Rpm's.....are they all equal?

[Feedman]

I was thinking....can you believe that??

On a typical engine...the revolutions per minute is @ the crank correct?


If so...would a smaller crank say a 4 cylinder have more rev's @ 5k than a larger v8 model......@ the same rev's....


Reason I ask is this:

If you spin a ball....the center moves faster than the outeredges or the outside moves slower than the center, FACT.


A car can move @ 70mph down the road....if they have 14" wheels or 17" wheels.....

But the smaller wheels are going to have many more revolutions per minute than the larger wheel....


Am I over anyalyzing something....and not thinking clearly...after a full day of holiday cheer...

Someone set me straight.... 8)

[narfdanarf]

well one revolution is a revolution...now the force on the outer part of the crankshaft might be different, but a rotation is a rotation.

[Davis Silver Sti]

I'm going to say a REV is equal. (however its a very good question)
breathe, squish,bang, blow theory exist in all 4 stroke engines and would guess that 1 REV = 1 REV no matter the size of engine.

However, different cars will have different power output at various RPM's (duh I know) but the 1 rev vs. 1 rev theory should still be the same.

The Honda F1 engine (supposed to be one of the highest hp engines in F1) revs to an incredible 19,000 RPM's. Its also a 3.0L V-10. Despite all the amazing internals and engine management for such an engine, I'd still say that you can compare a 4cycl to a v-8 to a F1 V-10 and that all the RPM's are still comparable and that there is no RPM adavantage to having one type of engine than the other. (for RPM comparisons only)

Just my .02 but I'm interested to hearing a much better reason than mine;)

[ShortysTRM]

I saw a Fifth Gear where they tested an F1 car (Honda, possibly, but I don't remember it being the same color as the BAR Hondas) and he was talking about how the valvetrain was hydraulically operated, I believe, because cams don't do any good at 18,000 RPMs...ok, carry on

[Feedman]

I saw a Fifth Gear where they tested an F1 car (Honda, possibly, but I don't remember it being the same color as the BAR Hondas) and he was talking about how the valvetrain was hydraulically operated, I believe, because cams don't do any good at 18,000 RPMs...ok, carry on

My cams are manipulated by the crank via the timing belt....but Vtec is engaged/disengaged hydraulically.....

When I took my head apart...I finally understood how it actually functions...cool stuff....

I was just thinking about the rev thing the other night...thought I would post it up....

You all make good points.... 8)

[ShortysTRM]

This is a really dumb thing to say this far into my experience with cars, but I don't completely understand variable valve TIMING. I have been confusing variable lift with variable timing. I assume it is exactly what it says, variable timing, but how? I have theories, but that isn't what I want...

[Feedman]

This is a really dumb thing to say this far into my experience with cars, but I don't completely understand variable valve TIMING. I have been confusing variable lift with variable timing. I assume it is exactly what it says, variable timing, but how? I have theories, but that isn't what I want...

Its more or less teh same thing....different companies call it different things b/c certain words are trademarked.... 8)

[RobbieNelson]

Its more or less teh same thing....different companies call it different things b/c certain words are trademarked.... 8)

I'm getting ready to leave Logan to head towards Parkersburg, so I'll keep this short. They are not the same thing. VTEC is the simplest of the lot, giving basically two cam profiles that switch at a certain RPM. There are systems out there that can vary the timing and not just switch it. I think the USDM STi uses a variable system. I'll do a little research later. This is an intersting subject. I think you'll see more use of these systems in high output engines in the future.

[Davis Silver Sti]

This is a really dumb thing to say this far into my experience with cars, but I don't completely understand variable valve TIMING. I have been confusing variable lift with variable timing. I assume it is exactly what it says, variable timing, but how? I have theories, but that isn't what I want...

Here is Subaru's AVCS version:

Active Valve Control System or variable valve timing, as it is more commonly known, allows the engine to produce better performance yet also means it operates more economically and produces lower levels of exhaust emissions.

It's a great example of having your cake and eating it too!

The system is operated by a combination of computer controls and oil pressure to advance or retard the intake camshaft timing by up to 35 crankshaft degrees. In the old days the only way to advance or retard the engine's operation was by manually adjusting the ignition timing by altering the distributor's position and then you were stuck with whatever new setting you made.

With Subaru's AVCS, the adjustment occurs continually for the best operation of the motor at all times. By controlling the intake valve timing to suit the engine load and revs, AVCS optimises the engine's combustion process and efficiency.

This is achieved by advancing or retarding the intake camshaft timing to different positions relative to the crankshaft. As a result the intake valves, which are opened and closed by the camshaft, do their work letting the fuel and air mixture into the combustion chamber at slightly different times to produce the optimum performance.

The variation in the camshaft operating position is controlled by the ECM or engine management computer based on input signals from the airflow sensor, engine coolant temperature sensor, throttle position sensor and camshaft position sensor which send "electrical messages" to the ECM.

