Tuning Guide for the 924 Turbo (931)
930 Motorsport, Unit 23, Bank Quay Trading Estate, Warrington, WA1 1PJ Tel 07000 930930 or +44 (0)1925 242342 Fax +44(0)1925 417638
Please note the prices below are NOT up-to date and should only be used as a guide.
K&N Filter - Extract the best from the standard installation by fitting a K&N free flow air filter. Less restrictive and more efficient than the standard paper element, washable and comes with a 1,000,000 mile warranty. Available as a panel filter to fit the standard air box (£36) or as a 57i kit (cone filter) which replaces the air box completely (£45).
Charge Air Cooling - Winter tests in our 931 saw post turbo inlet temps of over 850C under load, hence why we have temperature problems in the summer. All turbochargers generate heat when compressing the inlet air, but because excessive temperature loses power & causes engine damage, Porsche de-tuned the 931s. The S1 is built with low compression & safe ignition timing and the later S2 is fitted with digital ignition control (DIC) (which retards the Ignition by I .5t'steps above 63 oC). However, since both these methods reduce combustion efficiency and power, Porsche and all other manufacturers now fit an intercooler to control inlet temperatures. As a rule of thumb every 10 oC drop in inlet temp will allow about 1 psi extra boost, the equivalent to around 5 bhp, so inlet charge cooling must be the first choice for improving performance.
Charge-cooler - In testing, our unique air-water-air charge-cooler reduced the full-power inlet air temperature from 85 oC to 35 oC (out-performing the Carrera GT intercooler by over 10 oC) and 40oC lower in-traffic temperatures. Since the airflow losses for the system are negligible, it was also no surprise to gain 20bhp at the rolling road with no other modifications. Engineered to fit without requiring bodywork modification, the system comprises of all new air pipes from the turbo to the throttle body via an air-to-water heat exchanger. A supplementary water radiator, electric pump and reservoir look after the cooling. Charge air passes over the cooling matrix in the exchanger, transfers heat to the water, which then off-loads the heat into the passing airflow from radiator. Available exclusively from 930 Motorsport..
Intercooler - The intercooler is simpler than a charge cooler in that it is merely an air-to-air radiator situated between the turbo and the throttle body, usually located in the front of the car to maximise the cooling airflow. Unfortunately the 931 has no space to get the pipework past the standard radiator, so our system includes a replacement high-output aluminium radiator and intercooler to fit into the existing bodywork without modification. Available exclusively from 930 Motorsport..
Exhaust System - Power gains can be achieved from improving the flow of the exhaust system in order to reduce the back-pressure on the turbo. Our single box stainless steel system allows enough flow for over 300 bhp engines and gave around 10 bhp on our 220 bhp development car. The system has a unique "straight through" silencer design to minimise backpressure and weight yet is quiet enough for road use. Available with 2.5" or 3" round outlet, fitted price only, £395 using the existing turbo/wastegate down-pipe.
Hybrid & Water-cooled Turbochargers - Both the S1 & S2 use an early design of KKK K26 turbo, the S2 having a slightly smaller compressor to improve the response. These stock turbos give peak torque at around 3500 rpm but sadly lack high rpm performance. We offer three hybrid turbos to improve performance. The V1 & V2 units are direct replacements for the original unit, with a CNC machined inlet housings and more efficient designs of K26 compressors to achieve different performance characteristics but without killing turbo response, the V1 for more mid range and the V2 for more top end power. The V2 unit fitted to a standard 931 S2 (at standard boost) gave 192 bhp on the rollers with strong power right up to 6000 rpm. Our V3 unit gives even better flow characteristics by replacing the restrictive compressor housing. This requires modification of the inlet system to incorporate a new recirculation system and is ideally suited to one of our charge cooler conversions for engines over 200 bhp. All our turbos are now available with a water-cooled bearing housing as used on the 944 Turbo. This feature dramatically reduces oil temperatures in the engine & turbo and eliminates bearing oil "burnout" associated with sudden switch off after high-speed use. Don't leave home without one. All versions, fully rebuilt £625 exchange or with water-cooling £825 exchange, call for details.
Boost Level - Increasing boost pressure will give more power, no doubt; by squeezing a mere 1 psi extra on our development S2 gave us 35Nm and 20bhp. However be warned that in our experience neither the S1 nor S2 will maintain reliability if the boost level is increased without charge cooling and ignition / fuelling optmisation. The simple way to increase boost is to fit a stronger wastegate spring. We have available the factory 962 spring to increase boost from the standard 0.65 bar up to 0.95-1 bar. Alternatively, an adjustable system can be fitted using a pressure regulator to feed counter pressure onto the top of the wastegate diaphragm, so assisting the spring to raise the blow off pressure. The precision valve is suitable for either engine bay or under dash mounting. We recommend its use only with an accurate in car boost gauge. Wategate spring £88, pressure regulator and pipework £125, both plus fitting.
