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Fuel injection for 36hp engine
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sleepywiesel
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PostPosted: Fri Oct 21, 2022 9:31 am    Post subject: Fuel injection for 36hp engine Reply with quote

In this thread I would like to introduce you to my thoughts of building a 36hp engine with fuel injection.
Feel free to share your thoughts and opinions!
So beetles with fuel injection systems are an old hat since there was the 1600i with electronic injection system.
But I am thinking about a mechanical direct fuel injection system for a 36hp VW engine using parts they had back in the day.
I came across the BD601 engine, made by Mercedes for several german war birds in the second world war. It was fuel injected. Due to that it had more power and a better fuel efficiency than carburettor engines.

What do I know so far?
-The Mercedes 300SL was fuel injected as well. Controls and the regulation of the pump are horribly complicated and without a very good machine shop and the possibilities of doing hundrets of tests it is not possible to modify the controll unit to fit a beetle engine
-The injection pump itself is not more than a modified diesel pump. There were mulitfuel engines that can run either on diesel or on gasoline. The pump need a special lubrication system for that.
-Porsche built 2 diesel prototypes (type 508) in the fifties. So it is possible to operate a dieselpump on a beetle engine. I wrote an email to porsche to find out how the pump is driven exactly. But they did not reply yet
-Due to space in the engine bay, money and time it will not be possible to do all the tests to build a propper pump control unit. So I have to stick to the regulation system of the ordinary diesel pump. That is just a membrane moved by to the pressure in the inlet manifold of the engine. That means the verhicle reacts very slowly to changes in load or engine speed. I thought that this is pretty much the same problem as with industrial VW engines which do not have acceleration pumps. So I decided to face the problem with a "hybrid system" consisting of a modified carburettor and the pump
-To feed the injectionpump I would like to use an electrical fuel pump which is hidden under the fuel tank
-The injectors will be fitted face to face with the spark plug, just like the double ignition systems do
-The injection itself will start somewhere at the end of the intake stroke to give the fuel enought time to mix up with the air plus to cool it down to decrease the compression work for the piston

These are the main points I have right now. I know that it is a very odd idea, but it stays in my mind for a long time now and it won't dissapear as long as I don't know if it is really possible or not.

I don't have a good engine yet to play around with. So this is just a theoretical thing for now.

What I can tell you is that this won't be a thread which will be updated every week. This is going to be a long journey.

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RolandD
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PostPosted: Fri Oct 21, 2022 4:16 pm    Post subject: Re: Fuel injection for 36hp engine Reply with quote

What is your year cut-off? The VW type III in 68 had d-jetronic.

Roland
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esde
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PostPosted: Fri Oct 21, 2022 5:16 pm    Post subject: Re: Fuel injection for 36hp engine Reply with quote

I had discussed this with some people while I was building the injection system for my 2 liter street engine. The biggest problem with a 36hp or any single port engine is the shared intake design. How would you mount injectors? Hypothetically you could use one injector for 1-2 and another for 3-4, then you would need to work out the firing sequence.
Of course we were discussing an electronic system, not a period mechanical system. It's a cool idea, wonder what it would take?
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Alstrup
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PostPosted: Sat Oct 22, 2022 12:53 am    Post subject: Re: Fuel injection for 36hp engine Reply with quote

The Kugelfischer systems were horrible crude and therefore very inefficient for street use. But at WOT the atomization was as good or better than what was averagely possible with carbs, especially in WWII The aviation engines had one other advantage. It was primarily "fixed" rpm engines, They werent, but they operated in a very narrow rpm band compared to an Automobile engine. So it was easier to meter the fuel for the engine. The idea with using a diesel pump instead should be possible. I think ther first challenge would be to find one that is small enough. If you do it this way you will have to have all 4 injectors active.
should you chose to go electric you can use 1 injector per side, no problem. Just double the cycle.
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sleepywiesel
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PostPosted: Sat Oct 22, 2022 6:06 am    Post subject: Re: Fuel injection for 36hp engine Reply with quote

@Roland: The car I'm going to use will be a '59 sedan. So I want to orientate on the systems of the DB601 and the 300SL. Because the d-jetronic is even more complicated and I would not know how to face the electronic problems. Because you need specific numbers like how many fuel you need at which rpm and load of the the engine.

