airbox/ no airbox

[alextrx850]

..Prob no need for filter oil Coxy,..the toe jam will grab the dust from those footy sox.

With my inlet snorkle and factory filter removed, the full throttle induction sound from the box is adictive.!

[coxylaad]

I am going to make a sort of half airbox for it, and fit the ramair filter around the velocity stacks from the 900 airbox.

actually a point on that, the velocy stacks on the tdm900 airbox are completely different lengths - one is twice the length of the other!

I have just bought a 900 airbox off ebay so I can have 2 stacks the same length. dunno whats going on there.

[fung]

if i remember correctly, killer is using carbs and stacks on his TRX900.
different height stacks may give both throats equal opportunity to suck air ?
maybe the shape of the box ?
or the efi and 270 crank fire combo with a common airbox ?
cheers
fung

[Mincehead]

I am going to make a sort of half airbox for it, and fit the ramair filter around the velocity stacks from the 900 airbox.

actually a point on that, the velocy stacks on the tdm900 airbox are completely different lengths - one is twice the length of the other!

I have just bought a 900 airbox off ebay so I can have 2 stacks the same length. dunno whats going on there.

Typically, shorter stacks produce better high RPM BHP and longer ones at lower RPM. This pretty much holds true on header length as well. Yamaha likely found a compromise during engine testing / dyno results by using two stacks of different lengths.

[dandywarhol]

Remember also the 900 has a 2 stage intake valve controlled by the ecu and vacuum
different ideas as to what its for but noise emissions and improved low rpm response seem to be favourites.
I'll dig out info from the Yamaha Technical Bulletin tonight.

[coxylaad]

interesting information, however its all going in the bin.

going to use the shorter pair of stacks into a home brew hybrid airbox. will report back.

[GARAGE HERMIT]

An engine with carbs/cylinders side by side will blow back fuel into the airbox when the inlet valve snaps shut whether it is a CV of slide carb. The 900 injector is basically an electronic carb, although it does inject nearer to the valves than a carb but the fuel mix will still blowback. The blowback aids lower end performance with an airbox because the adjacent cylinder will suck the fuel in along with the air - with individual pods the blowback is lost to atmosphere (that's why the underside of the tank/frame/your legs etc. get a bit petrol smelly.)

funny thing is this infamous blow-back never happened with all the triumph/norton twins i've owned and a little kaw 400 twin i had with pod filter's on, internet urban myth, ??

[dandywarhol]

Welcome GH - all input is appreciated on here.

I'd need to see the valve timing diagrams of the Brit bikes and the Kawa to comment. Having raced an 8 valve Rickman head Triumph sidecar outfit many moons ago, I can personally account for the fuel blowback stinging my neck and face at the end of a race!

[GARAGE HERMIT]

so you're thinking it's the valve timing overlap causing this blow back,?

[dandywarhol]

I think it's a combination of things, including valve overlap and the shock/pressure wave produced when the valves snap shut. I think valve timing because it appears to be worse at low/mid rev range when large overlap is counterproductive to producing power - and why variable valve timing and multi-air design on modern(ish) engine design is less of a compromise.

It would be interesting to find out if VVT produces less blowback.....................

Looks like you've got a long stroke method in your avatar GH

[GARAGE HERMIT]

not trying to be clever, but if it was a case of the shock/pressure wave from the inlet valve closing, every bike would be blowing petrol mist out of the carb's, single's, four's, etc, that had pod filter's fitted,
with the std air-box fitted the thinking is that the blow-back from one carb is sucked back into the engine by the other carb, surely this would'nt suck all the petrol mist out of the airbox and you would get condensed petrol puddling in the bottom of the airbox,
i'm after a definitive answer to this pod filter's versus std airbox as i'm going to make a frame, and dont want to end up having to re-do it if i use the pod filter's and it does in fact cover me in petrol,
any pod filter user's out there, let me know,

[alextrx850]

Using the Ram Air filter over the blue inlets to my FCR41s ..doesn't cough back at all,
I've heard about the supposed problem to a fuel fire in the pods, and am wary of it, but my machine runs in good tune.

Is your avatar a selfie....

[coxylaad]

just to add to this.

I am running a sock filter bridged over the two trumpets, with no airbox at all. No running problems and no smell of fuel anywhere around the bike either.
This is tdm900 setup with throttle bodies and fuel injection.

However I am currently doing up an TRX tuned ex race bike, running hot cams and FCRs, that hasnt been fired up for year and it still stinks of petrol around the inlet area!

maybes its a carb problem?