[xj] V12 rev counter in IL-6

Hi all,

one minor problem with my FrankenJag Coupe is that the new
engine really starts to come alive (max bhp @5250rpm) when
the standard Ser 2 rev counter says it’s about to blow up.
At full throttle the tranny upshifts at well over 6k rpm.
Since I will probably change the speedometer for an
electronic Ser 3 one I thought of replacing the rev counter
for one from a Ser 3 V12 (which goes to 6,500rpm before
going into the red). Is there an easy way to rewire a V12
rev counter to work with a 6 cylinder engine?
BTW these cars really need to be used: all of a sudden the
driver’s window started working today;) Sofar the comments
have been nothing but positive, even from people who have no
idea what happened under the bonnet: a Ser 2 Coupe is really
a car that makes people happy when they look at it, even
with extremely dull paint such as mine (or maybe because of
it;) or a big Rhodesian Ridgeback dog sitting on the back
seat as if he were the king himself:). I imagine that seeing
one of these pulling a trailer with scrap iron (or to some
quite expensive Jaguar hardware) isn’t a daily sight for
most. It almost makes me cry throwing some stuff away, but I
only have one 20’’ container and until Tuesday to get it
filled…
Even the PO who came to see me was impressed with the
transformation and oddly enough he even liked the 18’’ Pentas:D–
Arnoud
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Just multiply its readings by 2, Arnoud!
;]–
Alex
79xj6L SII (BRG + wires)
86xj6 SIII (Black)
61 Sprite MkII (Red)
Menlo Park, Calif.

Arnoud wrote:

Hi all,

one minor problem with my FrankenJag Coupe is that the new
engine really starts to come alive (max bhp @5250rpm) when
the standard Ser 2 rev counter says it’s about to blow up.
At full throttle the tranny upshifts at well over 6k rpm.
Since I will probably change the speedometer for an
electronic Ser 3 one I thought of replacing the rev counter
for one from a Ser 3 V12 (which goes to 6,500rpm before
going into the red). Is there an easy way to rewire a V12
rev counter to work with a 6 cylinder engine?

===================================================
The archives and FAQ will answer many queries on the XJ series…
FAQs: http://www.jag-lovers.org/xjlovers/xjfaq/index.html
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Arnoud wrote:

Hi all,

one minor problem with my FrankenJag Coupe is that the new
engine really starts to come alive (max bhp @5250rpm) when
the standard Ser 2 rev counter says it’s about to blow up.
At full throttle the tranny upshifts at well over 6k rpm.
Since I will probably change the speedometer for an
electronic Ser 3 one I thought of replacing the rev counter
for one from a Ser 3 V12 (which goes to 6,500rpm before
going into the red). Is there an easy way to rewire a V12
rev counter to work with a 6 cylinder engine?

Not an easy way, Arnoud…

As the redline has no other function than a specific overrev warning on
the engine that was it’s of course not pertinent to the engine that is.
What the tacho shows is still the true rpms - and you can simply
disregard the redline.The SIII redlines at 5000 and runs out of space at
5500 - so neither is satisfactory if you want frequent readings in the
6000 rpm range. Since all engines have some rpm when they may blow up -
how do you know that your engine is safe at 6000 anyway? You may be
playing with fire…:slight_smile:

Most aftermarket speedos are switchable between 4/6/8, but how that is
done I don’t know - something might be gleaned from such knowledge? A
speedo repair shop?

Frank
xj6 85 Sov Europe (UK/NZ)===================================================
The archives and FAQ will answer many queries on the XJ series…
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In reply to a message from Frank Andersen sent Sun 13 Jul 2008:

For the higher rev same reason, I installed the V12 tach in my
Series 1 and had it converted to eight cylinders at a great place,
www.redlinegaugeworks.com. They do fast and good work for a
reasonable price. Mine has been working perfectly for about four
years now.–
The original message included these comments:

Most aftermarket speedos are switchable between 4/6/8, but how that is
done I don’t know - something might be gleaned from such knowledge? A
speedo repair shop?


'71 XJ6 383/200R, '74 XJ6 383/700R, '74 Nova SS Glendora, CA
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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If the tach is driven from sparking rate (like our XJs) then the conversion
just involves a change in the internal pulse-sensing circuit, which could be a
simple digital switch, or an analog adjustment (capacitor/resistor). In fact,
going from a 12cyl feed to 6, with a 12 gauge, just needs a pulse doubler on
the wire (wht/blu spiral) from coil -. A small series capacitor & a
transistor or two might be enough, since the cap would generate two, opposite
pulses of current for each up-down of the ignition pulses. The magic of
electronic differentiation (calculus)!

Using a 6 tach on a 12 could likely be done with a simple rate divider
(flipflop), using two transistors or an IC.–
Alex
79xj6L SII (BRG + wires)
86xj6 SIII (Black)
61 Sprite MkII (Red)
Menlo Park, Calif.

Roger Mabry wrote:

In reply to a message from Frank Andersen sent Sun 13 Jul 2008:

For the higher rev same reason, I installed the V12 tach in my
Series 1 and had it converted to eight cylinders at a great place,
www.redlinegaugeworks.com. They do fast and good work for a
reasonable price. Mine has been working perfectly for about four
years now.

===================================================
The archives and FAQ will answer many queries on the XJ series…
FAQs: http://www.jag-lovers.org/xjlovers/xjfaq/index.html
Archives: http://www.jag-lovers.org/lists/search.html

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