Have a question? you may find the answer here…

Why Jenvey throttle bodies?


Products and systems are all designed in house.

Many products are designed in conjunction with recognised engine experts.

Backed by a total induction system design, tool and manufacture service.

Jenvey throttle bodies are copied in appearance by a number of other manufacturers. These imitations may not offer the same performance, reliability, lightness or value.



Detailed attention to fuel mixing, distribution and flow.

Careful attention to injector position and angle, port characteristics, butterfly and spindle position and shape

Straight shot manifolds specifically design to suit our fuel injection throttle bodies.

8° shut angle (smaller than most) giving finer control at small throttle openings.

Constant development.


Reliability / Quality

All Jenvey products leave the factory ready to bolt onto your engine and win races.

PTFE - lubricated, phosphor - bronze bearings allow expansion float, extreme accuracy, low wear and resistance to temperatures over 200° C.

All major components / systems are backed by rig tests of over 1 million cycles.

Throttle bodies are individually tested before release.

Most parts are made in our own factory in the UK.

Proven in use worldwide.

We compete using our own products.



Weight is considered in every design (lightness wins races).



Continuous production improvements offset raw material price increases.

Discounts available for trade and quantity.

Comprehensive accessory, parts and spares service.

We are the specialists!

Throttle Body Selection

NOTE: It is assumed that the advanced engine developer will have access to the usual experience / software / dyno time. The advice on this page is not intended to replace these.


Which type of throttle body?

Twin bodies are the most straightforward solution for production engines, direct-to-head where available, or via a suitable manifold. 
Direct-to-head-bodies represent the simplest and neatest solution. They are harder to match to the inlet ports if this is required for the engine in question but have the advantage of being angled for best results, unlike a carburettor manifold. 

Single bodies represent the no compromise solution, particularly for competition use. The seperate manifold is easily matched to the inlet ports and the best mixture path is guaranteed. They are also available in fully tapered bore and twin injector types. Mounting, balance and maintenance are naturally more involved.


What is the best throttle body diameter?

There are several factors to consider when selecting throttle body diameter, power output, RPM, cylinder head design, engine capacity, injector position and throttle body position along the inlet path.

As a general rule of thumb a large bore results in lower flow resistance, a small bore results in better throttle response and more precise air/fuel ration mix. There are a few guidelines to be followed when selecting bore size and assumed BHP/cylinder using an assumed rev range up to 9000rpm.

BHP    Millimeters
35    40
40    42
45    45
55    48
65    50
There are exceptions; big v8s are one, they can still have a large bore and a low rev range.


What is the correct overall system length?

Induction length is one of the most important aspects of fuelling performance engines. 
In our experience an under-length system is the greatest cause of disapointment, with loss of up to 1/3 of power potential. There are a number of good books on the subject and the serious developer is referred to these and, in particular, dyno trials. A guide figure, from the face of the trumpet to the centre of the valve head is 350mm for a 9,000 RPM engine. Other RPM are proportional i.e. for 18,000 RPM the figure is approximately 175mm.

Any air feed system to an airbox or filter can have a large effect on the power curve and must be considered carefully particularly if the airbox is small. 
The induction system is part of a resonant whole from air inlet or trumpet to exhaust outlet and the ideal length is heavily influenced by the other components.


What is the best position for the butterfly?

The butterfly is an important aid to fuel mixing. When positioned too close to the valve this advantage will be lost whilst positioning far away may lead to a loss of response. 
As with the injector position (see below), higher RPM demands a larger butterfly to valve distance. A practical minimum figure for a 7 - 9,000 RPM engine is 200mm, whilst the maximum is dictated by the need to fit an air horn of reasonable length to achieve a good overall tract shape. One solution to this apparent compromise is the use of bodies with fully tapered bores which, in effect, extend the trumpet distance beyond the butterfly and into the manifold. For very high speeds above approximately 15,000 RPM, the ideal butterfly position is only just inside, or even outside the trumpet and a point is reached where a taper is no longer sufficient for good tract shape. For these circumstances we can supply bodies with the exponential trumpet shape machined into them as a special service, or barrel bodies which, by their nature, must be purpose designed in conjunction with the cylinder head.


Where is the best place for the injectors?

