15mm Plenum Spacer with Bolts, Insulating Gasket & Bell Mouth Trumpets

As a basic rule the air Plenum volume should be at least equal to the cylinder volume of the engine i.e. 4-5 litres of air for a 4.0 litre engine and 5-6 litres of air for the 5.0 litre engine.


TVR and Rover consistently used the plenum designed for the Rover 3.9 litre engine in all applications, this imposing a limitation of volumetric efficiency especially with larger engines, the 5.0 litre suffers most due to the undersized plenum volume.

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.

Our Plenum spacer and heat insulating gasket are designed to improve volumetric efficiency by increasing the available air volume to the cylinders, improving throttle response and overall performance.  This achieved by fitting or Spacer between the inlet manifold and trumpet base, resulting with an increase of 0.55 litres, a 15% increase of air volume that improves throttle response.
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%.


The Plenum spacer is manufactured from billet aluminium for strength and heat conductivity, to draw residual heat from the trumpet base to the plenum top where it is cooled by external air flow.  A cooler the 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.

Dyno results have demonstrated an increase in performance of 3hp/4ft lbs of torque.

Bell Mouth Trumpets

These bell mouth pieces were designed to improve the flow of air into the cylinders. The standard headers are not equal length so the trumpets were cut down to equalise this distance. That in conjunction the bell mouths increases power by 3bhp. Cut down lengths are supplied with the bell mouths.



Insulator Gasket

£21.50 including delivery

Engine size

Plenum Spacer with Extended Bolts

£105.50 including delivery

Insulator Gasket, Plenum Spacer and Extended Bolts

£118.50 including delivery

Engine size

Bell Mouth Trumpets with correct intake runner lengths

£124 including delivery

(does not include the base or the trumpets)
Engine Size
Please specify what camshaft

Complete package of all of the above

£211 including delivery

Engine Size
Please specify what camshaft