Why do people use flat-slides??
Max Walshe
to be very popular (and expensive from what I can tell). Why is a flat slide
carb so much better than a 'round' slide carb? Do they really warrant the
money seem to be prepared to pay for a set?
Max
Richard Sturges
Advantages of a flat slide over a round one are that the flat slide
is more, umm, flat. Seriously, the slide is lighter, and the overall
size of the carbs is more compact, thus fitting better in today's bikes'
cramped engine spaces.
Are they more expensive than roundslides? I don't think so. Do they
warrant the extra coin? Depends, how much money you got?
Rich Sturges "There is no justification for taking away individuals'
Falls Church, VA freedom in the guise of public safety."
- Thomas Jefferson
Michael Tiberio
> In rec.motorcycles.racing, ma...@visionware.co.uk (Max Walshe) writes:
> >I've read various articles about tuned and race bikes and flat slide carbs seem
> >to be very popular (and expensive from what I can tell). Why is a flat slide
> size of the carbs is more compact, thus fitting better in today's bikes'
> cramped engine spaces.
As someone that has run both flat slides and round slides on his bike
maybe I can shed some light on it. While everything Rich said is true I
believe the real reason is better atomization. A seat of the pants
reason is when I run flat slides on my bike, I feel a real kick in the
midrange when I get on the gas. You might say its jetting, but I feel I
had both sets set up correctly. As a matter of fact I can get that flat
slide feel out of my round slides with long v stacks. So perhaps thats
it, you get good mid range like long intakes would give, with good top
end power like short v stacks give.
Mike
Albion H. Bowers
In a previous article, stu...@oasys.dt.navy.mil (Richard Sturges) says:
>In rec.motorcycles.racing, ma...@visionware.co.uk (Max Walshe) writes:
>Advantages of a flat slide over a round one are that the flat slide
>is more, umm, flat. Seriously, the slide is lighter, and the overall
>size of the carbs is more compact, thus fitting better in today's bikes'
>cramped engine spaces.
Ummmm, I don't think so. you see, there is this guy, Kevin Cameron, who
seems to know a couple of things about bikes. Any way, Kevin (who's
probably forgotten more than I will ever know), seems to think that the
amount of air underneath the slide when it is closed has a dramatic effect
just as you transition from slides fully closed to opening up. Apparently,
this trasition means you get a cleaner power delivery, especially in places
like deep into a corner where the tires are just starting to slide and
having a carb system that _*BURPS*_ on you about that time is a good way to
end up road testing your helmet instead of simply riding down the next
straightaway.
>Are they more expensive than roundslides? I don't think so. Do they
>warrant the extra coin? Depends, how much money you got?
Yeah, they're a bit more pricey than the round slide variety. And if they
are worth it to you or not probably depends on how important (or costly)
your time is. I imagine that Kevin Schwantz's time spent in corners is
pretty expensive.
Funny, but 10 years ago, folks were asking the same questions about
PowerJets...
--
Al Bowers DOD #900 NASA Dryden Flight Research Facility
work: bow...@tifosi.dfrf.nasa.gov personal: ak...@yfn.ysu.edu
"...tactics always degrade strategy..." -Frank Bethwaite
Eric Murray
>In rec.motorcycles.racing, ma...@visionware.co.uk (Max Walshe) writes:
>>I've read various articles about tuned and race bikes and flat slide carbs seem
>>to be very popular (and expensive from what I can tell). Why is a flat slide
>>carb so much better than a 'round' slide carb? Do they really warrant the
>>money seem to be prepared to pay for a set?
>
>Advantages of a flat slide over a round one are that the flat slide
>is more, umm, flat. Seriously, the slide is lighter, and the overall
>size of the carbs is more compact, thus fitting better in today's bikes'
>cramped engine spaces.
I thought it was because they flow better than roundslide carbs.
>Are they more expensive than roundslides? I don't think so. Do they
>warrant the extra coin? Depends, how much money you got?
How fast do you want to spend?
--
Eric Murray er...@microunity.com
"Archiving the net is like washing toilet paper!"- Leader Kibo
Axel Fischer
>>Advantages of a flat slide over a round one are that the flat slide
>>is more, umm, flat. Seriously, the slide is lighter, and the overall
>>size of the carbs is more compact, thus fitting better in today's bikes'
>>cramped engine spaces.
>
>I thought it was because they flow better than roundslide carbs.
Yes, that's true. They give you an advantage of about 3hp over round ones.
-Axel
--
fis...@netmbx.de
Eric Bong
> I've read various articles about tuned and race bikes and flat slide
>carbs seem to be very popular (and expensive from what I can tell). Why
>is a flat slide carb so much better than a 'round' slide carb? Do they
>really warrant the money seem to be prepared to pay for a set?
In article <J3WH...@netmbx.netmbx.de>, fis...@netmbx.netmbx.de (Axel
Fischer) wrote:
>
> In article <1993Oct5.0...@microunity.com> er...@microunity.com (Eric Murray) writes:
> >>Advantages of a flat slide over a round one are that the flat slide
> >>is more, umm, flat. Seriously, the slide is lighter, and the overall
> >>size of the carbs is more compact, thus fitting better in today's bikes'
> >>cramped engine spaces.
