XJ650J airbox alternative (not pods, not stock either).

Hey all. I got myself an 82 650J about a week ago ....


Since then I've got some work done to it ...




After reading a LOT about using pods here, I decided against using the pods that came on the bike when I bought it. The stock airbox sounds better (per info posted here) but most examples of stockers I've found are scarcely polished turds, warped and funkified.

So my husband (WFO) and I came up with this little thing ......



I already posted it's construction and since I'm so lazy (tired? It's after 3am!) I'll just provide the link ...
http://www.ironhorsemotorbikeforum.com/ ... 1140#p1140
Go to page 3. The airbox mods begn there.

Hope it helps someone!

Thanks ... Abeja ....

 

Ok, I've been working on it pretty hard since it came home.



I'm working on color schemes. WFO gave me the idea of using the rear of the seat to make it look like a stubby cafe type fender. So when I take it down to Roberto here in town (where we have our bike seats done .. he's good and inexpensive) I'll have him do it in two tones to make it look like a rear fender. Exactly which two colors ... I have NO idea yet!



After much reading on these bikes, I decided to remove the Pods that come on it and go with something else. The stock airbox is ok, but most of the Ebay offerings are funky and warped. So WFO and I kicked it around, and after some time we came up with this setup for an airbox. It will be made of 2 inch steel exhaust tubing then WFO will TIG weld it all together. It will be held on to the carb bank with silicone tubing (available from many turbocharging parts suppliers everywhere). We both are hoping that it's volume is somewhere close to the stock airbox. Hopefully this will help us tune the bike a little easier.






Started with determining the size of the steel tubing. Turns out that 2inch is nearly perfect. And it turns out that the roll inside of a paper towel (called a *durder*) is almost exactly 2 inches in diameter. So for mockup purposes it will work just fine. We laid out the cuts using a piece of tubing that we're fitting up too ...


Then cut out the *fishmouths* from the airbox carb snouts. I cut them a half inch too long to make up for the gap between the airbox and the carb's bellmouth. This imaginary gap will be jumped with silicone boots later on....


They don't have to be perfect, this is just a mockup.


Check the log tube for fit ... again perfection isn't necessary. We're just making sure the idea even works at all for now.


Carefully fit it into the bike in pieces and start fitting it all together ...






Once you're satisfied with the fit, start taping it up. Keep in mind that this thing has to be able to come in and out of the frame once it's wleded up out of steel! So be clever...


It's like tack welding ...




Add the gas tank, check fitment again!....


And add the seat to check it all out ...


Once happy, take it allllll out and tape it up a bit better .....






Abeja ...

 

.. continuing ....

Put the airbox in, and add the tank and the seat. Check it all out very carefully for fitment.

The airfilter can be mounted further under the seat if I want, or angled differently, or whatever ..there's many ways to hang this filter. It's not in the way of the stock battery box or the stock underseat wiring setup at all! Nothing gets moved or hassled with under there.


Looking straight down yo can only just barely see the airfilter sticking out on the left side of the seat. It doesn't interfere with my leg at all.


Right side doesn't hit either ...




So there's a mockup of an airbox alternative .. it's not pods, it's not the stocker, and it's not too difficult to build. It allows the use of the stock battery box and electrics. And it's somewhat tunable in that different sized restrictors can be tacked inide of it's throat to create more vacuum. Or, a second intake tube can be added to the design rather easily as well. So if more air is needed there is room in the design for that. I think WFO did a smashing job if designing this for me.

After fitup is perfected take apart the mockup and use the cut tube ends as "pipe wraps" to get the notched fishmouths to fit perfectly prior to welding it up. Doing these mockups is really helpful to WFO when welding things like this up. Imagine this piece done in NICKLE! Wow.

I'm happy with the progress made so far. It's already looking like a motorcycle. So we've been busy in our shop! I just love this picture .....


More later ...

Abeja.

 

NICE... I like the concept... i was thinking of something similar myself... I will mock it up in paint... bbiab!!

 

I was thinking of doing something like this...

I would fabricate it from PVC i think... and then connect to it with the rubber boots that would go to the stock airbox...

The large single pod would be roughly where the stock airbox is...

I was also gonna make the air intake tunable with a butterfly valve that can be locked down...similar to the inside of a carb...

