Power Output

[Tintin]

I came across some comparable figures for the 4.2 engine the other day that surprised me. The output of the S1 Daimler Sovereign 4.2 was given as 173 BHP and the output of the XJ6 4.2 S1 as 245 BHP. In both cases, the 0-60 time was given as 8.8 secs and the top speed as 124 MPH. Of further interest, both the earlier Daimler Sovereign ('66 - '69) and the Jaguar 420 ('66- '68) with the 4.2 engines were rated at 245 BHP.

Can anyone enlighten me as to why the 4.2 S1 Daimler engine produces 72 BHP less than the 4.2 XJ6, 420, and earlier Sovereign?!

Robbie

[mike020150]

It's all to do with the standard the outputs were measured against. The 245bhp figure was measured gross which meant that Jaguar could quote the biggest figure possible (essentially for the US market where there was a horsepower marketing race). It was measured without engine ancillaries attached so was totally misleading in the real world. Without looking it up, the 173bhp figure sounds like the same output expressed using the DIN standard which is a more truthful way of quoting usable horsepower. Mike.

[Tintin]

Thanks Mike - I've learned something new today and good to have confirmation that the engines produce the same power!

You are right as to the 173 (actually 171) - it is quoted in the S1 Sovereign launch brochure as DIN, but I can't tell how the 245 was measured.

Robbie

[J44EAG]

I encountered similar issues with modern Jaguars some years ago whilst re-flashing the ECU on my 4 litre V8 S-type.

Jaguar quoted flywheel 281hp for an N/A V8 4 litre engine. The tuning house told me before the uprate took place that the initial dyno run would in all probability reveal 225hp in standard form. My car made 228hp with a K&N filter, new plugs, standard OE exhaust and a cleaned MAF sensor.

The reflash was performed and a big bore resonatorless Miltek exhaust was then fitted. FHP rose to 276hp for a cost of £1600. An expensive day with hp still below the original quoted figure by Jaguar. The drive away experience was a marked improvement with the car performing as if another cylinder had been added to the engine.

I then wrote an article on the session and asked the then X-type Co-ordinator to add his comments. His views were very much like those expressed by Mike H. The issue of what industry standard is applied to figures put out by different manufacturers came in for debate.

The difference in standards can be quite marked. Much of it also depends on what ancillary equipment applied load is applied during the testing. ie power steering, air con, alternator, water pump etc, etc.

I`ll not forget what I was told by the tuning house. BMW and Merc always produced a rolling road figure which equated with manufacturers published hp figures. Jaguar figures on the other hand always appeared to be 50hp down on the official hp output......

Mike K

[PaulGover]

It's a bit like hi-fi amplifiers. They used to be quoted in Watts PMP (Peak Marketing////////Music Power), which was about twice Watts DIN (constant sine wave power measured RMS).

[piman]

Hello Mike,

Rolling road power figures are a guess at best, for tuning a car they give a comparison to evaluate adjustments but cannot give accurate power outputs. I'm sure BMW and Mercedes, like all car manufacturers test their engines on an engine dynamometer, it's the only way they can practically set engine parameters.

Alec