Supercharged Blackjack Avion

[SILLYCVS]

If you look on the 2cv forums you can buy a ignition system around £160 ish that you alter to suit your requirements with a lap top,that is proving to be very popular and giving good results by all accounts

Whats the make?

[andrewc]

I think the ignition being referred to is the 1-2 spark system I mentioned earlier in the thread. I looked at this, but didn't like a couple of things about it, like welding a flag to the flywheel for example. I have no complaints about the prototype 123tune unit I'm using and that hasn't been the source of my problems - it was very simple to install and program from my iphone and the boost retard function it provides seems to be working fine.

[notsmartcar]

Was on international2cvfriends.com. Look up technical then 1.2 spark topic under lgpo . If it's not for you that's fine,l should have read all your thread , out of couriosisty have you spoke to Allan at silly2cvs to save time and probably money ... how ever keep up the good work with it becoming more than difficult to get Swansea to accept a larger capacity engines than left the factory nowgetting more power your way will be the way to go

[andrewc]

So its about time for a further update.

I've not touched the Avion much for the last twelve months for a variety of reasons - family, work, other car projects, etc., but if I'm honest the big issue has been my failure to make any headway against the problem of getting anything like a stable idle. When started in the garage the car continuously ramped up to 5000-6000 rpm before falling to 1000rpm and then ramping back up to peak rpm again every few seconds - quite disconcerting to me, my family and probably the neighbors and it also tended to rule out trying to work on the car after my daughters had gone to bed. I'd go out to the garage whenever I could find a suitable window and spend an hour or so playing around with SU needle, timing, mixture etc. plus hunting induction leaks with WD40 and get precisely nowhere. Eventually I stopped going out altogether for 6 months or so. The symptoms seemed to indicate a very weak mixture, and I ended up trying AAA and AAB needles, but that didn't really help. There are reams of internet pages devoted to "blower surge" but because they all relate to 6 litre hemi V8's in powerboats or drag racers its hard to believe it can be read across to a 602cc flat twin.

On Monday this week I had another go, and took the airfilter off to try and see how much the needle was lifting and how much I needed to lift it to drop the idle -something I should have tried sooner - the answer was all the way to the top. During this investigation I blocked off the entire intake mouth with my palm and discovered two things - firstly the "suck" was extremely powerful, secondly the engine carried on happily running. So I obviously had a massive air leak somewhere, much bigger than the hose/gasket type leaks I'd been hunting with WD40.

The only candidate I could think of for such a leak was a small aluminium plate I'd used to blank the underside of the supercharger outlet manifold. This was originally blanked off with a rigid, tough OEM plastic moulding much to deep to fit on my installation. This plate is buried under the manifold and not visible without stripping everything off the supercharger on my car. I got back out to the garage late on Monday night, got the manifold off and found the plate had indeed distorted, leaving a 1/4" gap on two sides of the base of the manifold. I've tried to attach an image showing the issue.

I went back out on Wednesday (note the adherence to convention regarding the sanctity of Valentines Day - thou shall not dabble in the shed/garage) and replaced the 2mm ally plate with some 1/8th mild steel, and bolted everything back together. I also tapped an additional hole in the manifold casting to ensure it was less likely for the plate to lift off the manifold face - the original plastic moulding was so stiff it was only secured with two screws. 22:00 was too late to fire it back up, so I didn't get to try it until Thursday. I put the timing back to 2015 settings, crossed my fingers, fired it up and it idled happily at around 1000rpm. I felt elation and frustration in roughly equal proportions. Elation that I'd tracked down the problem, frustration that I hadn't found it sooner.

With hindsight I think I can now piece together the sequence of events as follows. I commissioned the car in 2015 with a vee belt drive to the supercharger which was prone to belt slip but did provide boost sometimes. During initial running in 2015 I did experience one big backfire/blowback from pre-igntition, which probably blew off the plate. I hadn't fitted a blowoff/popoff valve - when fitting the charger my research seemed to indicate some do, some don't - and the plate obviously was the weakest point between combustion chamber and supercharger. Following this the engine still ran, although pinking symptoms was worse, and I seemed to have lost boost. At this point I decided to convert to polyvee to eliminate belt slip, and everything got even worse - I'm supposing because I did improve drive to the charger which sucked in more air, weakening the mixture even more and promoting the scary "blower surge" characteristics.

I will now be fitting a blowoff valve twixt blower and engine, and then it'll be an MOT for the first time since 2015. They say confession is good for the soul, so this thread must be doing mine a power of good - it all now seems so obvious what the problem was. How I wish I'd tried entirely choking off the carb intake earlier.

Still tis foolish to repine - the man who never made a mistake never made anything and hopefully its better news from here on in

[SILLYCVS]

One day you'll look back and laugh, or sob in corner, lol, keep going nearly there

[QFAD]

Hi Andrew,

Thanks for the update, was wondering how things were going.

Rabbit holes and unforeseen dramas are all part of the journey when delving away from OEM specs. My own assumed straightforward conversion from the Solex to an SU experience learnt those lessons. But overcoming the issues is so rewarding - the eureka moment when you discover why the weird symptom is occurring is just priceless (and as you say also frustrating!)

Looking forward to your next instalment.

[andrewc]

Blow off valve has now arrived. I'll see if I can fit it next week.

Thought an updated video showing polyvee drive and better connections between the carb, blower and inlet manifold was a good idea - the first video is nearly at 9000 views, which my partner says just goes to prove there are a lot of weirdo's out there

New video link here [https://youtu.be/q9P3HZ3c6Fo]

[howardjs]

Hi Andrew,
Just followed https://youtu.be/q9P3HZ3c6Fo

If I were an American I would give it an "Awesome"! But as I'm a Lancastrian I'll give a Well Bygum...
Can we look forward to a Six Rivers Blower Run?

BTW are you doing anything to increase the engine cooling, bigger oil cooler maybe with oil stat ...

Great job
Howard

[david]

On the supercharged Triking, Alan added a steam system for cooling the valves...into the intake..tank,water, element...and presume a switch...

[and eventually fitted a bottle of nosgas.which made a big difference...]

[andrewc]

Thanks for the additional comments. I will be on my Dad's River Run, but I've given up predicting which car I'll be in. It would be nice to be in the Blackjack but lets see.

Back when I was struggling with "boost surge" I did consider water injection, but I'm only boosting to 7 psi and the 2cv compression ratio is quite low at 8.5:1 whereas I think Guzzi vee twins are up around 10:1. I have put some octane booster in the tank though. I believe the original builder fitted a bigger oil cooler so I'll see how that goes.

Anyway, blowoff valve is now fitted. It's supposed to be a replacement for a VW 1.8T part, made in China and came with three different springs, so I took some dimensions and then calculated the different rates. The valve is assembled with the chosen spring compressed by about 15mm. The ID of the valve inlet is about 21mm, so its just a case of working out csa and then doing some sums. I've gone for the weakest spring, which by my maths should allow the valve to open if it sees 10psi. In the OEM installation there is supposed to be a manifold vacuum connection to help pull it open, but I don't need that with it just acting as blowoff protection from the combustion side.

Anyway time for some photos. First image shows the new plate I fitted to the supercharger outlet manifold, complete with extra M5 screw in the corner that was blown open. Next to it is the original ally plate sans additional screw hole. Next couple show the blow off valve installed - its black so a bit difficult to see, but hopefully the installation can be understood. An exhaust hose ducts any gases/vapours away from the exhaust and cylinder.

I haven't actually run it yet, maybe tomorrow