The Facts about Raceproved Parts, TVR Servicing & Caring for Your TVR
The Importance of Engine Set-up
The TVR engine is a wonderful piece of engineering with a great sound, great power and sharp throttle response so it's important to keep it maintained to a high standard.
Having your car serviced at Raceproved is an important first step in ensuring the long term performance and reliability of your engine, but what exactly is required to keep horsepower and driveability at their best?
An engine uses fuel which it burns to heat air in a cylinder to create pressure on the piston to generate power. The air is taken in through the inlet / throttles and the burnt gases are expelled through the exhaust. The components which control when the fresh air is taken in and the exhaust expelled are the valves and camshafts.
One of the key elements in a full 12000 mile raceproved service is to pay careful attention to the camshaft and followers condition and valve operations as any wear or clearance problems are responsible for poor low speed running and idle quality, high exhaust emissions or lack of horsepower.
TVR AJP8 and SP6 engines
TVR AJP8 and SP6 engines are known to have inlet valve clearances which close up over time. The main areas which are affected by clearances closing up are the very low speed ranges on small throttle openings. This is due to a problem which occurs during the valve overlap period of the camshaft operating phase. The overlap period occurs towards the end of the exhaust stroke – the inlet valve is opened before the end of the exhaust stroke to take advantage of momentum effects as the exhaust gas exits the exhaust ports at high velocity at high engine rpms. The scavenging effect of the exiting exhaust gas can create a low pressure in the combustion chamber which causes inlet gas to enter the chamber even before the piston has reached the top of the exhaust stroke and before the inlet stroke proper. This increases the effective volumetric efficiency of the engine, a kind of natural supercharging effect, however it only occurs at high rpm where exhaust scavenging is at it's greatest.
At small throttle openings a large vacuum is created in the inlet system between the throttle butterfly and the combustion chamber and as valve clearances close up there is a greater time where the inlet valve is open on the valve overlap period as the piston is moving up the bore on the exhaust stroke.
Because of the high inlet vacuum more of this exhaust gas moves into the inlet tract rather than out of the exhaust and this contaminates the fresh incoming charge leading to loss of power and smoothness typically at idle and slow speed driving around town. Valve clearances closing up rarely affect top end horsepower, but town driving and idle speed do suffer. Maintaining the valve train correctly ensures you have the smoothest and cleanest emissions engine as possible.
Once the fuel air mix is in the combustion chamber it must be burnt efficiently and this process is a controlled burn from the spark plug point outwards and the spark quality and duration is critical to good combustion in modern engines because of three important factors.
- The first factor governing the quality of combustion is the fuel used as modern unleaded fuels burn very aggressively, however they are difficult to ignite compared to leaded fuels of the past.
- The second factor governing combustion quality is that the mixture on small throttle openings is held under lambda control to be catalyst friendly. This weak mix is also difficult to ignite and burns very hot compared to richer mixtures used for larger throttle openings.
- Thirdly at small throttle openings and low revs the fuel air mixing is comparatively poor which may result in localised weaker mixes in the vicinity of the spark plug which are even more difficult to ignite. A well maintained ignition system is crucial to efficient initiation of the combustion process therefore and Raceproved ensure this is checked thoroughly.
The final piece to put into the engine puzzle is the final setting up of the individual inlet butterflies, this ensures that each individual cylinder is doing it's fair proportion of work which contributes to improve cold starting, a smoother more stable idle quality and crisp accurate throttle response.
Throughout this final engine setting up process the diagnostic computer is used to monitor all the engine sensor readings including the lambda sensor trimming, fan operation and overall operating efficiency.
If required this service process can be backed up with before and after rolling road power runs to validate the effect of proper servicing on your car.
Servicing
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