Tuning basics

Something you should know:
After every engine modification the CO% has to be checked throughout the rpm and load range to see if rejetting of the carburetor is needed. Any rich or lean mixture spots can seriously damage your engine. Setting up a carburetor properly is vital for the engine's life and is a specialist's job. However, with todays technology you can do this yourself. The "secret" is a lambda probe fitted to the exhaust. Click here for more info.

First some engine modifications where the engine internals are still left alone.

 

Air filter.
Fit a high performance air filter. Make sure it's fed with plenty of cold air either directly from a bonnet opening or using a tube. These filters don't have built-in sump breathers. The sump breather coughs out hot oily air which you don't want to feed into the engine inlet. The cheapest solution is to feed the sump breather back into the engine inlet through the airfilter (as per original). A better solution is to use a separate filter purpose made for sump breathing systems as can be bought from most performance airfilter manufactures. But these filters never keep oil the oil inside, especially on our boxer engines. The only truly satisfying option is to use an oil catch tank. This is a reservoir that catches the sump breather fumes, lets it breath with the outside world but directs the oil back into the engine (sump). Putting a high flowing airfilter onto a otherwise standard engine will normally not increase power.

 

Exhaust system.
Large diameter tubing and low resistance silencers, result in minimal resistance systems with low back pressure. Longer primary pipes before they join give more low down torque. Make sure both sides are equally long. Separate exhausts left and right should always have a balance pipe for decent cylinder filling at lower rpm. Putting a high flowing exhaust onto a otherwise standard engine will normally not increase power.

Lightened flywheel.
This improves acceleration. Effect is the same as the amount of weight reduced on the flywheel x total gear ratio, weight reduced on the car. The effect of a lightened flywheel can be noticed well even on a standard engine. But lightening the flywheel too much will result in in lumpy idling and less smooth pickup. Normally about 1/3rd of the original weight can be safely removed. While the flywheel is off, consider whether or not the clutch is up to the job.

Electronic ignition.
The 2cv can really benefit from a decent electronic ignition system. This results in less maintenance and a stronger spark.

 

Carburation.
The 2cv carb is very adequate. But this carb such as any carb has to be jetted correctly. Swapping the carb for a bigger one will give no gain (unless the original carb was not propperly jetted and the new one is better in this respect). Multiple carbs will give no gain, but they are usually fitted on shorter intake tubes.

 

Intake manifold.
Longer intake pipes between carburetor and head give more low down power but can reduce responsiveness. Short intake pipes (often found on twin carburetor systems) moves the power higher up the rpm range and reduces the torque spread. Putting a high flowing manifold (with a bigger or more carbs) onto a otherwise standard engine will normally not increase power.

Now we start modifying the engine internally. There are still plenty of bolt on modifications possible at this stage.

 

Displacement increase.
Overboring the barrels and fitting larger pistons will give more power but more importantly more torque. An displacement increase is a very good starting point for increasing the performance of your engine. Please note that bigger pistons are usually also heavier. As the pistons get heavier, the max rpm the crankshaft (crankshaft bearings and conrod bearings) can take will be lower.

 

Compression ratio increase.
This can be done by a number of methods:

1. Reducing the height/length of the barrels.
   This can be done by taking metal off the top of the barrels or machining the edge where the barrel sits on the crankcase. When used barrels are modified, take metal off the top, otherwise the barrels will need honing and new piston rings. When taking metal off the top of the barrels, make sure you get a clean surface finish. If not, the barrel will not seal properly on the head.

2. Fitting pistons with higher top.
   Not very practical, there are no easy available pistons for this.

Always make sure there is sufficient valve-to-piston clearance.

 

Camshaft change.
The camshaft has to be matched to the engine and what is required from the engine. A camshaft change really starts makes sense when other aspects of the engine have been changed as well. A camshaft with more duration / higher lift / more overlap / different ramp angle can improve power and torque. Camshaft profiles is an art in itself, and very few have mastered this art. Finding the right profile for the job can be very difficult.

• 2 cylinder engines:
  To change the camshaft, the engine has to be completely dismantled. When fitting a new or reground camshaft, be sure to use new / reworked followers.

