Porsche 917 flat 12 engine

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Foketry

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I know its more complicated than this, but FWIW the carb orifice size you eventually selected lands like so on these cross plots I made of various 4-stroke OS brand (methanol glow) engines.

Very interesting your analysis, I will take note .
in my engine, 2 out of 6 cylinders are in the intake phase at the same time. Let me explain better: one cylinder starts the intake phase while another cylinder is completing the intake phase, this roughly means that 1.3 cylinders are sucking simultaneously from 1 carburetor. So I thought that a large diameter Venturi was needed, instead small is better
 

Foketry

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What coil are you using? Also, could you say bit more about how you're using the electronic protractor to set valve timing? Is there a remote sensor or is the whole protractor attached to a degree wheel? Thanks - Terry

The coil I am using is for motorcycle, I think it can only work in conjunction with the GY6 electronic ignition
Regarding the electronic goniometer it is composed of 2 parts, a rotation sensor and a display
I use it for camshaft timing with this procedure: I fix the protractor the protractor to the camshaft (or to the crankshaft) to indicate the TDC of each cylinder, through the spark plug hole I introduce compressed air into the cylinder with both valves closed (each cam can rotate individually on the shaft )
I rotate the cam until I hear a flow of air coming out of the intake duct,
I rotate the exhaust cam until I feel that the flow of air stops , this is the exact valve crossover point, without overlap at TDC
If I want to overlap I advance the intake valve and delay the exhaust valve. In my case I look for the regularity of the engine rather than the performance, therefore little or zero overlap.
Are you using overlap?

Coil link

There is an interesting series of posts about this kind of ignitions on this forum, PaulC replaced the big pick up with a Hall sensor , works well !

I bought the electronic protractor in England, if necessary I provide the link to you

Greetings and congratulations for your splendid engine, you are a reference for me, I am learning a lot from you
 

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propclock

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I may be late to reply on this. But I have found CDI ignitions
make a LOT of electronic / rf noise. I suggest you try running
1 system and see if you get any sparks from the powered up
but hall removed from the distributor of the disabled system. Often the cdi #1 will trigger system #2. I worked on an engine with 2 distributors on a v8 made to look like a dragster. I finally had to go to Kettering to maintain the 2 distributors . Also beware of cdi units that have automatic spark advance .
Hard learned lessons.
Just for what it is worth.
You might try a resistor on the HV
coil output lead, 2k??? carbon composition if you have this problem.

Your engine is absolutely fabulous.
 

Foketry

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I may be late to reply on this. But I have found CDI ignitions
make a LOT of electronic / rf noise. I suggest you try running
1 system and see if you get any sparks from the powered up
but hall removed from the distributor of the disabled system. Often the cdi #1 will trigger system #2. I worked on an engine with 2 distributors on a v8 made to look like a dragster. I finally had to go to Kettering to maintain the 2 distributors . Also beware of cdi units that have automatic spark advance .
Hard learned lessons.
Just for what it is worth.
You might try a resistor on the HV
coil output lead, 2k??? carbon composition if you have this problem.

Your engine is absolutely fabulous.

I confirm that electronic ignitions make a lot of electrical noise, not only the GY6 but generally all those for engine models.
For example I had a bad experience with the 3D printer, it was printing for over 12 hours, I started my little Demon V8, the printer froze and I had to completely redo the part.
These 2 ignitions also generate rf noise but don't disturb each other and don't give problems to the distributors.
Strangely they don't have automatic advance, I don't know why
In any case, the ignition receives 3 impulses from the pick up for each revolution of the crankshaft, my engine model does not go below 1000 rpm, it means 3000 impulses, (6 cylinders ) , the automatic advance is already exceeded.
I am still in the testing phase, some surprises could happen, I take into account your suggestions, a 1 or 2 K resistance could be necessary
Thanks
 

Foketry

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Does anyone know of a carb that has a venturi size of 4.5mm or about. I am finding it hard to find any specs on RC carbs. Any help will be appreciated.

Ray

here Petertha has published 3 tables that can help you
 

petertha

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Does anyone know of a carb that has a venturi size of 4.5mm or about. I am finding it hard to find any specs on RC carbs. Any help will be appreciated.
Ray

Yes, this web site is a good repository of legacy engine articles, but you have to kind of data mine the information.

If you happen to know the orifice size of a commercial engine, you can sometimes get good deals on used carbs... with engines included LOL. There are a couple of RC forums out there to peruse or write a wanted ad. Sometimes Ebay too. They generally don't wear out, just get abused or gummed up. Tiny O-rings used to be hard to source but I just got a kit of tiny silicone metric ones off AliExpress for cheap.

Regarding new, Conley took over the Perry line & has progressive carb sizes & spare parts. Maybe not quite as appealing as die cast say an OS or Saito, but functionally probably do the same job & lower cost.

In that range you might find something in RC car carbs, but I'm on uncharted waters there. I think many are slide valves. And some of the lower displacement engines like 0.15-0.21 CI actually have big openings as a function of their rpm/application.

I would also add - pay attention to needle valve & throttle arm position if your engine application is somewhat constrained. Also the throat body diameter varies quite a bit between carbs, so it pays to have some adaptability in your manifold design if you want to try different ones.
 

Foketry

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The first pops
The engine works, but some improvements are needed
Ignition system: the pick ups are not stable
It is necessary to redo the supports, now they are 3D printed in plastic (PLA), I redo them with aluminum
The intake manifold ducts are too large, I had designed them for a 12-14 mm Venturi diameter carburetor, while a 6 or 8 mm carburetor gave the better results
Speed of air / petrol flow is higher with a 6 mm carburetor, the pulverization is better and therefore the cylinders furthest from the carburetor can be reached more efficiently. In fact cylinders 1 and 6 and 7 and 12 are colder than all the other 8 central cylinders because they are less efficient, poorer air / petrol mixture
 

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mayhugh1

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The first pops
The engine works, but some improvements are needed
Ignition system: the pick ups are not stable
It is necessary to redo the supports, now they are 3D printed in plastic (PLA), I redo them with aluminum
The intake manifold ducts are too large, I had designed them for a 12-14 mm Venturi diameter carburetor, while a 6 or 8 mm carburetor gave the better results
Speed of air / petrol flow is higher with a 6 mm carburetor, the pulverization is better and therefore the cylinders furthest from the carburetor can be reached more efficiently. In fact cylinders 1 and 6 and 7 and 12 are colder than all the other 8 central cylinders because they are less efficient, poorer air / petrol mixture
One of the best projects ever on this forum ...
 

propclock

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Well other than the great feeling you already feel
all I can say is, enjoy.!!
Nothing like the first run.
Fantastic.
You just might have pushed this guy over into pouring metal,
Great post, I have always followed , Just congratulations.
Paul
 

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