 

I see a problem with the design. But I might be wrong. The original Airbox was able to provide enough volume to draw air as each cylinder needed it because it had individual carb boots fitting to a large (relatively) volume box.

Pods also are able to draw their own air as each cylinder needs it.

With your setup, carbs 2 & 3 are going to be able to draw air more easily than 1 & 4. I would think that this will hinder performance and possible create tuning problems.

Pros...step in and let me know if I am way off base here.

 

That's. Bada$$. I wanna know how it all works out for you. Nothing like filling up an empty spot with a bunch o' chrome!

 

Nice concept.

My comment is on the last picture. Since you live around nice long straight roads, does your husband really think that he's going to keep up with that XJ?

:wink:

He's going to be begging you to trade! LOL

 

My concern is the volume of air available down the intake runner. You have some angles and increased length. They will cause restriction to air flow and you may have trouble providing enough air, particularly at higher RPM. At maximum rpm you will need an extremely high volume of air available. I'm not sure a 2 inch pipe approximatley 14 to 18 inches long with bends can provide what's needed. I'm not an engineer, but maybe someone out there is and can make the calculations. I would hate to see all that work go to waste.

The extreme angle to turn into 1 & 2 may leave those permanently starved for air. The velocity will be lost turning back at that angle. If you hade a large collector and ran the feeder to the manifold runners at 90 degrees it might help.

 

I wonder too if you're going to get weird dynamics in the air flow through that. The stock set up is essentially a short velocity stack into each carburetor opening into a relatively large volume chamber (the air box). The intake to the stock air box is pretty small, so I'm not concerned about the overall flow through your single pod. Have you considered a larger volume interconnect tube between the carburetors? It could even have a different than circular cross section (elliptical maybe).

Other than the fluid dynamics your rear corners at the #1 and #4 carburetors are sharp. Aside from the potential to snag clothing on them they break the lines of the bike. I'd recommend chamfering them a bit, so they blend in with the styling (as seen from the top).

 

The other solution is an equal length intake setup. Make the 2 & 3 intakes longer (curve up and then down to the common large POD connecter). But then you are lengthening the runners and you will change the effective torque curve of the engine. As MiCarl pointed out, its a short runner setup that is probably designed for high RPM horse power.

 

Your drawing needs a tweak or three.

The Airbox Inlet (stock) Regulates: CFM (Cubic Ft per Minute)
Total CFM is Shared by the Rack. ( CFM ÷ 4 ) = 1x
1x passes through Rubber Boot which acts as Velocity Stack and causes 1x to become SHAPED, SWIFT and above all: Non Turbulent.

The Non-turbulent column of air exiting the Rubber Boot "Mini-Velocity Stack"
provides:
POSITIVE Pressure upon the Intake Horn Atmosphere Vent providing AIR to be Circulated through the Vent --> Through the Main Air Jet --> through the Passage which exits at the Void surrounding the Emulsion Tube --> which passes through the Tubes Metering Orifices and: a) Gets drawn-up the Tube ... b) Atomizes Main Jet Fuel.

The Swift Column is further Compressed and Accelerated as it enters the Carbs Venturi: ==> Causing a LOWERING of Pressure at the Emulsion Tube's Top Outlet ==> Which draws the Surrounding Main Air at the Emulsion Tube to be pulled to the Vacuum ==> Siphoning Main Fuel.

IF, ... the INTAKE AIR is NOT Shaped before it reaches the Carbs Intake Horn:

The Carburetor DOES NOT Function Properly.

 

Hey all...

ok... i am probably about to step on some toes here... and i am new as well... double whammy... i do not mean to offend anyone i am just gonna state my humble opinion... and it is just my opinion and i am not claiming it is fact... =)

Disclaimer aside ;-)

So I read through a bunch of posts on pods and stock airboxes... and now this thread... I have sat and pondered this as I am trying to decide what to do with my xj.... I just went out and did a thorough examination of the stock airbox and then re-read a bunch of threads relating to air intake...

The stock is better argument seems to be making these points over all...

Pods or other custom air intakes do not provide the required amount of air for optimal performance... and these non-stock options may not provide it evenly across all the carbs... there is also the idea that the air is not coming in at the best angle for optimal performance... another is whether or not the air is at the right velocity... i know there are other arguments but these seem to make up the core of the concerns...

