Chevelle.fr Chevelle.fr
Visites

   visiteurs

   visiteurs en ligne

Webmaster - Infos
Articles

Fermer Achat Coup de Coeur

Fermer Anecdotes

Fermer Découverte des Autos US

Fermer Evolution Moteur 383ci

Fermer Infos sur les Chevelles

Fermer L'univers des Quads

Fermer Les Anciens Avions US

Fermer Les Autos Des Copains

Fermer Meetings et photos

Fermer Phases de restauration

Fermer Place aux Jeunes

Fermer Renaissance Muscle cars

Fermer Sequence photo détente

Fermer Technique automobile

Fermer Vidéos Runs & Meetings

Nouveautés du site
Bonjour à tous

Déjà 109 albums d'américaines dans le"Trombinoscope Us Cars".

Cliquez sur la marque d'automobile que vous souhaitez visiter

eeil y en a pour tous les genres !!!

Ma Boutique en ligne2vo 383
  1. Phase Resto: Remontage Capot, Insignes, baguettes...
  2. Historique des EL Caminos
  3. VIDEOS: Runs à Trappes et Nancy 96 + Dreux 99
  4. Redémarrage Moteur et Rodage A.A.C
  5. Installation Moteur Phase 1&2
  6. Sortie TH350 + Décapage Berceau
  7. Meeting US à Lisle Adam 15/05/2011
  8. Savoir lire les Infos d'un Pneu
  9. Identifier Un Moteur Complet SBC
  10. Phase Resto: Remontage après Peinture
  11. Phase Resto: Peinture de la Chevelle
  12. Achat coup de coeur: Quad KYMCO 500 MXU
  13. Technique auto: Changer Pipe Admin SBC
  14. Evo 383: Restoration du Compresseur B&M 144
  15. Evo 383: Installation Admission
  16. Remplacement joints soupape
  17. Evo 383: Installation Culasses
  18. Pontiac 1er Tours de roues
  19. Pontiac 1er Démarrage Moteur
  20. Dernières finitions mécanique
  21. Electricité et Finitions moteur Pontiac ALAIN
  22. Installation Moteur / Boite Pontiac ALAIN
  23. Assemblage Bas Moteur Pontiac ALAIN Phase 4
  24. Assemblage Bas Moteur Pontiac ALAIN Phase 3
  25. Anciens Avions US le F4-U "Corsair"
  26. Assemblage Bas Moteur Pontiac ALAIN Phase 2
  27. Assemblage Bas Moteur Pontiac ALAIN Phase 1
  28. Art et Déco à la sauce Américaine MUSCLECAR
  29. Resto Baie de pare brise
  30. Evo 383 Installation Distribution
  31. Evo 383 Assemblage bas moteur
  32. Nettoyage + Peinture Block Firebird
  33. Achat des pièces neuves Pontiac
  34. Evo 383 Installation Vilo/Paliers/Flesplate
  35. Démontage du 400ci de la PONTIAC à Alain
  36. Achat 1er US pour Alain (mon beau père)
  37. 1er ACHAT d'une ricaine
  38. Machine à vapeur et Muscles car
Trombinoscope US Cars
Lettre d'information
Pour avoir des nouvelles de ce site, inscrivez-vous à notre Newsletter.
S'abonner
Se désabonner
1 Abonné
Calendrier
Devinette

Je peux lire dans vos pensées. Vous n'y croyez pas ? Essayez ! Vous n'en reviendrez pas...


Théorie De La Compression Sur Un Moteur
Compréhension De Son Focntionnement

*** Décembre 2009 ***

 

(Traduction en cour de réalisation... dés que j'ai un peu de temps...merci pour votre patience ...Sauf si vous lisez l'anglais techniques sans soucis...tant mieux pour vous !)



(By David Vizard)
Compression Comprehension :
It takes the barest of mental agility to appreciate that increasing the CR will raise cylinder pressure, thus causing torque output throughout the rpm range to simply follow suit. What is less obvious is that the increase in output from the higher CR comes about largely due to an increase in thermal efficiency. The thermal efficiency is a measure of how effectively the engine converts the heat-generating potential of the fuel, when burned with an appropriate amount of air, into mechanical power. To explain all this (starting from the raw fuel and air to the output at the flywheel) is rather more complex than we have the space (or inclination) to deal with, but no matter, as the most pertinent and relatively simple part applying here is not.
If a 2:1 and a 15:1 cylinder start at the same pressure, the 15:1 cylinder's pressure decays at a far higher rate and in so doing delivers the power to the crank mostly before 90 degrees after TDC is reached. Unless supercharged, a 2:1 cylinder would only achieve about 200 psi and as such, the difference in power be-tween the two ratios would be represented by the shaded green area.
Simple Theoretical Power Gains :

At low rpm, port velocity and pressure waves are too weak to produce any cylinder ramming. Couple this to the fact that even a short cam of some 250 degrees of off-the-seat timing will not close the valve till about 50 degrees after BDC. Fig. 3 shows the typical extent of piston motion back up the bore before the intake closes for three cams. Because of the delayed intake closure we find that during the period the piston moves up the bore from BDC until the valve closes, a significant amount of the induced air is, at low rpm, pushed back into the intake manifold. This means the volumetric efficiency (breathing efficiency) and thus the effective displacement of the cylinder is well below 100 percent. In other words, a 100cc cylinder with a static CR of 10:1 may only trap 75cc of air. This means the dynamic CR, at about 8.5:1, has dropped well below the static CR of 10:1. The bigger the cam, the more this effect comes into play.


