Tuning a R12 may be a little difficult.If you can find parts,a little easier.Main points are the engine,the suspension and the brakes.Let's start with the engine.The R12 production model is equipped  with the 73x77 1289cm3 engine.Increasing the power,acceleration and torque can be done by simply tuning it,or replacing the pistons,cylinders,crankshaft,etc.,with the 76x77 1397 cm3 of the R5(the engine block must be also replaced,or adjusted to fit the 76mm bore).(The 1565 77x84 Gordini engine also fits).The camshaft can be replaced with R15TL's(62/22 degrees,as opposed to 20/60 original),or with a R5's,but measure it carefully.The compression ratio can be increased to 10:1,but I don't recommend it.If you can get a 9,5:1 is well.(Get a specialised workshop to do it,never touch it without precision tools).A new plug set is absolutely necessary,try multiple electrode types from Autolite,or the fantastic W78G from Bosch.Do not put colder plugs.A thermic value of 170-200 is enough.The ignition setting must be checked carefully,with a timing light and precision rpm counter.Set the ruptor's contacts gap at 0.35-0.4mm,to have 60%Dwell.Never touch them again,as it modificates the initial advance very much.Calculate (depends on clutch plate diameter) the advance degrees in mm,mark the 5,10,20 degrees with fluorescent paint on the clutch edge(the 0 is marked),and check the centrifugal advance,which must be 20 degrees on the crankshaft at 2000rpm,vith the vacuum advance disconected.Increase or lower the springs in the distributor,until the values fit.The vacuum advance set is max 5 degrees at 850rpm,also check it.Using an electronic ignition (transistor switch) adaptable directly onto the existing sistem is very effective,and I strongly recommend to purchase one.Plug tension increases to 25-30KV,and cold starts are very easy.An electronic alternator relay(also a bigger alternator,replace the dynamo if you have one-it is not reliable and is very poor in terms of efficiency,a 60A alternator is good)and a good battery(I recommend a Delco Freedom >55Ah) is a must for constant 14V on the ignition system, making a constant relanti,and preventing overheating of electric components.Mount a new distributor and distributor cap,as they wear out fast(must be done before any ignition adjustment).The initial advance is a subtle adjustment,depending on the fuel used.My advice is to run on highest possible octane fuel,98octanes minimum.Carefully set the initial advance at 0 degrees(vacuum disconected),and progressively fast, accelerate the engine;increase it in 1 degree steps,listening to detonation sounds,if they appear(high pitched metallic sounds).If they are heard,return 2-3degrees and block the ignitor.Differences in 1-2 degrees ARE essential.Hear the engine in traction,and vary the initial advance,if the sound is weird,or there is a power or acceleration loss. I recommend around 5mm advance(clutch of 180mm diameter).It will increase power,and not affect the parts(detonation is a very serious problem,avoided with hi-octane fuel and rich fuel mixtures.Basically,it consists in explosions by compression,before the spark plug initiates the normal ignition-much like in a Diesel engine,caused also by deposits on cylinder and valve heads,and it can lead to piston failure).The advance can be increased if the carburettor is a multi-barrel,or rejetted.The carburettor is usually a 32 mm Solex.If you have a constant depression type S.U.,replace it.If you can make new intake manifolds,mount anything from 32 mmm single barrel to 4 barels(twin double barrel carbs-see R12Gordini),like Solex 34PIC,30CIC,40DDHE,even a 4A1 can be tried,or Weber 32/38/40/42/45 DCOE,38/42DCNF,32DIR/DARA.(Carburettor replacements require a fair amount of experience in carb jetting,and complicated procedures)-.However,the simplest way is to rejet the existing carb,the Solex 32 EISA .After many tests ,I recommend the following values: main jet 180,correction air jet 180(yes,the same value,for performance reasons,and allowing warmer plugs to be mounted),secondary jet 90,idle jet 40 or 42.5 ,acceleration pump injector 30-35Set the fuel level,adjust 12,7mm from the the carb lid to floater's mid ring.Adjust the acceleration pump so it can function throughout the entire rpm range(instead of cut at 2000rpm).