I think we are overthinking this whole thing.... and we are giving the designers at yamaha to much credit... i am not saying that they were not great designers... but in regard to this issue i think we are thinking about it more than they did.... =)

OK... the stock airbox... and incredible engineering feat?? i think it was designed to fit in the space that was left... and to provide clean oxygen...

1. the concern regarding the possibility of some carbs being starved for air because of the air coming a longer distance... the filter chamber on the stock airbox does not enter the airbox chamber in the center... it is actually almost directly across from carb 2... so carb 4 is getting the short end of the stick and carb 2 is by far the favorite child...

2. another concern... the 2 inch pipe may not allow enough air to pass through it... in the stock airbox... take a close look... when the rubber boots are correctly seated... how much space would the be between the end of the rubber and the back wall of the airbox chamber... about a half inch at the top ... but more at the bottom... but wait that means the air is coming in at a pretty sharp angle... to the next point...

3. in the stock airbox every carb has something totally different to deal with... carb 4 is getting air at about a 30 to 35 degree angle down and to the left... carb 3 about a 45 degree angle.... 2 almost straight on... and 1 much like 3 but from the right... and as the angle increases the bottleneck does as well..

4. size of the air chamber... i took a few measurements... and these are rough and will be generous regarding the volume of the stock airbox... but i am guessing its about 150 cubic inches... not including the filter chamber... a 12 inch cylinder with an inside diameter of 3.5 inches would be about the same cubic inches... and you could get that diameter down by using the same size openning between the airbox and the filter chamber as the stock setup does...

After looking at all the evidence... i would have to say that it seems as though the airbox was designed to fit into the frame and space they had left... that they were not really concerned about what direction the air was coming from... or making sure the distance to each carb was the same... or that really total volume was an issue... and since every filter manufacturer makes there filters a little different... some thicker than others... this would also effect volume and velocity... i think that they... for the sake of long term support of their equipment designed it to provide clean oxygen within a approximate tolerance... and if you were looking for the best your bike could do then you should probably use a yamaha oem filter... because they had control over the thickness of the filter medium... and therefore the amount of air available to the carbs...

This is something that would be easily measured and could be duplicated in a zillion different custom designs...

We are talking about a consumer grade vehicle here... something that could be sold all over the world at different elevations with different air qualities and still perform well driving them from one place to another... without having to stop and adjust your carbs as elevation and oxygen levels change... because oxygen is the part that matters in combustion...

I have a good friend that is an engineer and also the brother of a successful NASCAR racer... do you know that they tune their carbs hourly before the race... barometric pressure, temperature, and humidity effect optimal performance...

Consumer grade equipment is designed to be used by the masses all over the globe... getting optimal performance out of your bike is not gonna happen with the carbs that are on there... they are not designed to be pro performance pieces of equipment... they are basic and designed to function well in many environments... but not optimal for any one place or environment...

So to test my theory i went out and took the carbs off my 650... attached them to the 750... fired it up and took it for a ride with no air filter whatsoever... it started, ran, and idled... was it optimal... no... was a little sluggish at some points and was a little slow coming back to idle... but driveable... so i hooked up the air box...performance was similar... still got up and went for the most part... cruised at 60 fine... idled a little higher than i like so i tweaked that a bit... ran ok... and these are dirty carbs...

We are talking about some very solid and cool old bikes here... it is an internal combustion engine... it isn't rocket science...

And thankfully yamaha is good with quality control...cuz the tolerances are very nice for a consumer product...

So is there a optimal setup for these engines... of course there is... but that is not something yamaha put into the design... because optimal is only possibly in one place... and at one time... with the right conditions... and the right tweaks...

And optimal performance is not something you are ever gonna get close to with stock equipment...

i think there are many options that will work well on these bikes...

peace

david

 

Date of Manufacture:

January 1, 1981
. . . . . . . . . . . . . . . . . . . .

Date Pods Erratic Problem Solved:

TBA - Still Unresolved. (11,467 Days)
. . . . . . . . . . . . . . . . . . . . .

May 26, 2011 ( 11,468 Days )

 

Well thought out.

