22
votes
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What mechanical revolution is measured in "RPM"?
Ok, let's start from the same picture so we're on the same page:
These engines are four stroke engines, which means the piston goes up and down a total of 4 times, twice up, and twice down for each ...
- 9,326
17
votes
Accepted
How does the tachometer on my dashboard actually work?
While i'm not sure if there are mechanical tachometers like speedometers electronic tachometers are quite simple.
An electronic tachometer works like an old analog volt meter.
The speed of the engine ...
- 16k
10
votes
Why does my RPM drop when sitting idle at traffic lights?
I am presuming this is a gasoline engine. If so, the symptoms sound very much like the throttle internals are dirty. If gunge builds up on the butterfly valve, it can restrict the air required for a ...
- 24.9k
9
votes
Accepted
Checking the motor's RPM without an in-dash tach
You have a few options out there. There are meters that clip onto the ignition system that show the engine RPMs that are quite simple and cheap:
Tach meter at Amazon for example...
You can also ...
- 13.3k
9
votes
Accepted
2015 Honda Fit iVTEC - Shifted into 2nd Gear at Highway Speeds
Background
I would be primarily concerned with the i-VTEC cam related mechanisms. I do not see that this engine is an interference engine.
If it were an interference engine and you floated your ...
- 33k
8
votes
Accepted
Can diesel engine be harmed as easily as gasoline engine by over-revving?
The rev limit of a petrol (gasoline) engine is generally set to protect the internals of the engine. Less sporty engines are designed to a cost and their components may not have the strength or ...
- 1,698
8
votes
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Optimal RPM range for manual transmission
It is in fact true that driving at slightly (key word) higher rpms is much better (for both fuel efficiency and engine life. The rpm range for the two can be different).
Part 1. Engine life:
Every ...
- 468
8
votes
Optimal RPM range for manual transmission
It depends what you're trying to optimize. If you're looking for optimal acceleration, more RPMs are better. Most engines today produce peak power at redline.
As for optimal efficiency, there's two ...
- 410
7
votes
Accepted
How fast is one RPM on average?
This is a math-only question, and no one has explained the formulas. Also I like the idea of this simple question having multiple answers so...
RPM is Revolutions Per Minute, but we want a time in ...
- 13.3k
6
votes
2015 Honda Fit iVTEC - Shifted into 2nd Gear at Highway Speeds
It's very hard to say what damage, if any, will have occurred. All I can tell you is from my own personal experience. I once went from the red line in 3rd gear with a wide open throttle to 4th at ...
- 23.5k
6
votes
Driving car with half engaged clutch
To get us on the same footing, I'm going to assume by saying "clutch pressed halfway" you are suggesting the clutch be halfway engaged (meaning, you are still getting power from the engine, ...
- 153k
6
votes
Checking the motor's RPM without an in-dash tach
In addition to what JPhi1618 said...
You can set any standard tach up with clips. I did this with a cheap tach when tuning my truck.
They have 4 wires - positive, ground, signal, light.
...
- 8,443
6
votes
Accepted
Why can a motorcycle rev higher than a car, in spite of both reaching the same speed?
One important factor is the mass of the components. Smaller, lighter components and shorter strokes allow higher RPMs. Given equal RPMs, an engine with a bigger stroke will put higher stresses on the ...
- 1,587
5
votes
Can 100% calculated load be reached in neutral?
Doesn't it suck up only as much as engine speed and throttle position allows?
No, throttle position and engine load determine the quantity of air consumed.
It can be quite hard to understand at ...
- 39.1k
5
votes
Why does diesel engine have redline much lower than petrol engine redline?
Paulster2 is right, varying the injection timing with respect to the engine crank angle timing is the main way to control the combustion process in a diesel engine. In a conventional gasoline engine (...
- 51
5
votes
2001 Ford Explorer High Idle
The P1506 code is an idle air control overspeed error.
From autocodes.com:
The P1506 code means that the engine idle is out of factory specification. Sometimes the Idle Air Control (IAC) may have ...
- 5,245
5
votes
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Will a manual vehicle stall at low RPM without being on the accelerator?
In my experience, most manual cars can move along in 1st gear at idle – on a flat(ish) surface. I've only tried this in the process of teaching people to drive a manual. My hunch is that in 2nd and ...
- 14.4k
5
votes
Accepted
Volvo XC90 8V AWD car speed to piston revolution speed ratio changed after repair
Yes, I'd take it back to the shop to see if there is something they missed. While 300 rpm at 60mph is not a huge difference, to me this is about the difference of when a lock up torque converter isn't ...
- 153k
5
votes
Accepted
Does the flywheel really complete 33 revolutions per second when the engine is set to 2,000 RPM?
yes, that's correct. Now, rotating a flywheel at 2000 rpm is not a big deal: it's well within the capabilities of the material, as long as the flywheel is well-balanced.
Other elements in the engine ...
- 4,422
5
votes
Jeep Patriot RPM Gauge bounces / not right
I don't know for sure, but would bet the gauge itself is bad. One way you could check this is by putting an OBDII reader onto the port and check live data from the ECU to see if it matches what's ...
- 153k
4
votes
Accepted
RPM bouncing when in idle, especially when AC in switched on
The exact cause of the issue had been found to be that of a loose alternator belt.
When the engine was cold, the alternator had a slack in it and if the AC load is added on the engine, the rpm ...
4
votes
Accepted
What is rev matching, and how do you do it correctly?
The answers are vague because there is no scientific way to match engine speed to transmission input shaft speed. We do not know what the input shaft speed is. Matching is a learned skill and it ...
- 11.6k
4
votes
Will a manual vehicle stall at low RPM without being on the accelerator?
Obviously in a manual car with the clutch engaged there is a direct connection between the wheels and the engine. Also while switched on most engines have an idle setting designed to keep them running ...
- 1,596
3
votes
Can 100% calculated load be reached in neutral?
Engine load is determined by a ratio between current air flow and the maximum air flow at the same RPM.
The engine computer has a look up table of maximum air flow as a function of RPM for WOT ...
- 16k
3
votes
Accepted
Can 100% calculated load be reached in neutral?
Air flow is purely based on throttle position and engine revs on a normally aspirated engine, adding a charger (turbo etc) adds complication. With the throttle fully open, every inlet stroke is going ...
- 24.9k
3
votes
RPM bouncing when in idle, especially when AC in switched on
Or could be your mass airflow sensor because I have similar issues and that is what's wrong with my car
- 31
3
votes
Accepted
How do I know if car ECU has a REV Limiter?
Rev limiter is a bit of a misnomer since maximum engine RPM is a function of airflow. However there are such things as fuel and spark cut off which will disable either injectors or coil packs as a ...
- 10.7k
3
votes
Accepted
No Damage/ top fuel economy rpm shift point
As @racefever states, this is really subjective and hard to answer. I will try to do my best though.
Most of this is going to be done by feel. Every vehicle, even those of the same make/model, will ...
- 153k
3
votes
How fast is one RPM on average?
In a car rpm are very often shown. From experience you might know that for a normal car it varies between 1000 and 3000 rpm for normal use cases.
3000 rpm = 50 rotations per second = 1 rotation per 0....
- 131
3
votes
Torque reduces gradually after certain RPM
Torque is a rotational force. It is a measurement of how hard it is applying force that causes the crankshaft to rotate.
Torque is not a very good unit of measurement for an engine because it does not ...
- 261
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