Ou l'on reprale du collecteur standard pour SU twins....

[Renou]

Bonsoir,



"The factory supplied twin SU intake manifold with its straight shot into each port looks like it could not be better.

Not so!!
Certainly anything except an all out high RPM race engine needs some sort of balance pipe between the two runners to ensure a smooth idle and cruise.
Unfortunately the huge cross-over the factory put in causes a major disruption to the flow that is trying to get into the port.
This flow disruption is so bad, that the high speed air which is normally at the top of the port in the head is now at the bottom. This causes major turbulence and flow reduction when it gets towards the valve seat. The reason being that the short side turn into the cylinder requires the air speed to be slower to make this abrupt turn with any reasonable success, and the long side more gentle turn (spark plug side) can accommodate higher speed air.
However, what we have in this situation is the exact opposite of what works best.

Maniflow make tubular-Steel twin SU intake manifolds with a small diameter cross over tube located in a much less 'airflow critical' portion of the port runner.
This allows the balance required as mentioned above, but does not cause the turbulent airflow eddies that the stock manifold suffers from.

We have been seeing a consistent 4 - 5 HP gain on both 'A' & 'B' series engines using the Maniflow intake manifold compared to the stock factory supplied version.

Remember when choosing carburetors that the SU will ALWAYS make more low and mid range torque than a Weber, however, a Weber normally makes more top end.
What we have found with using the Maniflow intakes with SUs is we can get this good mid-range "grunt", and still come very very close to the top end power given by the Weber, especially if the carbs are modified as shown in David Vizards book: "Tuning BL's 'A' Series Engine," our part number B-01"


La pipe d'admission standard pour double carburateurs SU fournie par l'usine semble parfaite avec son jet direct vers les porst de la culasse.
Pas certain
Certainement tout en dehors d'un moteur de compétition à haut régime a besoin d'un tube de balance entre les 2 carbus pour assurer souplesse à bas régime et en régime de croisière.
Malheureusement la traverse énorme mise en place par l'usine provoque une perturbation du flux entrant dans les ports.
...
...
Maniflow a fabriqué un colleteur en acier pour 2 SUs dont le tube de balance est d'un diamètre réduit et localisé dans une zone qui dérabnge moins le flux entrant.
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Nous avons constaté un gain consistant de 4-5 bhp tant sur les moteurs serie A ou B en utilisant ce type de collecteur en comparaison de celui de l'usine
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Ce que nous avons découvert avec le collecteur Maniflow c'est la production d'une bonne pêche à mi régime et qui devient trés proche des performances d'un Weber en haut de la courbe ...

Le lien:
http://www.aptfast.com/APT_Parts/Bserie ... ifolds.htm

APTFAST qui en connaît un rayon sur ces types de moteur.
bonne soirée.