[xj-s] Hi-Po V12

["Kirbert" <palmk@mailer.gadcomm.net>]

Roger Bywater and I have been having a little discussion on souping 
up the V12, so I thought I'd forward a little more of his thoughts.  
Again, they prove to be enlightening.

------- Forwarded Message Follows -------
From:          Roger Bywater <101351.1414@compuserve.com>

> palmk@mailer.gadcomm.net:
> ...if someone were to put straight pipes on a V12, open up the air
> filter housings, and then sent you a Visa card number, they could
> end up with an engine that will safely run like a raped ape up to
> 7500 or so?  Because, if so, I think we can get you some
> business.

Nice to see you get so enthusiastic. Just one problem - it's not going to
work. There are two things that limit the breathing on the V12 as you
should know if you stop and think about it:-

1. The small diameter of the individual inlet tracts from the plenum
chambers. 
2. The small and pocketed exhaust valves (on the HE). 

Our High Torque manifold mods help the first as far as is practical by
increasing ram effect and by improving the flow conditions on entry and
through the tract.

The second is the real problem and is why all the high performance racing
V12s have been based on the old "flat head" design. Putting big exhaust
valves in doesn't help because the chamber walls are so close and leave no
room for flow around the edge of the bigger valve head. In fact if the HE
were not of abnormally high compression ratio, always a useful trick to get
a bit more top end power out of an engine that doesn't breathe, it would
struggle to produce the barely adequate power that it gives as standard. 

You can build an HE to 6 or more litres (we used to do a 6.3 using 98 mm
bore and standard crank) but all you really get is more torque low down but
not much more power.

Roger

-------------------------------

 -- Kirbert      |     If anything is to be accomplished,
                 |     some rules must be broken.
                 |          - Palm's Postulate

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