Tuesday, September 24, 2013
Wednesday, September 18, 2013
camshafts
Commonly referred to as cam,an engines camshaft is located just below the engines valve cover and is a long metal shaft with intermittent lobes that is secured at its ends,with a pulley or cog connected to the timing chain or belt. While Single Overhead Camshaft engines may only have one camshaft,others such as Double Overhead Camshafts ,twin cams,v configurations and w configurations have more than one camshaft to control the intake and exhaust valves.In cases where an engine has more than one cam,the intake and exhaust camshafts are identified by looking at the position of the intake valves/manifold or exhaust valves manifold.
The key to producing high torque from a naturally aspirated engine is to get the maximum possible amount of fuel and air into the cylinder.How well the engine does this is measured by its volumetric efficiency.In general,the more air/fuel mixture we can pump through the engine,the greater the torque.The two biggest factors affecting volumetric efficiency is the valve overlap angle and the intake valve closing angle.These are directly related to the choice of camshaft for your engine,and changing the camshaft profile will change the torque cover,and thus also the power curve.
The cam profile is changed either by grinding the lobes on the stock cam to acquire a larger valve opening duration or higher lift which are measured in degrees,the greater its lift,the more air is allowed into the combustion chamber.However,there are limits with performance parameters which some are diametrically opposed depending on the type and size of an engine.Besides grinding the lobes ,replacing them with a more aggressive aftermarket cam is another option.Suffice to say that a DOHC designed engine performs better and generally smoother when revved hard compared to a SOHC.
A performance aftermarket cam improves the breathing of an engine because the intake and exhaust valves would open longer (longer duration) and higher (high lift) allowing more air to enter the combustion chamber.They are generally available and described as stages in performance.The least performance would be stage one and so forth.
Regardless of the percentage of gain in performance,you can expect an increase in fuel consumption.Moreover,'aggressive" cams have poor idling characteristics,for street cars,cams with less than 270 degrees of duration are a suitable choice to retain smooth engine idling.On the other hand longer duration cams such as those used on race engines will affect low rpm drivability.Most performance camshafts move the power and torgue band higher up the rpm range by around 10 to 15%.These are hard gains that you actually feel and measure.
Most tuners would grind their cams with the proper lobe center straight up, if they acquire 2-3 more hp at the bottom end ,they would consequently lose 5 hp at the top and vice versa.The best alternative is to advance the intake cam slightly by 2-3 degree range,this would produce a gain of about 3 hp in the mid range and 1-2 hp on the bottom end with the loss of only about 1-2 hp at the top end.This setting is general rule of thumb for street or autocross where bottom end is desired.
When you grind a cams lobes for more lift,it retards the timing and you can use adjustable gears/pulleys to correct it, tuners have reported huge gains with the addition of an adjustable cam gear pulley,and tuned on the dynometer. In fact anytime you port the engine dead it is advisable to make use of adjustable cam gears or pulleys to restore proper cam timing.
Once more aggressive cams have been installed on an engine that is running its stock management it would probably take some for the ECU to reset to the new cam profiles,running rough at first.Even without the fine tuning of an aftermarket piggy back of standalone,the engine should feel more responsive and more eager to rev higher.
It is wise to take note that the more aggressive the cam profile the less bottom end performance it delivers.Radical change in cam profiles can also upset the OBD-11 and emission systems in general.
Overall higher profiles camshafts deliver good performance gates and its relatively easy to install.If you were going to build an engine with performance in mind,then these sticks of metal should be on your shopping list.
Monday, September 9, 2013
Most Profound Least Understood Experience...
.must be my entering the house of god.assembled at the vip s place afta subuh prayers, this was with the entourage of the current Permaisuri Agong,i was seated next to abah,whom adviced me ,juz because you are here does not mean you can get in.uncle mad three times rejected.ok bah ..i said.so..as the time arrived, the vip delegates got up.all escorted with armed guards to the kaabah.i was safely with abah at first , then as we got closer the crowds went wild,more so at the opening of its doors, i got pulled back and just managed to shout abah!abah!..to no avail.then a glistening handsome guard about 6 foot tall with that serene look,pulled my hand across the other guards said yaa laahh..to which i ran like hell to the kaaba,on the first step slipped and fell like neva b4,on landing in the kaaba on my bumb, sore by now,cried like a baby,knowing where i was.abah came over and said pray at all corners..i did and on that visit my intention was to rid of my darah panas habit of hitting my gf's at first blood,managed to safely bring back a mop we got from that place,and while wanted to thank that guard,never to be seen again,got a real scolding from a pakcik kelate.alls well,had wine on MAS on our flight back.ohh..my pariah habit alhamdulilla went away,other bigger ones crept in until i am now part of the main act to be slaughtered by my own family,so i ask again.was i suppose to stay away.only god knows and to show me why i was allowed in.abah went in twice and he was basically murdered by the family and loved ones.
p/s everyone after that asked me..u look up YAZ??..hehe..
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