Motor Vehicle Maintenance & Repair Stack Exchange
Motor Vehicle Maintenance & Repair Stack Exchange

Questions tagged [rpm]

RPM = number of Revolutions Per Minute. Most commonly an acronym for engine crankshaft speed.

An acronym, which in the context of this website, most commonly refers to engine speed. RPM = revolutions per minute of the crankshaft.

1 RPM = 2π/60 Radians per second = 2*180/60 degrees per second

196 questions
19
votes
6 answers

Engine power specification at different rpm?

Car companies advertise the power of an engine at different rpms. Car 1: 80 PS at 6000 rpm Car 2: 85 PS at 6500 rpm What does the power at different rpm mean? Does it mean Car 1 has better power than Car 2 because it's at lower rpm? Or does the rpm…
user3041058
  • 407
  • 1
  • 5
  • 7
18
votes
4 answers

Why does diesel engine have redline much lower than petrol engine redline?

Why do diesel automotive engines redline at around 4500 rpm whereas petrol ones go to 6500-8000 rpm? Does this have something to do with the compression ratio?
saurabh64
  • 1,082
  • 2
  • 10
  • 13
17
votes
2 answers

What mechanical revolution is measured in "RPM"?

I do realize that it stands for revolutions per minute, but what are the revolving pieces that are measured? Assuming it is the crankshaft, is RPM calculated by the crank shaft sensor, or by some other means? Why do some old, carbureted cars not…
method
  • 2,770
  • 12
  • 45
  • 61
16
votes
4 answers

Does accelerating faster worsen fuel efficiency?

I've often heard that accelerating harder makes for bad fuel efficiency, but have yet to be given a sound explanation of why. Naturally this makes me question this advice. Now obviously when you accelerate harder, more fuel is being pumped into…
andrewb
  • 1,056
  • 6
  • 14
  • 22
16
votes
3 answers

Is it harmful to drive at high rpms

Does driving at high RPMs (3000-3500) in a manual transmission car cause any extra wear and tear to any mechanical parts? It obviously hurts gas mileage, but does it hurt anything else?
purpleACR
  • 717
  • 3
  • 12
  • 27
14
votes
1 answer

How does the tachometer on my dashboard actually work?

Recently, I asked a question about the speedometer, how it works and how accurate it is. But that got me thinking... how does the rest of the dash actually work? I understand that the RPM measurement is a measure of the rotational speed of a…
Max Goodridge
  • 7,957
  • 19
  • 53
  • 105
12
votes
4 answers

Optimal RPM range for manual transmission

Are there optimal RPM ranges for different vehicles? I've been told it's better for the engine to drive at slightly higher RPMs (e.g. 2500-3000 for my Tacoma) than low (1000-1500). I understand a lot depends on the gear sizing and ratios for…
amphibient
  • 6,777
  • 42
  • 102
  • 139
12
votes
6 answers

Why does my RPM drop when sitting idle at traffic lights?

While I'm sitting idle at traffic lights I put the car into neutral. The engine stays idling at about 1000 RPM. However every now and then it drops down to about 500 RPM and then quickly back up to about 1200 then goes slowly down to 1000 and stays…
Aequitas
  • 221
  • 1
  • 2
  • 6
11
votes
5 answers

Is it bad to drive slow at low rpms in 4th or 5th gear? Do you get better gas mileage?

Obviously running your engine at too high an RPM for too long isn't good. But what about running it too low? not so low that it stalls or lugs, but within around 1,000 RPM? Would you get better gas mileage? Would it wear out the engine or…
Jerreck
  • 866
  • 6
  • 12
  • 23
10
votes
5 answers

Why does the power output peak and then drop as engine speed increases?

I have been looking at the power bands for my car (2000 Opel Agila 1.2) recently, as I want to work out when it is best to change gear and stuff, as I have no life! This is the approximate graph I made up in Excel comparing power and torque: Why…
George
  • 6,605
  • 38
  • 86
  • 123
10
votes
1 answer

Why doesn't my rev limiter bounce?

I have a BMW 630i Steptronic from 2007. If I floor the pedal in neutral the RPM is of course limited, but it doesn't "bounce" like regular rev limiters. Instead it keeps a constant and "clean" RPM. My old Audi A6 Multitronic 2008 did the exact same…
jhovgaard
  • 203
  • 1
  • 2
  • 5
8
votes
1 answer

Engine revs up when braking

Background: 2012 Honda Civic EX, 5-speed automatic, with no mods except a non-stock tire (ran over a large bolt). I keep it maintained per the manufacturer's manual and always see the Honda dealership that sold it to me new for maintenance. 20k…
allquixotic
  • 509
  • 2
  • 5
  • 12
7
votes
1 answer

Short shifting after full throttle

Other than normal wear and tear, are there any detrimental effects or added harm done to the engine by going full throttle in 1st and/or 2nd gear, then shifting up well before redline (say 4k rpm on a 7k rpm engine)? Would it, for example, cause…
MooseLucifer
  • 6,027
  • 4
  • 28
  • 55
7
votes
4 answers

2015 Honda Fit iVTEC - Shifted into 2nd Gear at Highway Speeds

I was just driving on the highway and went to pass someone uphill, so I went to put it into 4th gear (from 5th or 6th). I somehow made the mistake of putting it into 2nd and the engine screamed and probably hit about 9k or 10k RPMs (redline is like…
Kevin Evans
  • 1,206
  • 4
  • 13
  • 36
7
votes
4 answers

Minimum RPM at idle speed

Looking at wikipedia, For a passenger-car engine, idle speed is customarily between 600 rpm and 1,000 rpm. For buses and trucks it is approximately 540 rpm. In case of many single-cylinder motorcycle engines, idle speed is set between 1200-1500…
SeanJ
  • 543
  • 3
  • 11
  • 17
1
2 3
…
13 14