Citroen GS/Super Ami Flat Four

Discussion in 'General Auto Conversion Discussion' started by mz-, Jan 22, 2010.

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  1. Jan 22, 2010 #1

    mz-

    mz-

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    Everyone knows how the Citroen 2CV and Visa twins have been used for many single seater aircraft. This larger GS / Super Ami engine is a seventies flat air cooled four cylinder engine in the 1 litre class and could be an upgrade to two seaters with somewhat similar tech still.

    Interestingly, it has two overhead camshafts driven by toothed belts, and a single valve driving enclosure on both sides. I don't know if this means that it was designed for higher revs, meaning possible problems in aircraft use.

    Citroën GS + GSA boxer engine





    Comments?
     
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  2. Jan 22, 2010 #2

    Starman

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    It might need a reduction gear, at first I only noticed the rpm at max torque and thought it was rpm max hp.

     
    Last edited: Jan 22, 2010
  3. Apr 5, 2011 #3

    amphibian

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    I am a pilot , and also a Citroen GS owner. Infact I have had Citroen GS's in different countries around the world. I know the engines well from a driving in a car point of view.
    There have been people in south America whom have also used these engines in aircraft. They use reduction gears.


    Because it is a boxer engine, twin overhead cams is the logical way to run it, if you think about it. You have two banks of cylinders. The engines do rev exceptionally well. They thrive on high rpm's. They are sweet at 6000, 7000rpm plus. I used to cruise at max speed of around 100mph plus for hours , equating to around 6,500 I think from memory.I have even nudged speeds way over this down hills.
    This is based on the 1222cc engines that I have had. (I have also had cars with the 1015cc and 1299cc engines). In my "racing" driving style I used to take them way past 8000rpm. (Just to prove they could do it--ore for show off rather then gaining me quicker acceleration)

    I am saying this for a reason. Any rpms above 3600-4000 these engines love---especially 4500 plus. Beneath this they are a little coarser and less "dynamic". You expect this on any car, but because these engines really are awake and more responsive above this...you really want this rpm for these engines. So use a prop reduction gear to get your engine in this sweet spot of rpm...as naturally your prop rpm you don't want at these levels.

    My engine rpm choice for a cruise would be based on 4500-5000rpm if I was designing a plane, based on my knowledge of these engines in road use.

    Some engines seem to take a little longer to warm up than others ( I have never figured out why exactly--even when timing etc is all spot on, and swapping carbs over).So make sure you have allowed sufficient warm up time (obviously) if they are being used in aviation. When a little cold they can cough and splutter rpm *until* warmed up properly. This requires very dynamic playing with the choke cable in *driving on the road* conditions with varying rpms.

    I have driven cars with these engines for 19 years.

    One note of caution. I have found these engines bulletproof. I have done many thousands of miles in them. However twice in my life I have discovered that a *pattern* (non Citroen original rotor arm in the distributor.......(the plastic groove that holds it in place on the metal rotor arm body) has given way. "Intermotor" was that brand. The first time leaving me stranded the first time beside the road. The second time it obviously fractured leaving play in the rotor arm.....leaving me to limp home at about 1000 rpm max coughing and spluttering. Of course the motor factor shops said "we never had problems with this manufacturer for other cars". Perhaps most cars dont do 8000rpm plus.
    Fit only genuine Citroen parts for the rotor arms. I can not stress that strongly enough.

    *Earlier* 1015cc engines had an issue, in so far as the oil cooler/over cooling meant a very slow warm up. The carb is heated by a separate pipe that runs from the exhaust manifold and through the carb body...to get it up to vapourisation efficient temperature. Being a boxer engine the carb sits on top of the engine, and the exhaust drops out the bottom of the engine. So the carb is a long way for heat conduction from the exhaust. being an air cooled car, it has an oil radiator/cooler that sits behind the fan (attached mechanically to the crankshaft) in ducting. Early 1015cc engines hadn't quite got the balance right.

