Custom Airfilterbox question

[TommyPettersen]

Hi.

Not sure if this will be in the correct category..but..

As i am building my Hybrid RD 350ypvs have begun looking at how to make an airbox. The stock one does not fit any more because of modified frame, and i don't want to use powerfilters or that 2 in to 1 thingy.. I have been thinking of making an airbox out of Stainless steel. Is that a bad idea? Will there be resonance sound or other issues? I know the R5 had metal airbox. And i could spray some kind of structural paint on the inside if it is needed.. Any thoughts?

[two-stroke-brit]

i would use aluminium as easier to work with and lighter .
but SS will work.
i have seen thin sheet rubber glued to the inside to dampen sound and vibes on this sort of thing .
mark

[Questo vecchio rz]

If you think you are going to have room to build a metal box in there? And that's the route you choose, then go at it.
I don't think any material you use will genuinely affect performance in any way that would be percivable.
If It were me, going through all that hassle I'd rather do a Fiberglass or Carbon mold, but if your metal fabrication and welding skills are good then awesome. No sq box w pop rivets...lol
Obviouslly metal would absorb heat more, but that's being " nit picky". From a engineering viewpoint , carbon, ABS etc..with a calculated airbox volume would be ideal.
IMO RZs run dammed good with a stock airbox or modded, 2-1 intake , or individual filters, so a decent custom airbox should be just fine. Perhaps a coating applied to the inside like Plasti-dip or one of Rubberized coatings avail in a spray can everywhere.
In theory help any sound reflection/ vibrations & also reduce intake charge temps. But heat saturation may ultimately be the same no matter what material you use. Just do it and enjoy your craftsmanship

[dinamos]

Fabricating materials aside, you might want to consider the volume of an air box and how that will fit into your frame.

Anybody know the CC volume of an OEM air box?

roger

[TommyPettersen]

Thanks for informative and supportive answers..

I tried to google "Airbox volume calculation" and there was alot of complex theory and formulas etc etc..

Before reading up on that:

In short, can i fill a stock yamaha airbox with water then measure how much that was, then make sure the new airbox is aprox the same volume? And if so do i measure up to the filter only, or include the volume of the lid?

I were planning to use a motorcross filter of some kind as they are free flowing and function the way they should on twostrokes..

[Questo vecchio rz]

In short, can i fill a stock yamaha airbox with water then measure how much that was, then make sure the new airbox is aprox the same volume? And if so do i measure up to the filter only, or include the volume of the lid?

I think you answered your own question, I wouldnt worry one second trying to be exact as the stock airbox. Even stock 26mm carbs are capable of exceeding what the stock reed cage can deliver to the motor, keep it as close as you can and you should be fine, You might have trouble equaling the stock volume, depending on where you place battery etc..If significantly smaller volume I wouldnt even bother starting the project, I think your performance could suffer, if you could equal it or better, then give it a go.
There are really far to many variables involved to predict what youll end up with, just think it out logically, keep it as simple and airtight as possible thats your best shot.
If you want to play Japanese engineer then research & calculate, volume/pressure/intake lengths/materials/temps/airflow/intake restrictions etc.. Thats awesome but in the end, it probably would work equal to any of the other intake methods avail, which isnt a bad thing.
If you do it, post your progress its all intresting and fun to read.

[nzminis]

different bike i know
but

I Mate of mine put a kx 500 motor in a zxr250 chassis and was having heaps of issues with the air box
pod filter was rubbish , also ram charging was not so good
so they made a few air boxes , 1st was small and they could never tune it
2nd was a little bigger than the stock mx bike box ,
worked perfect

just need a very still flow of air , pulled air from under the back tail

all what was said above sounds correct to me :)

[OldTZracer]

The volume is more critical than the construction material so make it as big as you can fit... The larger the volume, the easier it is for air to be drawn into the engine - & more air means more horsepower. However, you may want to wrap your airbox and/or the bottom of the tank with Dynamat or similar sound deadening material to soften the intake noise.

[TommyPettersen]

Thanks for all input so far.. I do have some more questions.. about the filter/s and where to mount them..
I did read somewhere that two strokes supposedly likes to have some distance between carbs and filter.. But on many motorcross bikes filters are mounted directly on the wall leading in to the carbs.. The Banshee has this as well.. but maybe that is all compromise??
I made some crappy drawings in "paint" that shows my options of filter mounting.. please give input on which you would think is best design...

here is the first one:

filterbox 1 version.jpg (25.13 KiB) Viewed 2747 times

This is the one i would prefer to make.. but my concern is that filters are fairly close to carb "intakes" and the large area high up in the box will not be of use??

Second version:

filterbox 2 version.jpg (24.33 KiB) Viewed 2747 times

Here the airhorns have been moved to the top under the tank, And filter mounted on the wall close to the carbs.. That gives a large area between the intake of the box and the carbs...but filters mounted that close to the carbs aren't optimal??

third version:

filterbox 3 version.jpg (24.49 KiB) Viewed 2747 times

Here are things mounted pretty much like the original design with the filter on top. I can choose to have forward or rearward facing airhorns..

Since i have a done alot of changes on the frame, moved the battery to the tailsection etc, i think that i might be able to increase the size of the airbox slightly over the original one.. which should be good. I did read about that guy who fitted a Banshee box and that is a larger box too, on the same engine.. i guess that speaks for it self too..

Forgot to say: My engine is stock other than K2-tec pipes and Keihin PWK and vforce4 reads.. No porting.. even stock bore..

What do you guys think?

[RuZty]

Filter into the airbox, not out of it. Large surface area to filter air into the box equals longer filter life and no restriction into the carbs from the box.

[dinamos]

Filter into the airbox, not out of it. Large surface area to filter air into the box equals longer filter life and no restriction into the carbs from the box.

You need a large air box to hold the biggest air filter that you can fit.

Your drawings are a little vague but it brings a suggestion to mind. Know anybody that can vacuform plastic?

roger