[xk-engine] Small or large valves head, outside signs?

Hello, I have an XK motor from an XJ SII that has been
worked on by its PO. Is there a way to know, without taking
it apart, if the cylinder head is a small or large valves one?

Thank you.–
1975 XJ6C - LHD
Sunnyvale, United States
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In reply to a message from Eric318 sent Sun 6 Mar 2011:

If it has a Series 2 head you don’t know what he has done
to valve sizes without looking. If you are wonderi g if it
has a Series 3 head then the rear is not drilled for the
earlier cambox end plugs. I’m not too clued-up on US spec
engines though and your late S2 were different.

If the manifold is off then the S3 ports are a fraction
bigger but you can’t eyeball the valve seat or valve head
to check the size.

Pete–
69 E-type OTS 99 Daimler Super V8, Long nose D-type replica
Cambridge, United Kingdom
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I have put up a reference chart for XK heads, which may help:

http://www.westnet.com/~mfrank/cylheads.html

There may be mistakes in this chart, corrections welcome.

Mike Frank

At 02:12 AM 3/7/2011, you wrote:

Subject: [xk-engine] Small or large valves head, outside signs?

Hello, I have an XK motor from an XJ SII that has been
worked on by its PO. Is there a way to know, without taking
it apart, if the cylinder head is a small or large valves one?

//please trim quoted text to context only

In reply to a message from Michael Frank sent Mon 7 Mar 2011:

That is a nice chart, assuming it is accurate I would not make any
effort to get an intake valve that is 1/16th’’ bigger. Straight
port might make a difference, but 1/16th’’ just does not seem worth
any extra effort.
P.–
Peter J. Smith, 1966 3.8S MOD
Carson City Nevada, United States
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In reply to a message from carsoncitysmith sent Mon 7 Mar 2011:

Peter,
It depends on your goals. Racers love the bigger valves. We hog
aluminum away to make the ports as big as possible and the series 3
allows us to go a lot more more than that 1/16th…
For the street? Actually it helps even at low RPM… It’s not just
the 1/16th inch larger across. It’s the area around the valve
which totals a lot more. I suspect the flow increases by more than
20%–
The original message included these comments:

port might make a difference, but 1/16th’’ just does not seem worth


MGuar
Wayzata Minnesota, United States
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