Do four valve singles use a "longer head pipe" on one port to help scavenge the other exhaust port???

 and so on "back and forth" if you follow my drift? I've noticed two
things about hot new 250/450  4 valve/cylinder four stroke (with 450's
running way over 100HP/liter or 60hp from only 450cc's) singles. I
know they now have =>13:1 compression ratios but that plus their 12K+
RPM red line burn timing on a big 450cc piston is very noteworthy even
considering premium gas but getting about 133HP/liter from NA even
relatively heavy titanium cam actuation gear (valves/rocker boxes-if
present) and titanium rods to thwart the extremely high piston speeds
tendency to break rods on a conventional big bore design. So does
anyone know the secrets of say a CRF450X in eking out significantly

make "ooh say 400+ hp/liter" but that's on a twin moto-GP bike not a
less spiritedly tuned motocross 250 two stroke making maybe 60-70 hp
from 250cc;s thus doing <300HP/liter in such a reasonable (wide power
band) state of  tune.

I've X-posted this additionally to Reeky/rec.motorcycle.tech as there
may also be some good motor-heads over there.

Bob Nixon..

 
I've not heard of anything like this for scavenging. I suspect that
the reason why one header is longer than the other, on some singles,
is simply because they have to be different lengths as they curve
round the cylinder to one side or the other to unite in a single can
(those that do, that is, rather than singles with a 2-into-2 system,
as it were).

 
If this is not the case then singles are at a GREAT disadvantage (even
more-so than with Twins, Triples & even Four, six & V-8's compared to
the magic GP 22,000RPM V-10's of yore that were the perfect # of
cylinders for a four stroke in terms of co-cylinder scavenging with a
normally aspirated (non turbo or supercharged) four stroke engine.
V-12's, W16s starting to have >frictional and balance components above
RPM's >18,000 or so when compared to the V-10 at up to 22L RPM.

OTOH crankcase scavenged two strokes generally work as well at making
HP in a single configuration as they do as multi's due mainly to the
Kadence[1] effect of each cylinder's exhaust acting as a solid state
supercharger using resonance of the sound wave back filling prior to
exhaust port closure at over-pressures of 1.5 to 1.8 their normal 100%
volumetric efficiency. At the same time exhausting the last burned
charge from that cylinder. Intake and transfer posts also require no
extra mechanical energy, rather using sophisticated porting & timing
to accomplish moving the gases around the engine without any valves
save the reeds valves in one form of this engine and a hollow ported
crankshaft in those last MGP 250's & 500's + still in the Single MGP
125 and still used in current 100/125 & 250cc Go-Carts. Four strokes
also have a slight edge with high speed straight run gasses over
filling the cylinders (up to 120%) prior to intake valve closure on NA
engines at high RPM witch is also cumulative as the number of
cylinders goes up. Also four stroke "valve train relative weight" and
gas velocity are the main reasons that in Super-bike and SS racing
allow Twins and triples a handicap of 250cc's for twins and 75cc's for
the  Super Sports.Superbikes allow 4's of 1000cc displacement and
twins of 1200cc's

[1] Kaydency effect: do Wikipedia 2 stroke engine search for diagram
"as my search engine no longer gives the URL's directly anymore"
     also search wiki for Kaydency for a detail from the 1st article.

------------------------------from wiki---------------------
Different two-stroke design types
A two-stroke engine, in this case with a tuned expansion pipe
illustrating the effect of a reflected pressure wave on the fuel
charge. This feature is essential for maximum charge pressure
(volumetric efficiency) and fuel efficiency. It is used on most high-
performance engine designs.
"EXCELLENT MOTION DIAGRAM MISSING" from cut & paste.
Although the principles remain the same, the mechanical details of
various two-stroke engines differ depending on the type. The design
types of the two-stroke engine vary according to the method of
introducing the charge to the cylinder, the method of scavenging the
cylinder (exchanging burnt exhaust for fresh mixture) and the method
of exhausting the cylinder.
---------------------------end wiki-----------------------
The whole engine volume game changes completely when sup/turbo-
chargers are introduced especially with two stroke Diesel engines and
even more-so when both a scavenge supercharger and multiple
turbochargers are introduced due to "virtually" no limit to feedback
boost pressures of Diesel engines when compared to "octane limited
spark ignited engines". example of V-12,16 2 stroke Diesel with both
multiple superchargers and four turbo's.




Bob Nixon..

 

I think this is generally accepted. It's a helluva job to get much more
than 100bhp/litre from a single and have an engine that's particularly
usable.

I know Gold Stars and the like were credited, back in the day, with
50bhp sometimes, but that was in the day before proper dyno testing.

The best roadgoing big single I ever rode was the Honda XBR500: capable
of about 110, and I think claimed output was 44bhp. Given its
performance and small size I really doubt whether much more than 35bhp
made its way to the back wheel.

Yamaha's SR500 was even less powerful - still a huge fun bike, though.


Yes, yes, two-stroke tech is well understood and rather different.


--
BMW K1100LT  Ducati 750SS  Honda CB400F  Triumph Street Triple
Suzuki TS250ERx2 GN250.  Only seven bikes now.
Try Googling before asking a damn silly question.
chateau dot murray at idnet dot com

 On Dec 2, 12:23 am, totallydeadmail...@yahoo.co.uk (The Older
Gentleman) wrote:

[...]


Forgive me and I'll try not to make a political (2stroke vs 4stroke)
nightmare of this but.....Would you believe me if I told you that
there is a part of the ROTAX company or at least partially related via
stock holding etc that Evenrude (a leader in two stroke outboard boat
engines) has been selling snowmobiles with modern two strokes (direct
injection-air not fuel in the crankcase along with lube oil) with
cleaner EPA#s  and more fuel efficient 2 stroke 600cc sled than the
Yamaha R6 engine powered competition. They both have around 200HP/
liter but the 2 stroke with a broad range power exhaust valve is a
fairly mildly tuned twin whereas the R6 engine is an i4 in a very high
state of tune, especially where peak RPM and torque are concerned. The
Evenrude E-tech 2 stroke still has a total loss lubrication system but
at only about 1/4th of conventional two stroke oil consumption. Now
all that is needed is an oil filtered (no oil above the scraper oil
control ring) wet sump conventional bottom end or like current 4
strokes with normal oil changes and eventually plain bearing high
pressure lubrication with even a big end rod bearing cooling squirt to
the top of the piston. Anyway, I believe we will see a  non wasteful-
like a four stroke even idling direct two stage or (stratified
charging like a diesel using no air throttle during idle & cruising
loads and a second high output normal spark ignition stoichiometric
charging with the air throttle used) two stroke within just a few
years. Such an engine would be both cheaper to build and even more
reliable than current four stroke engines.

http://www.snowmobile.com/manufacturers/ski-doo/2009-ski-doo-mxz-adrenaline=
-600-etec-review-722.html

Moving right along with the times comes 1st the small light off-road
type motorcycle using brushless DC electric motors & state of the art,
light weight, lithium polymer batteries with a "solid" 100 or > mile
range between recharging. Next comes the longer range larger cages and
bikes-:)

http://www.transmotec.com/?gclid=CNaY09ftzqUCFQQ_bAodyA8Dlg
http://en.wikipedia.org/wiki/Lithium-ion_polymer_battery

Bob Nixon...