Where one injector is to be used per cylinder the best compromise position is immediately downstream of the butterfly. This gains maximum advantage from local turbulence and gives results surprisingly close to the optimum at both ends of the rev-range. This is the recommended position for most applications. 
For performance at low RPM, economy and emissions the injector needs to be close to the valve and firing at the back of the valve head. This is the favoured position for production vehicles. 
For higher RPM (very approximately 8,000+) the injector needs to be near the intake end of the induction tract to give adequate mixing time and opportunity. The higher the RPM, the further upstream the injector needs to be. As a result, use of speeds above approximately 11,000 RPM may give best results with the injector mounted outside the inlet tract altogether (see our remote injector mounting). It is common to fit both lower and upper injectors in such a system to cover starting and low RPM, as well as high speeds.


What is required for a complete fuel injection system?

Besides throttle bodies, linkage and manifold (if required) typical components are; A management system, wiring loom, fuel pump, fuel pressure regulator, fuel injectors, appropriate plumbing, air horns and a ducting / filtration system for the incoming air.


What type of injector?

Dimensions: All Jenvey injector mountings and fuel rails will accept either the standard 'O' ring mounted injectors for 14mm bores as supplied by Bosch, Weber, Lucas, etc (64mm between 'O' ring centres) or the shorter 'Pico' style injectors (38mm between 'O' ring centres). 
There are a number of other injector types, using the same 'O' rings but with different lengths. These can be used on our twin throttle bodies with ease, but may require different fuel rail mountings on individual bodies. Please specify which you are using when ordering throttle bodies and fuel rails. 
Flow-rate: When fitting our throttle bodies to an otherwise standard engine bear in mind that increased power means increased fuel demand and the original equipment injectors are therefore usually inadequate.


What manifold to use?

When injecting into the throttle body (e.g. our types TB, TH, TF, TA, direct-to-head and SF, SS or ST//1), most of the mixing occurs within the manifold section. It is therefore important that the manifold is suitably proportioned to evenly accelerate gas speed and thus help fuel mixing and distribution. The straighter the run in to the ports the better. A manifold which curves in the same direction as the valve throats is preferred to one which causes the flow to pass through an "S" bend.

What throttle potentiometers will fit Jenvey bodies?
We use relatively popular mechanical interfaces for the throttle potentiometer. Popular types are; Colvern CP17 series (as supplied by Jenvey), Wabash 971-0002 and (via fitting kits) throttle pots from Novotechnik, Penny & Giles, Marelli and Weber. A number of production car throttle pots (e.g. Rover K series) will also fit directly to the bodies. 
The Colvern CP17 throttle potentiometer may be mounted to either end of most installations and spindle rotation is typically 82o.


Can Jenvey bodies be pressure charged?

Jenvey bodies can generally be used with boosts up to 6 bar, although we recommend that you contact our technical department if boost of more than 2.5 bar or temperatures above 150ºC are expected. Some models require special treatment for high pressures and/or temperatures.

Can Jenvey bodies be connected to an Air Bypass valve?
Components and complete kits are available to connect the output from an ABV to throttle bodies. More information is available on a specific instruction sheet.


What is the best Air horn ( Trumpet / Stack / Bellmouth)?

The air horn serves three main purposes;

1) To convert the pressure difference between bore and entrance into air velocity with the minimum of energy loss.

2) To act as the interface between the induction system and the atmosphere, i.e. the point at which pressure waves change sign and direction.

3) To complete the system to the required overall length.

For ease of description the air horn may be considered in two parts; the 'flare' and the 'tube'. 
The main job of the flare is to spread the low pressure zone over the largest possible area, to reduce local pressure reduction, whilst guiding incoming air into the tube with minimum disruption or induced vortices. The flare should be shaped to encourage air to enter from the sides but not from the rear of the mouth. This is achieved by either finishing the mouth with a sharp edge when the arc is a little beyond 90o from the air horn axis or by folding material back, parallel to the axis, when the arc is at, or just below, 90o to the axis. 
The main job of the tube is to accelerate the airflow smoothly and progressively. This is best achieved by an exponential shape, i.e. one where the radius of curvature is increasing constantly until the angle of the sides matches the next part of the system, usually the throttle body. 
It should be noted that the requirements for fuel injection and carburation do not always coincide and the best horns for one may not suit the other.

Engine Management Systems (ECU)

Systems known to have been used with Jenvey Dynamics throttle bodies

Emerald, England.

Web site: www.emeraldm3d.com , E-Mail: emeraldM3D@aol.com

DTA Race Electronics, England.

Web site: www.dtafast.co.uk , E-Mail: link@dtafast.co.uk

Autocar / Lumenition, England.

