Paul or anyone.
 Looking at the Kinsler racing goods catalog I noticed that their
 butterfly throttle fully closes 14 degrees before perpendicular. Is
 this design point to keep it from jamming when shut Obviously the
 throttle plate then will not be perfectly round but an ellipse.
 Also does a throttle have to completely close Cold starts may be one
 reason perhaps but that is not such an issue with programmable
 injectors. I am concerned because the high vacuum forces on the throttle
 plate may bend it unless I chose stainless.

 Doug in Japan.

 Yes that is what it sounds like to me.
 Usually throttles don't close completely as the engine needs
 air for idling. The carb idle adjust screw changes the throttle
 opening during idle. Not to be confused with the carb idle jet screw.

 Kinsler has some neat stuff so everybody should download their catalog.
 http://www.kinsler.com/page--HandbookCatalog--2.html
 Particularly useful are their bell mouths for intake runners.

 Paul Lamar

Many FI systems used to have idle air bypass - allowing the throttle
plate to close completely. Air through the bypass is controlle
d by a
separate (sometimes feedback, temperature adjusting, solenoid
operated) valve.

Regards,

Matt-

Guys
Thanks. I'll go ahead and make up a butterfly valve on Friday.
Everyweek I am logging ten hours in the school machine shop and it is
finally paying off. Some parts however are faster to make from a rough
sketch and then cut to fit then pre design if you know what I mean. Real
world meets design world sort of thing:) Those parts will be documented
after their dimensions are fixed however.

Doug in Japan

Doug,
All current butterfly carbs are set up to prevent closing to 90. Several
reasons for this, the first you got right off, to prevent jams. Second; and
similar to the first is to prevent damage in the event of a backfire. It
also prevents the linkage from going over center and trying to open the
wrong way. Lastly, the closer the butterfly is to vertical the more variable
the plate position will be at idle. Most carbs have a series of holes near
the closed point to control the idle mixture better. Those holes need to
open in the proper sequence to transition properly. If on the other hand if
you are making a throttle body it is as critical. I would still go with a
slight angle, it will work mor
e reliably.

Bill Jepson

Bill,

Thanks. I will be in the shop today and will try to whip up a 15mm thick
52 or 53mm ID throttle body disc with the welded shaft stubs idea for
least aerodynamic resistance. Unsure whether to go with brass bushings
or mini bearings. I am leaning towards using the bearings. Your
thoughts

Doug

Doug,

The last of the motorcycle carbs used bushings. They used the filled
nylon or specialty plain bearings check Garlock, or Bushic/Shamban
as a couple of compaines I've used in the deep dark past.Real mini
bearings are fine but use sealed ones because they will get dirty
and jam otherwise. one other thing to concern yourself with is
will your throttle body be blown That is will it be before or
after a turbo or supercharger you may need to seal the shafts.

Bill


Bill,

Thanks for the leads. I got the throttle body  lathe work finished today.
Final dimensions are 80-OD and 53-ID.  and 12mm thick.  Didn't have
tube handy and had cut it out of 6061 T6 rod.  Made more shavings then
part:)
Next week I'll use the end mill to put  some flats on the sides and bore
the shafts.  I can make a   Teflon bushing as I haven't found anything
that small from Glacier/Garlick Co.  Be nice to not have to make
everything though.  I can get sealed mini bearings from NSK  but I am
not happy with the thickness. The ten mm OD size  is only 4mm thick I
would like to have twice that. Doubling them up is a possibility but
design overkill and heavy

 I could be running 5 psi max and at high altitude, and if so the delta
P will be high enough the   might leak as you remarked around the shaft.
That fact pretty much means I will  have to make the bushings..I am
exploring a variety of sealing methods now. Minn air pistons seals a
possibility.
The bigger challenge is getting the throttle plate designed and into
Solid Works so it can be laser cut.  Modeling it is easy.  It is just a
14 degree slice through a 53mm OD bar.

Doug