The controlling factors influencing the best intake-to-exhaust ratio for maximum output (and this does assume all the available space for valves is used) has been a much-debated subject that, for the most part, has left the reader little or no wiser. The often-touted 75-percent rule is usually accepted without further question. In reality, the value is far from fixed. The optimum intake-to-exhaust ratio could range from as little as 0.75:1 (for a low CR supercharged engine) to as much as 1:0.6 (for a very high-compression naturally-aspirated engine). What is usually not appreciated here is that the CR is, for the most part, the controlling factor. Because the high-compression cylinder delivers energy to the crank much earlier in the power stroke, there are implications we can take advantage of. The most obvious is that the exhaust valve opening can be made earlier and held open longer. This can be done for improved high-rpm output without significantly impacting the engine's low-speed output. The rule here then is that the higher the compression ratio goes, the smaller an exhaust valve is needed to get the job done. This in turn leaves more room for a larger intake.

Note the minimal raised crown on this Calico-coated Lunati piston. It was used in a 441-inch small-block Chevy to achieve a 13:1 CR in conjunction with this chamber form (also coated) in a conventional 23-degree heads.


Top-notch ring seal starts with an equally top-grade bore and hone job. Always have the bores honed with a deck plate and with a finish as recommended by the ring manufacturer.

At this point it is pretty clear that making the most of the potential that can be had from high compression is a goal worth pursuing. But as the ratios sought get higher, counter-productive problems can begin to arise. Probably the most commonly seen of these is due to the final combustion chamber shape achieved when all the stops have been pulled out. The problem here is that as ratios much above about 10:1 are required, the only way to further minimize the volume after maximizing head milling is to have a raised crown piston. Up to a point, this is okay, but if the crown intrudes into the chamber too far, it can severely compromise the flame travel, resulting in a very ineffective combustion process. As to how much can be lost, suffice it to say I have seen a hundred horsepower disappear because of a piston crown intruding an eighth inch too much. The rule here is that unless you know what combination of chamber and crown form works or are prepared to do the necessary R&D, don't go overboard on crown intrusion into the chamber. For typical small-block V-8 from Chevy, Chrysler or Ford, a good rule of thumb is to use no more than 100 to maybe 125 thousandths crown height in your quest for a high CR.

My extensive testing has shown Total Seal rings can produce zero leakdown and can continue to do so for as much as 100,000 miles. Here is how they work: Firstly, the gap for the lower ring is on the opposite side of the bore where it is sealed off by the upper ring. Gas pressure, communicated from the top side of the piston, passes down and through the gap as shown or through the radial gas ports if the piston used has them. This pressurizes the backside of the ring, ensuring firm contact with the cylinder wall. Because both upper and lower rings are virtually in contact with the bore, no leakage route exists.

Gas porting is a technique whereby compression and combustion pressure is communicated to the backside of the ring, thus pressing it more firmly against the cylinder bore wall. Piston deck-located ports such as seen here work well for a drag race engine but plug up too easily for an endurance engine.

 
 
Compression Ratio Gas Porting
Gas porting is a technique whereby compression and combustion pressure is communicated to the backside of the ring, thus pressing it more firmly against the cylinder bore wall. Piston deck-located ports such as seen here work well for a drag race engine but plug up too easily for an endurance engine.
Having a high compression ratio brings about greater demands on cylinder sealing. The higher the pressures involved, the more attention needs to be paid to details. The first part of the equation toward sealing up the cylinder is to make sure your machine shop hones the block right. This should involve the use of a deck plate to simulate the distortion brought about by the stresses of head bolt tightening. Next, make sure your machine shop is aware of the type of piston ring material being used so they can apply an appropriate finish. Then give the bores a good rub down with a new Scotch Brite pad and plenty of Gunk engine cleaner. After that, scrub (with a stiff brush) the bores with a strong liquid detergent and hose off with hot water. After you are sure they are clean and grit-free, hose the block down and spray the machined surfaces with WD-40 to prevent rust.

Seen here is the mode of operation for both vertical and radial gas ports. The vertical gas ports have been favored by drag racers for many years but the trend is toward the radial type, which is used for endurance engine.


Compression Ratio Gas Porting
Seen here is the mode of operation for both vertical and radial gas ports. The vertical gas ports have been favored by drag racers for many years but the trend is toward the radial type, which is used for endurance engines.









Date de création : 29/12/2009 @ 20:00
Dernière modification : 30/12/2009 @ 01:35
Catégorie : Technique automobile
Page lue 16264 fois


Imprimer l'article Imprimer l'article

 

Personne n'a encore laissé de commentaire.
Soyez donc le premier !

 
Recherche




Google 1
Annonces Googles 3
Google 2
Extra Free Box 0

Sondage
Quelle voiture américaine Sportive préférez vous ? (Votez 1 seule fois Merci d'avance)
 
Chevelle
Mustang
Camaro
Transam/Firebird
Nova
Corvette
Baracuda
Challenger
Charger
Gto
Résultats
Chevelle 66 2 portes ss
Meilleurcafe.Com

logo_cafe_160x120.jpg

Bataille Navale

L'amiral Micro, à la tête de sa terrible flotte, vous défie de venir le combattre. Relèverez-vous le défi?

W3C CSS Skins Papinou © 2008 - Licence Creative Commons
^ Haut ^