The ECM then sends a signal, based on the information it has received, to an oil control valve positioned at each of the intake camshaft sprockets. These have an actuator chamber inside them, that when filled or drained with oil pressure to advance or retard the camshaft timing over a range of 35 crankshaft degrees. This happens instantaneously and is continuously variable depending on the constantly changing conditions the engine is operating under. The oil control valve uses engine oil supplied at the same pressure as in the rest of the motor via two passages.

A computer map in the ECM is the "brains" of the operation and has been set to provide for optimum valve timing for stable idling, improved fuel consumption and low emissions in the medium speed range and maximum power at high revs and high engine loads.

When the engine is running at medium revs - 2000 to 3500 rpm - and the engine load is small with a light throttle, say when cruising on the open road, the intake valve timing is advanced. This reduces intake air blow- back thereby improving fuel consumption.
Increasing the overlap of the intake and exhaust valves is also significant, because when they are open at the same time exhaust gas recirculation is promoted. This reduces NOx exhaust gas emissions and much of what does go into the exhaust system is recirculated through the turbocharger to be burned again in the combustion chamber on subsequent occasions.

When the engine load increases at medium revs, as it does when you accelerate, the intake closing time is advanced to take advantage of the intake air inertia - the speed at which it enters the combustion chamber - to create a supercharge effect on the incoming air and thus increase its velocity.

At high revs and under heavy load - when the accelerator is pushed to the floor - the AVCS creates an intake and exhaust valve and a scavenging effect so the exiting exhaust gases effectively suck more air and fuel mixture in through the intake valves. As the intake valve is closed at the end of the intake stroke of the piston, air intake efficiency is improved and engine power output is increased.

At idling speeds, say when stuck in traffic snarl-ups, the AVCS alters the intake valve timing to improve idling stability and reduce fuel consumption and exhaust emissions.

[Feedman]

Its more or less teh same thing....different companies call it different things b/c certain words are trademarked.... 8)

I'm getting ready to leave Logan to head towards Parkersburg, so I'll keep this short. They are not the same thing. VTEC is the simplest of the lot, giving basically two cam profiles that switch at a certain RPM. There are systems out there that can vary the timing and not just switch it. I think the USDM STi uses a variable system. I'll do a little research later. This is an intersting subject. I think you'll see more use of these systems in high output engines in the future.

This is a really dumb thing to say this far into my experience with cars, but I don't completely understand variable valve TIMING. I have been confusing variable lift with variable timing. I assume it is exactly what it says, variable timing, but how? I have theories, but that isn't what I want...


Omg...here we go...lol....

The reason I said they were more or less the same is b/c in essence they are...depending on how you read into it....

Question: Difference between Variable Timing and Variable Lift....


Vtec for example....stands for Variable Valve Timing Electronic Control.

It controls both timing, obviously and lift....through the Vtec lobes on the cam, it changes the lift and duration of the valves which indirectly causes timing to be changed......


The reason I don't understand the question....is b/c as you drive...any newer engine..changes timing...thats just how they operate...its a fact of life.....so saying its something special really doesn't make since to me....

Maybe I am missing something......anyone care to elaborate......??

8)

[RobbieNelson]

The reason I don't understand the question....is b/c as you drive...any newer engine..changes timing...thats just how they operate...its a fact of life.....so saying its something special really doesn't make since to me....

Maybe I am missing something......anyone care to elaborate......??

8)

Your talking about ignition timing. Variable ignition timing has been used on cars since the 60s I think. The special stuff is in the valve timing.

[m pwrd 3]

Here is how BMW's VANOS works

VANOS is a combined hydraulic and mechanical camshaft control device managed by the car's DME engine management system.

The VANOS system is based on an adjustment mechanism that can modify the position of the intake camshaft versus the crankshaft. Double-VANOS adds an adjustment of the intake and outlet camshafts.

VANOS operates on the intake camshaft in accordance with engine speed and accelerator pedal position. At the lower end of the engine-speed scale, the intake valves are opened later, which improves idling quality and smoothness. At moderate engine speeds, the intake valves open much earlier, which boosts torque and permits exhaust gas re-circulation inside the combustion chambers, reducing fuel consumption and exhaust emissions. Finally, at high engine speeds, intake valve opening is once again delayed, so that full power can be developed.

VANOS significantly enhances emission management, increases output and torque, and offers better idling quality and fuel economy. The latest version of VANOS is double-VANOS, used in the new M3.

VANOS was first introduced in 1992 on the BMW M50 engine used in the 5 Series.

how it works
Here's how it works:

In overhead cam engines, the cams are connected to the crankshaft by either a belt or chain and gears. In BMW VANOS motors there is a chain and some sprockets.

