Need Airbox or Airfilter

A

adas

Well-Known Member

• 14 September 2006

• #1

Aloha, I need advice on an airfilter or airbox for my setup. I need it quiet so a foam one will not work. Here is my setup

Minarelli Horizontal LC . DD aprilia
Tuned carters
Larger reed block and 35% bigger reeds
42mm stroker crank
Oko 21
Polini Variator and wider belt
Polini Evo 70cc tuned
Yasuni 16

Anyone adapt or create a silencer/airbox that keeps good airflow? thanks Frank

 

melf #50

Well-Known Member

• 14 September 2006

• #2

I use a Kart airbox , there are many shapes and sized , and the noise is reduced a lot more then an open fiter , and it works at least the same

here are some examples :

http://www.euroscooters.nl/shop/index.php?cPath=39_275&osCsid=73a2f943029dbb21f6ceea7d1fffa9a9


I have the airbox under the seat , in the helmet-compartement , and also fitted the inside of the compartement with soft material. the sound is minimum like that.

 

A

adas

Well-Known Member

• 14 September 2006

• #3

Aloha, good advice, I will use the helmet box and line with sponge material and connect a flex pipe from the carb. I think this will work nicely to get the sound lower than the sound level of the exhaust. frank

 

melf #50

Well-Known Member

• 14 September 2006

• #4

I use a PVC drainpipe in 90 degrees on the back of the carburator , I use 70mm. in combination with a Malossi straight manifold. on the back I have made a aluminium piece so the PVC pipe will fit on it.

 

A

adas

Well-Known Member

• 14 September 2006

• #5

Aloha, did you try only a foam sponge filter inside the helmut box after you insulated the box? Was this OK instead of the Kart airbox? Tomorrow I will get the plumbing PVC fitting 50mm, with screw connecter to attach to the helmut box. Also the flex pipe to allow the engine to move independant of the helmut box. frank

 

melf #50

Well-Known Member

• 14 September 2006

• #6

the difference between open filter and airbox can be heard very much in my opinion.

my airbox is only atached to the carburator btw , not to the helmet box

 

A

adas

Well-Known Member

• 6 October 2006

• #7

melf #50 said:

the difference between open filter and airbox can be heard very much in my opinion.

my airbox is only atached to the carburator btw , not to the helmet box

Click to expand...

Aloha, Now I have to come back to making the airbox because the carb noise is driving me nuts in the city.
To understand you correctly, you attach a 70mm diameter PVC angle to the "bell" intake of the carb and this passes through into the helmet box. The engine moves and the helmet box does not so you have a bigger hole to allow movement? Then you instal an airbox inside the Helmet box on the PVC?

I tried some flex pipe from carb to inside the helmet box, but was only 50mm and it ran very rich and like shit, so I must try 70mm or larger.

frank

 

melf #50

Well-Known Member

• 6 October 2006

• #8

the whole bottem has to come out

but this will only work if you use a straight manifold (malossi or Polini) , but on minarelli with a oko 21 you'll have to also put on a "wig" (wedge) ,and a altered subframe.. and that would be very expensive then..

if you would use a 21mm Dell orto you can use the std airbox withhout problems in the std manifold

 

A

adas

Well-Known Member

• 6 October 2006

• #9

Aloha, OK the whole bottom I see. Now I already have the rear facing OKO using the RD400 intake manifold (mounting holes modified) and with a 5 inch bent tube. this mounts the carb bottom just clearing the starter. I only had to modify the top bar of the mount to "bend upward" maybe 1 inch to allow the 5 inch long tube to enter the intake manifold. The carb is on the same angle as with the wig. frank

 

A

adas

Well-Known Member

• 11 October 2006

• #10

Aloha, well I found a nice combination of quiet and no restriction filter.
I used a 50mm 90 degree PVC elbow that clamps around my OkO 21.
This goes into my helmet box through a hole that allows the carb
to move and not bind on the hole.
Then I installed a 70mm PVC "T" in the helmet box on the elbow
and mounted 2 free flow sponge filters on each opening.
This is free flow and the jetting is the same as if I had an
open carb with no filter. I is resonably quiet.
(I can hear the Yasuni 16 now)
and gives a very deep sound, but I will insulate the helmet box
to make it super quiet a little later. The nice thing is that
is free flow and does not have the restriction of an air-box.
Frank

 

melf #50

Well-Known Member

• 11 October 2006

• #11

an airbox is not a restriction , some people think that more air is better , a littlebit can be better yes , but not more and more and more...

 

A

adas

Well-Known Member

• 13 October 2006

• #12

melf #50 said:

an airbox is not a restriction , some people think that more air is better , a littlebit can be better yes , but not more and more and more...

Click to expand...

Aloha, IMHO. I feel the standard airbox is a major restriction The airbox/intake method is very very important and the more air/fuel mixture the better, up to the point of air flow slowing down to not allow proper atomization, but that would not occur on a 21mm carb! More air is why I went from 12mm to 21 mm carb. (of course with correct fuel mixture). The dynamics of air entering the bell of the carb must be very interesting to watch if you can see it in a wind tunnel effect. Even with a free-flow sponge air filter you have to rejet, compared to using no filter at all. With using a velocity stack you have to re-jet as well so paying close attentiion to air intake side is almost as important as the expansioin chamber, so I say more unrestricted/predictable/constant air the better. (ram air is a different matter)
frank