Valve Timing, XJ6 Cams

Hello, I cant seem to find this information. It seems like there may be some phase differences in the camshaft between the models. I’m going to be using an XJ6 camshaft in an older XK engine. Can someone confirm the following:

Inlet open 15 BTDC, inlet close 57 BADC, exhaust open 57 BADC, exhaust close 15 ATDC.

Thanks in advance,

Bill

Sounds about right to me.

Thanks Robin!

The manual gives inlet 17 BTDC and 59 ABDC and exhaust 59 BBDC and 17 ATDC for early(ish) versions, Bill. Where did you get data? Difference is likely immaterial though I thought all 4,2 6 were born equal in this respect…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)

Hey Frank,

You’re right probably doesn’t make a difference. Maybe someone can explain the implications of a degree here or there. Here’s the snippet I found on the forum which I assume is from the XK120/Mark VII Service Manual.

2fac25b6271823e9badaf1a241a60bf0fdfa2edf

Incremental, William. Overlap is a sort of engine tuning; overlap crudely allows incoming air to flush out exhaust gasses giving ‘fresher’ mixture and more power. However, higher inlet air speed is required as overlap increases - to be effective. Which means the engine idle will suffer, and fuel consumption increases. It’s a very complicated subject with many factors involved…:slight_smile:

So there is a trade-off; Jaguar opted for an overlap that improves performance in a specific rpm band that is suited to expected Jaguar driving styles - and a reasonable idle…:slight_smile:

That said; some have tweaked the cam timing a couple of degrees to improve idle…so…

Frank
xj6 85 Sov Europe (UK/NZ)

1 Like

Perfect, just the response I was looking for.

-Bill

William,

the SI 2.8 l ROM indicates inlet open 15° BTD, inlet close 57° PTD, outlet open 57° BTD, outlet close 15° PTD. Unfortunately, my SII ROM doesn’t give this information.

Good luck

Jochen

75 XJ6L 4.2 auto (UK spec)