Engine Development
Toyota 4A-GE — Formula Atlantic 1600 cc
At the heart of the InGear Starlet is a highly developed Toyota 4A-GE 1600 cc engine, built around Formula Atlantic specification components and engineering principles.
The engine combines genuine TRD Atlantic components, extensive internal preparation, dry-sump lubrication, a heavily developed big-port cylinder head and a late Atlantic-style fuel-injection system.
The result is a naturally aspirated 4A-GE designed around high-rpm reliability, airflow efficiency, precise engine control and motorsport durability.
Bottom End
The engine is based on a Toyota 4A-GE 7-rib block, which has been crack tested, internally deburred and polished before machining.
The block has been torque-plate bored and decked specifically to suit the piston combination and maintain accurate bore geometry under operating conditions.
Internal components include:
TRD Formula Atlantic crankshaft
TRD Atlantic Carrillo connecting rods
Wössner forged Atlantic-specification pistons and rings
Custom steel main bearing caps
ACL Race bearings
ARP main stud kit
Lubrication is handled by a dedicated dry-sump system, incorporating:
Custom fabricated dry-sump oil pan with integrated oil scraper
Peterson high-volume dry-sump pump
Remote oil filter system
TRD cylinder-head oil-feed modification
Ported oil drain passages
Engine protection and data acquisition are integrated through:
30 psi oil-pressure safety switch
Haltech oil-temperature sensor
Haltech oil-pressure sensor
Additional custom components include:
Custom engine mounts
Custom front oil-pump cover
Custom water-pump delete plate
Cylinder Head
4A-GE Blue Top Big-Port — Atlantic Specification
The cylinder head is based on the Toyota 4A-GE Blue Top big-port casting and has been extensively developed for high-rpm naturally aspirated operation.
The ports have been extensively modified and the head flow tested to optimise airflow through the complete operating range.
Cylinder-head specification includes:
Extensively ported and flow-tested big-port cylinder head
Supertech Atlantic-specification valves
TRD shim-under-bucket valve train
Titanium valve spring retainers
TRD valve springs
TRD 11 mm lift inlet camshaft
TRD 10.5 mm lift exhaust camshaft
ARP head stud kit
Cometic 1.3 mm head gasket
Custom-built adjustable cam gears
Custom cam-seal retaining plates
TRD Atlantic cam cover
Inlet camshaft synchronisation sensor
ARP cam-cover stud kit
The adjustable cam gears allow the inlet and exhaust camshaft timing to be precisely dialled in to optimise the engine's power curve and suit the final induction and exhaust configuration.
Intake & Fuel System
Induction is based around a TRD fuel-injection throttle-body system configured to late Formula Atlantic specification.
The inlet system incorporates:
TRD individual fuel-injection throttle bodies
Match-ported inlet manifold
Custom aluminium ram tubes
Siemens 800 cc fuel injectors
Custom outboard injector system
Modified 4A-GE 20V throttle-position sensor
Custom throttle-linkage system
Haltech intake-air-temperature sensor
ITG air-filter system
The outboard injector arrangement provides additional fuel delivery further upstream of the intake valves, complementing the primary injection system and taking advantage of the high airflow and engine speeds generated by the Atlantic-style induction package.
Combined with the extensively developed big-port cylinder head, TRD camshafts and individual throttle bodies, the intake system is designed to provide maximum airflow, sharp throttle response and strong high-rpm performance while retaining precise electronic engine management.
Transmission & Driveline
Elite Racing Transmissions IL200-6S Sequential
The InGear Starlet runs an Elite Racing Transmissions IL200-6S six-speed sequential gearbox, selected for its extremely compact packaging and lightweight construction at under 30 kg.
The gearbox uses a custom ratio set together with interchangeable drop gears, allowing the overall gearing of the car to be changed without altering the differential ratio. This gives us a practical way of tailoring the transmission to different circuits, tyre diameters and operating conditions.
With the power output and competition use of the Starlet, the IL200-6S operates close to the upper end of its intended application. Because of this, the gearbox is maintained under a preventative service programme.
When the car is being actively raced, the gearset is assigned a defined service life and is removed and crack-tested annually, allowing fatigue or damage to be identified before it develops into a gearbox failure.
Gearbox Lubrication System
As part of the transmission development programme, we have engineered our own improvements to the IL200 lubrication system.
The gearbox uses an external lubrication circuit incorporating:
External gearbox oil cooler
Electric circulation pump
Internal oil spray rail within the gearbox casing
Gearbox oil-temperature monitoring through the Haltech ECU
The internal spray rail provides controlled oil delivery directly within the transmission rather than relying solely on conventional splash lubrication.
