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Systems

Three bore families. Every air-cooled flat six.

All Rennen ITB systems share the same elliptical roller-barrel architecture, EN-AW 6082-T6 construction and hard-anodised finish. They differ in bore specification, matched to your engine’s displacement and cylinder head ports.

Rennen roller-barrel ITB bank with three velocity stacks, front view Small bore · 2-stud

Small Bore ITB System

For 2.7–3.0 litre engines with 2-stud heads. Intake bore options: 39 mm or 41 mm.

Small bore →
Rennen roller-barrel ITB triple throttle body bank, hard-anodised gunmetal grey Medium bore · 2 or 3-stud

Medium Bore ITB System

For 3.2–3.6 litre engines with 2-stud or 3-stud heads. Intake bore: 42 mm.

Medium bore →
Rennen roller-barrel ITB bank with tall velocity stacks, three-quarter view Large bore · 3-stud

Large Bore ITB System

For 3.6–4.0 litre engines with 3-stud heads. Intake bore: 45 mm.

Large bore →
System selector

Which ITB system fits your engine?

Final bore specification is always confirmed against your cylinder heads at quotation. Custom bore sizes are machined on request.

At a glance

System comparison

 Small BoreMedium BoreLarge Bore
Engine size2.7–3.0 litre3.2–3.6 litre3.6–4.0 litre
Cylinder heads2-stud2-stud or 3-stud3-stud
Intake bore39 or 41 mm42 mm45 mm
Optional stacks45 mm bore × 120 mm48 mm bore × 120 mm50 mm bore × 120 mm
Optional plenum flanges-48 mm bore, 54 mm OD50 mm bore, 57 mm OD
Throttle elementElliptical roller barrel - bore fully clear at full throttle
Material & finishCNC-machined EN-AW 6082-T6 aluminium, hard-anodised gunmetal grey
IncludedComplete throttle bodies (not manifolds only) · throttle linkage incl. rod ends · fuel rails with bracket for short or long injectors · ready to fit, no modifications needed
InjectorsMade for EV6 type; other injector types made to order
Custom boresAvailable on request
Between sizes, or building something unusual?

JSR Engineering machines custom bore sizes on request. Send us your displacement, head and camshaft specification and we’ll recommend - or machine - the right bore.

What’s in every system

Complete throttle bodies, ready to fit

Every Rennen ITB system ships as complete individual throttle bodies - not manifolds only - with actuation, throttle linkage, and the vacuum and crank-trigger hardware needed to run a standalone ECU. The three body sizes cover 2.7 to 4.0 litre engines; bore is matched to your displacement and head type.

Rennen ITB billet throttle actuator and mounting bracket on a roller-barrel throttle body
Throttle actuator · billet bracket
Rennen ITB throttle linkage with return spring, rod ends and billet arm supplied with every system
Throttle linkage · rod-ends & spring
Crank trigger wheel TIG-welded to the pulley, installed on an air-cooled Porsche flat-six for standalone engine management
Crank trigger wheel · TIG-welded to pulley
JSR billet vacuum log with black tube set and push-fit fittings supplied with the Rennen ITB system
Vacuum log, tube set & fittings
When ordering

What we need to specify your system

  1. Engine size2.7 · 3.0 · 3.2 · 3.5 · 3.6 · 3.8 · 4.0 litre
  2. Cylinder head type2-stud or 3-stud
  3. Intake boreDiameter in mm - or let us recommend
  4. Air conditioning compressorYes or no. An A/C option with a flat right-hand-side throttle body is available.
  5. Fuel injectorsThe ITBs are made for the EV6 injector type; other injector types can be made to order.
  6. Crank pulley diameterCrank trigger wheels are engine-specific - the 964 uses its own, and pulley diameters vary by model. Provide your diameter and we machine a wheel to fit, TIG-welded to the pulley.
  7. Coil-on-plug ignition?On the 964 the cam sensor is in the distributor, so to run coil-on-plug a new cam sensor must be installed. Let us know your ignition plan.
Specify your system

Tell us about your engine.
We’ll quote the right system.

Every quotation is matched to your displacement, cylinder heads and engine management. Custom bore sizes are available on request.

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