    Over time these carb preheat pipes can become clogged with deposits like "hard, cohesive, sandy coal"! This slows down warm up time as the hot exhaust gases can not feed up to the carb to heat it.

    In very cold winters (way sub zero) the engine can be too cold. The cooling fan (air cooled engine) overcools the engine. This results in poor fuel consumption. I once got an accurate worst case consumption figure of 16mpg (touhing on 12mpg once) in slow town driving (imperial gallons not US gallons). In general summer driving 32mpg was the norm for economic...and 28mpg if I was pushy, regardless of road type. (Motorway/main road/B road). So keep these engines warm. In aviation though you would not have the air cooling fan on. You would just have the exposed cylinder fins. So this may not be an issue at all. Please note this was never a reliability issue(the temperature)....but a fuel consumption and warm up issue.

    One hears of people worried about breaking cambelts with fatigue. In 19 years of driving 7 cars with these engines, this has never been an issue for me. I only have one Citroen GS now. It is 34 years old. I think the people that worried never replaced the belts.

    I have other cars ranging to 3 litre 24 valve V6 fast cars. But for me (in a car) the 1.2 litre Citroen GS engine is one of the most pleasurable engines to drive with. Drive a nice well set up one...you will love it. A rough Citroen GS will be one of the worst cars you have ever driven though. I still often prefer to use this car, for driving pleasure, than my other cars with engines that develop 333% more power (200hp compared to my GS's 60hp). It is a sweet engine . Aviation is more constant though in engine dynamics.

    Parts are harder to come by now...so I doubt many more people will be using them in aviation. Sadly I think it is an engine now that time has surpassed. I hope this helps anyone that maybe thinking about it. I love this engine in a car. I would love to fly a plane with one. However I consider that other more modern engines probably have more going for them in aviation terms.
     
  4. Apr 6, 2011 #4

    deskpilot

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    Well said Amphibian, a sweet engine indeed. It was years ago, and back in the UK when I had my GS Club. Like you, I drove it with passion, often red lining it. Never missed a beat. Much smoother than a VW and much lighter than a Subaru. I have thought about putting one in an aircraft but always came back to the need for a reduction box. As you say, they're getting hard to find nowadays, even down here in Oz where cars don't rust out. They usually reach the end of their road when the c/v joints give up the ghost.
    Given the chance, I'd drive another one, and put one of their engines in a plane.

    Anyone know what hp to expect when the hydraulic pump for the suspension is removed. Being as it delivers about 2000psi, it must be quite a drag on the motor.
     
  5. Apr 6, 2011 #5

    amphibian

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    Hi Doug,

    The increase in horsepower , I would say, is marginal with the hydraulic pump removed. I would perhaps say it is negligible.

    I used to remove the hydraulic pump when I dropped these engines into the Citroen 2CV. The 2CV uses a conventional master cylinder for braking and does not need the hydraulic pump and nitrogen accumulator spheres that the Citroen GS (and DS etc) has, as I am sure that you know. So I do have experience of that too.

    However I can not compare like for like......because I could never run the GS without the pump, or the 2CV with it. Different cars, different weights, different aerodynamics. So I have no hard facts on comparisons.

    Yes the pump operates at up to 2000-2500 psi. But unlike more modern Citroens that have larger pumps ......the actual pump on a GS is small. The number 4cc pops into my head. On a GS it is a single piston pump, (it is on the crank after all). Other later Citroens have multiple (chambered) larger volumed pumps.

    Basically look at your thumb nail. That is the profile/surface area roughly of the top of the piston pump for the hydraulics on the GS,and the stroke being (roughly) the length of your thumb from its lower knuckle to the top. Guessing 4cm.

    Removal is simple, but allow time as you need to remove the engine cowling to get to it. You take the pump out and then just make a blanking plate (flat so easy) to cover the "pump hole depression" in the crankcase where the piston was. I am sure you are aware of this as you have had Citroens, but I am spelling it out for others whom may not be aware.

