Hi Roger, thanks for the positive feedback. With almost every engine that
we build, we learn something new. Enzo Ferrari was fond of saying that the
‘Best car he ever built, will be the next one he builds’. I try to instill
this philosophy in all of my staff, especially where it applies to the
building of an engine.
The point of my posting regarding Eric’s dream engine, was to try to
prevent him from wasting his money on things that he mistakenly (IMHO)
believes will significantly enhance the performance of his car.
If you are rebuilding the engine anyway, then polishing and porting it will
obviously do some good, even without the other things which I have
suggested should be done in conjunction with such work. I would suggest,
however, that polishing and porting alone will see very little performance
increase. Even on one of our standard engine rebuilds, we carry out
moderate polishing of the hemispherical domes and ensure that the cast is
not too rough at the relevant points of flow. The whole idea is of course
to improve the flow over the inner head surfaces, and to provide as
immaculate and as well sealed a combustion chamber as possible.
With our performance engines, we go significantly further with this
activity, and also do other things as follows: We double cut the valve
seats, install larger intake valves, higher lift/longer duration cams,
stronger valve springs, and set the lash (the clearance between the top of
the tappet bucket and the bottom of each camshaft lobe) at .005" and .009",
rather than the .004" and .006" that a standard (series one) engine calls
for.
Most of our performance engines tend to be built to 10:1 (or even higher)
compression specs. In this form, you really do need to have better than
standard flow through the exhaust manifolds and the exhaust as a whole. We
use a big bore, polished stainless steel header and exhaust system which I
obtain through Dick Ames in Florida. It is built by Langford in England,
and is a superb product.
If you are staying at 9:1 (or thereabouts) compression, you can get away
with the standard manifolds, although you only have to look at them to see
that the flow through them can never be particularly effective. You can buy
9:1 forged pistons which will enhance the performance of your engine over
an original spec piston. They are significantly lighter, of course, and
when used with top quality rings, such as Total Seal, suffer from none of
the ‘blow by’ that I have seen reported here on the list and elsewhere.
Forged pistons such as these have to be set up ‘looser’ in the cylinders,
to allow for their expansion when hot - hence the quality of piston ring
being of paramount importance.
We use the stock intake manifolds on all triple SU set ups, and find that
it works fine.
When you come to swap out your engine, Roger, I suggest you give serious
thought to a lightweight flywheel. That will give you a real and
significant increase in your car’s performance, for relatively little
financial outlay.
The above is intended as a brief, non-technical outline: If you would like
to know more precise details, I would be glad to provide you with them
directly. In the mean time, I have recently put a feature on my web page
(this is not a commercial plug) that will follow the complete rebuild of an
XK engine (140MC in this case), from disassembly through to completion. I
will include costs, product information, tips, and all the little things we
will do to try and make the engine the best one we have ever built (i.e.
the next one).
Best Regards,
Dan Mooney
Classic Jaguar (USA), Inc.
www.classicjaguar.com