MG ZR Forums banner
1 - 15 of 15 Posts

·
Registered
Joined
·
1,050 Posts
Discussion Starter · #1 ·
Right, was bored in a massive traffic jam yesterday and got thinking about this. RPM = Revolutions per minute, so at 7000 RPM does that mean that the pistons are going up and down at 116 times a seconds? Even if a revolution is counted when all 4 piston go up and down

so 7000/60/4 = 29.1666r thats still alot of times those pistons are going up and down?

Am i correct or getting the wrong end of the stick? I was thinking is RPM measured by the revoultions that the crack shaft makes or is it the pistons?

please explain.....


cheers tom
 

·
Registered
Joined
·
3,224 Posts
At 116 times, i dont think youd even see it turning would you...
 

·
Registered
Joined
·
3,224 Posts
Do you see a Household tube light flash? they flash at about 50-60times a second (don't quote me on that).
Ive seen textile eaving machinery spinning at upto 150 rpm when i was working in that industry, but never seen anything spinning at 7000 rpm.
 

·
Registered
Joined
·
3,224 Posts
So in relation to engine size say 1.4 how does this relate to RPM? Like how many rev's of the crank does it take for the engine to process that amount of fuel?
 

·
Registered
Joined
·
12,564 Posts
So in relation to engine size say 1.4 how does this relate to RPM? Like how many rev's of the crank does it take for the engine to process that amount of fuel?
What amount of fuel?

1.4 is the displacement of the cylinder which is determined by the piston diameter and stroke, this give the volumetric displacement that is filled with air, hence with 4 cylinders you get a total of 1.4 lts of displacement.

Depending on mapping the ECU will insert the correct amount of fuel based on load/rpm/boost etc.
 

·
Premium Member
Joined
·
3,616 Posts
So in relation to engine size say 1.4 how does this relate to RPM? Like how many rev's of the crank does it take for the engine to process that amount of fuel?
Twice. It's a 4stroke engine, 1reverlution is 2strokes, so needs two for the full 4 strokes, (all 4cylinders will cover the 4strokes), making the 1.4litres worth of capacity all used.

A rotary engine however, only needs one reverlution, this is why, even though their internal capacity is 1.3, they get classed as a 2.6 as such, because they have 1.3 worth of power every 1rev (in comparison to the 1.4 k series which gets 1.4worth of power every two revs)
 

·
Registered
Joined
·
3,224 Posts
Twice. It's a 4stroke engine, 1reverlution is 2strokes, so needs two for the full 4 strokes, (all 4cylinders will cover the 4strokes), making the 1.4litres worth of capacity all used.

A rotary engine however, only needs one reverlution, this is why, even though their internal capacity is 1.3, they get classed as a 2.6 as such, because they have 1.3 worth of power every 1rev (in comparison to the 1.4 k series which gets 1.4worth of power every two revs)
Ahaaa gotcha, cheers.
 

·
Registered
Joined
·
3,224 Posts
trying to understand engines makes my head hurt
Its not too bad, its just one of those things i reckon you need a sort of hands on experience with to understand it well. And those folk saying stuff that just isnt the case just complicates it further.
 

·
Registered
Joined
·
12,564 Posts
Purchase a book called: "engine combustion fundamentals" Mcgraw hill iirc.

Tis a yellow book, very very scary.

Chemistry/thermodynamics etc, intresting read (skipping the chemistry bits)
 
1 - 15 of 15 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top