    Yes I agree with you. I have never understood why this engine was not used more for homebuilts, whereas the VW unit is. Having also owned a boxer engined Alfa Sud Sprint in South Africa (The car/engine people rave about), my preferred engine was the GS. You won't hear many (former) Alfa owners say that! The performance was near enough identical. The Alfa just *felt* faster because it was lower, tighter and you did not float along on a bed of fluid, like only old school real Citroens can.

    My Alfa also died by throwing a rod through its crankcase in the semi desert areas a few hours from Capetown. I lent it to my flight instructor in South Africa whilst I was away. I don't think he checked the oil level that had to be topped up now and again. Flight instructors aye :devious: ;)

    As you in Australia, my current GS engine came back past you on the way back to the UK. As well as South Africa I used to live in New Zealand (brilliant gliding and flying generally :) ) I brought my DS back from NZ with my GS engine in the back.

    In my dreams, next time I go back to Australia/NZ I would like to fly myself like Sir Francis Chichester did. I definitely recommend reading his book.

    Mike
     
  6. Apr 8, 2011 #6

    deskpilot

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    Hi Mike. Looks like this may become just our thread. Maybe that's because this engine isn't generally known about, or that it's just too high revving and people aren't happy with having to use a big reduction ratio. Maybe it's just not a practical solution and parts are getting scarce. Whatever it is, I would still like to try and use one some time in the future. As you say, some have been used, albeit infrequently, in the past and to my knowledge, successfully. So, I ask myself, how can we make one of these engines more suitable for use in an aircraft?

    Question one. Taking that larger 1299cc as a basis, can it bore bored out to a bigger volume? If so, are there pistons and rings readily available for such a conversion?

    Question two. Can the cams be built up and/or reground to bring the max torque in at a lower r.p.m.? If so, is it going to lower the performance in any other way so as to make that mod useless?

    Question three. Would it be practical to turbo-charge this engine?

    Over to you. What do you think. Anyone else, your thoughts are also welcome.
     
  7. Apr 8, 2011 #7

    amphibian

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    Capacity can be bored out to 1400cc and 1600cc (max). *However* Citroen produced quality engineering. By boring it out you will reduce the integrity of the finned (air cooled engine) cylinders. One highly respected independent Citroen engineer site says the max bore out size will reduce the wall to 1.5mm and goes onto say it "will reduce reliability".

    The original poster talks of this as a 1970's engine. It was. However the Citroen GS/GSA was produced until 1986. The engine was produced, under licence, by Automobiles Craiova in Romania until 1990. A similar story in Slovenia happened, and I think the GS was produced until 1991 in Indonesia. Parts are not quite so rare as some people think.

    Turbos and fuel injections have been made. I read you can bump the power up by about 60hp with turbo.

    I think you can appreciated the quality of the original engineering in these clips and can "feel" the engine response.
    I am sure you can imagine this burbling sound at the threshold :) Perhaps you can see why I advocate the higher rpms for the engine. What is the point in having the engine held back, limited by prop speed.

    With these engines the hotter they run the better the performance. You can notice it. So high rpm good. Gives you a larger window then for performance and climbing, yet same time keeping the engine warm in descents.



    YouTube - Citroen GS Turbo

    YouTube - Citroen GS Fuel Injection Conversion

    YouTube - Citroën GS Advert

    Sideslip well.
     
  8. Apr 10, 2011 #8

    amphibian

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    To add further to what was said previously:-

    I apologise for the rambling nature of this text. It is actually quite hard to think about how to put complex ideas down without winding elaborations. According to records there are only 20 GS's on the road in the UK, so I figured I would put my 19 years GS engine experience down for all to see--before it vapourises. It is a collection of my thoughts. I put this down incase it is useful to someone at some point. I hope it is clearer than mud to read!

    During the course of my driving yesterday in my Citroen GS (with said engine this post is about), I drove it for 9 miles specifically attempting to evaluate its responsiveness at varying rpms, with respect to aviation, in light of this post.

