Joe's Blog

In general variable valve timing allows for a change in the duration, timing and lift of the intake and exhaust valves within an internal combustion engine.  Let’s dive into each of these, explain what they are, and see how they can help an engine make more power, make more torque at lower engine speeds, and increase fuel efficiency.

Background

Before we can talk about how variable valve timing works and the effects, we need some background information.  Valves are what an engine uses to ‘breath’.  The intake valves control the amount of fresh air (and typically fuel) into the combustion chamber which houses the spark plug.  The exhaust valves allow the spent fuel and gases to leave the combustion chamber.  They are key factors to how an engine will perform.  The camshaft(s) are what open and close the valves and are driven by a timing belt or timing chain.  The timing belt is driven off of the engine crankshaft.  Camshafts are typically long, round solid pieces of metal precisely cut in the shape of a tube.  They contain ‘lobes’ on them that, in an overhead valve engine, directly actuate the valves.  The camshafts (an intake and exhaust camshaft) spin to open and close the intake and exhaust valves by these lobes pushing on the top of the valves.  The camshaft journals are polished round pieces that fit into the bearings on the head and where the camshafts spin on.  These will have a small hole in them for pressurized oil to flow out of so that they will spin easily on the bearing.  Without the oil, there would be metal to metal contact and the journals would become scoured.

Figure 1 - Camshafts

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The turbocharger is a most excellent device that I love dearly.  It is a form of supercharger that forces additional air, under pressure, into the engine so that additional fuel can be added to create more engine power.  Whereas a supercharger is driven off of the engine crank, typically with a drive belt, the turbocharger has a ‘turbine’ section.  The turbine sits in the exhaust path very close to the head, and hence very close to the combustion chambers.  It is driven by the hot exhaust gases.  One would think that it would be the flow of high pressure air that spins the turbine, but it is also the significant amount of heat that drives the turbine.  If you were to measure the temperature of the exhaust gas before and after the turbocharger, you would see a significant temperature drop.  This heat would otherwise be wasted out the exhaust pipe, but on a turbo engine, it is more fully utilized to create more engine power.  It is for this reason, that turbochargers really came into use during the first gas crisis in the 1970′s. » Read more…

Nissan Leaf

The Nissan Leaf is the first ‘real’ mass produced 100% electric vehicle, and costs about $33,700.00 – which is a lot.   It is about $26,000 after the federal tax credit – which is a lot better.   It has a claimed range of somewhere between 62 and 138 miles which is where the problems start.  The range, as with any car, depends on how you drive, the outside conditions (temperature and pressure), and the accessories that you use (A/C, etc..).  In the leaf, however, heat is a big drain, whereas in a conventional car it isn’t.  Heat in a conventional car is basically waste heat that is produced whether you have the heat on or not.  In the Leaf, heat should be almost instantly available, but is using the battery ‘fuel’ to produce it.  Turn on the heat in the Leaf on a 30 degree day, and your range can drop by 12 miles.  Doesn’t seem like a big deal, but when your total range might be 80 miles, 12 starts to sound like much more. » Read more…

This text hopes to describe what exactly turbocharger lag is, why it is getting such a bad reputation, and why that bad reputation is usually unfounded.

Turbocharger lag is, for practical purposes, the time it takes the turbocharger to spin up and make useable boost pressure after you plant your right foot.  The turbocharger is driven by hot exhaust gases passing through the turbine side of the turbocharger assembly.  Before the turbo can make positive boost pressure, that is pressure above atmospheric pressure, there must be enough exhaust energy to spin the turbine.  The only way there can be a substantial amount of hot, high velocity exhaust gases passing through the turbine, is if the engine is under a significant load.  Once that occurs boost pressure is created, more fuel can be injected, and hence more hot exhaust gases produced to spin the turbo even faster.  What a wonderful cycle! » Read more…