Just reading this post, never knew I'm having vulcano's in my engine .
Now I know where all the power is comming from.....

Seriously, there are many things to increase power from these little bastards, it's a shame we don't know all the in and outs to do it right......

Reading this I believe with

modified cam
modified pistons and barrels
electronic injection and ignition
modified exhaust.....

well about 45 hp out 602 cc with 2 fingers in your nose and over 20km at a liter of petrol????

All this trauma for what?

Keeping us from the street (Dutch saying)

Once upon a time the 2cv was 1 of the most fueleconomic cars of the world.... nowadays it isn't by far, a beamer 5 series uses the same amount of fuel!!!! All I want to do is bring fuelconsumption down....

I think in about 3 or 4 years we pay 4 euro's for a liter of petrol so 3 litres less at 100km will save you 12 euro's..... and ofcours I'am having a lot of fun/satisfaction programming these little microcontrollers....

Who has the most cars on their signature?

I run 9:1 in my turbo 2cv...

Yes how simple can it be.

Anyway, if we can go back to the question originally posed by azuiper, didn't he specifically request advice about increasing the compression ratio by machining the barrels, as his existing pistons and barrels are perfectly servicable?

I don't understand why some folk have such a problem with this, considering that every engine used for 2CV racing in the UK during the last 20 years has had its barrels shortened and the cylinder heads machined as well.

Much the same story in other branches of motorsport, particularly those using motorcyle engines, which is in effect what a 2CV engine is...
In some instances, technical advice on altering the compression ratio ( and other details) was available direct from the engine's manufacturer.
http://kawtriple.com/mraxl/porth2tune.pdf

Those 7.9:1 pistons were designed to allow an engine to run on 91 octane unleaded fuel without altering the standard ignition timing .
Since 95 octane is available everywhere in Europe, it's azuiper's choice if he wishes to modify his engine and regain that 'missing' horsepower, isn't it?

ken

So next question...... what gives you more power....

9:1 compression 36 degrees of advance ( engine just not pinking)
11:1 compression 32 degrees of advance ( engine just not pinking)

or why not 12: 1 at 27 degrees


(advance numbers are guesses but you know what I mean...)

anyone......

on our pump petrol a 9:1 needs about 32* and 8.5:1 gets up to 34* its a toss up as to which produces more useful power

ipgo
afraid I'm 'having lots of fun' getting my income tax & VAT returns sorted before the deadline of 31st Jan at the moment, but this article should give some pointers regarding your (hypothetical?) question.
http://www.contactmagazine.com/Issue54/ ... asics.html

I found the most interesting sections to be those covering "location of peak pressure (LPP)", "minimum spark for best torque (MBT) and also the limitations of the 'hemi' cylinder head design, in particular its tendency to suffer from detonation when the boundaries were pushed...

ken

edit, copied and pasted that last section
CHAMBER DESIGN
One of the characteristic chambers that people are familiar with is the Chrysler Hemi. The engine had a chamber that was like a half of a baseball. Hemispherical in nature and in nomenclature, too. The two valves were on either side of the chamber with the spark plug at the very top. The charge burned downward across the chamber.

That approach worked fairly well in passenger car engines but racing versions of the Hemi had problems. Because the chamber was so big and the bores were so large, the chamber volume also was large; it was difficult to get the compression ratio high.

Racers put a dome on the piston to increase the compression ratio. If you were to take that solution to the extreme and had a 13:1 or 14:1 compression ratio in the engine pistons had a very tall dome. The piston dome almost mimicked the shape of the head's combustion chamber with the piston at top dead center. One could call the remaining volume "the skin of the orange." When ignited the charge burned very slowly, like the ripples in a pond,, covering the distance to the block cylinder wall. Thus, those engines, as a result of the chamber design, required a tremendous amount of spark advance, about 40-45 degrees. With that much spark advance detonation was a serious possibility if not fed high octane fuel. Hemis tended to be very sensitive to tuning. As often happened, one would keep advancing the spark, get more power and all of a sudden the engine would detonate, Because they were high output engines, turning at high RPM, things would happen suddenly.

Hemi racing engines would typically knock the ring land off, get blow by, torch the piston and fall apart. No one then understood why. We now know that the Hemi design is at the worst end of the spectrum for a combustion chamber.