Also available are amazing electronic boost control systems from HKS, GReddy or Apex-i . We prefer the HKS EVC4, which has state of the art fuzzy logic electronics "learn" the boost characteristics of the engine and maximise power under all driving circumstances. The control unit has a digital display of charge pressure, high and low settings (set at say 1.0 and 0.7 bar) for dry/wet driving, and a flash boost level for short duration power Increases for overtaking. Systems from £485 fitted & mapped.
Camshafts - Alternative cam profiles are available to widen or extend the torque spread of the engine and raise the max power rpm to extend the useable power range. Since the standard cam is good for over 225 bhp, we recommend all other tuning options are progressed before the cam is considered. Prices from £325 exchange.
Ignition Management - Used on our own S1 and S2 development cars, programmable ignition enabled us to achieve the maximum potential of the S2 engine to exceed Carrera GT performance at only 0.8 bar boost. Since the S1 distributor system is reliable but crude and the S2 DIC control is better but unreliable (and £600 to replace), our ignition management package gives significant improvements in reliability, driveability, power and torque. The ECU lends itself to a variety of installations from distributor ignition only, distributorless ignition or ignition & extra fueling. Using input parameters of engine speed, throttle position, manifold pressure (MAP), inlet air temperature and water temperature, the ECU controls single or twin ignition and optional injector drivers. By using two ignition drives, a high output twin coil unit can be used to fire the cylinders in pairs, so called "wasted spark" as all spark plugs fire once per revolution and the spark on the exhaust stroke is wasted. The spare driver may be used to control a supplementary fuel injector for high power applications. With built in fuel pump and cooling fan control, the software also allows soft and hard rev limits to be set. System price from £700 plus fitting and mapping.
Engine Management - Full electronic engine management systems are available to completely map the fuel and ignition systems. Because this requires replacement fuel injectors and supply pipework the installed cost starts at around £3000. Call for more details.
Engine Building - Improved performance must never be at the expense of reliability. The 931 engine is generally a very reliable engine which responds well to tuning, but unfortunately there are a few inherent weaknesses which can cause problems. The most common faults are oil breathing, head gasket failure and piston damage due to detonation. We undertake all levels of engine building (standard to full race) and have solutions to these and other problems. Call for more information or prices.
Limited Slip Differentials - The standard differential is a geared mechanism inside the final drive of the gearbox, which allows torque to be transmitted to a pair of driven wheels when turning at different speeds, i.e. when cornering. Whilst fine for most applications, the standard differential also allows all the torque to be transmitted to a spinning wheel, so losing traction and hence acceleration. For performance applications, the use of a LSD is the best way to eliminate this traction problem but can make the car difficult to handle in the wet.
Two types of LSD are available for both the 93 1 gearbox, one manufactured by ZF and one by Quaiffe. The ZF or plate type LSD works on an allowable slip, locking the output to both wheels with friction plates when the slippage reaches a preset percentage. The Quaiffe or gear type LSD is a torque sensing device, using internal gearing to increase to torque to the driving wheels until both wheels break traction. The standard fitment by Porsche is the ZF unit, still available at around £1500 new, the Quaiffe significantly cheaper at £850, both plus fitting. Both types have their merits, so call for availability.
Clutch & Flywheel - Although the standard clutch is ample for most applications, a lightweight clutch or flywheel can save up to 8kg, so reducing engine inertia to improve response. Various packages are available with organic, carbon/kevlar or sintered metal ring or puck centre plates and lightweight aluminium covers to increase the torque capacity for racing or highly modified engines. Call for details.
Suspension & Handling
Alignment & Lowering - Correct wheel alignment is critical on all 924s, especially as all the wheels are independently adjustable for camber and toe-in. The torsion bar design allows for ride height adjustment on the rear, although usually the suspension beam has to be removed to lower by more than 20 mm. For the front, shorter springs will be required to reset the height. A typical 20mm lower and 4 wheel alignment takes around 8 hours, total cost around £340 Including springs.
Dampers - The standard shock absorbers were made by Boge or Sachs, both fine for all round road use but unfortunately limited in their suitability for fast-road or track use, especially with a more powerful engine. No matter which type are fined however, all dampers must be considered past their best after about 60,000 miles. For uprating standard cars with a better quality gas shock we recommend Koni Specials, but for fast-road use we prefer the Koni Sport gas pressurised dampers which can be adjusted to suit the drivers requirements. Altematively the non-adjustable Busteins offer improved durability and performance but may be too hard for some in road use. All kits come as replacement front strut inserts and new rear dampers. Prices per set are: Blisteins £385, Koni Special £277, Koni Sport £375 with fitting typically £95.
We also have available on-car adjustable, ride height adjustable damper packages with shorter bodies for race applications. Please call if a more radical package is required.
