SNAIL

silc · Posted: Thu Oct 09, 2008 6:03 pm Post subject:

ah ok... thanks for the information Backfire... it's good to know then... Confused

Not sure what to do yet with this engine except for the pistons and barrels that I've received today with the full set of seals Twisted Evil

I'll put some pictures as soon as I can...
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Deuche Fester · Posted: Fri Oct 10, 2008 11:21 am Post subject:

I've been reading along the thread, some very useful information here. But one thing comes to mind, and i cannot help asking this. Why not just use a VISA block to gain 50bhp, in stead of using 9:1 barrels and pistons to only gain 32bhp ?

Currently i am planning the rebuild of my deuche, and apart from the optical stuff of channeling and repainting and all, i would like to start engine tuning as well as the others here.

silc · Posted: Fri Oct 10, 2008 6:08 pm Post subject:

Hello Dennis...

A visa engine is not the solution for me... As mention in the begining of my post and the post in "Your ride", I want to keep it origanl. I just want to improve it a bit with some fine tuning. A visa engine involves a modification of the gear box, or put the gear box of a visa... which I don't want to do...

9.1 compression pistons, custom air filter and exaust is just a way to gain a bit of power by keeping the original mechanic... more or less... Moreover I just want to cruise with the 2CV... not racing with it Wink

But if you do the change on your Deuch with a visa engine good luck and send us some pictures and comments... it would be very interesting!!!

Cheers bro...
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backfire · Posted: Fri Oct 10, 2008 6:45 pm Post subject:

But visa engine is so simple to use on 2cv gearbox. the only thing you have to do is make 2 holes for the ignition sensor, that´s it. Or if you want to keep org look, readjust the sprocket from the flywheel and install a 123 igngition with modified cam, that way it looks org.
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Lionel · Posted: Fri Oct 10, 2008 9:40 pm Post subject:

Matt Black · Snailer Joined: 11 Oct 2008 Posts: 25 Location: Holland

in my opinion, do it right, or don't do it at all..

just fitting higher compression barrels and pistons is a waist of money..

fit visa pistons and bored up 2cv barrels, fit a powerairfilter and breatherfilter, (K&N for example), put bigger jets in your carb, take 1/3 of the weight of the flywheel, and fit a bigger diameter exhaust, this should do the trick quite well...

Visa engines are ok, but good parts are getting harder to find, also the standard ignition system of the Visa is crap, but there's a kit available to fit a 123Ign.

Or even better, find a Ami Super chassis and fit it with the GS 1300 engine..
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EirikJ · Snailer Joined: 23 Jan 2008 Posts: 36 Location: NOrWAY

Kustombart · Posted: Sun Oct 12, 2008 2:10 pm Post subject:

First of all, let's get clear what we are talking about here, with a little theory.

Power = Torque x revs.

There, I said it. A lot of people have a hard time getting their heads around the "torque" concept. This may explain it a little. Torque values depend on how much fuel you can convert into mechanical energy per revolution. Power is the result of that torque, multiplied with the rpm. So, to increase max horsepower, you can either increase max-rpm or increase torque.

Now, what does it do, I hear you ask? Max horspower is only available at max rpm, so that (along with wind- and other resistance factors and gear ratios) determines your top speed. Torque determines your rate of acceleration, your "pulling power". It is useful at any rpm, for instance driving along at 80kms and wanting to overtake. When you press down on the pedal, it depends on your torque value at that rpm how the car responds. If you have low torque at that rpm, you may have to shift down from 4th to 3rd gear.

Back to practicality: I have had both AM2A (8,5:1) and AM2 (9.0:1) engines in the same car, with same carburettor (and jets), original airfilter and I can detect no difference in performance. Theoretically, increased compression means faster burning of fuel in cylinder, so better efficiency and more torque. There may be an increase in power and torque but I have not found it.

The biggest difference I have noticed is to first make sure that the engine is in good condition. Valve clearance must be set properly, you can test compression to see if the piston rings are still OK, set the ignition right, make sure you have the right spark plugs and that they are in good condition (as well as the leads and connections), clean airfilter, good oil filler tube and a clean oilcooler and decent oil to keep the engine as cool as possible. Clean the carb, fit a new fuel filter, check fuel pump membrane and check for air leaks around the carb. You may be surprised to see how much difference it makes (as noted before by my dutch colleague). Trying to tune an engine that is not already in perfect condition is useless.

What I have found in daily use is that an electronic ignition is the first thing to get, as it helps in starting (stronger spark), as well as providing better pick-up because of better ignition advance curve. Moreover, it saves you the trouble of adjusting and changing points, which is often, if you drive it daily.

If you are going to use the car for daily cruising, doing big distances occasionally and taking a lot of extra weight once in a while (friends or parts etc), you want to make the car more driveable. This means more torque over the entire rpm-band and the ability to do high rpms for a long time (for highway cruising).

If you want more torque, it is vital that you get more air into the engine first, then rejet the carb to get the mixture back up to the right numbers. The size of the jet determines how much fuel gets mixed into the inlet air. The bigger the jet, the more fuel you can add, limited only by fuel pump capacity (in extreme cases).

In the 80's carbs were set up not to get max performance out of the engine but to meet emission standards, depending on the country of sale. It may be set too rich, to minimize NOx emissions or maybe set too lean, to minimize CO emissions (not to be confused with CO2, where the light 2Cv performs very well). Rejetting your carb on a rolling road, or using a lambda sensor can give you up to 3hp more, cheap & easy!