Web site: www.lumenition.com , E-mail: autocar@denaploy.co.uk

EFI Technology / Ole Buhl Racing, England.

Web site: www.obr.uk.com/ , E-Mail: sales@efitechnology.co.uk

Hestec Engine Management Systems, Finland.

Web site: www.hestec.fi , E-Mail: info@hestec.inet.fi

MBE Systems, England.

Web site: www.mbesystems.com , E-Mail: info@mbesystems.com

Michl Motorsport, Czech Replublic.

Web site: www.michl-motorsport.cz , E-Mail: info@michl-motorsport.cz

Motec Australia and Europe (England).

Web site: www.motec.com.au Europe: admin@moteceurope.co.uk

Pectel Control Systems, England.

Web site: www.cosworth.com/products/racing-electronics/ , E-Mail: enquiries@pectel.co.uk

Racetech Developments, England.

Web site: www.racetechdev.co.uk , E-Mail: info@racetechdev.co.uk

Please note that this is not a complete list and will be updated as further information becomes available.

Large Single Throttle Bodies

Why not just use a large single throttle body?

The choice of thottle body size for the typical road car is a compromise between two opposing needs; to allow sufficient air flow for the engine to achieve its full power potential and to keep the butterfly small enough to allow a progressive throttle action at low openings.


The engine designer has a number of tricks available to help match these opposing needs. The no. 1 solution is to use a linkage which favourably varies the ratio between pedal movement and throttle action. For example, our SFG (big single) throttle body rotates the butterfly 1.4o for the first 10o of quadrant rotation (5.5mm of cable travel) and 20o for the last 10o of quadrant rotation. Other solutions include shaping the bore of the throttle body such that the gap on one side of the butterfly remains small for the first part of butterfly rotation or using two butterflies opening sequentially or using electronic throttle control.


The above techniques allow the designer to use a sufficiently large throttle body bore that rarely limits engine performance to a measurable degree. It follows that enlarging the original throttle body will only make a useful gain when other aspects of the engine have been changed to substantially increase the power output. The most likely change due to a larger throttle body, if any, on an otherwise standard engine is a car that goes slower round corners due to lack of fine throttle control for the driver. At best, there may be a slight improvement in response (see below).


It helps to understand the relationship between size and output to consider that a 2L Formula 3 engine produces 200+BHP through a 26mm (531 mm2) restrictor and a 75mm throttle body is eight times larger at 4,418 mm2! Similarly, in an experiment to curb the power of 270 BHP touring car engines, we reduced the size of the single throttle body to less than 44mm (1520 mm2) before there was any noticeable reduction. A 75mm body has three times the flow.


The single throttle body has a number of benefits for the mass producer. It requires no balancing or fine tuning since all cylinders are drawing from a common volume. It is cheaper to make than multiple bodies and, for everyday motoring, has the advantage that throttle response is gentle and delayed. This is because sudden opening of the throttle must first fill the entire induction system before the engine gets the full benefit. This effect is well suited to the needs of the inexpert driver since, whatever the throttle position, torque builds slowly and nothing happens suddenly.


Multiple individual throttle bodies are used in all naturally aspirated true race engines, most motorbikes and some hig performance road cars (e.g. BMW M series) i.e. where the driver prefers to be in full control. They have a number of advantages. The most obvious to the driver is virtually instantaneous throttle response whilst the individual inlet tracts allow true length tuning of the inlet system which has a large influence on torque and power output. In a well designed throttle body system the positioning of the injectors and butterflies aid fuel mixing, very important in higher RPM (i.e. above 5,000) engines.


In summary; 
Single throttle bodies; 
Are simple to set up. 
Are cheap to make. 
Make engine response gentle – will not frighten the average driver. 
Are easily silenced. 


Multiple throttle bodies; 
Make engine response lively. 
Increase power and torque by improving mixture quality – particularly at higher RPM. 
Increase power and/or torque by resonance tuning – when correctly lengthed. 
Give no-compromise performance.

Butterflies, Barrels or Slide Throttles

Before the mid-1980's, carburettors and mechanical fuel injection were the only choice to fuel a racing car engine. Selection of air valve type was simple and apparently carved in stone. Carburettors used butterflies and injection used slide throttles. Motor bikes and their history are a special case but what follows is true for any performance 4-stroke petrol engine.

