Hi Paul and others,

    I was quite puzzled on that "fuel cloud" phenomenon, have never
    seen/heard it before. I'm not sure if it was fully covered before,
    so...

    I found this discussion thread when looking for info about nox boosting.
    It's quite good on explaining the thing.

    "Fuel stand-off - intake reversion - what are the causes?"
    http://www.eng-tips.com/viewthread.cfm?qid=190526&page=1
    <http://www.eng-tips.com/viewthread.cfm?qid=190526&page=1>

    Originally i got the name for phenomenon from this article:
    http://www.carcraft.com/techarticles/116_0406_nitrous_350_chevy/index1.html

    There was some papers listed later on thread:

    "Intake bell-mouth effects"
    http://www.profblairandassociates.com/pdfs/RET_Bellmouth_Sept.pdf

    NACA paper on induction manifold dimensioning
    http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930090861_1993090861.pdf

    NACA paper on induction manifold dimensioning - pipe length
    http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930084998_1993084998.pdf

    And later, article about exhaust manifolds
    http://www.ssheaders.com/header.htm
    <http://www.ssheaders.com/header.htm>

    Cheers,

    Petri

    I first noticed this around 1965 on 800 HP small block V8 Chevy
    Chaparral racing engines. The fuel mist was being blown away by the
    speed of the car. This is what I did about it. I designed this
    air box and had it installed on the Chaparral 2D and the problem
    went away. Perhaps just out of sight and out of mind. The car went on to
    win the Nurburgring road race in Germany so it obviously worked.
    As far as I can tell this was the first ram air box on a race car.
    Now common practice on almost all race cars today. Of course the P38
    and the Me109 used similar ram air boxes years before.

    Last year's 245 HP 2nd gen 13B p-port had it. This year's 264 HP RX8
    p-port
    engine had it in spades. You can find a video of it on the web site.
    http://www.rotaryeng.net/intake.html

    This years engine generated 20 more HP. Both in the same
    7300 RPM range. Strangely this year's engine had 3 inch shorter runners.
    Both had downdraft Weber carbs as did the Chap. 1965 V8 Chev.

    Although we did not run it above 4000 RPM I did not notice it on Mark
    Suspinski's 13B p-port engine when running with EFI and 25 inch runners.
    That is not to say it won't do it at higher RPMs. Mark should have
    constructed an air box by now.

    I suspect it has to due with the carb venturi. Air must be shooting
    out of the intake runner sucking more fuel out of the float bowl and
    then back into the engine. I think the engine is flooding
    with excess fuel. In other words the mixture is probably down
    around 8:1 or worse. IMHO the engine is drowning with fuel.
    The BSFC is real bad when this happens and the engine stumbles.
    So too is the gallons per hour read out from the dyno flow meter.

    Perhaps one way of dealing with it is to restrict the size of the
    fuel hose to just enough to get peak power at 12.5:1 I am going to try
    that on the low pressure fuel injection I am now building.

    Paul Lamar ...No rotor no motor.

    ----------------------------------------------------------------------
    Petri,


    This report "Intake bellmouth effects" is great.


    Paul,

    Thank you for the photos of the Chaparral. At the time of that
    Chaparral Nürburgring victory (living not far from there) I was just a
    little boy, but knew the car from my racing car pack of cards (?) very
    well. Reading my first motorsport magazines some years later I learned,
    that the win of this single American car with its automatic
    transmission
    versus all the Ferraris and Porsches was really a sensation on that old
    hilly racetrack. For me this is one of the nicest race cars up to now.

    Reiner

    Thanks Reiner. Other than the ram air intake box I had little to do
    with
    that design. I had a lot more to do with the 2F design and that is
    why it is
    so different than the 2D. The 2D body was done by stylist mostly while
    I tried to bring low drag aerodynamic principles to the 2F design shown
    here.
    It was so different in fact that I had to fight for it within the
    organization.
    Some people thought it ugly. Consequently it still looks modern to
    this date
    40 years later.

    The ram air box was built in to the rear of the body. The front and
    rear panels were Plexiglas so the driver could see through it.
    The carb air intakes were just above the rad air intakes on either
    side of the car. The car was required to carry a spare tire by
    the rules. One could see the reversion by looking in the inside
    rear view mirror. Also note the oblique mounted radiators. Another
    feature years ahead of it's time.

    The 2F set lap records at race tracks all over Europe that stood for
    a couple of years but the transmission was under-developed and broke
    down in
    every race except the last one. The BOAC 500 at Brands Hatch England
    where the 2F won.

    Consequently the 2F is my favorite Chaparral.

    Paul Lamar ...No rotor no motor.


    Paul

    I just found my book "Chaparral" by Richard Falconer/Doug Nye. This 2 F
    had really some amazing new details (especially that big rear wing) ,
    which became common to most racing cars of the next generations. So
    congratulations for that, even if 40 years to late. Are there more books
    (technical side) of that Chaparrals in the US?

    Reiner

    The first edition of that book was not very accurate. Both Jim Hall
    and I called him on it and he modified the book in a later edition
    adding an appendix in the back with information from me.  Pete Lyons
    wrote a small 96 page book or pamphlet called CARS IN PROFILE NO4.
    The Chaparral 2, 2D and 2F. Profile Publications Limited, Coburg
    House, Sheet Street, Windsor Berkshire, England. Whew!

    Apparently it is very rare as google
    knows nothing about it. Pete lived at my house in California when
    he wrote much of it in 1972. As far as I know Pete is still alive and
    living in Big Bear California. I have not been in touch with him
    since 2002. Pete is also a pilot. Here is his last known to me
    email address.

    Pete Lyons <bigbearlyons@earthlink.net
    <mailto:bigbearlyons@earthlink.net>>

    I have one or two other books on the Chaparral at the hangar.
    They contain mostly photographs.
    --
    Paul Lamar ...No rotor no motor.


Hey Paul,

Tangent warning!

I don't think I've ever seen a race car that modulates down force based
on steering angle.  Seems like it would be a good idea - diminish drag
in the straights, increase down force in the turns.  For that matter,
why not variable aerodynamic yaw control as well?  Is it more efficient
to generate a bunch of down force so that the tires can grip well enough
to turn, or would it be better to have the car "fly" around the corner
by varying the angle of some vertical foils?

End tangent.


Matt-

Steering angle can be zero while cornering. Yaw angle is changing.
Tire grip is more important. The tire friction coef. can exceed 1.
Also one must stop quickly and accelerate well. Both functions
are increased by aerodynamic downforce.

Download my AIAA tech paper to read a lot more about it.

http://www.rotaryeng.net/who.html

"Worlds first mathematical technical paper on how wings
and aerodynamic down force improves the cornering speed
and handling of race cars. Written by Paul Lamar presented
to the American Institute of Aeronautics & Astronautics
April 1968 4.5 meg pdf."