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16V 4age – Quad throttle / ITB adapter


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16V 4age manifold to suit quad throttles

These adapters facilitate the conversion to individual throttle bodies (ITB’s) sourced from a 4age 20V engine. Machined from a billet aluminum plate this product makes for a bolt on upgrade that quick and easy to fit.

It is compatible with all of the front and rear wheel drive top water outlet / bypass pipe variants as well as all of the 20V throttle types. See the sections below for more information.

Advantages and design features

Currently there are a few existing choices for manifolds on the market, but we wouldn’t of bothered to release our own had we not been able to offer some clear advantages over all other options.

– Angular Port profile: Manifolds that hold the throttle bodies on an upward angle are hardly new but the issue is in their angled transitions. The norm is to just have a straight port and the face that has been welded / machined at an angle relative to the port. This method makes for a very easy construction but the issue with this method is that when air is forced to change in angle more than a small degree the laminar air flow layer will separate causing turbulence and a resulting flow restriction because of it. Our manifolds have no angular steps whatsoever, the air from the throttles goes straight into the manifolds ports and follows around curved runners with gentle radii to let the air enter the cylinder head at the exact same angle as the cylinder head ports. Using this method and also transitioning from the round throttle holes to the oval port shape of the head without a single step or protrusion requires much more time and the use of true 5-axis machining processes, but this is the single best option there is.

Below are some of the other key points of interest.

– Machined out of single solid aluminium billet: Not welded together in a design that is likely to fatigue.

– Requires no custom modifications to fit: Bolts to OEM manifold base using the original fasteners.

– Throttle locating dowels: Just like OEM manifolds the throttles are positively located. Without these all the throttles require careful initial alignment and a full recalibration when even a single one is loosened.

– Port match: Near ideal transitions on the faces to and from this adapter.

– Port profile / transitions: No edges, corners, changes in angles or anything but a smooth internal port finish for the least amount of drag / turbulence.

– Vacuum provision: Threaded with multiple outlets and comes with both barbs and plugs to leave the choice up to the individual.

– Throttle compatibility: Suits either of the 20V throttle body types- See under “Throttle selection” for more information.

– Light weight: With material only where required these are light despite being machined from a solid block.

Parts compatibility

– Engine type: Use the drop down menu to choice for which of the two types of 16V 4age head the manifold is to suit.

– Throttle bodies: The flange mounting suits all 3 types of 20V throttles. The inside port match suits the Silvertop throttles however each of the flanges on the manifold have the outside profile of the larger Blacktop. With this the Silvertop throttles can be bolted and used directly. On using Blacktop throttles they require only light internal port matching to suit. We chose this option as it avoids any performance compromise with a universal design. See the next section for more information.

– Top water outlet: This manifold is designed such that it will suit either the front or rear wheel drive water outlet. However if a barb is fitted to the bottom of the #1 throttle and the front wheel water pipe is used then the steel water bypass pipe will need to be modified to be able to clear.

Throttle compatibility / choice

– Specifications: There are two different types of throttle body from the 20V 4age Silvetop engines, both of which have a 43mm diameter blade. The Blacktop engines feature a larger 45mm blade.

– Throttle selection: Despite being larger using the Blacktop throttles will likely cause a loss of power for most applications. Only highly modified 16V engines will be able to make use of the extra airflow they offer, for all other uses the higher air speed from the smaller Silvertop throttles will likely make more power. In addition the Silvertop throttle bodies are almost always significantly cheaper and easier to source.

Parts supplied

– Billet machined adapter plate with locator dowels

– Vacuum barbs x 6

– Vacuum block off plugs x 6

– Bolts & washers for throttles to manifold

– Throttle bodies and velocity stacks ARE NOT supplied.

Installation notes and dimensions

– Throttle mounting: Due to clearance issues this manifold holds the throttles upside down.

– Engine setup: These manifolds have not be test fitted in a front wheel drive car so they may cause some packaging issues.

– Engine management / ECU: After fitting quad throttles it’s highly suggested to fit a new stand-alone / aftermarket ECU and have the engine tuned.

– Angle: The throttles are tilted 15 degrees upwards from the face that bolts to the cylinder head.

– Length: Measured from the middle of the opening on either side these manifolds there is a distance of 55mm.

Optional extras

– Throttle gaskets: A set of 4 gaskets to go between this intake manifold and the throttle bodies. Please choose the type applicable to the throttles being used.

Additional information

Weight1.45 kg
Dimensions40 × 7 × 9 cm
4age Engine type



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