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RE: [turbobike] Supercharging little things

George Gorman (george_gorman@aapl.com.au)
Tue, 26 Oct 1999 16:25:20 +1000

It'll be pretty interesting.

To the best of my knowledge, turbocharging a 2 stroke destroys all the
exhaust resonances.

The 1998 Axcess Australia Concept Car used a supercharged 2 stroke engine.
It was a spark ignition engine, but used diesel- style injection, ie into
the cylinder after the transfer and exhaust ports had closed, leading to a
4-stroke level of HC emissions. It was supplied by orbital engine company.

Large ships use supercharged 2 stroke diesels.

I think you may have a large problem with tuning your carb if you
supercharge your 2 stroke. Becaus ethe 2 stroke engine/exhaust will act like
a variable valve, with the flow friction of air in/exhaust out dependent on
the revs, I think you will get lots of boost while building up to powerband,
and then lose it when you hit powerband. Maybe you should aim for your
supercharger to switch off when you hit powerband.

**The author has no practical experience with turbos or superchargers. No
responsibility can be taken for any 2 stroke tuning tips either!!!!**

George Patrick Gorman

> -----Original Message-----
> From: owner-turbobike@natvideo.com
> [mailto:owner-turbobike@natvideo.com]On Behalf Of shammar@nsk-corp.com
> Sent: Monday, October 25, 1999 11:04 PM
> To: John-Boy Cadwell
> Cc: turbobike@natvideo.com
> Subject: Re: [turbobike] Supercharging little things
> 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.....
> Regards,
> Bob
> 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.