With the advent of electronic fuel injection and a more adventurous (better funded) approach from the leading engine designers, it was discovered that butterflies, whilst sometimes (but not always) giving slightly less power than slides, inevitably gave better lap times. The explanation was simple; butterflies give more progressive throttle control, improved transient conditions and aid mixture quality throughout the RPM range.

As a result of these discoveries most (possibly all) of the leading car race engine manufacturers switched to using butterflies. Lap times continued to tumble but there was a problem brewing for the future.

As peak RPM increased year by year, the required induction system length reduced. At the same time the ideal butterfly to valve distance increased. Over about 15,000 rpm, the ideal butterfly position falls outside the induction system - clearly useless. Enter the barrel.

The barrel has some but not all of the attributes of a butterfly. Opening is reasonable progressive and like the butterfly, it is easily packaged. The great advantage is that it can be made as a continuation of the port shape, regardless of profile (slides would overlap), and thus be placed near or even in the cylinder head. This allows for a very short system to suit the 18,000+ RPM which is now common. Any compromises (poor idle control, tendency to stick, poor flow vector control, etc.) were once believed to be offset by the sheer power available at these RPM however most (possibly all) of the leading car race engine manufacturers (e.g. F1) had switched back to using butterflies by 2006. It follows that barrels on a sub 15,000 RPM engine will suffer from the compromises without gaining the possible benefits. **

The main advantage of the barrel, maintenance of port profile, can be obtained by using fully profiled butterflies. These are made to precisely fit the port profile and are shaped in cross-section to achieve the required characteristics, minimum drag, controlled turbulence or whatever else best suits the application. This is now the preferred solution for top end engines used in Formula 1, World Super Bikes and some sports-racing engines. Jenvey Dynamics supply these for specific applications since they must be designed to suit the engine and cylinder head used.


In summary: 

Butterflies are best wherever they can be used. Jenvey Dynamics have a design and make service for engine - specific profiled butterfly bodies. 
Barrels are suitable for engines running at over 15,000 RPM and must be designed to suit a particular engine type. Jenvey Dynamics have a design and make service for engine specific barrel bodies. 
Slide throttles are best reserved for classics, if the rules prohibit a change. 

Copies of Jenvey Products

A number manufacturers make and sell throttle bodies and linkages that are intended to be copies of Jenvey products.

Whilst the products may look similar please consider that a company that is unable to design its own products is unlikely to understand the manufacture of that product and the exacting specifications and tolerances that are critical to safety.

All new Jenvey throttle bodies have the Jenvey logo cast in (except TC twin bodies, SFC 1 and 2inj) as do most of our manifolds.  Where possible we include a permanent logo on our products.  If you have any concern that you have been sold a copy then please contact us. sales@jenvey.co.uk

If you have any evidence that these other manufacturers are trying to pass-off their products as Jenvey throttle bodies whether it be written, anecdotal or otherwise please contact us. sales@jenvey.co.uk

Heritage DCOE Throttle Bodies

Will it work on my....?

These units are designed to work on any car running DCOE carburetors, allowing for the system requirements detailed below.


What else is required to complete the conversion?

The main additional item required is an aftermarket ECU and wiring loom. The system has been developed to be used with any standalone ECU. A high pressure (3 bar / 42PSI) fuel feed will be required. See fuel system recommendations on www.Jenvey.co.uk FAQ section - with swirl pot, without swirl pot. Filtration and throttle cable installation will also be necessary.


Where is the fuel rail?

The fuel rail is contained within the lid, which also clamps the injectors in place.


What fuel injectors do I need?

The injectors are specific Bosch units selected to fit this application at 350 cc/min. Larger capacity injectors will be available from February 2017.


What throttle position sensor do I need?

The Throttle Position Sensor is built into the unit, so is supplied as part of the Throttle Body.


Is it sidedraft or downdraft?

It fits directly to the sidedraft DCOE flange - being fuel injected it can run at any angle including upside down. Please note, we have a variety of other DCOE Throttle Bodies to suit all applications.


Are any engine mods required?

No specific engine mods are required.


What sizes are available?

40, 45 and 48mm are available, All the bores are parallel without the requirement for venturis.


Will the throttle bodies work with forced induction?

Yes, please advise this when you purchase.


What improvement will I get over Carbs?

Development has shown massive torque gains at the bottom end with significant power gains at the top end. Fuel economy has been approximately 50% improved and emissions have been drastically improved. Alongside very good starting and rock solid idle. (Please note back to back testing was done with a very well setup carbureted car with a system developed over many years - TDS comparison testing was done with an early map, i.e. there is more to come!)