    I will perhaps alter a little of what I said earlier. It is important to realise I still standby what I said earlier and the ease of high rpms for these motors. Previously though I advocated an aircraft engine (not prop) rpm cruise of between 4000-5000rpm. I would be happy with that still.

    However my judgement may have been slightly coloured by the fact that in "zippy" driving, you like the rpm to be at this level for instance response, being between max torque and power. I would be happy to extend my engine rpm window downwards.

    The unit still feels very smooth, and is obviously quieter, down to 3000 rpm. It was a sunny day here yesterday so all the car windows were open :) so noise is more noticeable. Pick up is compromised (for road driving conditions, as you would expect) being outside the torque band, with max torque being between 3250-3600 rpm depending upon the particular engine.

    From an engine balance/temperature maintenance and "pick up response" perspective I would not like to have this engine cruise rpm beneath 3000 rpm. It feels more 'wishy-washy and wallowy'. Beneath 3000 rpm it is not "on the ball".

    So therefore it would depend upon your propeller "window of use" envelope.

    Although 3000 rpm is sweet on this engine in the car, this is lazily wafting the car (even in top gear) at a fraction of its potential. However: how different would 3000 rpm be under more sustained loading is the point to consider. I know it is very sweet at 3600rpm plus under loading, because I have tried and tested that.

    In summary my recommendations would be:-

    Don't have your (Citroen GS) engine rpm in cruise beneath 3000rpm. These engines happily go *way* past 6500rpm ( I sometimes take my car to 8000rpm, but mostly change gear in when I drive energetically at 6000rpm- because it "feels" right).

    In order to prevent descent cooling at reduced rpm, you may want to perhaps set the figure between this and the ones I mentioned in previous postings. I would worry about setting my cruise rpm too low, because of excessive cooling.

    In light of my experimental car drive, I would perhaps now would narrow my engine rpm cruise to between 3500-4500. I do stress that I have not studied propeller margins and operating envelopes which obviously have to be considered in tandem.

    What I can say is never set your engine cruise rpm beneath 3000rpm for Citroen GS engines . The responsiveness goes.

    So surely , I am assuming, the best way forward is prop reduction gearing.

    Please note my ramblings are base on 19 years experience of *road* driving with these engines, and 22 years driving with other air cooled Citroen engines (the 602cc and 652cc units which have also been used in aviation). It is possible that those that have used these engines in aviation, may have found that they can operate at lower rpms happily, as the loading component is "prop thrust" rather than car weight, and so there will be different dynamics. I am purely trying to guestimate the rpm that I would choose from my driving experiences. (Yes I am a pilot too, but have never flown with this engine).

    I have also demonstrated that it is perfectly manageable to continue driving these cars on 3 and even 2 cylinders with the HT leads removed. I never tried one cylinder on the GS engine but on a side note on the Citroen 2CV engine which is 2 cylinders, I once drove 150 miles, mountain roads, on one cylinder after the spark plug blew out, taking the thread with it.

    One final point to point out. My engine temperature/cooling experiences are based on driving cars, with engines , obviously, in the car. The engine in the car does not have exposed cylinders to the outside air like in some planes. The engines have their own air cooling cowling. In the car the engine is actually overcooled. The cooling rate experienced in an aircraft may therefore differ.

    Don't bounce too hard on touchdown!

    Mike
     
  9. Apr 11, 2011 #9

    deskpilot

    deskpilot

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    Hi Mike, enjoyed your 'ramblings' but personally, I wouldn't put any weight behind the car v aircraft comparison. Too totally different environments. On the other hand, I viewed some of those Utube vids and found some interesting stuff there. Like the Subaru Fuel inject system, nice, but how does one take elevation into account. Does FI need altitude compensation? I'm no engineer and have never worked with injectors of any sort.

    I started to think along the lines of a turbo charged FI system with a reduction box, but then, would the extra power be sufficient to carry the extra weight?
    I've not come across any evidence that the engine was produced in Indonesia, where did you find that info. If it's correct, I wonder if the same quality of manufacture is there.
     
