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Re: [turbobike] Supercharging little things

Mon, 25 Oct 1999 09:04:10 -0400

Well,  I haven't personally ever tried a forced induction scheme on a 2-stroke
but it can be done.  Your just have to watch out for too much overlap in the
port openings, similar to using a cam that is too long on a 4-stroke.  If it is
a mild "play bike" type of engine you'll have a better chance of having mild
port timing in it.  If it is highly "ported" for peak power this could be a
problem.  Two strokes respond very well to porting combined with the proper
sized expansion chamber (resonator) and the result is a poor-man's supercharger
without one.  Volumetric efficiencies much greater than 100% can be achieved in
narrow rpm bands.  Modern day two strokes have variable port timing to widen
this band.

I you were to try to supercharge you 80cc bike, the air requirements for 100% VE
at 9000 rpm are 0.08L x 9000 rpm = 720 L/min, since it aspirates once per engine
revolution.  This is about 44cfm.  Assuming you want to double the volume of air
that you will aspirate, then you'll need about 88cfm capacity from your
compressor at 15-20 psi.  That's not a whole lot of air.  For example, I have an
800cfm compressor on my ZX-11.  A general rule of thumb is that you need 160 cfm
for each 100 Hp.  So, your 88cfm would be good for 55 HP.  An 800 cfm compressor
is good for 500 HP.

The supercharger would be simpler than a turbo since all you need to do is
modify the intake system, rather than a complete setup with exhaust, waste gate,
etc.  Of course, you still need to make a drive off the crank or clutch basket.

If you do this we need to see dyno results before and after, of course.....


John-Boy Cadwell <Jcadwell@gonzaga.edu> on 10/25/99 12:20:16 AM

To:   turbobike@natvideo.com
cc:    (bcc: Bob Shammas/EQA/Nsk-Corp)
Fax to:
Subject:  [turbobike] Supercharging little things

having been on the mailing list for a little while, I suppose it is my
time to open my mouth, however uneducated it will sound...  Being a
college student, and perpetually on the short of cash end of the
spectrum, my inability to turbocharge something big is not a reflection
of lack of interest.  I have however, fallen into an early yamaha 80cc
two stroke, and was curios.  I have read the post earlier about the
"dirt cheap supercharger" and was curious as to the realism of this
claim.  If it would work I have the fabrication knowledge and facilities
here at my school, (I am in the engineering program, and can use the
machine shop), but not having a large base of knowledge about
implimentation I would not want to destroy an otherwise functional
motorcycle by cutting it up to find out it does not work.  Is using an
emissions air pump really possible?  What sort of flow requirments would
it need at say 9000 rpm?  I would use the bike primarily for road racing
in the mini moto classes.  I firmly believe that I could more cheaply
turbocharge this bike using a smog pump to attain power than by trying
get power by trying to port, polish, pipe, and whatnot.  But if this
idea is not feasible I would appreciate input.  i am under the
assumption that supercharging would be simpler and less complicated than
turbocharging?  Is this correct?  what are the advantages and
disadvantages of each?  ?Has anyone ever tried anything this small?
What are the things to think about?  Any help would be splendid, thanks
for your time... John Cadwell, Jr.