P38A Thor engine RPM

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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
 
oakey said:
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
Click to expand...
Half the number of cylinders.:)
 
oakey said:
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
Click to expand...

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;).

oakey said:
I now believe that the rev counter measures crankshaft revs but not yet convinced of that
Click to expand...

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:eek: I know it’s a lot to ask

J
 
I did it for a cavalier years ago and cant remeber the answer cos was for other reasons lol
Is the nanocom picking up the raw data or does it do the sums?
That makes sense Kermit
 
oakey said:
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
Click to expand...

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.
 
friends-joey.gif
 
Grrrrrr said:
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.
Click to expand...

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:eek:. Other than that I know nothing:confused:.
Its too early in the morning to be thinking I need to go do some manual labour:D.

J
 
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