[NO.FX]

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

 

[new 160]

It's crankshaft revs.
So each piston goes from one position through one up/down cycle for each rev. thus your original 116.5 at 7000 rpm was correct.

 

[Superspy]

aye, thats right, now you understand why an engine needs lubricating! lol

 

[bendjunkie]

and why to rev faster they need balancing and uprated/strenthened parts.

 

[ZRBlue]

At 116 times, i dont think youd even see it turning would you...

 

[bendjunkie]

At 116 times, i dont think youd even see it turning would you...

Do you see a Household tube light flash? they flash at about 50-60times a second (don't quote me on that).

 

[ZRBlue]

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.

 

[Hob]

More RPM = way more stress, imagine f1 with 18+ k rpm

 

[ZRBlue]

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?

 

[Hob]

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.

 

[bendjunkie]

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)

 

[ZRBlue]

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.

 

[black_sunrise]

trying to understand engines makes my head hurt

 

[ZRBlue]

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.

 

[Hob]

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)