Carburettors

[Parksy]

Gday all

Won't be far off from completing the nitro v8 engine and I need to look at the intake side of things. What size bore should I look at with the carby? Engine cylinder bore is 22mm.
Do people usually make their own carburettors or purchase ready made units?
This is a four stroke engine btw.
Any tips or helpful hints on this subject is most welcome.

Thanks for reading

Andy

 

[Parksy]

Anyone able to help?

 

[canadianhorsepower]

Anyone able to help?

there is a carburetor in the download section.
1 would go 3 time the size
what fuel are you going to use??

 

[gbritnell]

Hi Andy,
Attached is a drawing for a carb that should work fine. You will have to change the mounting flange to suit your needs. I use it on my Holt engine which has a 25 mm bore.
gbritnell

View attachment HOLT CARB SMALL.pdf

 

[canadianhorsepower]

Hi Andy,
Attached is a drawing for a carb that should work fine. You will have to change the mounting flange to suit your needs. I use it on my Holt engine which has a 25 mm bore.
gbritnell

He will use this on a V8 nitro
will it be big enough ??

BTW congratulation for your
Craftsmanship Award of the Year th_wav

 

[Parksy]

Thank you all. I appreciate your help.

Thanks gbritnell for sharing your carb design. I absolutely respect your work and efforts and find your work amazing.
With regards to your carb design, am I reading it correctly, the Venturi is only about 4mm (after converting to mm)?
My understanding is that number of cylinders is irrelevant, but Venturi size is a huge importance.

Engine will be run on nitro fuel, but would like to one day convert it to petrol.

 

[canadianhorsepower]

My understanding is that number of cylinders is irrelevant, but Venturi size is a huge importance.

Totally wrong, take your cylinders and assume they are children.
the more you have the bigger the door fridge must be.

as for the venturi it's another way to look at it .

assume you are tuning a piano and you are working on a special note
b in our case 3500 rpm then you would tune your venturi for the best tuning at that RPM . this explain the variable venturi on motor cycle. They need the best they can get at every RPM.

Engine will be run on nitro fuel, but would like to one day convert it to petrol

this is fine cause no engine mod will be needed (it want be perfect) but you can feed enough stuff (fuel ) for your engine to be happy. jet size is 2.2 time the volume from Nitro to gas. so shut the needle down a little and it will work


good luck

 

[t.l.a.r. eng]

Most multiple cylinder engines have only one intake valve open at any given time through the crank revolution, so treat the carb as one carb filling one cylinder at a time.

If the individual cylinder volume is 25 cc, then use a carb sized for a 25 cc cylinder.

When you follow the firing order slowly on the engine and think about it, it makes sense.

 

[Parksy]

Had some luck today. Went to a hobby shop to pick up some nitro fuel and ended up walking out with a carby at half price. Cheating yes, but at least if I have issues, troubleshooting will be easier.

 

[gbritnell]

Thanks Luc,
I was totally blown away when I got the news.
gbritnell

 

[canadianhorsepower]

Thanks Luc,
I was totally blown away when I got the news.
gbritnell

I was blown away to

of the fact you didn't get it YEARS ago
Rof}Rof}Rof}

 

[canadianhorsepower]

Most multiple cylinder engines have only one intake valve open at any given time through the crank revolution, so treat the carb as one carb filling one cylinder at a time.
If the individual cylinder volume is 25 cc, then use a carb sized for a 25 cc cylinder.
When you follow the firing order slowly on the engine and think about it, it makes sense.

so what you are saying is

don't use a 2 barrel 4 barrel or multi carburetor

one single carburetor would do the same.........

then a lot of engineers waited their time

if you check the video you will see that there is a lot more then one intake valve
open at the same time

[ame]https://www.youtube.com/watch?v=N2y77vEKorI[/ame]

 

[t.l.a.r. eng]

Understand what you mean, however for our model engines they just need to run and are not expected to do much work other than to overcome internal friction.

Full size engine doing work need more air, fuel volume to produce useful power.

Air molecules do not scale down to our models size. Air fuel mixture has weight that can be used at an advantage on full size engines but the advantage goes away with the small size.

Even the mighty four barrel is nothing but 4 simple carburetors joined together usually with progressive openings to use the extra fuel air volume. Experements have usually shown several smaller carburetors usually have better driveability than one large one.

 

[barnesrickw]

I guess as long as their is enough air at the right velocity to draw and vaporize the fuel going through the Venturi all should be fine right?