(A very important part is a fuel filter before the fuel pump,and a fine particles filter before the carb,as rust or gasoline gums can obliterate the jets.Also wash the carb in special washer or 110octane fuel once a year-the brass jets and rubber parts in fuel only!).Carb tuning can be done checking the plug color.Up to 2000rpm,the idle jet can adjust the mixture.Color should be brown,with clean isolators;grey is too lean,black,smoked is too rich;oil on the plug means it isn't working.Set the plug gap to 0.5mm with normal ignition ,0.7-0.9mm with electronic ones.Check color after 10 min run on flat road,at constant rpm(1500,2000,2500,...5000-using a inferior gear at hi-rpms).Cut engine imediately after stopping the car,and watch the color.At high rpms it is better to be more dark,because the hi-speed air intake makes lean mixtures,leading to detonation,low performance,and engine overheating.A too lean or too rich mix will make the accelerations go slow;a very rich mixture changes the engine sound very much. See that all pieces of accelerator pedal,including cable,are intact.With this jet values ,you'll easily reach 100km/h in 3rd gear(1,48/3,777 gear ratio).If you can ,mount a air intake (see R12G);never lose the air filter-shortens the engine life for very little power boost.Lose the first exhaustion silencer,replace it with a pipe of the same length(once sold by the factory).Polish the intake and exhaust manifolds on the inside,and also piston heads and valve heads.Make sure the valves' springs are new-it is a major power loss reason.Make 1.5mm rings from brass,and place them under the springs-this will make for precise valve timing at hi-rpms,and the sound of engine will go a little whistling.Adjust the valve gaps(make sure the valves close firmly on their seat when you assemble the engine).Get rid of the heavy ventilator fan and mount light plastic one.For better acceleration,you can take some weight off the clutch plate,but do not exagerate-it will become fragile.Half a kilo will do,if it is a heavy one.If it is a thin one leave as it is.(I dont recommend rod thinning-use it to even the rod weights and just that.This gets us to piston balance-make sure the weight differences are under 1gm,best 0gm.)To end the engine section, make sure the distribution chain is new,or you'll get a trembling engine at all rpms,or backfires-if it has over 25000kms,change it.The oil must be in the SJ range,I recommend Castrol GTX3 15W40,or better Castrol Racing 5W60.A high pressure oil pump from a R18 can be useful.The original brakes are not very efficient.Get a double-circuit brake pump-like R Fuego's,or a larger DBX Bendix with by-pass(also putting a new back brakes limitator,with return circuit).If you want performant brakes,never put a servo-it loses pressure quickly and blocks the front of the car when it kicks in.The R12 is an under steering car,so if you need,increase the pressure on the back brakes from the limitator(it works from 32bar-no load to 40 bar-full loaded car).As always,theR12G's breakes(front ventilated discs,back discs) are an optimum,if you can find them.In all cases put new friction surfaces-Bendix originals.Get some alloy wheels-the steel original ones are heavy and not very confortable,as well as 4.5' in width ,with 155R13S tyres.Maximum width of tyres is 195 (to fit underneath the body ),so get 5.5' or 6' wheels with 185/60R13H or 195/55R13H tyres , (the entire wheels from R5GT Turbo-they are perfect).These values will increase significantly the overall acceleration, and ,mostly,the stability. New shock absorbers are a must. Get some Koni Reds,or equivalent,with action adjustment.In combination with the new tyres,you can correct the car to neutral steering,or even oversteering(if you lower the pressure in the back tyres).Mount the R12G stabilisation bars(25mm front,20mm back),or mount twin stabilisators in the back(2x14mm)-but it is not a very good choice,as the front is heavier.Check the wheels' angles on an electronic tester(make sure the front and back wheels are parallel,perpendicular on the ground,and the body's longitudinal line begins and ends at the same height(for this last one,3,15 degrees will do, or H5-H2=50mm).Test the car on low adherence road(sand,grass,etc.),perfectly flat,and see if front or rear goes first in a fast turn-be extremely careful not to flip the car on one side-an experienced competition driver gets it easy under control,a less experienced one,not.NEVER TEST THE CAR ON PUBLIC ROADS !-it is dangerous both for you and the others,as you don't know the exact reactions of a car during tests following performance improvement modifications.Do not exceed the speeds: 45 in 1st gear,76 in 2nd,110 in the 3rd,150 in 4th.You can check the maximum speed only on closed roads,specifically designed for this purpose,with adequate security-you don't have rollbars or airbags,and R12's frame,although crash tested,is not that strong.(If you can,get a 5speed gear box,also from a R12G-you'll not go faster in terms of maximum speed,but the acceleration will go faster-on winding roads especially).
                          RENAULT 12 TUNING