Moving up to 38mm carbs, which manifolds should I use

[racerclam]

UFOs work well , I build alot of carbs and all round slide carbs get them along with venturi dividers . The new UFOs are easier to install than the old ones , I helped Lon on redisgning them for this purpose .

Rich

[~JM~]

What are UFO ?

[Plasticman]

What are UFO ?

Dime City Cycles has a nice explanation on them.  You can purchase UFOs from many places.

DESCRIPTION
The UFO is a simple, trouble free, aerodynamic piece that fits VM Mikuni carburetors from 30 mm through 44 mm. The UFO makes a normal round slide carburetor out-perform the more expensive flat slide carburetor by eliminating turbulence and increasing air flow and velocity, creating a highly atomized fuel charge. Normal gains are 3/4 to 1 HP per 100 cc of engine displacement on 4 stroke engines and 1 1/2 to 2 HP per 100cc of engine displacement on 2 stroke engines. (Minimal rejetting and tuning are required).



Source: https://www.dimecitycycles.com/ultimate-flow-optimizer-ufo-mikuni-vm30-vm32-vm34.html

Rob

[pdxjim]

I had RB install divider plates in my TDR's TM28ss carbs about 10 years ago.

Hard to tell the improvement as he did a bunch of other stuff (bored carbs to 29.5mm, skimmed head, etc)at the same time.

Will def be going in to do the reeds and intake as soon as I'm done with my LC, as the TDR is still running the 30 year old stock reeds and it feels pretty flat thru the midrange and made a lot less power than I expected when I had it on the dyno last year. 

[racerclam]

UFOs are also available for  banshee 26mm carbs . I modify UFOs to fit other sizes also  wuite often .

Rich

[teazer]

Has anyone seen any published results of airflow or power with UFOs or dividers?  I'd love to see the smoke effects or even better actual CFM changes and dyno results at part to full throttle.

[teazer]

You could just buy a set of OW31 reed valve TZ750 cylinders if the rules allowed it, or a set of TZ350G 6 port cylinders and add reed blocks and boost ports.

With all the crazy shit people do these days you'd think someone could take an OW31 cylinder, remove the water jacket and fabricate/weld some fins on it so it would be legal to race against the RD400s. 🤔

Or just mill 6mm or so off the top of some RD400 pots and slide the same amount under with a lift plate.  That would get port timing into the same region.  Now all we have to do is to remove the port dividers and replicate 3G3 6 transfer ports. And that would still need much larger reed boxes and cages. Arctic cat or Polaris XCR triples come to mind as alternatives.

TZ750 cages are too small for TZ750 cylinders.  They were fine on a 90hp motor, but not so ideal for more power.  I use Blaster reeds on a single 700 (TZ750A) barrel and 6 petals on a 375.  There are probably better reeds out now and to be clear, I bought the 6 petal cylinders.  I can't claim credit for them.

But if the class rules are stock cages, that sort of limits things.

[racerclam]

I dont have dyno results on my dividers . But lots of customer results . You can see some on the testimonial page of my web site  richstaylordporting.com  what you can expect is linear power on ANY machine you put them on . There is a RD 400 road racer in that page that I did all the port work on as well as carbs , His first report before I did any port work was a much harder pull out of corners and he did dyno it and also gined 1 hp through out although that is not alot , the stronger linear power was . There is also a 2016 TM 125 on there that proved my thoughts that with the dividers a power valve would not be necessary , so he disconnected the electronic PV and connected it to a choke lever cable acuated PV and he reported better performance from off idle to top . I have done many carbs for some customers , I jst compleated a 6th carb for one guy and have done 15 for a top snowmobile racer . Doinf four more right now . THEY WORK . The ones RB did used only dividers at 1/2 throttle  which has sone benefit , BUT does not compare to having one at  1/2 qnd 3/4 throttle positions , its like opening 4 small carbs in series , air speed stays constant . If any one want more evidence I can hook you up with my customers directly , They wouldnt mind at all.

Rich

[1976RD400C]

Have you decided how your bike is going to inhale yet?   

[Plasticman]

Have you decided how your bike is going to inhale yet?   

Probably in big gulps.

Rob

[1976RD400C]

TZ/RZ sized single petal TDR reeds installed

[85RZwade]

Oh yeah, that's the stuff!
Wade