Antiroll Bars - Stiffer antiroll bars reduce body roll in cornering and improve turn-in and stability through bends. We recommend using the 944 Turbo bars consisting of a 27mm front and a l8mm rear. The rear bolts on in place of the original, the front will require use of the late 924 or early 944 front wishbones and mountings with modified 944 arb mounting brackets. Well worth the effort, especially as bars are available used from around £40 per end.
Springs and Torsion Bars - Although uprated and shorter springs are available for the front suspension, larger diameter torsion bars are required to increase the rear spring rate, ideal for reducing body movement during cornering without seriously affecting the ride quality. Unfortunately larger diameter bars are expensive (from £240 per pair) and fitting required the removal of the rear suspension beam (around £400 labour). Call for details.
Wishbones - The front wishbones tend to bend and corrode, the bushes also wearing significantly over the years, so do not overlook these parts when looking to improve the handling performance. The new specification bushes are fine for most applications, call for prices. Although uprated bushes are available for the front A-frames, rear spring plates and rear trailing arms to remove the compliance from worn original bushes, we do not recommend these for road use as they can cause excessive noise and significantly reduced comfort levels. Call for more details
Front Strut Top Mount - Suitable for mainly track use to eliminate all compliance from the upper strut mounting. These cartridge units bolt in place of the standard top mount and are fitted with a replaceable spherical bearing. Also need to be used in combination with a shorter spring and shock as they increase the ride height by 20mm. Price £160 per pair plus fitting.
Basics - As with any aspects of performance improvement always make the first priority getting the best out of what you have. Secondly do not overlook basic items like wheel alignment, tyre pressures and tyre choice which can all significantly affect braking performance.
Fluid - Change the brake fluid at least every two years and preferably before every track outing with a top quality DOT4 fluid. We use ATE Super Blue Racing in all our cars whether for road or track use, this fluid exceeds DOT4 specification and is suitable for extreme heat conditions, price £1 5.45 per litre. We do not use or recommend silicone fluids of any manufacture.
Cooling - Additional air flow through the disc minimises heat build up the complete brake assembly to help resist bad fade or fluid boiling. Duct the air flow through the valence to the front brakes to assist cooling. Scoop kit available spring 2000.
Hoses - Suitable for road and race use, our braided brake hoses are designed to cope with the extreme duty of competition. The rigid sidewall construction eliminates the expansion associated with rubber brake hoses, so reducing pedal effort and travel. Price for the complete car set £49.95.
Pads - Choice of Mintex 11 44 (fast road) & 11 55 (race) and Porterfield carbon/keviar composite pads. For general fast road use the Mintex 11 44 are ideal, or for track days try the 11 55 compound. For the best performance with standard callipers and discs we recommend the Porterfields. These pads work from cold and have outstanding performance, but may cause excessive squeal during light use on the road. Some performance pads can not be fitted with wear sensors. Prices Mintex £77/£41 fr/rr, Porterfield £107/£1 02.
Discs - The best performance discs in standard sizes that we have found are original Porsche units, available from us at £43/56 fr/rr per disc. In our experience these discs seem to have a better material quality than typical aftermarket units and are ideal for use with all performance pads.
Big Brake Kits - Using the original 1 978 3.3 Turbo floating disc assemblies we can convert the 931 to have serious stopping power as fitted to the Carrera GTS. The 305x32mm discs are clamped onto an aluminium mounting bell which bolts onto the standard 93 1 front hub, using either the 930 or 928S4 calipers with brackets to fit the original stub axle mountings. Kit price from £1 000. Alternatively we can also fit the new Porsche four pot monobloc calipers to thicker front and the original rear discs. Full kit of new front & rear calipers, brackets, hardware, discs and pads £1 325 plus fitting. More radical packages are available, call for details.
Wheels & Tyres - Why not take advantage of the current surplus of 1 6" 964 (911 Carrera 2/4) and 986 (Boxster) wheels on the market? With sets of 6&8" 964 Design 90's going for £250 to £300 and new (!) 6&7" Boxster sets for £400 why not modernise the look of your 93 1 for less than the price of a set of new tyres? Call for availability.
Prices subject to change without notice, all prices plus VAT. 930 Motorsport accepts no liability for damage or additional wear to vehicle components as a result of fitting tuning parts. 930 Motorsport are independent Porsche specialists and are not affiliated to or associated with Porsche A.G. or Porsche Cars Great Britain Limited.
930 Motorsport, Unit 23, Bank Quay Trading Estate, Warrington, WA1 1PJTel 07000 930930 or +44 (0)1925 242342 Fax +44(0)1925 417638
Quite a few years ago we built a modified Carrera GT replica for a customer and, amongst other things, we fitted our own distributor-less ignition system and charge cooler conversion to end up with 220 bhp & 330Nm at 1.0bar and 210bhp/300Nm at 0.8bar.
Colin Belton Owner, 930 motorsport.