Hi Chris & Kelly + List
When talking about different stages of cylinder head tuning the Moss
TriumphTune Performance Manual (my source of tuning information) has the
following to say for 'up to 1500cc models' i.e. spitfires:
"Work on the cylinder head centres around making the best diameter of the
inlet port to suit and give maximum power potential. We have found that
increasing the size of the inlet valve to 1.457" and very carefully flowing
of chamber/valve throat area will produce good torque and allow top-end
breathing for spring/racing use. The increase in exhaust valve sizes
improves the flow of the port for maximum power.
The Stage II Head - using standard valves reshaped is ideal for mildly
modified engine - standard or fast road cam. Anything over this type of
modification we would recommend the large inlet Stage III head for it's
improved flow by the reshaped TT valves and further modifications to the
chamber design. For competition use, the Stage IV head with large inlet and
large exhaust valves and special shaping of chamber is essential."
The various stages of car-tuning of course include much more than only
changing the head. fitting your standard spitfire with a stage IV head
wouldn't do much in increasing the performance I think if you do not upgrade
airfilters/airintake, carburettors, silencer, camshaft etc.
Anyway I think in general cylinder head tuning stages follow this pattern:
stage I: factory standard
stage II: reshaped and polished valves
stage III: increased size of inlet valves and possible reshaping of chamber
stage IV: increased size of outlet valves and definitely reshaping of the
chamber
probably also the valve springs are upgraded.
The manual also has a picture of a stage IV head showing the enlarged inlet
and outlet valves and chamber reshaping. If interested I can scan and post
it to anyone individually.
That's about as much as I could come up with. All book wisdom as my spitfire
is still standard after ten years of dreaming about more power. But back in
reality I always come to the conclusion I don't need more power for the kind
of (small) roads and cruising trips that I like to take my spit on. It would
only complicate things, make it (even :-) ) more dangerous. Before
increasing power I would like to increase breaking power, upgrade
suspension, etc. handling in general.
happy spitting,
Emiel.
1979 Spitfire 1500 TC Brooklands Green (just a shade more beautiful than the
ordinary British Racing Green)
Barcelona, Spain.
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