>> 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/ >
>>
>>
>> --
>> 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 bell mouth
would be beneficial in terms of drag reduction by delaying the
transition point from laminar to turbulent (then separation)
with favorable 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 "bell mouth" has is to act like an effectively
longer pipe. It doesn't really "make for faster flow" because the
vacuum
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,
impedance modeling) 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 "bell mouths" due to acoustics forming an
almost impenetrable layer. Just simply adding a bell mouth 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 bell mouth 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.
-----------------------new info------------------------
Ed Anderson discovered this pdf file. Real interesting on the subject of
Bell mouths. Thanks Ed.
http://www.profblairandassociates.com/pdfs/RET_Bellmouth_Sept.pdf
Too big to publish so download it. You won't be sorry you did.
I found this part of the pdf to be particularly interesting.
Looks like an elliptical horn drastically reduces spit back.
Paul Lamar ...No rotor no motor.
Ha ha. I like the writing style anyway. :)
Regards,
Matt-
So Matt how do you rate the overall pdf on technical merit?
Paul Lamar
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