@esde: The injectors will be positioned in the combustionchambers. So one injector for each cylinder. They will be orientated like twin plugs. Ninamashr have started a very nice thread where he gave the positions. I will use these positions for the injectors.
https://www.thesamba.com/vw/forum/viewtopic.php?t=451493
But you are addressing another problem I see: Due to the single carb setup the intake ports do not have the same lenght. Because of that there will be differences in the amount of air sucked into the cylinders. But I will ignore that Laughing

@Alstrup: Exactly. The limited rpm band of the aviation engines is what brought me to think about the diesel pump. Because the beetle engine is not really a high rpm engine as well.
The point with the size is a big one. I purchased a pump from a 200d merc. These are the smallest 4 cylinder pumps which were built in high numbers. I would like to find out what type of pump porsche used on the diesel beetles. (Does anyone have pictures of the diesel beetle in the porsche museum?)
It is possible to adjust the amount of injected fuel by changing the rolls of the followers. That limitates the lift and the volume.
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PostPosted: Sat Oct 22, 2022 10:32 am    Post subject: Re: Fuel injection for 36hp engine Reply with quote

Isn't it be better if you just use a hilborn fuel injection it would also qualify for vintage speed ...but I remember hearing those mechanical fuel injection are not really good for Street use/ long driving ...it's good for drag racing though....
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sleepywiesel
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PostPosted: Sun Oct 23, 2022 12:35 pm    Post subject: Re: Fuel injection for 36hp engine Reply with quote

I see...
I've thought that the Kugelfischer injections were actually good for general use because this system is very well thought through as well and used in serial cars like the BMW 2002tii. I haven't spoken to someone who is familiar with the mechanical injection stuff because I'm just surrounded by carburettor experts Smile

The hilborn injection would be a soultion for a high perfomance engine. Plus I'm not planning on buying a costly thing that might work well but doesn't give me the opportunity to learn something. But thanks for the input though!
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RolandD
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PostPosted: Sun Oct 23, 2022 6:46 pm    Post subject: Re: Fuel injection for 36hp engine Reply with quote

The D-jetronic is NOT digital - no programing. It assumes that the manifold pressure is an accurate representation of the quantity of air in the cylinder at the end of the intake stroke. If you could raise your displacement to 1600 ccs, and ran a stock cam with dual port heads. It would not need any modification/adjustments.

If you insist on direct injection, I would indeed study the Kugelfischer system.

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slalombuggy
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PostPosted: Tue Oct 25, 2022 3:15 am    Post subject: Re: Fuel injection for 36hp engine Reply with quote

Are the injectors you are going to use built to withstand the stresses that they will be exposed to in a direct injection application?

The tips will be exposed to extreme heat and combustion events, direct injection injectors are built vastly different than injectors that are placed in the intake runners.
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sleepywiesel
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PostPosted: Wed Oct 26, 2022 11:20 am    Post subject: Re: Fuel injection for 36hp engine Reply with quote

slalombuggy wrote:
Are the injectors you are going to use built to withstand the stresses that they will be exposed to in a direct injection application?

The tips will be exposed to extreme heat and combustion events, direct injection injectors are built vastly different than injectors that are placed in the intake runners.


Good point.
I would use the original diesel injectors. That should be the easiest solution.
One problem I have with this is the missing lubrication of the inner parts. But I have to go a bit more into detail here. I have the literature, but no time to read it Rolling Eyes
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RolandD
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PostPosted: Wed Oct 26, 2022 5:10 pm    Post subject: Re: Fuel injection for 36hp engine Reply with quote

The Rabbit diesel injectors are rather wide, You might want to look at the early TDI injectors. I believe they where much thinner.

Roland
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