The combination of forced oil circulation, additional cooling and temperature monitoring gives us much greater control over gearbox lubrication and operating temperature during extended competition use.
Sequential Shift Control
The Starlet's flat-shift system has been developed to allow two different shift-control strategies to be tested and used through the Haltech engine management system.
A two-channel Hall-effect rotary position sensor monitors the position of the gearbox selector drum, while an NPN 12 mm proximity sensor monitors movement of the gear lever.
Having both signals available allows the ECU to determine both driver shift request and actual gearbox selector movement.
This gives us two primary control strategies:
A timed ignition/torque cut triggered by movement of the gear lever
A torque-reduction strategy referenced to actual selector-drum position
Using both inputs has allowed us to experiment with ignition-cut timing, torque reduction and restoration during the shift event, with the objective of achieving fast, repeatable and mechanically sympathetic sequential gear changes.
Rather than relying purely on a fixed-duration flat shift, the selector-drum position provides direct feedback of what is actually happening inside the gearbox during the gear change.
Gear Ratios
Gear Ratio
1st 2.420
2nd 1.867
3rd 1.563
4th 1.333
5th 1.142
6th 1.000
Drop Gears: 20:21
Differential Ratio: 4.777:1
The combination of the six-speed close-ratio gearset, interchangeable drop gears and fixed differential ratio gives us considerable flexibility when setting the car up for different circuits and performance requirements.
Driveshaft Development
The driveshaft has also formed part of the Starlet's ongoing driveline development programme.
We have tested a carbon-fibre driveshaft together with several different yoke and CV-style joint configurations, evaluating the effects of weight, rotational inertia, joint behaviour, reliability and driveline characteristics.
The car currently runs a steel driveshaft, which has proven to be the preferred solution for the present configuration.
As with many areas of the Starlet, the final specification is based not simply on using the lightest or most exotic component available, but on testing different solutions and retaining the combination that provides the best overall performance and reliability.
Suspension & Handling
The InGear Starlet uses a highly modified TRD N2-specification front suspension setup, combined with a fully adjustable three-link rear suspension and Watts linkage.
The entire suspension system has been developed with competition use as the priority. There are no rubber bushes or compliant mounting points in the suspension pick-ups or anti-roll bar systems, giving direct control of wheel movement and allowing precise adjustment of suspension geometry.
Front Suspension
The front suspension is based around extensively modified Toyota KP61 struts, incorporating custom-valved Bilstein shock absorbers, fabricated coil-over spring platforms and reinforced strut assemblies.
The stub axles have been strengthened with additional reinforcing ribs, together with a structural sleeve positioned between the wheel bearings to increase rigidity under high cornering and braking loads.
The front springs are 450 lb/in and run on thrust-type needle roller bearings at the spring perches. This allows the spring to rotate freely during steering movement, reducing spring wind-up and friction within the strut assembly.
The upper spring mounting hats are also custom manufactured and incorporate additional thrust-type needle roller bearings, further reducing friction during spring and strut rotation.
At the top of each strut, adjustable pillow-ball upper mounts provide precise camber adjustment.
The front anti-roll bar is a 21 mm TRD N2-style unit fitted with adjustable end links, allowing the system to be accurately set up and preload to be controlled.
The lower control arms are custom TRD N2-style adjustable arms, providing adjustment of both camber and caster.
The steering arms have been modified to reduce bump steer and are used in conjunction with custom roll-centre correction blocks, helping maintain the correct steering and suspension geometry at the Starlet's lowered competition ride height.
Rear Suspension
The rear suspension is built around a shortened Toyota RT40 differential housing, located by a fully adjustable three-link suspension system and Watts linkage.
The Watts linkage provides accurate lateral axle location and incorporates an adjustable rear roll centre, allowing the rear suspension geometry and lateral load transfer characteristics to be tuned to suit different circuit and handling requirements.
Rear damping is handled by custom-valved Penske ex-NASCAR shock absorbers with single-way adjustment, matched to 300 lb/in rear springs.
The three-link system incorporates adjustable anti-squat geometry, allowing the rear suspension behaviour under acceleration to be tuned.
A specially designed upper push-bar arrangement also helps control rear axle movement under braking, reducing axle lift and improving stability during heavy braking and corner entry.
Rear roll control is provided by a custom 16 mm adjustable anti-roll bar.
Unlike a conventional axle-mounted arrangement, the anti-roll bar is mounted inboard on the chassis, reducing the amount of mass carried by the live rear axle and therefore helping to minimise unsprung weight.
The result is a highly adjustable competition suspension package focused on geometry control, minimal compliance, reduced unsprung weight and precise chassis response, while retaining the fundamental layout and character of Toyota's lightweight KP61 platform.
Gallery & Additional Project Content
