Key wrote:Yoshi wrote:philgtt wrote:au banc (les vrais CV...)
C'est une association qui me fait toujour marrer car les vrais chevaux on ne le trouve pas sur les bancs
Mais groso modo sur le fond je ne suis d'accord avec toi
inside00 wrote:et donc peut-etre moins lourd?
Niveau vous semblez tous pensez qu'un K20A fait 3 tonnes
Mais d'apres les anglais il est plus leger qu'un Rover K VVC
Plus leger, faut voir. Je suis comme Saint Thomas: je veux des preuves
Ceci dit, il n'est pas vraiment plus lourd.
La difference avec le Rover est plutot la distribution des masses. Le centre de gravite du moteur est plus haut (culasse i-VTEC plus complexe et donc plus lourde) et moteur place " a l'envers", echappement vers l'arriere, qui impose de decaler le moteur vers l'arriere dans la voiture. D'ou le leger changement d'equilibre de la voiture et surtout les problemes de cardans "en biais".
et voici voilou ! le Rover 97 kg et le k20 158 kg !
tiré du Sandsmuseum :
"Engine Weight Comparisons
All of this tends towards an engine that weighs in, as standard, fully dressed at 96.5 kg. Compare this to the Honda S2000 engine similarly equipped with standard manifold clutch and fluids at 158 kg and the Toyota 1.9 VVTi engine at 137 kg. The Rover engine"s compact size and weight are a significant advantage in a lightweight race/sports car of the Lotus 7 type or the Elise. Note, a full race K Series weighs 78 kg including 7 kg of fluids. Compare these figures for output in terms of power to engine weight. See Table 1.
...
However, this tells only part of the story because most of the Japanese engines like the old 1.8 VTEC and the new I VTEC engines are all short stroke, big bore engines, all of which have a relatively narrow power band. The K with its 89.3 mm stroke produces a lot more torque and spread over a wider engine speed range. This makes the K"s power to weight ratio all the more remarkable in the context of lightweight sports/race cars, and given its more advanced construction than all but 2 or 3 of its most recent competitors, it is clear that the K has a very strong claim to be the best 4 cylinder engine around. In fact, given the huge weight penalties of the Japanese engines and the backward design of the new 2.0L Ford " indeed most of the engines around at the moment, the only clear competitors to the K"s crown are the motorcycle derived engines.
The limitation of any normally aspirated engine, that is an engine that is using engine speed to pull the fuel mix into the cylinders and hence produce power, is piston speed. Piston speed is a function of both engine speed and stroke. To put the K"s ability into perspective the Honda S2000"s 2.0 litre engine the one that the Lotus people on the one make series aspired to, revs to 9000 rpm as a production engine. With an 84 mm stroke this achieves a piston speed of 4960ft/min, with its longer stroke the K achieves this at 8460 rpm, something the standard K bottom end is perfectly capable of, with the sole modification of forged pistons. The R500 engine achieves a piston speed of 5390 ft/min at 9200 rpm [ the R500"s rev limit has of late been cut to 8500rpm, in an attempt to stem the failures of this engine], a figure that the Honda engine would only match were it to be revved to 9,800 rpm. The point is that big bore short stroke engines are conceived to make high engine speeds possible, the penalty is poor torque, the Honda 2.0 litre S2000 producing just 151 lb/ft @ 7500 rpm, a figure easily eclipsed by the 1.8 litre K equipped with Piper"s 1227 cams which will give a very similar power output to the Honda engine. So, the Honda is not such a special engine. It does have a very strong and stiff block, being a copy of the K Series" design, but suffers from its enormous weight of 158 kg in standard form fully dressed (figures from the Vemac Car Co.) more than 60 kg heavier than the standard K. The only really attractive part of the Honda"s design are the roller cams which do reduce friction in the valve train but in every other respect the K is a more efficient and effective design than the Honda.
All this of course is on the assumption that the K can do this reliably, and the truth is that not only is there a perception of a fragile engine but there have been an enormous number of problems, from gasket and liner failure to complete catastrophe with the bottom end and on everything from the numerous privately modified engines, to the flagship models of commercial sports car manufacturers.
So what is going on here? Well, there are myriad of hysterical myths and oldwives tales told about the K, but there is also some kitchen sink engineering being done by the tuning companies. The only way to put this straight is to look at the engine, element by element."