Air box design - Weber/Mikuni w/horns

[Tony D]

You take notice of the shape of that plenum and how it differs from the S20/432 airbox.

Having owned multiple cars with factory Solex and Mikuni Multiple Carb Setups, non use the TWM Design, but are more or less permutations of the S20 Box Pictured above...

 

I think the velocity air, and diffused air inside makes a big difference - this was shown on Monzster's thread under pressure.

If you look at atmospheric pressure as just that, and not 'vacuum' then the plenum design of the S20 and the surge tanks makes sense. You want an area of diffuse pressure surrounding the inlet air horns, in a slightly positive pressure if at all possible... 

[Tony D]

There was one poor guy who coughed into his TWM, the plastic started on fire, melted, got sucked down the Weber and plugged the booster venturi letting that cylinder run way lean and "boom' there went his head gasket.

I ran the TWM Open unit for years. I think the open face helps with the draw into the barrels. Though ultimately it just crumbled from the SoCal Atmosphere. Ran it from 90-maybe Y2K on and off various vehicles with my Mikuni 44's and Weber 40's

[z-ya]

According to Dave Rebello, running one of those style air boxes is detrimental to max power. He recommends the ITG or another open air style filter. There was around a 10HP difference on the 3.2L he built for John Jeffery. John has now switched back to the ITG setup.

 

I run these RAMAIR filters on my Datsun 1200. They slip on and off easy, and stay on, even with rubber chunks flying around the engine compartment on the track:

 

http://www.ebay.com/itm/3-x-RAMAIR-Carb-Sock-Air-Filters-MG-MGC-MGC-GT-6cyl-Weber-40-DCOE-/390873883975?hash=item5b01e62547&vxp=mtr

[Gareth. J.]

Do the RAMAIR filters have an internal spring? I had some 'uni filter' socks get sucked inside out and into the stacks on my old triple set up on a track day. 

[ryant67]

It's a shame that the TWM airbox proves detrimental to top end horsepower, but other box designs have been tested and shown improved midrange torque and no loss of top end horsepower.  

Thankfully I not attempting to emulate the TWM design terribly much.  

I don't mind pushing on with this project - worst comes to absolute worst, I still have my ITG backplate and can just buy a new filter and be out some money.  Might as well have some fun and see if I can build something a little different though.  

[z-ya]

The RAMAIR filters do not have a spring, but the hole is quite small, so they get a very good grip on Mikuni horns. Probably the same for Weber horns.