Modified air intake manifold

[ejdirin]

I'm not sure if anybody has tried this, but I'm interested in making an air intake manifold that uses a single air filter located off to the side of the bike. My idea was using some sort of pipe (copper was my initial thought because its lightweight and easy to work with, but I found out it gets pretty expensive once you go above 1.5" ID) and 2 couplers (a 90 degree elbow and T-coupler) to bring the intake to the side of the bike. Pretty simple in theory...connect the 90 deg elbow to one carb, the T to the other, connect them with a tiny length of pipe and use another small length to bring it out to the side.

My questions are 1) Has anybody tried this? 2) Is this going to work? My thought is that the amount of air the filter is exposed to on the side of the bike will make up for the decrease in filter number. But I know things aren't that simple with carbs....

I've seen some guys selling a manifold on eBay that'll convert the 650 into a single carb system, but I'm just interested in moving the filter.

Any thoughts/ideas/pictures? Thanks!

 

[weekendrider]

A member(retired) of some other forums did the exact conversion you asked about with copper. Unfortunately the pics in those threads have been deleted or moved from the photobucket host site.

 

[Visegrippe]

I would just worry about balancing, one or the other could take all the air, t's tend to not do what you think, but I'm no expert.

 

[cheftay]

i dont know if balance would be much of an issue if you were to use lightweight metal/ or even plastic to construct it. i know harley has a similar set up...
http://www.knfilters.com/images/press/2009-Harley-Davidson-Street-Glide_63-1122.jpg

 

[ejdirin]

Yeah. Like anything with building a bike project, its gonna be a lot of trial and error.

Hey weekendrider, I know some of the old retired forums still have their postings up as read only. Would I be able to find the guy that way?

Anybody have any ideas about what to use besides copper pipe/couplers? I thought of PVC, but those couplers are so bulky. My buddy also mentioned maybe an old car exhaust.

 

[angus67]

I picked up a used pair of V8 headers for 10$. the flanges were all bent to hell, but I was only after the bends in it anyways. Yeah, find a set of beat up headers, and go from there. if you can weld, no sweat! did you want the copper because sweating a joint is easier?
And, Cheftay, I think he meant balance as in both carbs getting equall amount of air, one not stealing from the other.

 

[Visegrippe]

Yeah, I haven't had a chance to get back on, but basically your asking one to suck air past the other, at low air velocity, this would tend to favour the first carb, but at higher velocities it could form a venturi efect and actually create negative pressure through the first carb. Like I said before, I'm no expert but have had to deal with surprises like that recently at work.

 

[Sundie]

With a simple T, the airflow would be bad (performance wise), for several reasons, unless you knew the exact length of the pressure wave of the intake valve closing - but even then, you can only average it out, and either low end or top end is going to suffer. And a "T" makes the air take a hard turn. Which = turbulence, back pressure, crazy reflective waves, etc etc.

Air flowing at the speeds an engine sucks it in has quite a bit of mass. What happens in a T is that one cylinder will suck it in, getting it moving, then the valve closes. The air will actually compress against the valve as this happens, then "bounce" back. If you can time this correctly, the wave will come back to the T at the precise moment the other intake valve is opening and force air through there. But good luck with that... It's probably more likely to push back out the carb.

In a car, you have enough space to make a big enough plenum volume that this effect is essentially negated - thus a single carb/tb is fine. The intake plenums in bikes just don't have enough volume (because of lack of space) to deal with this.

That's one of the reasons most (if not all) "modern" bikes have a carb/tb for each cylinder. If they don't, it's a purely aesthetic/manufacture cost decision.

 

[Sundie]

Wait, i think i totally misunderstood - you're making a single intake *before* the carbs, and still using two carbs? Uhm. While that would be an interesting experiment, i'm fairly sure carb tuning will mess with your head - the farthest carb will receive less air than the closest. the reason this happens is that the farthest carb has to fight against the closer carb.

 

[cheftay]

ohh ok...i'm catching on now.

 

[angus67]

if you want just the filters to turn to the sides, why dont you just use individual bends? One bends 1/4 circle to the right, and one 1/4 circle to the left.

 

[inxs]

- or turn ya head

- seriously, im just joking...its not quite that simple

 

[weekendrider]

ejdirin, his user name was "retired". The pics are gone but here is his description.
"I wanted to make an air cleaner that fit with the "old" looks of the bike rather than just put two paper cleaners on the carbs.
The air cleaner housing is made out of 2 inch diameter copper plumbing fittings. The filter is for a 2-barrel carb."
His build thread is pretty interesting. Search for posts by "retired" at 650 rider or XS650 Forums. Like I said the pics are gone but he does a good job of describing it.

 

[ejdirin]

Thanks weekendrider. I'll check it out. Good to know that it can be done...now the question is, once its done, will it run?

 

[72XS2]

Why don't try with two filters, one coming from each side. The same effect but on both sides and no more problem about carb sucking more air than the other.

 

[angus67]

Why don't try with two filters, one coming from each side. The same effect but on both sides and no more problem about carb sucking more air than the other.

you should try that, I think 72 has a great idea there.

 

[Visegrippe]

I kept wanting to suggest that and kept getting interupted mid-post... sigh.

'Nother vote for one out each side, don't think I've seen it before.

 

[ejdirin]

That sounds like a cool idea. You'd think you'd get better airflow too because the filters would be hanging in the breeze. And simple too. If I end up doing that, I'll definitely post some pics.

http://www.pexsupply.com/Cello-WP7-32-2-CxC-90-Elbow-901000-p

After looking at how nice those look, makes me want to put a bunch of copper parts on the bike....

 

[big al]

I've been watching this discussion and at first thought that it was a neat idea until it clicked.I think your biggest and only problem would be the carbs themselves as they are CV's and depend on vacuum to open them and the vacuum signal is kept seperate with stock airboxes but not so with a single airbox feeding both carbs wich would allow the intake pulse of each carb to affect the other.Now having said this a single carb two into setup like the picture above works great as i have built several variations of it.
That setup results in better bottom end response and torque with a small loss on the top end.Sort of like the comparison between the old triumphs tr6 single carb would outpull the twin carb bonneville on the bottom end.
That's my story and i'm sticking to it.

 

[Sundie]

The stock airboxes are not strictly "separate", since there's a joiner between them. But the difference between that and a (relatively) small single path are huge.

I agree with your point that the carbs being CV would indeed be the largest problem with running a joined pipe upstream of them. Forgot about that. Thinking about it, i kinda doubt that the slides would ever open fully (if maybe at all), since there could conceivably be as much (or more, if the pipes are smaller than the twice the area of the head intake runners) vacuum on the upstream side as the downstream side.

That means you'd need a 76mm (for 38mm carbs) intake pipe, or about 3 inches.

I'm thinking there's not a lot of space to snake a 3"id pipe around the frame in the stock bike.