Subject: p-port butterflies
From: Rotary Engine
Date: 10/12/2006, 12:53 PM
To: AA-me

Paul,   I am planning on running a twm throttle body for my initial
p-port intake system , at least until I get all the bugs worked out of my
install.  I have heard that the slide throttles in general may not be
quite as forgiving as a carb or TB at or near approach  throttle
settings and I'm just a little concerned about adding the slide throttle
to a lot of other things to be concerned with on initial flights. My
thought is to use a Wiggins clamp where racing beat uses a hose
connection and this enables me to swap to carbs for remote bush flying
and efi  TB or slide throttle for local flying.

My question is what size TB would you recommend for the 1.875 I.D.
p-port insert.Would the efficiency be improved by slightly oversizing the
TB to make up for throttle plate restriction. TWM provides 48,50, and 55
MM TB's in the 3000 series.

My plan on the primary injectors is to possibly weld an injector boss on
the insert before boring and epoxy and install it as close to the rotor
housing as possible. The injector bosses in the TWM  TB would be used
for the secondary;s.

Check out weld on injector bosses at sdsefi.com.  very clean install and
for $37 hard to beat.

What are your thoughts on TB size and injector location

Thanks   , Geir

All  you guys concerned with the slide throttle position
as a function of HP generated make the hole in the Teflon
tear drop shaped. Don't make it round. I'll do a drawing for
you shortly. You can have your cake and eat it too.
-- 
Paul Lamar ...No rotor no motor.

-------------------------------------------------

Here is the dwg. I added an inch to the back plates on
the rear housing end (car). An unanticipated advantage is
the total throttle cable travel is increased from 2 inches
to three inches making fine adjustments easier.

I can understand if you don't want to build one of these and just
throw money at the problem by buying a TB but be advised
butterfly's will cut the HP and burn slightly more fuel.

Best use the 55 mm TB but then you will have to make a smooth
transition from 1.875" (47.625 mm) to the 55 mm throttle body.

If you use the 48 mm instead you will lose more HP and burn more
fuel and you will still have to make a smooth transition.

-- 
Paul Lamar ...No rotor no motor.

------------------------------------------------

Hi Paul,

Please explain the teardrop slide.  All I can see is turbulence at WOT
as the charge rushes by the edge of the teardrop.
How is this better than a lens shaped orifice at idle setting with the
plain circular hole.
BR, Dave McC

Well the slide almost never stays in that position for long.
Perhaps for awhile on approach. In that case you don't really
care about the turbulence. But the rate of opening area, as
a function of throttle cable position, is lower so it is
a bit easier to set a specific engine RPM.

You get turbulence past the butterfly all of the time.
-- 
Paul Lamar ...No rotor no motor.

-----------------------------------------------

Paul , Assuming I use a pair of 55mm TB's, what might you suggest as a
minimum length for the taper from 47.625 to 55mm.

Thanks, Geir

Good question. I would guess an S curve three  or four
inches long. Are you using a 180 bend in the runners?

BTW what are you paying for that set of TB's ?

Paul Lamar ...No rotor no motor.


Paul,     Yes , I am planning on u-bends in the range of 22-28''

The bore center to center is 120 mm

I am able to get the TB's at close to wholesale.

Thanks,  Geir

I forgot to mention the TWM throttle body spacing is the same
as a Weber carb. As such it is too close together. You need
the butterfly's further apart and close to the rotor housing
else your long runners will store contaminated with exhaust gas
mixtures that will result in extreme misfiring at low RPM. That
is why the slide throttle is located close to the rotor housings
as possible. That is also why Everette Hatch put the butterfly's
inside the rotor housings.

Paul Lamar ...No rotor no motor.

Paul,     I planned to incorporate the center to center difference of
the TB's with the same adapter plate that would couple the p-port stubs
to the TB's . I am guessing the throttle plate would be about 4-5" from
the outside of the rotor housing . This would add roughly 2-3 " to that
of the slide throttle distance.

I have a tough time debating your slide throttle with all the time and
testing you have put into the design, not to mention my minimal time
involved with the group . I do have some experience with Teflon products
in racing application and I am a little concerned with the possibility
of the Teflon fracturing due to fatigue and/or cold intake temps during
startup and potentially being ingested. I have had Teflon shatter under
extreme cold and race applications on snowmobiles. Is there any data on
Teflon to put my concern to rest.The throttle response at approach speed
( in my case 45-60 knots) and the integrity of the Teflon are my only
concerns,other than that ,once again the dyno run speaks for itself
performance wise.

Thanks for your time,   Geir

I need to see a sketch or 3D of what you are proposing.

It is hard for me to believe the Teflon will shatter in
close proximity to a 200 degree F engine but I guess anything
is possible at -50 degrees F below zero. Our metal car door handles
used to snap off in the winter time in Northern Ontario.

Since we went up to 3/8 thick Teflon the slide is now cannon
proof. According to McMaster Carr Teflon is good down to -350 F.
Are you planning on going to the moon? :)

Are you sure those snowmobile parts were Teflon?

Paul Lamar ...No rotor no motor.

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