  10. Apr 11, 2011 #10

    amphibian

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    Hi,

    I am nothing to do with any Citroen car club, but I used to participate in some discussions last decade! There has been considerable work/research and practical tuning of all of the Citroen air cooled boxer engines, by engineers and enthusiasts alike.

    It is important to realise that all (*) of the Citroen air cooled engines (GS/Amis/2CV's/Visa (air cooled Visa that is)) have twin choke carbs (*except the very early 2CV's and other flat twins, to the best of my knowledge, being the exceptions).

    One choke opens up at lower throttle opening and then the other overlaps and comes in also with continued throttle application. This (possibly) gives you more re-jetting options *should* that be necessary.

    You can feel this in the accelerator pedal in the cars. It gets slightly stiffer when the 2nd choke opens up. One could power up to speed using both chokes, then de-power into cruise until you felt the 2nd choke close for economy.
    (De not confuse the term carb-choke with the different "manual" choke used for cold starting)

    Sounds perfect for aviation is you ask me.You have your climb out, cruise climb, then ease back onto one choke for economy and cruising.

    A whole myriad of carb jet combinations have been experimented with, tried and tested. People have also had one carb for each side of the engine also. Then of course there are the turbo and fuel injection systems that have been made also.

    There have even been Citroen 2CV's made with 2 spark plugs per cylinder, and 2 ignition systems also. An obvious requirement for aviation. There are also several independent companies producing electronic ignition systems for 2CV's. Depending how far one wants to go these could always be remapped.

    If one wishes to explore any of these options, it really would be worth trawling these sites. However once in a while I have noticed , even on some of the most well respected sites, that a fact is wrong. This is often based on proposed theoretical top speeds etc, where upon I have *proven* to the contrary. Please note I am not saying that one thing or another should be done, like rejetting etc. I am just saying there has been extensive testing done in the Citroen enthusiasts world on Citroen air cooled engines.

    One tip from the 2CV world. Some fully laden 2CV's, on struggling with steep gradients in the high Alps, used to remove the air filter. Some reported this worked very well to restore engine power.As pilots we are used to alternate air too! This could be a consideration for altitude too if you are concerned. For those that are unaware the 2CV engine is half the swept volume size/ and roughly half the power of a Citroen GS engine.

    As far as the Indonesian GS production goes. You can find some information on the net. I hope this works.

    mattysk.otripod.cm/types/abroad.htm
    Citroën GS and GSA by Mattijs Kemmink

    I have never been to Indonesia though, and so I wasn't there in 1991 to confirm this with my own eyes!

    Mike
     
  11. Apr 16, 2011 #11

    JMillar

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    Sounds like you are talking about it having primary and secondary bores? Very common on hot-rod type engines here. The secondaries are either driven mechanically from the linkage, which is what you are talking about, or by vacuum.
     
  12. Apr 17, 2011 #12

    Petrus

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    I have to agree with Mike about the GS 1220 engines. I have had three of these cars - engines never gave any troubles. 1) Engine revs: I once tried to over rev this engine, its rev counter registers up to 8000 if memory serves me right: I revved it many times way above this with not as much as a splutter - It really does sound sweet above 8000. 2) Cooling: I stay in South Africa where summer temperature can easily reach 30 C and up. I remember hearing a big noise with a slight engine vibration one day way back... the vibration disappeared and I could not find any problem, a week later with ave temperatures 25 to 30 C the engine seemed to loose power when doing hill climbs (harsh driving). When I pulled over smoke came out the engine compartment due to excessive heat. Only then did I discover the fan (20 years old then) had disintegrated a week earlier. We left it to cool and drove back home - did not use a drop more oil than usual! I am sure that modification of the exhaust system may provide max torque at lower revs, but I agree that 4000 up is where the engine comes to life. Top speed is quoted as 140 km/h for car but I have done 160 without any trouble. I would stick to the Weber carburetor with long induction pipes as this raises low end torque. Unfortunately I doubt whether a downdraft carburetor would work on a plane?
     

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