>> Paul
      >>
      >> I noticed many intake designs have constant diameter intake
      pipes while
      >> Guru Racing and a few others taper theirs down to the intake port.
      >>
      >> I will make my intake manifold out of carbon or some other heat
      >> resistant
      >> glass epoxy GRP so I am free at the moment as to the course and
      >> profile they
      >> will be.
      >>
      >> I thought to go from 60mm id at the intake plenum with the
      adjustable
      >> length
      >> portion being able to extend another 120mm within the intake
   intake
      >> plenum.
      >> From the plenum to the slide throttle, a distance of about 320mm I
      >> would
      >> like to taper the tubes down to 50mm gradually over their length.
      >>
      >> Injectors are right after the slide throttle so fuel mist
      separation
      >> is not
      >> an issue. Other than being a pain in the butt to construct the
      >> tapered pipe
      >> are their any disadvantages or advantages to such a design?
      >>
      >>
      >> Thanks
      >>
      >> Doug
      >>
      >> It is mentioned in:
      >> Scientific Design of Exhaust and Intake Systems. Philip H. Smith
      >> and John C. Morrison Published by Robert Bentley. ISBN
   0-8376-0309-9
      >>
      >> http://www.rb.com <http://www.rb.com/> <http://www.rb.com/>
      >>
      >>
      >> --
      >> Paul Lamar ...No rotor no motor.
      >
      > Doug,
      > Concerning information given to me on inlet manifolds.
      > My understanding is that any reduction (such as a Venturi) in an
      inlet
      > is a
      > restriction. However if a small restriction increases velocity
      without
      > choking the flow, it has an advantage for VE.
      > Alternatively any increase in size (especially toward the engine
      end) the
      > flow will slow and will be a disadvantage.
      >
      > I'm advised that THE OPTIMUM SHAPE is a megaphone shape starting
      > larger at
      > the outmost end and ending at the port, in a even taper. The air
      flow
      > starts
      > out larger than the port, builds pressure and speed, but like you
      > said, the
      > hard part is building the darn thing!.
      >
      > Probably the same reason why those tapered exhausts work so
   well in 2
      > strokes .
      > George ( down under)
      >
      >
      > Do you have any mathematical theory to support this contention
   or is
      > it an
      > opinion? If it is an opinion do you have (or the person that
      expressed
      > their opinion
      > to you) have any empirical data to support their contention.
      >
      >
      > Paul Lamar ...No rotor no motor.

      Hi Guys;
      Attached is a pic a local fellow sent some time ago detailing a
      comparison of various intakes.
      I would love to know the source - unfortunately he could not find
   it...
      I'm guessing the front top surface of any laminar flow airfoil
   revolved
      into a body of revolution like a bellmouth
      would be beneficial in terms of drag reduction by delaying the
      transition point from laminar to turbulent (then separation)
      with favourable pressure gradients. 2D airfoil software (such as
   xfoil)
      shows this. 3d multi-element or CFD results would be nice :)

      I have heard of performance increase claims in the 15-25% range -and
      many rules of thumb for tapered gradients.
      Check out something like the following for claims of big results:
      http://www.bpinitiatives.com/products.html
      There is no question you can reduce drag but the big question is how
      much turbulence results in optimal power
      and at what range of intake velocities? as is being done with
   some of
      the latest turbulent flow intakes?

      Fuel routing is greatly simplified if all the injectors are in a
   closely
      spaced row nearer the housings.
      I vote for the adjustable length intake for maximum flexibility with
      varying ambient conditions and just in case our exact
      calculations and reverse engineering don't match reality :)
      Cheers
      Cary

      That is really interesting Cary. Thanks for the data. We knew the
      bell mouth was
      worth about 5%.
      --
      Paul Lamar ...No rotor no motor.

   The real effect that a "bellmouth" has is to act like an effectively
   longer pipe. It doesnt really "make for faster flow" because the vacumn
   signal at the source, i.e. port, is a function of VE. The "bellmouth"
   allows for a more rapid transition to laminar flow in a shorter distance
   which is the same as having a longer pipe allowing for the Re number to
   drop until is it turns into fully developed flow. You can get the same
   results but having a long pipe but this is limited due to space and
   acoustics.

   The other more important thing is the acoustics more so that
   anything. You need to tune your lengths based on wave theory (helmholtz,
   impedence modelling) since acoustics will actually spit fuel air back
   out if you are not careful. Go look at the video on youtube.com
   <http://youtube.com> of the
   Renault F1 v10 running on the dyno and you will see the vapor getting
   spit right back out of the "bellmouths" due to acoustics forming an
   almost inpenetrable layer. Just simply adding a bellmouth to something
   may end up hurting you if you are starting to fall off of ou tuning
   peak. It would be real interesting to see someone run the numbers on a
   rotary running at the 6000rpm you guys are always talking about. I have
   a SAE paper that shows how to calc impedence methods and a simple way of
   doing a realworld test with microphones and a manifold.

   Rob Woods.

   You need to read the web site Rob: http://www.rotaryeng.net/intake.html

   The spit back is common to all tuned manifolds I have seen.

   That is one reason why I designed this air box for this car.
   If you have a picture of an earlier race car with this feature please
   send it to me. I think it was a first.

   Paul Lamar

   Paul,
   I love the Chapparal, so don't take this as an insult, but the 40HP
   volkswagon was one of the first engines to use a control plenum. The
   oil
   bath air cleaner was designed to control spit back. Many people wondered
   why they ran WORSE without an air cleaner! The Chapparal may be the
   first contemporary race car to use one though. Everyone in those days
   wanted to run wide open bellmouth intakes.
   Bill Jepson

   It may have been a control plenum but was it ram air? It is the ram air
   feature I am referring to on racing cars. Back in those days just about
   all car engines
   had some type of air cleaner or other device sitting on the carb. Here
   is a Model T

   With wide open bell mouths stuck out in the air stream the standoff fuel
   mist
   would be sheared off with a consequent high fuel consumption.

   Paul Lamar ...No rotor no motor.

   Touche'
   Ram air it was NOT! The fact is that it was a "tuned" length pipe but
   drew air from
   within the engine compartment, definitely not ram air.
   I loved the innovation in the Chapparal cars, I know GM was heavily
   involved with
   some of it But Hall was a sharp manager as well. Did you get in through
   the GM
   connection Paul? OH yea Jim was a damm good driver too!
   Bill Jepson

   Nope. The way I got the job was I talked to Jim at Watkins Glen and
   we started corresponding
   on vehicle dynamics. He flew me down to Midland for an interview and
   loaned
   me his 300SL Gull Wing while I was there :) I was not all that
   impressed with
   the Gull Wing :) Severe swing axle and aerodynamic over steer.
   --
   Paul Lamar ...No rotor no motor.


You've just killed my dream Paul - a 300SL Gull Wing.  Oh well, even
with some faults, I'd still love to have one...  :)  For a similar
amount of money however, I'd probably take a nice Lancair Legacy instead..


Matt-

It was an interesting car alright but that was before anybody knew anything
about road vehicle aerodynamics. Also it was years before the Germans figured
out the high roll center jacking effect. Porsche and BMW used it right up through
the 80's and into the early 90's as I recall. Late air cooled VW's still had it. The
Brits were 20 or 30 years ahead in suspension geometry. It must have been the metric system.
Newton was a Brit :) The Brits built better WW II fighter planes as well.

I still don't know what a Pascal is. Is'nt that some sort of computer language? :)