x 1.6mm ERW tube plus some 25 x 25 x1.6mm ERW tube
Suspension pick-up brackets and other brackets from laser cut & folded 1.6mm steel sheet
Monocoque element was laser cut from 1.6mm aluminium sheet with half of the rivet holes laser cut. Sheets were folded and then joined together and to the steel frame
Monocoque joints & attachments: Methacrylate adhesive with 4mm rivets - VM100

Fire Extinguisher
Lifeline Zero 2000 4.0 litre Fire Marshal situated in passenger space - LIF 106-001-001
Flexible tubing to 6 nozzles
Twin pull cables to base of roll bar and dash

Seat shell made from carbon / polyester composite
Seat lining moulded in polystyrene bead / epoxy compound
Seat covering is Nomex cloth
Seat adjustment is available
Seat Belts: TRS 5 point harness - 14A7000

Bodywork comprises four regions of composite panels; nose, bonnet, tonneau / side fence & rear
Nose is gel costed glass / polyester moulding that has exit ducts for the front radiators and covers the front wheels
The bonnet is lightweight Carbon / core / carbon moulding in polyester with front opening for engine cooling and cold air intake for the carburettor
The tonneau covers the passenger space and the side fence is to the right of the driver. Both are lightweight carbon / polyester composites
The rear bodywork is supported on the tubular frame and crash structure surrounding the fuel tank. The rear bodywork hinged at the rear to give access to the fuel tank and has extra crush capsules to the rear of the tyres. The rear wing is carried by this bodywork which is made from gel coated GRP and is heavy
Wing mirrors have carbon shells and glass reflectors. They are on adjustable stalks
Body panels are secured by various fasteners including over-centre latches, 3D printed catches and special Formula 1 type ratchet screws

Carbon rear wind made with sandwich skins by the infusion process - W = 1510mm D = 290mm
Wing section approximates to NACA profile - 4513
Vertical wing supports from rear bodywork at 1/3rd 2/3rd locations made from carbon / polyester
Wing has gurney flap at trailing edge and flat end plates - h = 8mm, Plate 320mm x 155mm
Four wing angles of attack are made by selection of bolt hole in wing mounting - 2, 7, 11 & 14 degrees
Maximum wing height above the ground (constant for all angles) - H = 860mm
A diffuser is fitted under the rear axle, made from carbon / core / kevlar laminate - Plan approx. 1000 x 730mm
Diffuser raises front to rear and has vertical sides - H = 100 to 215mm
A horizontal splitter projects forward of the nose and is the full width on the nose - D = 130mm
Splitter is a sandwich panel with Hexcel and other core materials. Skins are in kevlar and the leading edge is a formed aluminium tube. Splitter hinged at rear to be raised when entering trailer - d = 20mm
The shape of the splitter is complex with end vortex devices, diffuser elements and central 'hump'
Sidepods are formed from Dibond (an aluminium skinned plastic panel) and mounted on steel tubular frames cantilevered from the chassis
The lower panels of the side pods are an 'aerodynamic' shape

AIM logger (now superseded); dash display connected to SmartyCam (superseded) - Pista MXL Pro05
Internal logging of lateral G, logger temperature, battery voltage & engine RPM
Display is reconfigurable and incorporated 'change lights', warning lights, lap times, RPM and much more
SmartyCam also has GPS receiver to yield position and GPS derived speeds & accelerations
Four wheel speeds can be logged together with 12 other analogue channels. Typically these include: brake stroke, throttle stroke, lambda, surface temperature, oil temperature, oil pressure, water temperature and longitudinal G
Sensors are reconfigurable to suit requirements using remote terminal boxes and Binder 719 plugs
Displacement sensors are reconfigured throttle position sensors from scrapyard cars
PLX wide band Lamba sensor module with Bosch LSU 4.9 probe - PLX-0107

Maximum weight at end of a race - 491 kg
Weight of driver with kit - 85 kg
Car weight without driver - 406 kg
Weight distribution Front / Rear - 48.5 / 51.5
Weight distribution Left / Right - 50.6 / 49.4

Engine: Running in / Normal: Mineral 10w40 / Synthetic 10w40 - 3.5 litre
Gearbox: Kerax HyperDrive KXR Fully Synthetic 75W90 - 1.3 litre
Rear Axle: Mogal Semi-synthetic GL5 75w90 - 600ml
Brakes & Clutch: DOT 4 synthetic as required
Cooling: Water / antifreeze mix at 33%, Bluecol as required
Petrol: Shell V Power 99 octane - 10.4 litre

Wheel Base - 2000mm
Track - 1280mm
Chassis ground clearance Front / Back - 48mm / 100mm
Max Width of car bodywork - 1570mm
Max Length of car, nose to tail - 3335mm

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Steve Boother
Posts: 276
Joined: Sat Jul 19, 2008 12:49 pm

Re: SDAR/17

Postby F1300Tony » Mon Mar 07, 2022 5:37 pm

So that is how it is done!
Do I take it that Payen head gasket thickness is before use?
Posts: 751
Joined: Sun Apr 17, 2011 4:14 pm

Re: SDAR/17

Postby Dave Robson » Tue Mar 08, 2022 6:42 am

Just one way to do it Tony!
The gasket thicknesses are difficult to measure accurately. I've quoted my best guess for the uncompressed thickness and use 1.6 & 1.9 mm in the compression ratio calculations.
Dave Robson
Posts: 213
Joined: Mon Oct 15, 2007 2:41 pm

Re: SDAR/17

Postby F1300Tony » Tue Mar 08, 2022 9:36 am

Thank you, Dave. I have recently measured a used gasket of unknown origin and the thickness averaged 1.6mm around the bore seals.
Posts: 751
Joined: Sun Apr 17, 2011 4:14 pm

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