Admission:longueur,diametre,trompettes,emplacement injecteur

[DoZe 0]

Bon sorry, mais c'est en anglais !
(j'ai refait un peu la mise en page pour que ce soit un peu plus digeste a lire)

Throttle Body FAQs

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

What is the best throttle body diameter?

Factors influencing size are; Power output, RPM, cylinder head design, cylinder capacity, position of the throttle body in the inlet tract and position of the injector.

Choice of bore size is a balanced compromise resulting from the following:

1) A larger bore leads to lower flow resistance, but obeying the laws of diminishing returns.
2) A smaller bore leads to better throttle control and response (never underestimate) and improved fuel mixing.
3) The system should be considered in total - from (at least) trumpet flange to cylinder and proportioned accordingly.

Basic references for BHP per cylinder, assuming ca 120mm from butterfly to valve head and a max of 9,000 rpm are:

Up to 30 : 30mm
Up to 33 : 32mm
Up to 39 : 35mm
Up to 46 : 38mm
Up to 51 : 40mm
Up to 56 : 42mm
Up to 65 : 45mm
Up to 74 : 48mm
Up to 80 : 50mm
Up to 87 : 52mm
Up to 93 : 54mm

These power figures may be increased by up to 10% in a purpose - designed and well proportioned system.
As butterfly to valve distance increases, butterfly size will need to increase in proportion to system taper and vice versa.
Lower revving engines and those with injectors placed before the butterfly will generally accept a larger body.


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. (incroyable hein ? )

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 ca 175mm.

The induction system is part of a resonant whole - from trumpet to exhaust outlet - and the ideal length is heavily influenced by the other components.

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 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 low 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 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 90 degrees from the air horn axis or by folding material back, parallel to the axis, when the arc is at, or just below, 90 degrees 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.

At the intake end this should blend smoothly with the flare. 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.


Comme c'est dit au début, c'est juste a titre d'information.
RIEN ne remplace le Banc d'essai et l'expérience.
Il faut retenir qu'une admission parfaitement accordé (ainsi qu'un echappement en parfaite adéquation) et les phénomènes qui en decoulent peuvent apporter un gain ENORME a un moteur.
Certain préparateur profite du banc pour accorder l'admission, on peut aussi grace a certain soft calculer cela de facon assez exact (mais le banc reste quand meme le juge de paix).

C'est hélas, a notre niveau, difficile à mettre en oeuvre sans avoir d'outils de mesures.

Dans la pratique et de facon courante, les moteurs de moto sont souvent les plus travaillés a ce niveau (Ex: Hayabusa)





Cela est crucial bien evidemment sur un moteur atmosphérique

[bozo-merlin1 0]

si je vise environs 400cv ca veut dire qu'il me faudrait des papillons de 54mm hors d'origine c'est un seul de 60

ce calcul doit etre valable sur sur un atmo, sur les moteur turbo l'air "forcé" doit diminué la taille (enfin j'espère)

Rem3 ou Doze, c'est quoi le diamètre des paps de GTi-R

[DoZe 0]

hello

Bon pas encore l'info, j'ai demandé vite fait a Rem3 y savait pas non plus.
Te tient au courant des que !

[DoZe 0]

Ah ben voila du bon

2 superbes calculettes pour travailler tout ca aux p'tits oignons !


http://www.revtronix.com/techinfo/calculators/throttlebody.php

et ici

http://dairally.net/daihard/chas/MiscCalculators/DaiPipes.htm


j'dois retrouver encore un pitin de document sur le positionnement et l'importance de l'angle des injecteurs, je sais plus ou je l'ai foutu !

Apres je sais que y'a un soft specialement fait pour ca et qui marche pas mal du tout (faut que je retrouve le nom). Bon sinon apres dans le truc superpro topmoumouth ZE soft de mecanique des fluides y'a FLUENT v6.3

http://www.fluent.com/software/fluent/

Mais bon faut arreter apres