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Dwell angle vs coil saturation


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Iv'e been having a bit of a think recently :yawn: (yes I know but it interests me) about the relationship between optimum dwell angle vs optimum coil saturation for 4,6 and 8 cylinder engines and it all gets a bit muddled in my head so an open question feel free to chip in

 

Question: As the number of cylinders increase the dwell angle must decrease (as there is still only 360' on the rotor) and if that assumption is correct then will the optimum coil saturation density also proportionally decrease with increasing numbers of cylinders

 

Pete :confused:

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Also those distributors like for example on Rolls military B60, B80, B81 and Jaguar J60, wartime British vehicles with certain screened distributors (inc. Daimlers) have two sets of points with half the number of cam lobes, and one set of points operating half the number of cylinders.

 

regards, Richard

Edited by Richard Farrant
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Thanks for replies Radiomike and Richard,

 

these would seem to confirm the conclusion I came to......... that for optimum coil density to be achieved (variously quoted between 60% and 70%) a four lobe cam is the ideal configuration set to give between 37 and 42 degrees of dwell. So this leads me to wonder about 6 cylinder engines which only have one set of points, it would seem that they operate at sub optimal coil density ??? or is this compensated for by closing the the points gap down?

 

Pete

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Thanks for replies Radiomike and Richard,

 

these would seem to confirm the conclusion I came to......... that for optimum coil density to be achieved (variously quoted between 60% and 70%) a four lobe cam is the ideal configuration set to give between 37 and 42 degrees of dwell. So this leads me to wonder about 6 cylinder engines which only have one set of points, it would seem that they operate at sub optimal coil density ??? or is this compensated for by closing the the points gap down?

 

Pete

 

Pete,

It would seem you are thinking too deeply. There are thousands of 6 cylinder engines running with single sets of points without issues. What the most important thing to adhere to is keeping the points adjusted to the specified gap for the that engine or distributor type.

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Pete,

It would seem you are thinking too deeply. There are thousands of 6 cylinder engines running with single sets of points without issues. What the most important thing to adhere to is keeping the points adjusted to the specified gap for the that engine or distributor type.

 

:-D don't worry Richard I'm not having a brain melt down, I have to admit to a certain amount of Devils Advocate here, as you know I've had a number of six cylinder motors all of which performed perfectly well with single point set ups.

 

What started me down this line of thought was the relationship between dwell time and coil saturation and how various manufactures addressed the problem,as an aside while rooting around for information I found reference to dual point distributors for six cylinder engines unfortunately what they were fitted to wasn't recorded. As you mentioned in a previous post it's a common set up on V8's but I hadn't ever come across a six cylinder dual set up any idea what they were fitted to?

 

Pete

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The 28 HP Bedford engine when fitted in the 15 cwt Bedford MWR uses a different type of distributor with two sets of points and no vacuum advance /retard .would this be because it was a screened distributor although it would still be expected to perform on the road the same as any other Bedford 15 cwt .

Nicky

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:-D don't worry Richard I'm not having a brain melt down, I have to admit to a certain amount of Devils Advocate here, as you know I've had a number of six cylinder motors all of which performed perfectly well with single point set ups.

 

What started me down this line of thought was the relationship between dwell time and coil saturation and how various manufactures addressed the problem,as an aside while rooting around for information I found reference to dual point distributors for six cylinder engines unfortunately what they were fitted to wasn't recorded. As you mentioned in a previous post it's a common set up on V8's but I hadn't ever come across a six cylinder dual set up any idea what they were fitted to?

 

Pete

 

It was not me but radiomike7 who mentioned V8's, but they are different in that they do have 8 lobes on the cam.

 

I mentioned examples of straight six and eight cylinder engines with dual points and 3 and 4 lobe cams respectively, here are a list off the top of my head, of military ones;

Rolls Royce B60 (6 cyl) and B80/B81 (8 cyl) [military and civilian versions]

Jaguar J60 (6cyl) [4.2 litre ohc]

Daimler Dingo and Armoured Car (different engines)

WW2 Humber armoured vehicles with screened dist. (6cyl sv)

Bedford QLR and MWR with screened distributor (6 cyl 28hp)

Austin K9 with screened distributor (6 cyl 4-litre)

Commer Q4 with screened distributor (6 cyl ohv)

 

too name but a few ..........

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The 28 HP Bedford engine when fitted in the 15 cwt Bedford MWR uses a different type of distributor with two sets of points and no vacuum advance /retard .would this be because it was a screened distributor although it would still be expected to perform on the road the same as any other Bedford 15 cwt .

Nicky

 

I guessing Nicky it may be more to do with reduction of RF interference in this case, see also Richards list of 6 cylinder vehicles fitted with dual points.

 

Pete

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In some cases engine improvements and critical calculations were carried out by people who had not seen the engine or piece of equipment that they were working on. Like Sir Stanley Hooper, who was a mathematician he got 10%more power out of a Merlin without seeing one or Mrs Shilling.who improved its ability to perform in combat.

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