The crankshaft drives a sprocket on the exhaust cam, and the exhaust cam sprocket is bolted to the exhaust cam. A second set of teeth moves a second chain that goes across to the intake cam. The big sprocket on the intake cam is not bolted to the cam, for it has a big hole in the middle. Inside the hole is a helical set of teeth. On the end of the cam is a gear that is also helical on the outside, but it's too small to connect to the teeth on the inside of the big sprocket. There is a little cup of metal with helical teeth to match the cam on the inside and to match the sprocket on the outside. The V (Variable) in VANOS is due to the helical nature of the teeth. The cup gear is moved by a hydraulic mechanism that works on oil pressure controlled by the DME.



http://www.bmwworld.com/technology/vanos_cutaway.jpg


Information

VANOS is a combined hydraulic and mechanical camshaft control device managed by the car's DME engine management system.

The VANOS system is based on an adjustment mechanism that can modify the position of the intake camshaft versus the crankshaft. Double-VANOS adds an adjustment of the intake and outlet camshafts.

VANOS operates on the intake camshaft in accordance with engine speed and accelerator pedal position. At the lower end of the engine-speed scale, the intake valves are opened later, which improves idling quality and smoothness. At moderate engine speeds, the intake valves open much earlier, which boosts torque and permits exhaust gas re-circulation inside the combustion chambers, reducing fuel consumption and exhaust emissions. Finally, at high engine speeds, intake valve opening is once again delayed, so that full power can be developed.

VANOS significantly enhances emission management, increases output and torque, and offers better idling quality and fuel economy. The latest version of VANOS is double-VANOS, used in the new M3.

VANOS was first introduced in 1992 on the BMW M50 engine used in the 5 Series.

how it works
Here's how it works:

In overhead cam engines, the cams are connected to the crankshaft by either a belt or chain and gears. In BMW VANOS motors there is a chain and some sprockets.

The crankshaft drives a sprocket on the exhaust cam, and the exhaust cam sprocket is bolted to the exhaust cam. A second set of teeth moves a second chain that goes across to the intake cam. The big sprocket on the intake cam is not bolted to the cam, for it has a big hole in the middle. Inside the hole is a helical set of teeth. On the end of the cam is a gear that is also helical on the outside, but it's too small to connect to the teeth on the inside of the big sprocket. There is a little cup of metal with helical teeth to match the cam on the inside and to match the sprocket on the outside. The V (Variable) in VANOS is due to the helical nature of the teeth. The cup gear is moved by a hydraulic mechanism that works on oil pressure controlled by the DME.

At idle, the cam timing is retarded. Just off idle, the DME energizes a solenoid which allows oil pressure to move that cup gear to advance the cam 12.5 degrees at midrange, and then at about 5000 rpm, it allows it to come back to the original position. The greater advance causes better cylinder fill at mid rpms for better torque. The noise some people hear is the result of tolerances that make the sprocket wiggle a bit as the cup gear is moved in or out.

Double VANOS

Double-VANOS (double-variable camshaft control) significantly improves torque since valve timing on both the intake and outlet camshafts are adjusted to the power required from the engine as a function of gas pedal position and engine speed.


http://www.bmwworld.com/technology/vanos.gif

On most BMW engines that use a single VANOS, the timing of the intake cam is only changed at two distinct rpm points, while on the double-VANOS system, the timing of the intake and exhaust cams are continuously variable throughout the majority of the rpm range.

With double-VANOS, the opening period of the intake valves are extended by 12 degrees with an increase in valve lift by 0.9 mm.

Double-VANOS requires very high oil pressure in order to adjust the camshafts very quickly and accurately, ensuring better torque at low engine speeds and better power at high speeds. With the amount of un-burnt residual gases being reduced, engine idle is improved. Special engine management control maps for the warm-up phase help the catalytic converter reach operating temperature sooner.

Double-VANOS improves low rpm power, flattens the torque curve, and widens the powerband for a given set of camshafts. The double-VANOS engine has a 450 rpm lower torque peak and a 200 rpm higher horsepower peak than single-VANOS, and the torque curve is improved between 1500 - 3800 rpm. At the same time, the torque does not fall off as fast past the horsepower peak.

The advantage of double-VANOS is that the system controls the flow of hot exhaust gases into the intake manifold individually for all operating conditions. This is referred to as "internal" exhaust gas re-circulation, allowing very fine dosage of the amount of exhaust gas recycled.

While the engine is warming up, VANOS improves the fuel/air mixture and helps to quickly warm up the catalytic converter to its normal operating temperature. When the engine is idling, the system keeps idle speeds smooth and consistent thanks to the reduction of exhaust gas re-circulation to a minimum. Under part load, exhaust gas re-circulation is increased to a much higher level, allowing the engine to run on a wider opening angle of the throttle butterfly in the interest of greater fuel economy. Under full load, the system switches back to a low re-circulation volume providing the cylinders with as much oxygen as possible.

[Feedman]

The reason I don't understand the question....is b/c as you drive...any newer engine..changes timing...thats just how they operate...its a fact of life.....so saying its something special really doesn't make since to me....

Maybe I am missing something......anyone care to elaborate......??

8)

Your talking about ignition timing. Variable ignition timing has been used on cars since the 60s I think. The special stuff is in the valve timing.


You are right...I didn't read Davi's thread completly....

8)