So don’t invite passengers in to your 2cv, your lose torque up hill. You’ll get another talk when going down the hill, hehe
The exhaust system on A-models is only doing one thing, making the damn thing silent.
When the exhaust valve opens, the piston will easily push the gasses out with no help from the exhaust system. I’m still keen to learn about 2cv torque and exhaust
Where do you get your info from? I can’t find any on 2cv’s

Neither have we, and my Dad's been using them for about 25 years now!

I never fit a full length, although I do like how they sound, as they're more expensive, don't last as long (sideys last pretty much forever) and cost more.

Oolong is right, you dont need to read it in a book or cut an paste from some website.

Drive up a hill and note how long it takes
Go back down disconnect the heat exchangers and repeat, noting how much longer it takes.

The cross box provides a vital role in the exhaust back pressure making the engine produce its peak torque at a much more useable rev range.

My friends have spent many hours on a dyno with the racer and you have to spend a long time tuning a 2-1 exhaust to get the same performance as the standard exhaust, let alone better it!

Sean

Well I like to learn, please explain how? How do you measure that? Up a hill...??? Sorry for being sceptic, where does the back pressure comes from and how does that make the motor fun faster up at hill.

Power = work done/time
Moving a car up a hill is a set ammount of work (mass Vs gravity)
Time it and you get a rough measure of power, at least one that you can make a meaningfull comparison with. OK?

Hot expanding gasses travelling down a pipe, shut the valve closing the pipe and the inertia of that gass caries on down the pipe reducing the pressure behind the valve at the closed end.A restriction in the pipe can cause the pulse to bounce back up the pipe. A shock wave can pass up and down the pipe

2 pipes with exhaust gases doing as above alternating, join the pipes and as one pipe presureises it sends a pulse up the other one. Those pulses can be used to help/restrict the charge leaving the cylinder. Add valve timing : if the inlet and exhaust vales are open at the same time the inertia of the exhaust can help suck the inlet charge into the combustion chamber.

Exhausts are a black art that i know very little about( its like astro physics i claim to know nothing of it beyond that which i experience on my day to day existance) its not just about noise reduction.

Ok for the theory but as someone who clearly works on cars you should have experienced trying to drive a 2cv with a holed crossbox?

as for removing a rusty one:

Bigger hammer
Sean

Yes I repair 2cv’s every day, have also driven many A-models with holes in the front muffler. I have not notice any decline in torque, maybe I’m ignorant not paying attention to the performance.
I just can’t see why a 2cv should lose torque. The front muffle and the torpedo mufflers have no resistors inside them, which can build any pressure after the valve has closed. It is a straight pipe system with chambers to reduce noise. When the exhaust valve opens, the inlet is closing allowing the piston to push the gasses out. When the exhaust valve is closing and fully closed, the remaining gasses in the exhaust go nowhere until the next lot of gasses is pushed through. The gasses are hottest when leaving the cylinder and the exhaust manifold. From here they cool down and do not expand. On other cars yes it is a different matter but 2cv no.
I may be wrong but I would love to see some data on this. Maybe do a torque test in a test roller bench, that should give the correct result.

for the 3rd time -

Drive up a long hill as fast as you can and note how long it takes with a stopwatch.
Disconnect the cross box and do it again and post the results here!

No need to use a rolling road this will give you a measurable indication of the power the car produces( thats why car performance is often quoted as 0-60mph times) ok so not in Kwh or Bhp but in a measurable comparative way.
Your understanding of the 2cv exhaust is way too simplistic, and i fear a wind up.
If you still do not believe that the 2cv exhaust is actually a tuned component then im afraid there is nothing more i can to add to this and i feel that this is just goading me into some juvenile pissing competition.

Sean

Well back on track, its all done! thanks to tom for his guidance it worked a treat. took me about half an hour to free the sucker, best noise in the world to hear that thing hit the ground!

Wrote this a bit earlier, net went down. I see Sean has given a good description of the wave forms set up in an exhaust. I can't understand why you think a 2CV engine should be any different to any other four stroke motor in this respect, Viking. I take it you're a parts supplier/fitter, not a motor engineer?


Viking, I don't think you're a sceptic at all. You have your ideas, we have ours. You certainly have set me thinking how you know that a 2CV with just the header pipes goes as well as a standard one - have you really driven one like that?

Experience coupled with some knowledge of the science is my approach, together with a sensitive arse - my 'seat of the pants' can detect a slight drop in engine output as revs rise with the van side exit pipe rather than the correct, full length one.

This business of a collector box is an odd one, plus there is the joining pipe which runs under the carb, which some in the Specials club say has a smoothing effect on combustion as well as heating the carb area - having removed it they have found engines would no longer run right, often with straight through exhausts sans Xbox, it has to be said.

I have often wondered exactly what goes on with the Xbox which makes the engine efficient. I know the basics and so understand the huge complexity and in reality, the black art of exhausting an engine. There is a link here to exhaust tuning and one here which begins to suggest how complex collector boxes are, non-2CV related tho.

Neil says it all when talking about how hard it is to better the factory original. I would argue that goes for every other part of the car. Take the air filter - it's beautifully designed to swirl the intake air into a vortex.

I once bought a Special which had a pancake filter sitting in the airstream. The car struggled to beat 70mph, even with a Lomax 2-1 exhaust. After not a little experimentation, the car would pull 95mph, through use of a Peugeot air box/filter unit, a ram box and trunking.

As I said above, check out older Alfas to see the exquisite lengths they went to on the inlet tracts, and the exhaust headers.

I am a fully qualified Citroën mechanic back in Denmark a long time ago. First the common trade school but at the same time ‘’forced’’ to sit the Citroën school at Citroën Copenhagen. Here we learned how different Citroëns were and we were given strong lessons on how to work on ‘’their’’ cars.
Back to the exhaust. From memories, the ‘’extra’’ heating pipe also fitted on GS is to heat the fuel mixture to correct temp. The intake manifold is too long, reducing the temp before entering the cylinder. Yes the 2cv and GS can drive without but not properly. Most people wouldn’t notice.
Take the GS and the CX, they do not have the front cross box as they don’t need it. Only the rear muffler and it is used to reduce noise, nothing else.
I do understand the principal of the exhaust system but I am a stubborn bastard. Can’t agree that the 2cv needs the cross box in order to keep the torque but I have been wrong before and will be happy to test it one day.