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 CitroŽn 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?


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!

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.

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!

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!

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.

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).

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.

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.

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.

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.

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.

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.

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).

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!

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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2cv accessories.