I do think you have overlooked a couple things that may (or may not be significant).

- In the stock air box the velocity of the air will be slow compared to that moving down a 2" tube. The lower velocity means less turbulence where it goes over a sharp edge.

- Pressure drop in a moving fluid is proportional to the length of a narrowed tube it moves down. Because there is effectively a long 2" tube to any carburetor it may well get less air than in the stock set up.

- There are also inertial effects because the flow into each cylinder starts and stops. If I remember my rules of thumb a longer "stack" is better at high speed where a short one is better for low end performance. Since all the carburetors share a length of the stack they may also affect each other.

I think your analysis of the air box is probably spot on. I'll bet the airflow management to each carburetor is largely done by the boots and the molded in entry horn. The air box is whatever would fit and hold a filter. I wouldn't be at all surprised if running the bike with just the boots and no air box at all would deliver very satisfactory results.

 

I too ran the bike with nothing on it and it seemed to run just fine. But, that is an entirely different thing than unequal length runner funneling from one source.

The air box as originally designed is as MiCarl stated; a stagnant environment that the air is drawn from straight shot or not to number 2 cylinder. Plus it has to go through a filter further breaking up any straight shot.

I just think that pods would be preferable to an unequal length design in terms of long run.

Now, if looks are more important than performance, I clearly should drop it.

Perhaps I should anyway.

 

Thanks for the opinons, everyone. What has to be considered here is ... this is a mockup. This was designed to create discussion.

We understand how important it is to shape the airflow as it enters the carb. Perhaps incorporating some of the stock inlet "v-stacks" could help with that.

However .. how much of that is killing an ant with a hammer? We've seen tons of different engine designs that use *conveniently* shaped airboxes that seem to defy fluid dynamics, yet work within very acceptable levels. The operational range of such consumer devices is pretty broad. So my engine won't look "optimal" on a dyno with tubes and senders connected to it monitoring every single aspect of airflow and energy output. As long as it's rideable, and doesn't smell rich, and kill me at the gas station ... we're in happyville guys!

Owning motorcycles means something different to everyone. To some folks, it is all about totally optimizing the engine to the Nth degree, and having every I dotted and T crossed. To others it's all about the tactile experience of the road. And yet others love the feeling of testing fate riding at speeds that test your bravado (and your tires!).

So we'll take everyone's suggestions into consideration. In the end, no matter how much pre-design and theory you throw at it .. it must be wet tested. So we'll watch plugs carefully, make sure the carbs are as 100% as we can get them, and go from there. If this airbox doesn't pan out, it adds to the scrap pile.

Keep in mind .. it is an airbox, not an intake manifold. We've seen some pretty ugly evils actually work in this area.

From what we can tell, the order of preference sounds like:
1.) Stock airbox. Problem is finding one that isn't a warped box of crap.
2.) Something along the lines of this *log* I've posted here.
3.) Pods. Finicky and for the *tuners* of the world.

I was told a long time ago that "If you like spending more time under the bike, drag race. If you like spending more time ON the bike, road race." Well, I'm not one to spend my days wrenching. I would rather get that part done and spend time riding. That's what I get out of the motorcycling experience.

Speaking to some of the ideas mentioned. Why can't the stock V-stack boots be used to connect the log to the carb bank? Or ??? I've seen so many airboxes that were dynamic abomintaions that this little log thing looks glamorous by comparison. I mean, the bikes seem to run ok even with out any preflow shaping at all. Sooo ...

Thanks tons for all the cooly input. If I didn't want discussion I would not have posted it. So thanks again fellas. It's all good.

 

Haahaa! Thanks, but I dunno. That bike of his is a 1982 V45 700cc V4 Magna ... 80hp and 25 pounds lighter than mine and kinda warmed over/lightened up. Legendary for their day from what I understand.

But he has been eyeballing my bike like some fresh cut of meat since we got it home. I have to shoo him away from it so's he doesn't drool on it too much. (haahaa!)

Thanks for the compliment!

Abeja.

 

I any case, it was just a mockup. Thaks for the help. To be honest I'm fairly discouraged at this point. I just gave in and went searching fleabay for a stock airbox again. Perhaps I'll find one worth droppng coin on.

Just wish the pods weren't such a pain to tweak. They sure are easy to look at.