concensus on treedragon's airbox mods?

[nonook]

Just stumbled across 'treedragon's' airbox mod's dated 7-24-10'.  Did everyone agree enlarging intake runners from box to carbs worked?

[Cdnlouie]

There is a huge consensus that the stock airbox (with early 82 model modification incorporated - I.e. vacuum controlled flapper) works just fine, if that is any help.

If you are not a highly trained professional with at least the equivalent of the Japanese airbox designers understanding, I would not recommend making any airbox mods.  If you are looking for more trouble than you already may be having that is the direction to head.  This is not a commentary for or against another man's idea, it is simply a universal statement against anyone who contemplates an airbox mod without great understanding of what they are doing and trying to achieve.

[Extent]

I find it particularly interesting that with their attempt to fix the stumble the factory actually added restriction to the airbox, and dyno charts done with no airbox at all show not insignificant power losses across the entire band.  I am entirely unconvinced that any enlarging of the stock system would provide any positive gains unless someone can provide comparative dyno charts showing the opposite.

Now if you're going to build a new airbox from scratch and are specifically tuning the individual parts to work with each other, then you may be able to get something.  But that goes far far beyond "make bigger-moar air"

That's my gut reaction to it.

[The Prophet of Doom]

When I bought my 550 it had no air box, just a couple of oiled foam socks and mufflers with no baffles, identical velocity stacks, 120/120 air jets and 125/125 mains.  My experience with this set up was it accelerated like a screaming banshee, but had a massive off-idle lag.  I ditched it, and went stock though later found that the lag was caused by an unclean accelerator nozzle.
My initial setup for the current build will be without the air box

[Rikugun]

roro, please let us know what your results are with the modified intake tract.  8)

I can understand Cdlouie's passion for keeping the bike in stock form and especially for street use but as I recall treedragon seemed to have some success with his mods. I realize his results were not dyno verified but anyone looking for more power may want to experiment with his methods.

What happened to treedragon? It seems he is no longer a member?

[Rick G]

Many have tried , over the years to eliminate the air box (all "modern" sport bikes have them) The problem is that the carbs are really too big for that size cylinder and will over carburette at low rpm. Today fuel injection and a computer take care of the problem, but in 1982 this is how they did it. I personally  have never seen a Vision run right with out the air box. Good luck!

[treedragon]

Just a quick thought or two on this while I am (unexpectedly) still around the place.

Currently, and for some time now, my airbox is as empty as I can get it except for the extended carb trumpets. The breathers from the valve covers are running to a small overflow bottle tucked away out of sight in the frame and the airbox vent holes sealed, after several thousand k's it only has a film of oil in it

The flapper valve is still there, it is needed.

There is no internal air filter, I filter the air intake with externally mounted filter foam that I keep well oiled.

Performance - improved. The group I ride with know this, we don't hang around and on the first ride after doing it one asked "Ok so what have you done to it this time"

The only hint of a downside is a very occasional, and a slight very short lag, at the bottom end before I have any useful revs on. I feel this may be rectified if I were to play with the adjustment of the flapper valve.

However as I am getting close to finally dropping in the original spec Cosworth cams I am not too concerned as it will likely all need re-doing anyway, we will see  ;D

[iain]

Good to see you back Bro
Iain
NZ

[AdvRich]

Another factor to consider is an air box acts as an intake muffler and this little boy can howl pretty well with just some clamp on filters, which might be fine for an afternoon of hooning, but gets old when commuting or touring. Airboxes also help to protect from rain or to pull in air from a cooler source or take advantage of a still or pressure area of airflow over the cycle/vehicle.

[JohnAMcG]

Why let highly trained professionals have all the fun.  What's the worst that can happen.  I remember reading about the mods a while back, and there was a lot of anecdotal evidence I heard about doing things to extend the velocity stacks.  Let us know how it works out. 
I am not ready to start chucking parts out of my bike yet, I still may need to put a few in before she really comes to life. 

[Raj1988]

I found a 10-15 % increase in fuel economy PLUS a more responsive feel after creating the trumpets... I rode over 8000kms with them and they are here to stay

[Protonus]

I found a 10-15 % increase in fuel economy

What does that equate to in mpg before/after?  My bike averages about 42mpg.  I've seen as high as 46mpg and as low as 38.  I usually beat on her a bit, lot's of accelerator pump shots that I'm sure hurt my MPG lol.  It's a 82 with full 83 style fairings, stock jet size AFAIK but rebuilt carbs at least once, currently sync'd afaik.  I normally run 89 octane.   I have the late model actuated flapper airbox.

[jefferson]

I'm not familiar with the longer trumpets thing you did. Is this inside a stock airbox? How long did you extend them and how did you do it. I kind of like that kind of mileage increase.

Jeff

[Raj1988]

From 40-46 before and regularly 50+ in average riding conditions

[vadasz1]

So Raj your numbers are 40-46 MPG before correct?  So before if you got 46 MPG then you went approx. 207 miles (331 kms)on a tank of fuel?  And now that you are getting 50 MPG you are getting 225 miles (360 kms) on a tank.

I am usually getting about 150-160 miles (240-256 kms) on a tank of fuel.

If you are really getting that good fuel consumption I think it is in order to make this modification a sticky with all the pictures possible and VERY detailed instructions.

[QBS]

A good running '83, at legal highway speeds, mostly flat lands, and not much headwind will get a little over 200 miles before its' rider begins walking.

[treedragon]

My reasons for the trumpet extensions (using a spare pair of XZ trumpets) was for improved power delivery, I got it, particularly in the midrange and this could likely be improved more if one got a bit nitpicky about it.

My fuel economy is as follows:
Thrashing it with lots of high revs and mucho cornering ie lots of accelerator pumping --- 18 to 20k per litre
Normal road riding, fairly constant throttle --- 22 to 24k per litre, sometimes more if it is all flat and I am feeling road legal is the way to go.......  :police:

However I do use acetone in the fuel (approx 1ml per litre) and it gives me an extra 2k's per litre. These are consistent figures taken over many thousands of kilometers with a calibrated speedo (after market).

 

[Rick G]

I checked my mileage once .
, it was 49 and a fraction at , mostly 65 mph.

[jasonm.]

I find it particularly interesting that with their attempt to fix the stumble the factory actually added restriction to the airbox, and dyno charts done with no airbox at all show not insignificant power losses across the entire band.  I am entirely unconvinced that any enlarging of the stock system would provide any positive gains unless someone can provide comparative dyno charts showing the opposite.

Now if you're going to build a new airbox from scratch and are specifically tuning the individual parts to work with each other, then you may be able to get something.  But that goes far far beyond "make bigger-moar air"

That's my gut reaction to it.

Dyno readings are ONLY done on a FULL TTHROTTLE application. They have no bearing on 90% REAL normal driving/riding...

[Rikugun]

 A dyno test is done at WFO if that's all you're interested in. Extent claims the charts to be from the entire RPM band - although I have not seen them.  Just sayin'  :)