>
> Yes, that's true. They give you an advantage of about 3hp over round ones.
I hope I got the quotes right. I'm not sure if the origional question
was answered. I believe Max Walshe intended to ask why a person modifying
a motorcycle engine would replace the stock carbs with flat-slide carbs.
Which is different than comparing flat-slides to round-slides.
The stock carbs on most motorcycles are vacuum operated and are refered
to as CV carbs. The CV means "constant velocity" and refers to the velocity
of the air flowing through the carb body. The hand operated throttle is
connected via a wire to a set of butterfly valves located on the cylinder
head side of the carburator slide valve. There is a pressure diferential
across the butterfly valve. Opening the butterfly, by twisting the hand-
grip, decreases the pressure drop across the butterfly. At full-open,
the pressure on the upstream side of the butterfly is the same as the
cylinder head, which is lower than atmospheric (see note 1). The slide
valve has a hole in it near the butterfly valve, on the end of the valve
which is in the carburator throat, the end which also holds the needle.
The hole, refered to as the reaction hole, allows the pressure inside
the slide valve chamber to be the same as the pressure on the upstream
side of the butterfly valve. There is a diaphragm on the opposite end of
the slide valve from the reaction hole. Atmospheric pressure is maintained
on one side of the diaphragm and cylinder head vacuum, minus the pressure
drop across the butterfly valve and the reaction hole, is on the other side
of the diaphragm. Varying the position of the butterfly valve, changes the
pressure inside the slide valve, The slide opens with low pressure and
holds position for a given pressure against the force of a return spring.
As the slide valve opens, it opens the apperature of the carb body,
allowing
more air through and simultaneously lifts a tapered needle allowing more
fuel in to keep the mixture ratio constant. The vacuum operated slide
on a CV carburator governs air/fuel delivery from quarter throttle to
three-quarter throttle. The main disadvantage of the CV carb is the
time constant of the vacuum operated slide valve. The main advantage
is that the carb is controlled by engine demand.
Flat slide carburators are not CV carbs. They are of the family of
slide-type carburators where the throttle control (the twist grip) is
connected directly to the slide valve in the carburator via a wire.
There is no butterfly on the slide-type carb (unless the carb has a
butterfly choke valve). The opening of the bore of the carb is controled
by the operator alone, not by the cylinder vacuum (which is related to
engine demand). Without the butterfly valve, the air/fuel flow is less
restricted, allowing better charge delivery and therefore higher power.
The butterfly also causes turbulence which also restricts charge delivery.
(you want turbulence in the combustion chamber, not in the induction pipe.)
The slide carb also allows imediate response to control input, no delays
from the vacuum control time constant. The main disadvantage is that the
average rider is not aware of engine demand, making the slide-type carb
dificult to operate at low engine speeds where cylinder head vacuum, not
carb apperature, limits charge delivery. However, on the track, one should
not be operating a motorcycle at low rpm and the disadvantage of slide
carbs becomes a moot point.
To answer the origional question, flat slide corburators are prefered
over CV carbs for racing applications because they are less restrictive.
THe flat slides are better than the round slide-type carbs because the
velocity profile across the aperature of a flat slide is more constant
than the velocity profile across a round slide. Round slides are cheaper
because the manufacturing process are less expensive for round holes
and shafts than for rectangular holes and shafts.
Note 1: On 4-strokes, the intake valves open during the piston's intake
stroke, which causes a low pressure in the cylinder, cylinder head and
intake tract. On a two stroke, the low pressure occurs during the induction
phase, when the piston is on the upward stroke, following the closing of
the
transfer ports.
Have fun,
Eric Bong DoD #0270
1987 FZR750 1991 VFR750
(looking for a cheap VTR 250)
Team Iguana Racing
"We're not squid, we're lizards!"
--------------------------------------------------------------
Disclaimer:
The opinions expressed in this posting are my own, and
not necessarily those of the Stanford Linear Accelerator
Center, Stanford University, or the US Department of Energy.
Bryn Williams
[lots of informative stuff about why people use flat-slides for racing]
Just thought I'd post to say a big thanks for that article - informative &
well written IMO,
Cheers,
Bryn
---
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| Bryn Williams |
| Department Computer Science and Applied Maths, <will...@cs.aston.ac.uk> |
| Aston University, <willi...@kirk.aston.ac.uk> |
| Aston Triangle, |
| Birmingham B4 7ET Tel. +44 (0)21 359 3611 x4671 |
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David Dawes
There is such a thing as a CV carb with a flat slide (my DR650 has one).
Also I believe that the GSX-Rs have CV slingshot carbs (half flat,
half round slides). RGV250s have non-CV slingshot carbs. The slide
shape doesn't imply vacuum or cable operation.
David
--
------------------------------------------------------------------------------
David Dawes <da...@physics.su.oz.au> DoD#210 | Phone: +61 2 692 2639
School of Physics, University of Sydney, Australia | Fax: +61 2 660 2903
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You run and you run to catch up with the sun, but it's sinking
and racing around to come up behind you again. -- Pink Floyd, "Time"