Daimler series 3 spark plugs and bhp?

[Jag 1979]

I have a Daimler series 3 1979 fuel injection, and I want to order some spark plugs.

However, im given conflicting information.

Im looking at NGK Spark Plugs Ignition Replacement 6 Pack BP5E 4669 but it says these are for a Jag 1982 onwards and with an engine of 205bhp. (4.2)

It say mine is a 169bhp??(4.2)

Why does mine have less power and why wont these spark plugs fit?

[mike020150]

A quick look in the 1978 Jaguar workshop manual on my desk lists the spark plug originally specified for the first fuel injected 4.2 litres (last of the series 2 and first series 3 cars) as the champion N10Y. Different plug manufacturers' plugs have slightly different heat ranges so there is some overlapping when you check out equivalent plugs. The NGK plug (BP5E) isn't always listed as the direct equivalent for the N10Y but it seems to operate in a similar rather than identical heat range.
In the seventies, quoting power outputs moved from the older and exaggerated gross and net SAE figures to the more reliable DIN standards often quoted today. Hence, quite apart from variations due to different compression ratios and emission standards, it was possible for the same basic engine in a model to be attributed wildly different power outputs. For example, the 4.2 litre with triple carbs in the E-Type is usually listed as having 265bhp in high compression form. In practice, the output is generally accepted to have been less than 200bhp when measured to the later DIN standard. I recognise 170bhp as the DIN figure usually quoted for the 4.2 litre fuel injected 4.2 litre engine. Mike.

[Jag 1979]

Hello Mike, thank you for that detailed information.

Yes, the bhp makes sense now that you have explained it.

However, as for the spark plugs I have never been a big fan of Champion spark plugs. I have had many Champion spark plugs give up the ghost.

That being said, I may give them a try and see how things go with them.

Once again, thank you Mike

[PaulGover]

...In practice, the output is generally accepted to have been less than 200bhp when measured to the later DIN standard. I recognise 170bhp as the DIN figure usually quoted for the 4.2 litre fuel injected 4.2 litre engine. Mike.

My memory may be going, but I thought the UK 4.2 with SU carburettors was about 190 bhp DIN, and the fuel injected, by Series III, was 205 PS (which are slightly less than horsepower, but near enough). The wikipedia article gives the 170 PS DIN for the US version with Zenith-Stromberg carbs (and other emission controls no doubt).

[mike020150]

Paul may well be correct. My comments were primarily about the wide range of numbers quoted at the time whilst Jaguar and others were moving from a variety of over-optimistic measurement standards towards the more modern DIN standard. Before responding initially, I checked the familiar sounding 170bhp DIN for early series 3 cars with one of Paul Skilleter's books which also used that same number. However, after Paul Gover's challenge, I have found other, later references to UK high compression cars quoted at 205bhp DIN so it's entirely possible that my memory was tainted by the 'emission' versions used elsewhere in the world. Mike.