80's redux, more specific TZ-250's, Priller-250 ect

Bob Nixon wrote:

>Thanks, Bryan. I had a 78 400 Daytona Special (last year for the RD
>series). The 400's had a bit lower power band but it made the bike a
>bit less hyper and the 78 had butterfly valves at the exhaust output
>that reduced emmisions and they got 60MPG. Great little bike for a
>100-200 miles day but not the fun and room of my GS1000 for camping &
>stuff back then.

It would have been a 1979 RD400F. The exhaust throttling valve was in a bolt
on housing, not part of the cylinder.

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On Jun 8, 9:30 am, phil scott <p....TakeThisOut@philscott.net> wrote:
> On Jun 7, 10:12 pm, Bob Nixon <bigrex2....TakeThisOut@yahoo.com> wrote:
>
>
>
>
>
> > On Jun 7, 9:03 pm, phil scott <p....TakeThisOut@philscott.net> wrote:
>
> > > On Jun 7, 8:53 am, Bob Nixon <bigrex2....TakeThisOut@yahoo.com> wrote:
>
> > > > Now that I've gone backwards to smaller displacement two stroke bikes
> > > > (due mainly to them being light & my limited strength etc), bikes like
> > > > Honda's old triple V-400cc two stroke (saw one at seca once), Zuk
> > > > Gamma's, RD-500's, my RZ-350, 250 race Prillers & the venerable TZ-250
> > > > like AB either own's or did in the past.
>
> > > > BTW, while watching MGP 250, 800 from Magello IT last week on SPEED
> > > > the announcer stated than the 250's were topping out on a radar @ 175
> > > > MPH down that long front straight, while the 800's were just a hair
> > > > under 200MPH. I was also taken back a bit by how little difference in
> > > > lap times at a large track like Mugello. I figured the math and those
> > > > little 250's must be putting old at least 100 HP and weight <275 lbs
> > > > and host mostly ~100lb riders.
>
> > > > Does anyone have any hard data on the race or MGP 250cc or even 125cc
> > > > race bikes?
>
> > > > PS. Got a call from the repair shop yesterday. I should have my RZ
> > > > back within a week.
>
> > > have fun bob,
>
> > > you might also look at the latest batch of high end ultra light
> > > motards, not the japanese ones that are most heavy or non licensable
> > > on the street such as the yz yamaha 500's. light and fast but not
> > > licensable
>
> > > some can be lowered by various means, you can get 3" on the seat
> > > usually, and 2" front and rear shocks.
>
> > > Phil Scott- Hide quoted text -
>
> > > - Show quoted text -
>
> > Thanks, Phil but I've never been able to stomach 4 stroke singles,
> > especially without an electric starter:)
>
> most big singles gots an electric starter these days.
>
> one point you may be missing is the vastly increased amount of fun as
> the machine goes lighter, especially when you have the same
> horrsepower, the 500 singles wheelie in all 4 gears... not so much
> because of the HP, but the light weight. the older two strokes
> are too heavy for that, a heavy fun penalty comes with that
> configuration.
>
> now if you dont like the singles, but did well with the sv twin, you
> know of course about the new v twin motards, one of those would be a
> hoot for you... also, guys racing those turn them in every year, you
> can get one used cheap on ebay when they come up.. one season of
> racing is not enough to tear up the bottom end, just the rings and
> valves...you can fix that.
>
> then you have 60 hp or so in a 250 lb frame...thats about 5 times more
> fun than the same hp in a 350 lb frame... you can test that by
> finding a fat chick sometime to put on the back of yer bike.

Phil, my 60 stock HP RZ-350 has a dry weight of 310 lbs and with it's
5.3gallon gas tank, 1.6 quarts or propolyne gycol, 5 lbs battery & 1.5
quarts of tranny oil is about 360 fully wet. Add another 160lbs for me
geared up and we have a "bike and rider" weight of <500lbs. or really
lighter than a 550 Priller twin motard with roughly the same stock HP.
And lets face it. 4 strokes singles/twins, these days, are pretty
"PUMPED OUT" from the factory with 12.5:1 compression, big titanium
valves and rod, wild cam & large FI, where'as a stoke two smoke is in
a pretty mild state of tune.

BTW, A four stroke single is the worst case condition for HP, with no
co-cylinder exhaust scavenging, hugely SLOW valve train compared to an
I4 and one big piston moving 4-5 valve springs ( huge reciprocating
mass) and are thus limited to about 12,000RPM instead of 16-17,000
like a multi.

OTOH, a two stroke single only has a larger piston mass to deal with
and is not helped much at all by multi cylinder arrangements like a
four stroke as each cylinder scavenges on it's own. That's the main
reason the 500 4 cylinder two stroke had four seperate pipes and
seperate sealed crank cases. If any thing > friction trumps the
smaller piston mass in multiple cylinder 2 strokes and they have less
tuning HP the more cylinder you add. As I recall the old TZ-750's made
less HP than the later 500cc engines, partly due to technology and the
rest those larger pistons on the 750. To push this out to the max,
3-5cc two stroke model car singles put out over 1000HP/liter @ >40,000
RPM. Nothing short of a jet figher engine can even come close to this
potential.

Bob Nixon, RZ-350, Chandler AZ.