However, the 2CV engine is set up as standard to make the most torque at the widest rpm-range, to make it as driveable and flexible as possible. Changing air filters and exhaust is a way of increasing torque (and power) at some point in the rpm-range but it doesn't necessarily mean it wil be nicer to drive! Any tuning of inlet and exhaust (and rejetting carbs after!) usually means shifting the peak torque to higher rpms. This means engine will be more racy but will have to be revved to get performance. In extreme cases, your girlfriend may stall it while driving away.

Also, if you load your car up fot the holidays and drive in heavy traffic, having low torque at low rpms is a real pain because you will have to let the clutch slip a lot and downshift every time you encounter a hill.

The easiest and cheapest way to increase torque all over the rpm-range is a "power tube". Cheap and easy to install, it will gain you 2-3 hp (with rejetting of carb) without any other modifications. It doesn't increase inlet airpressure as some people think but it provides the engine with cool air, which holds more oxygen. More oxygen means more fuel can be burned, over entire rpm-range.

Also a good way of improving torque over entire range is to increase engine volume. Visa pistons and cylinders do that very well, fitted to a 602 crankcase. Why not fit a Visa engine instead? Must be easier. Yes it is but the Visa engine has a heavier crankshaft and can run less rpms. Therefore, you gain torque but lose max rpm and the power output is about the same.

Matt black mentioned reducing flywheel weight. This does nothing for your torque or power output but it does change the behaviour of your engine. The flywheel is there to make the engine run more smoothly. It is a big weight which spins fast and it makes it more difficult to increase or decease engine speed. Therefore, it absorbs the blows from the two pistons per four crank revolutions and makes the whole thing run smooth.

Resisting changes in engine speed makes it hard to rev quickly. You will notice with a 2CV that it takes a while for the engine to come up to speed when you press the loud pedal. Decrease the weight of the flywheel and it will start to respond better and feel more racy. There is a downside. When you approach a hill, a heavy flywheel will resist changing engine speed so your car speed will be maintained. Lightening the flywheel means you will lose speed faster and it wil APPEAR you have less torque.

Finally, I want to say something about the nicest (and most costly) way of improving max power through higher rpms: engine balancing. Normally, cast connecting rods, crankshafts and pistons are a little unaccurate when produced. They may vary in weight, just a few grams but this will cause vibration in the engine. Vibration takes energy away from the process of burning fuel, so essentially, it means a loss of power. If you take the engine apart, you can weigh the pistons and connecting rods to match them by taking weight off the heaviest one. A crankshaft can be balanced, too but only dynamically (like a wheel is balanced). This is done n the factory, but not to a very high degree. It means a lot of work but can reslut in a very smooth engine. You may have to change to stiffer valve springs if you get to very high rpms.

As for reliability and ease of repairs, I have to say that if you suddenly knock a hole in your sump, you are doing something very wrong with a 2CV engine. If you maintain a 2CV engine the way it was described by Citroen and not tune it to run 45hp @ 8.000rpm, little can go wrong.

I have driven thousands of highway kilometers at full speed, on 95 octane unleaded, often in 30 degree heat, many times with two people and holiday luggage and always lugging around a heavy Acadiane chassis and wooden body. I always drive pedal to the metal (traffic alowing) and I do not have excessive valve wear, loss of compression, it doesn't use oil and it starts and runs smoothly.

This is my experience of daily driving more or less tuned engines in the last years and driving tuned 2CV's, Burtons and Lomaxes while working for Burton Car co.

And they all lived happily ever after. The End
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Matt Black · Snailer Joined: 11 Oct 2008 Posts: 25 Location: Holland

did you really just wrote all that? Wink

but as Bart states, it's hardly noticable if you only change your pistons and barrels, that's why i said it's a waist of money to do only that.
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Kustombart · Posted: Sun Oct 12, 2008 3:42 pm Post subject:

silc · Posted: Sun Oct 12, 2008 7:02 pm Post subject:

Well... what can I say except: nice post and thank you Wink

But I still keep the idea of 9:1 pistons... My 2CV is originally tuned with a 7.2:1 ration. So I should see the difference... and as I have received the set already... Razz

After readding your post, the only thing that I might change in my plan is the electronic ignition system... but I'm not sure... If you keep the original system and if it is well tuned, there is no troubles... I had mine running for 9 years as daily drive and I never had troubles.... even after 3 month without starting the engine and in a cold weather... anyway... This post is very interesting and I need to think of all of that cause the main idea is to get a nice running engine... and not a racy one...
Cheers mate
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Yeah baby yeah!!!

Harley · Posted: Mon Oct 13, 2008 5:41 am Post subject:

Kustombart · Posted: Mon Oct 13, 2008 9:48 am Post subject:

@silc: sure dude, do what you want! I don't know everything, I can just say what my experience is. Let us know how it turns out!

@harley: any decent engineshop which does tuning would be able to do it for you. It's quite common practice on racecars. It's even better to do it dynamically with the conrods connected. Warning: it may be quite expensive.
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EirikJ · Snailer Joined: 23 Jan 2008 Posts: 36 Location: NOrWAY

Kustombart, thanks for you're opinions about the 9:1 vs 8,5:1 and the "powertube"!
Since I havent tried any of these things my self, it's great to hear from others who have.

0,5:1 increase in compression is not much, and I did not think it would be noticable. But many have said so, even ECAS in uk, so who am I too say otherwise Wink

So it seems bigger bores and pistons is a more safer way to go for noticeable increase in power.

So, Matt Black, (should have been Jack Black Laughing

) is it safe to bore up standard 2CV sylinders to fit visa pistons? The walls are thick enough?
And where do they sell Visa pistons and rings? The rings must be compatible with the 2CV-sylinders. The Visa and 2CV sylinders isnt of tha same material have I heard.
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EirikJ · Snailer Joined: 23 Jan 2008 Posts: 36 Location: NOrWAY