
	The Plenum Spacer
	The Plenum spacer is manufactured from 15mm billet aluminium for strength and heat conductivity. This allows efficient drawing of residual heat from the trumpet base to the plenum top, and cooled by external air flow. A cooler trumpet base transfers less heat to the air mass passing to the cylinders.
The spacer is easy to fit with no modifications required. When fitted, the plenum top still fits under the existing bonnet lines and windshield lower mesh of the Griffith and Chimaera. TVR used the plenum designed for the Rover 3.9 litre engine in all applications, thus imposing a limitation of volumetric efficiency especially with larger engines; the 5.0 litre suffers most due to the undersized plenum volume. As a basic rule the Plenum volume should be at least equal to the cylinder volume of the engine, this allows the engine to complete one combustion cycle without drawing any air from atmosphere. The plenum spacer gives an increase of 0.55 litres, a 15% increase of air volume that improves throttle response. All three engine sizes benefit from lifting the inside face of the plenum away from the top of the trumpets. By raising the plenum 15mm we allow an easier passage for the charge to flow into each manifold. Dyno results have demonstrated an increase in performance of 5hp & 6 ft lbs of torque.

This image shows a view cut through the plenum assembly. It shows the lack of clearance between the top of the trumpets and inside face of the plenum

Thermal Gasket
The induction air within the plenum is also heated by direct thermal transfer from the cylinder block via the intake manifold and trumpet base; in addition if a Supercharger is fitted the induction air temperature will rise due to compression of the air mass. Increases of air temperature lead to an expansion of air volume, reducing the potential air mass in the cylinder with a resultant loss of engine performance. To reduce heat transfer from the engine, a heat insulating gasket is incorporated between the intake manifold and the trumpet base, the gasket being produced from hi-spec material developed to insulate the engine block from the heat generated by turbochargers. Heat transfer between surfaces is reduced by approximately 20%

Bell Mouth modifications
These bell mouth pieces were designed to maximise the flow of air into the cylinders. These give big improvements when fitted to the 5 ltr engine trumpets. The bell mouths also give improvments over any flared type trumpet so there are still gains to be had when fitting to the 4 ltr and 4.5 ltr enignes.
The standard headers can be cut down to further increase the clearance and improve power further. That in conjunction the bell mouths design increases power by 4 bhp. Instructions on reducing header length are supplied with the bell mouths.