[racing] XJ40 Performance

hi all,

I am an avid engine tuner having extensively modified the good old british
leyland A-series engine.

However, the basic concept of an engine is simply as a large air pump. The
more air goues through the more power comes out. So, if I can get more air to
flow into my AJ6 engine then more power will be produced. Of course this only
touches the mere tip of the iceberg when it come to engine tuning, but i did
notice on the old jaguar XK-SS D-type le mans racer, which had a straight six
engine and did in excess of 190 MPH, that it obviously was set up to flow
much more air and gases than the more conventional AJ6 setup.
This is primarily due to the unrestricted passage of air into the engine
through a large filter and the most critical part of the induction system was
the exhaust manifolds, on the xk-ss racer, they were very streamlined and
offered little resistance to the waste gases, but on modern road jags, and
especially the XJ40 the manifolds are very restrictive, the gas has to come
out of the cyclinder and do a sharp 90 degree turn to go sideways and then
down a little before entering the front pipe.
I will try to scan an image of the ideal manifolds from the XK-SS and post to
this list, however on the UK spec models, I do think the air intake system is
quite restrictive, and can be improved upon to give that extra pick-up when
driving. Also I must stress that fuel in the UK is very poor, octane levels
are crap !!, want of a better word, If you drive in the Uk as i do, then
please pay the extra for Super Unleaded, it has higher octane than 4-star and
runs the cat much smoother, as the cat needs octane rated fuel of at least 96
Thanks for your time, if any one is interested in tuning their XJ40 please
mail me and we can collaborate on ideas.

Ashfield Electronics

Ashelectro@aol.com wrote:

I will try to scan an image of the ideal manifolds from the
XK-SS and post to this list,

Just a quick note:

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Gunnar Helliesen | Bergen IT Consult AS | NetBSD/VAX on a uVAX II
Systems Consultant | Bergen, Norway | '86 Jaguar Sovereign 4.2
@Gunnar_Helliesen1 | http://www.bitcon.no/ | '73 Mercedes 280 (240D)

i have not found any supermarket filling stations that sell super unleaded,
plus, not many normal stations sell it either, I think shell and esso are the
only ones who sell the good stuff !!!..

I’ms glad you think it improves performance, as i may have been imagining

I did read some very interesting HP figures regarding petrol grades and the
AJ6 engine 3.6 L version…

These stated that on normal fuel it produces 225 HP and with using super
unleaded they stated figures of 248 HP…

This seem a littl eexagerated to me, however with the correct ignition timing
it would not be impossible.

any way , let your tank get into the flashing red then stick about half a
tank load of super, and then see if the responsivness stays with it…

I must admit though, throttle response does seem a lot better with the super

86 sov

just thought i’d tell you some info i got from the horses mouth…

I asked shell what the octane rating of their fuel was, and the answers were
as follows :

premium unleaded 95 RON

4 star leaded / low lead 95 RON

super unleaded 98 RON

so if they are correct then 4 star as not only lowered in lead content but
also octane content aswell…

i get absolutely no difference when using premium or 4 star, so would support
their answer that they are same RON rating…

86 Sov