SHORT 2CV TUNING GUIDE
BY ECAS
2CV PARTS
This is a short & basic guide to tuning the 2cv engine based
on the writer’s experience building endurance race winning
motors (our car wins the 2001 24hr Mondello park race 22
miles in front of our nearest competitor!), read
garbage elsewhere (elsewhere on the internet!) but believe what
you see here!
Email us if you can find non - misleading 2cv tuning info, we
will link to it!
Q1. Can I buy some
bolt-on goodies to make my slightly tired, oldish 2cv engine take
me, the family and our trailer tent up hills on the motorway at
70mph?
Q2. What about a more
open sports air filter?
Q3. That exhaust box
under the gearbox is very restrictive, a good two into one system
should work wonders?
Q4. I’ve heard you
can bore out 2cv barrels & drop in pistons from a 652cc
Citroën Visa.
Q5. Can I lighten the
flywheel to improve power?
Q6. Can I fit twin
carburettors?
Q7. What about
gas-flowing the cylinder heads?
Q8. Can I change the
camshaft to get more power?
Q9. Can I raise the
compression to increase power?
Q10. Can I get a power
increase for free?
Q11. What about
‘tappets’, I’ve heard you can get more valve lift
if you set them with smaller clearances.
Q12. Can I fit bigger
valves to the cylinder head?
Q13. Ignition timing,
will advancing the ignition a little extra help performance?
Q14. If I increase the
2cv's power output do I need to add extra oil coolers or larger
oil filters?
Q15. Can I fit the
Visa 652cc engine to the 2cv?
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A1. SHOULD I BUY BOLT ON GOODIES? No, but a
set of new piston rings, a de-coke including valves ground-in and
a new engine breather will probably work wonders!
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A2. DO I NEED A 'SPORTS' AIR FILTER? Stick to
the original system, ensure pipes & clips are intact, rolling
road testing has shown it to be the best. A more open filter will
give you no more than an impression of speed by loud induction
roar and a constant smell of petrol. Many ‘project’
cars suffer bad running due to poor air filter design and removal
of the carburettor – warming exhaust manifold balance pipe.
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A3. IS THE EXHAUST RESTRICTIVE? Stick to the
original crossbox unless going for a camshaft change, the exhaust
is not restrictive to the breathing capacity of the 2cv engine,
indeed if replaced with a ‘large bore’ system it just
serves to slow down gas velocity – the last thing required!
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A4. BIG BORE? This is possible but it’s
not that easy, firstly the outer barrel wall of a 602cc
2cv6 (74mm bore) is the same dimension as that of a 435cc 2cv4
(68.5mm bore). 2cv4 in standard form does not suffer partial
seizures, 2cv6 sadly does. Visa pistons are 77mm bore size,
taking another 3mm from bore diameter causes barrel wall
distortion when hot which is aggravated by the head capacity of
the 2cv6 being smaller than the Visa, more compression = more
heat! Visa pistons also weigh 140grms more per pair than the
equivalent 2cv6, at approx. 5000 engine revolutions per mile it
is possible to work out a power loss simply because of the
extra piston mass changing direction at the end of each stroke!
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A5. LIGHTEN THE FLYWHEEL? Yes, lighten the
flywheel to give instantaneous faster acceleration, no more power
though and you’ll loose tractability up hills and in city
traffic.
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A6. FIT TWIN CARBS? Both Lomax & Blackjack
Avion kit car makers make twin carb. set-up for their 2cv based
kit cars, we have no experience of direct comparison with
original Solex set up. Forget any other substitute central
carb. though, the twin choke standard Solex is eminently
tuneable. A full fuel injection system will be available
shortly! (Not suitable for road cars yet).
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A7. GAS FLOWING? Attempt this only if you
really know what you’re doing! In most cases you’ll get
a drastic loss of mid range torque if you simply make the head
‘flow’ more volume, removal of the seat inner diameter
takes away a ‘squeeze’ point and stops the charge being
trapped in the combustion chamber.
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A8. CHANGE THE CAMSHAFT? Yes but the way this usually
works is to allow the engine to rev. higher, producing more power
at those higher revs. there is always a compromise, that is the
loss of mid range torque you can regain some of this by
increasing the compression.
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A9. INCREASE THE COMPRESSION? Now we’re
barking up the right tree, this is worth doing, the
standard UK market 2cv6 has 8.5:1 compression ratio, 9.0:1
barrels & pistons are inexpensive, fitting these gives a big
improvement with no need to change carburettor jetting.
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A10. CAN I GET SOMETHING FOR NOTHING? Not
quite, but you can ‘skim the heads’, well not exactly
but this is a generic term for what you can effectively do.
Remove cylinder heads and barrels, about 30mm above the end of
the barrel is the ‘shelf’ where the barrel mates to the
engine block, you can have 0.30mm removed from this surface for a
useful power gain. Your engine will now be 0.60mm shorter between
each inlet/exhaust port so some skill may be required to juggle
manifold to fit properly. This mod. requires no jetting changes.
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A11. WIDER TAPPET CLEARANCE? Quite the
opposite, setting valve clearances tight will give inaccurate
valve timing, particularly on older engines with worn cams and
followers resulting in power loss and burnt valves. You should
set 2cv6 valve clearances at 0.20mm minimum but ideally 0.30mm
for best response.
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A12. BIGGER VALVES? Yes but it will only help
performance with a full race camshaft, turbo charging or
supercharging, 2cv6 valves are big enough for all other uses.
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A13. IGNITION TIMING? Keep within recommended
maximum advance, experience of UK 2cv racing has shown that
optimum maximum total (this figure includes the initial 8
degrees static) advance is 33.6deg. before top dead centre, in
practice this equates to 10 flywheel teeth (before top dead
centre).
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A14. EXTRA OIL COOLING? No you will
not need this for even a fairly highly tuned 2cv6 motor since the
forced cooling (by fan) is immensely efficient, the oil cooler is
fitted immediately behind the fan (has no thermostat so
circulation starts immediately).
For kit cars where the engine cooling fan and ducting are removed
then you can have trouble, principally though with overheating of
the barrel underside which can distort & cause partial
seizure, sadly no amount of extra oil coolers or devices to
increase oil capacity can cure this - only the passing of copious
amounts of air - the way the engine designer intended!
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A15. CAN I FIT A VISA 652CC ENGINE? A
Visa 652cc motor has the same stud spacing to fit the engine to
the gearbox, it also has 2 cylinders, for the rest of it, well
it's like fitting an engine of a completely different make! The
Visa was often bought by an ex. 2cv owner who believed the 2cv
went for ever with no maintenence and carried their belief to the
Visa!
Visa engine problems
include:
1] Badly worn camshaft because the engine was reliable it did not
break down and get a service, moisture in the oil vapourises and
pushes all the oil away as the camshaft moves the cam follower.
2] Excessive piston ring wear because the nicasil lined aluminium
remains abrasive and does not hold oil like the cast iron of the
2cv, worn rings means excessive oil consumption - no oil means
crankshaft dead!
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Go to 2cv accessories.