• 4 cylinder engines:
  The camshafts can be changed without even removing the heads. When fitting a new or reground camshaft, be sure to use new / reworked rockers.

 

Cylinder head work.
When modifying the heads and or valves, make sure the valves and valve seats are suited for running on unleaded fuel. There are quite a few books around about cylinderhead improvement, so use them.

• Enlarged ports, ports matched to manifolds / manifolds matched to ports.

• Low resistance flow paths.
  Getting rid of those casting edges and making the turns in the system more open help the cylinder head to breathe properly.

• Bigger valves with different angle or 3 angle valve seats.

And if you really want to built a strong and powerful engine all parts of the engine have to be looked at.

 

Crankshaft work.
 

• Crankshaft balancing, lightening, aligning, reworked oil ways.

• Con-rod balancing and aligning.

• Improved bearing material.

But carburetors and mechanical ignition never really free the full potential of an engine.

 

Full engine management.
ECU controlled fuel injection and ignition. This is done with a programmable ECU (computer or black box) which is connected to all other hardware (sensors, regulators, etc). The ECU is programmed by laptop (usually) to give the right injector time and ignition timing according to engine load, rpm and environmental conditions. Getting an ECU from another car will not work since every engine has different fuel and ignition needs. 

All this extra power puts an additional strain on the engine so we have to take some precautions.

 

Temperature management.
Any power increase will also increase the amount of wasted heat. This heat has to go somewhere or the engine will overheat. Therefor sufficient cooling needs to be available. On an air-cooled engine there is not much else to do then cool the oil. To reduce oil temperature there a 2 basic options:

1. Increasing the amount of oil in the system. The easiest way of doing this is by fitting a larger oil filter. On 602/652 engines this involves modifying the oil filter bracket or making a new one.

2. Fitting a bigger or additional oil cooler. This can be done by taking of the original oil cooler and repositioning a bigger one in the cold air stream. Make sure there is enough protection from stones and such and use braided hoses. Another option is leaving the original oil cooler alone and fitting a sandwich plate under the oil filter. This is a plate with 2 hose connections which connect to an additional oil cooler. The plate can be fitted with a thermostat so the engine can get to working temperature easily and the new oil cooler only cools when needed.

Before and after making modifications to the oil circuit, measure oil temperature and pressure at several points in the system. This way you know what is happening under the bonnet. On any tuned engine, oil pressure and temperature should be visible on a meter in the dashboard. Warning lights alone are not enough, they will only light up when it's too late.

 

Other things you need to know.
Here are some things you need in order to understand and use the information given here:

• The 2cv, Dyane, Mehari, Ami 6 and Ami 8 are technically identical unless noted otherwise.

• If it says 2cv somewhere, 2cv, Dyane, Mehari, Ami 6 and Ami 8 is what is meant unless noted otherwise.

• The Ami Super is technically completely different from all the others.

• The combined name for the 2cv (AZ), Dyane (AY), Mehari (AYCA) and Ami (AM) is A-type.
  This is because all official Citroën type names start with an A.

• This pages deals mostly with post 1970 A-types. For information on using older cars and or parts don't hesitate to contact me.

• The 2cv AK (AK350) and AKS (AK400) have Ami chassis with Ami longer and larger diameter spring retainers.

 

The car around the engine.
Higher then standard output engines put an additional strain on all other components of the car. Tuning is not just about more power. The rest of the car has to be up to it as well.
Some questions which can help find the weak points on your car:

1. Have their ever been repairs to the chassis?

2. Is there any rust on the body?

3. Are the brakes, tires, driveshafts new or nearly new?

4. Does the gearbox make noise, or crunch sometimes?

5. What about the legal aspects of modifications planned?

If any of these points is not ok, you should get the car in good condition before you start to change anything.

 

Buying tuning parts.
When buying parts from specialists, find out how the warranty is. Tuning is a very easy way to make money for many people and can leave you with serious problems when their stuff breaks! Confident specialists will give some warranty. Also, how is the "track record" of this company? Don't just listen to what specialist tells you, ask around. Parts break, especially tuning parts. Ask around to see how warranty cases have been handled in the past. Know what you buy. Especially with camshafts this can be very difficult.