Homemade custom cast aluminum intake manifolds

[phantomaz]

Hello all , I found 2 reasonable priced keihin fcr mx carbs



which are mounted on dirtbikes and some atv. Since they can't be tilt more than 30 degrees ,I had to find another mounting decision. I couldn't find anyone with fcr mx on ducati but there were 2 possible mounting positions I could imagine. The second one was very extravagant and I didn't know if it will work ... still don't know because only the manifolds are almost ready but didn't started the engine yet.
So what I did was ,put the carbs where I want , cut the old manifolds and glued the pieces . The idea is to lock the 2 holes to the desired new position. /it is very hard to me to explain what I want in english /
The pictures will explain better.



I did the molds ... I don't have all the photos because during the process I haven't my camera with me.


this is the chopped and glued manifold fixed in plaster


when I have the position of the income and outcome holes , I can star making the manifold from wax.


I put hot wax in the molds to make this two pieces from wax /I don't have picture of them/


when I get them form wax ,positioned them in the plaster from the picture above. Than what I needed to do was to create the tube. The entry is 40mm the exit is 35mm. To make this tube from wax ,I needed to have the lumen of the tube from some solid material ,and to put 4mm wax plate onto it ,when I remove the solid material /in this case plaster - but first I shaped it from wax ,made a mold and cast it from plaster/ will stay only the wax plate with the shape of the plaster.


And these are the manifolds ready from wax.




Unfortunately now I haven't my camera with me and the pictures of the aluminum manifolds are with poor quality made with my phone





Now I need to sandpaper them ,some machine work to make a smooth surface on the flange where it contacts with the engine head.
But what about the inner surface ,should I polish them ,or for carb manifolds the surface should be rough?

this is how they  will look on the bike ,but hard to imagine ,the shots are not good











Now someone will tell me correct jetting for fcr on the sea level , I will ride to around 5000 feet. thanks!

[Greg]

I don't care for the side mounted carbs, but I do admire your skills in fabbing the manifolds 

[Speeddog]

I've got no info on jetting.

But like Greg said, outstanding work! 

[phantomaz]

Thanks for your support

I am still waiting for jetting information. How do you guys think ,if I ask "sudco" will they give me this info ,I will buy the jets and needles from them maybe.

[xcaptainxbloodx]

awesome skill in casting the intakes but intakes that long are going to hamper performance, as will the pods that the location will necessitate.  I would be interested in seeing dyno charts before and after.

as for jetting, the custom intakes  will affect fueling so while sudco will probably be able to get you something close, you will probably have a bit of trial and error ahead of you.

[phantomaz]

Yes, they are a little bit longer ,but no more than 1.5cm. I knew it will affect the performance ,but I suspect it won't be much. Maybe the big problem will be jetting them, and dyno will be needed, but when am I going to do this ... don't know.

[Skyshadow]

Nice custom work!

[xcaptainxbloodx]

Yes, they are a little bit longer ,but no more than 1.5cm. I knew it will affect the performance ,but I suspect it won't be much. Maybe the big problem will be jetting them, and dyno will be needed, but when am I going to do this ... don't know.

1.5cm may not be a lot of length but by having the mounted on the sides you are forcing the air to go through a few acrobatics before getting to the intake valve.

our engines work best with large quantities of directed (or still) air. by running pods you are providing a small quantity of turbulent air, by mounting them on the sides you are asking that air to do a 90* angle  just to get into the carb, and then to tumble down a tube into a ~30* bend where it hits the cylinder. not ideal, and could potentially make less power than stock. 

what you really want to do is cast the shortest, even intakes you can while maintaining a proper level for the carbs. then fab a custom airbox with some fancy forward facing snorkels. Ive got a book ill try to dig up that has a formula for getting a ballpark on how to fab snorkels and airbox size based on the size of your carbs if you are interested, but much of it is trial and error.

I hope im not being to harsh, your casting skills are pretty awesome. Id hate to discourage you from future posts.

[Raux]

i think the length is dependent on the diameter. shorter = fatter, longer = narrower.  the old carbies had long narrow ones, the new FI have short fat ones.

and the new FI have a 90 degree bend on the top going into the air box. especially for the horizontal cyl.

[lazylightnin717]

1.5cm may not be a lot of length but by having the mounted on the sides you are forcing the air to go through a few acrobatics before getting to the intake valve.

our engines work best with large quantities of directed (or still) air. by running pods you are providing a small quantity of turbulent air, by mounting them on the sides you are asking that air to do a 90* angle  just to get into the carb, and then to tumble down a tube into a ~30* bend where it hits the cylinder. not ideal, and could potentially make less power than stock. 

I remember reading a discussion a while back and seem to recall FI bikes do better with large volumes of still air whereas carbed bikes do better with turbulent air. I've no scientific evidence to prove my point but I can gladly search for the thread.

And nice custom work there 

[battlecry]

Nice.  That is like something out of Britten.  Good work. 

[xcaptainxbloodx]

turbulent air wont burn as clean or even as directed or still air. the discovery of this (as well as the benefits of airbox resonance)  is why you stop seeing airboxless works bikes in the late 70s early 80s.

its a lot of science to get it perfect, but if you want something to set your bike apart from the rest a custom fabbed CF airbox with scientifically set intake lengths will do it..

[battlecry]

Maybe things have changed, but for many years one of the goals of cylinder head design was to have turbulent, swirling, air/fuel mixture in the chamber.  Why do you suppose that is not the case anymore?

[ducpainter]

Maybe things have changed, but for many years one of the goals of cylinder head design was to have turbulent, swirling, air/fuel mixture in the chamber.  Why do you suppose that is not the case anymore?

I think the turbulence is required once the air passes the carb slide/throttle plate. It also helps to eliminate the laminar flow in the intake runners.

The air just outside the carb mouth should be as still as possible.

That's why airbox size/design is so crucial to high performance engines

[Skyshadow]

I think if you have a forward facing cone you should be fine. You don't need STILL air on a carb'd bike, more like directed air. To get a idea of what I mean, while driving down the highway stick your head out the window. first face forward and inhale... pretty much stuffs air down your throat. then turn your head to the side (left if your in the driver seat) and inhale... much much harder to do.