SPITFIRE MkIV & 1500

EXHAUST SYSTEM . K&N SPORTS AIR FILTERS . SU CARBURETTORS
18
Performance
& TUNING
Engine Tuning continued...
A: Sports Air Filters, Extractor manifold and Silencer system.
B: Carburation enlarged or changed, as model requires.
C: Modified Cylinder head, to improve the gas flow efficiency and
economy through the engine.
D: Performance profile camshaft to allow the engine to produce improved
power at higher RPM.
If you prefer to install the camshaft or cylinder head in a different order,
then the power increase will be altered and the full potential of the
component may not be realised until it's associated component is
installed.
On some models the installation of Weber or Dellorto carburettors at an
early stage can be very worthwhile if you are contemplating carrying out
a full conversion later. We list the recommended sizes to be used for each
model, there is not normally any benefit in going larger than this unless
the car is used for outright competition use where the top-end power can
be improved with the obvious loss of low speed tractability.
The engine can be improved easily, but do not forget to also look at the
rest of the car to make sure that the road holding/braking is going to be
adequate to cope with the new performance.
Exhaust System
Sports Exhaust Manifold
The fitting of an extractor manifold is the first step to improve power
output. They improve exhaust gas flow allowing the engine to breathe far
more efficiently. Our large bore 4-2-1 design tubular manifolds are
produced using mandrill bending equipment to give full diameter pipe
bends.
Sports Exhaust System
All our TriumphTune exhaust systems are of the straight through design for
the efficient extraction of gases with optimum back pressure for
maximum performance. All systems are supplied with clips and
mountings but when being use with the standard down pipe an adaptor is
required.
Twin GT 'Oval Box' System
This very efficient exhaust system has two 'oval' silencers (and 1.75"
diameter chrome tailpipes) that give a real sporty exhaust note, but is
within the UK noise regulations.
Twin GT 'Round Box' System
Although this sports system with its twin 'round' silencers & large bore
acoustic chrome tail pipes has a quieter exhaust note - especially useful
on long journeys, it is still a very effective performance exhaust system.
K&N Sports Air Filters
K&N filters - with their advanced filtration system, are acknowledged as
being one of the most efficient air filters in production, and are essential
for fast road & competition work. They use the suspended oil system of
filtering that allows the engine to breathe properly.
The elements must be cleaned and re-oiled (normally after approx. 12 to
15000 miles) using the correct fluids or they will 'clog up' impairing
breathing.
SU Carburettors
If maximum power from SU's is required, there have been a number of
articles (see Books & Manuals) about how to 'flow' these Carburettors
and, if followed carefully, will allow them to perform much better at high
RPM.
For road use, it is beneficial to replace the 'butterfly' with the plain type,
these are available from stock.
In some cases the fitting of 0.100 jets & needles to HS4 carburettors can
improve petrol/air mixture for maximum performance, this is usually only
required when used for racing.
SU Carburettors continued...
948/1147cc
These engines were fitted with twin HS2 carburettors (except Herald
models which had Solex). These can be retained, although for improved
mid and top end power the increase to HS4 1 1/2” carbs, as fitted to all later
Spitfire 1500 models, is worthwhile, but the inlet manifold must be changed
for the TT1358A - which will also suit Stromberg 150CD’s.
1300cc HS2 (1.25")
The twin HS2 Carburettors are adequate (just) for 1300 engines, but if good
performance is required then use the HS4 Carburettors. The HS2 can be
usable up to 'PlusPac B' (see Stage Tuning) but would be the limiting factor
after that stage. For some race regulations it is necessary for these to be
retained, if so, there must be a lot of work carried out to the internals to
achieve maximum power and air flow.
1500cc HS4 (1.50")
The HS4 when fitted to the 1500 cars can handle more power up to the
'PlusPac C' (see Stage Tuning) conversion adequately and be reliable (but
not with the Waxstat jets), without there being any major loss in
torque/power. Check the carburettor build number carefully before
ordering any parts. See also Fuel System in the Restoration section.
Needles
For use of alternative needles please refer to Page 41 in this tuning section
Grose Jets (Part Number GAC9201X)
Grose-Jets (with their modern technology) don't stick open like the old
'needle & valve' units. (Jets are sold individually)
Waxstat Jets
These jets can give problems on late 1500 models in hot weather/town use
as they tend to 'weaken off' the mixture too much when hot and don't allow
a good idle, this can be corrected in two ways; new waxstat jets or, our
conversion kit (TT1459) to normal fixed jets that will cure the problem.
BRADFORD 01274 735 537 . BRISTOL 0117 923 2523 . DARLINGTON 01325 281 343