how high can you safely rev a stock F20c?
10-26-2010, 12:42 PM
#21
Originally Posted by wadzii,Oct 26 2010, 06:23 PM
how do you think Mitsubishi motors work at high rpm, they only have 4 crank teeth.
the custom crank triggers we use on b and h series engines run 12 teeth and have no problem at 11k rpms, OE s2000 stuff has more than enough teeth on the crank trigger to maintain accuracy at very high rpms.
the custom crank triggers we use on b and h series engines run 12 teeth and have no problem at 11k rpms, OE s2000 stuff has more than enough teeth on the crank trigger to maintain accuracy at very high rpms.
How can an engine run with only 4 crankshaft trigger tooths??
10-26-2010, 12:52 PM
#23
Originally Posted by gernby,Oct 26 2010, 10:28 PM
Are you sure about the duration of the intake cam? The duration of the intake stroke would only be 3.75ms at 8000 RPMs, so it seems surprising that the intake valves would be open that much longer than the intake stroke.
These cam angles are designed for high engine speeds where only a limited time is available for filling the cylinder.
The above values are for the stock intake cam and measured just when the valve opens or is fully close. These are not comparable to the sometimes used 1mm valve lift angles.
10-26-2010, 07:04 PM
#24
last time I check an object in motion stays in motion unless another force acts against it. How can an engine instantly stop rotation and reverse direction? Especially with the heavy flywheel as found in the AP2?
10-26-2010, 08:14 PM
#25
Originally Posted by GrandMasterKhan,Oct 26 2010, 11:04 PM
...How can an engine instantly stop rotation and reverse direction? Especially with the heavy flywheel as found in the AP2?
10-27-2010, 06:04 AM
#28
We have NOT gone off topic. The issue of how high the rev limitter will allow the engine to go above the rev limit is critical. If you don't want your engine to hit 8700 RPMs while the rev limiter is engaged, then you have to set the rev limiter to ~8500. How is that off topic?
The discussion we've been having over the last several posts is about "why" RPMs continue to rise after fuel cut. I say the ONLY possibility is that the ECU is allowing too much lag in the RPM calculation. Others say its because inertia is causing the engine to continue accellerating after fuel cut. Which is not possible.
I see that GrandMasterKhan has already looked up "inertia" on Wikipedia, so I'm surprised he's still confused. Inertia is the resistance to changes in motion. However, acceleration IS change in motion (increase in speed / decrease in speed / change in direction). Therefore, Inertia is the resistance to accelleration, and will not CAUSE acceleration! The only way the crank will accellerate is if there is a force (combustion) that will overcome it's inertia, and cause acceleration. When that force goes away (fuel cut), inertia will take over, and accelleration will go to 0 (instantly). However, the friction and aerodynamic drag will exert force that will overcome the engine's inertia, and cause deceleration (instantly). This does not mean in any way th the crank stops spinning, or reverses directions. It just means that it quits speeding up the very instant fuel is cut. Well, I guess you could say it quits speeding up after the last fueled power stroke is completed.
The discussion we've been having over the last several posts is about "why" RPMs continue to rise after fuel cut. I say the ONLY possibility is that the ECU is allowing too much lag in the RPM calculation. Others say its because inertia is causing the engine to continue accellerating after fuel cut. Which is not possible.
I see that GrandMasterKhan has already looked up "inertia" on Wikipedia, so I'm surprised he's still confused. Inertia is the resistance to changes in motion. However, acceleration IS change in motion (increase in speed / decrease in speed / change in direction). Therefore, Inertia is the resistance to accelleration, and will not CAUSE acceleration! The only way the crank will accellerate is if there is a force (combustion) that will overcome it's inertia, and cause acceleration. When that force goes away (fuel cut), inertia will take over, and accelleration will go to 0 (instantly). However, the friction and aerodynamic drag will exert force that will overcome the engine's inertia, and cause deceleration (instantly). This does not mean in any way th the crank stops spinning, or reverses directions. It just means that it quits speeding up the very instant fuel is cut. Well, I guess you could say it quits speeding up after the last fueled power stroke is completed.
10-27-2010, 10:55 AM
#30
While the final acceleration force is "gone" it happens AT the limiter thus the final acceleration forces are still present beyond the limiter for a very short while, it could be just enough acceleration to cause the rotating mass to speed up to the ~200+ rpm beyond the limit you mention?
But you are certainly correct that the engine should not continue to accelerate. Think about the car itself and its 2900lbs of interia, you are accelerating full throttle, fastest rate, in 1st gear with a constant acceleration force. Then suddenly you lift and put the car in neutral. Does it continue to speed up, NO. Because the force causing the acceleration is gone.
But you are certainly correct that the engine should not continue to accelerate. Think about the car itself and its 2900lbs of interia, you are accelerating full throttle, fastest rate, in 1st gear with a constant acceleration force. Then suddenly you lift and put the car in neutral. Does it continue to speed up, NO. Because the force causing the acceleration is gone.