4 pulse/rpm for petrol, 3 for diesel. They are both 4 stroke, i need to know why they are differentother than *reasons*
I would guess the number of cylinders divided by 2 for 2 rotations of the crank.
I would guess the number of cylinders divided by 2 for 2 rotations of the crank.
Shirely it would be easier to multiply by 2, for 1rotation
.Never did like dividing stuff
.J
Shirely it would be easier to multiply by 2, for 1rotation
Never did like dividing stuff
J
Nor do computers. Quicker to multiply by 0.5 than divide by 2, or so I was told.
I do come down on the side of if it aint broke dont fix it but also understand why we need to know stuff Just because....
I also believe that one engine rev is one cycle of the engine which is two revs of the crankshaft and one rev of the engine on a single cam 4 stroke engine
I now believe that the rev counter measures crankshaft revs but not yet convinced of that
I can understand (just) the 4 pulses per rev but no idea why diesel is only 3
Just because....I also believe that one engine rev is one cycle of the engine which is two revs of the crankshaft and one rev of the engine on a single cam 4 stroke engine
I now believe that the rev counter measures crankshaft revs but not yet convinced of that
I can understand (just) the 4 pulses per rev but no idea why diesel is only 3
tomcat59alan
Well-Known Member
Half the number of cylinders.I do come down on the side of if it aint broke dont fix it but also understand why we need to know stuff
I also believe that one engine rev is one cycle of the engine which is two revs of the crankshaft and one rev of the engine on a single cam 4 stroke engine
I now believe that the rev counter measures crankshaft revs but not yet convinced of that
I can understand (just) the 4 pulses per rev but no idea why diesel is only 3
I'd not realised the diesel was 6,Half the number of cylinders.
I do come down on the side of if it aint broke dont fix it but also understand why we need to know stuff
I also believe that one engine rev is one cycle of the engine which is two revs of the crankshaft and one rev of the engine on a single cam 4 stroke engine
I now believe that the rev counter measures crankshaft revs but not yet convinced of that
I can understand (just) the 4 pulses per rev but no idea why diesel is only 3
Please
It’s called Revolution Per Minute, not cycle per minute.
The rev counter measures and is calibrated for whatever signal it is given. The electrickery gods at LR/BMW decide with the throw of a dice for all I care
Some get the tachometer reading from the alternator, do we really care what that signal is
.How good are you at math?
Hold your car in a gear log speed and RPM then work it backwards from wheel dia/diff ratio/transfer box ratio/ whatever gear ratio. Wonder what you would come up with
.Or you could just trust us
I know it’s a lot to askJ
Maybe this will help
https://www.cars.com/articles/what-does-rpm-mean-in-cars-1420697442798/
"...rpm measures how many times the engine’s crankshaft makes one full rotation every minute, and along with it, how many times each piston goes up and down in its cylinder."
https://www.cars.com/articles/what-does-rpm-mean-in-cars-1420697442798/
"...rpm measures how many times the engine’s crankshaft makes one full rotation every minute, and along with it, how many times each piston goes up and down in its cylinder."
tomcat59alan
Well-Known Member
Had chips fer me teeOh,yes and that's why a chiipped diesel will keep up with a 4.0
Hopefully I'll get a response fron BBS before too long
I do come down on the side of if it aint broke dont fix it but also understand why we need to know stuff
I also believe that one engine rev is one cycle of the engine which is two revs of the crankshaft and one rev of the engine on a single cam 4 stroke engine
I now believe that the rev counter measures crankshaft revs but not yet convinced of that
I can understand (just) the 4 pulses per rev but no idea why diesel is only 3
Here's my reasoning but it is just a guess. I'm sure it'll be written down somewhere or a trained mechanic will correct us:
Diesel is 6 cylinders. 2 rotations per firing cycle. So you put timing pips at 120 degree intervals and you know when each cylinder should fire = 3 pulses per rotation of the crank. V8 is 8 cylinders with 2 rotations per firing cycle. So you put timing pips at 90 degrees and once again you know when each cylinder is due to fire = 4 pulses per rotation of the crank.
I might be totally wrong, of course.
Had a beer so my imagination is in charge of my mouth.
Does it mind? I mean do you ask permission first at leastNo.
Nano takes it through the OBD port..
As I seem to have started something, I would like to point out that the 4 or 3 pulses is the signal given out of the ECU to the tach, What goes in or how the ECU deals with it I dont know
.So how they come up with the 4 or 3 is a guess other than its an easily calculated number of the amount of tangs/pips on either the crankshaft or camshaft.
The ECU knows where the engine is by the missing tang on the crankshaft, It knows what part of the cycle it is on by the camshaft sensor, from that it can work out where to spark or inject on a count of tangs on the crankshaft.
Thats how I read it anyhow
. Other than that I know nothing.Its too early in the morning to be thinking I need to go do some manual labour
.J
