turbo sizing

jb24 at chrysler.com jb24 at chrysler.com
Fri Dec 19 18:26:47 GMT 1997


>>
>> A while ago there was a discussion here about turbocharging a
>> two-stroke, and the general consensus was that it couldn't be done,
>> or was very difficult, at least. So how is it done?
>>
>> Stuart.
>
>First off I want to say that I am admittedly no expert on 2 stroke
>engines.  The only one I have ever owned was in my 175 Yamaha Enduro.
>However, I am quite familiar with their operation I would would venture
>to say that there is no reason why a 2 stroke couldn't be turbo'd or
>supercharged.  I would agree that it would be more difficult to
>achieve high levels of boost but providing that the reed valves are
>stiff enough to counter the highest boost but not so stiff that they
>won't open during the downstroke of the piston then you should achieve
>some gains.  Granted, you will be likely to have a great deal more
>of blowby into the exhaust if turboing a 2-stroke but it should work
>to some degree.
> I would agree, though, that turboing or supercharging a 4-stroke
>does make a little more sense and will make better gains (at least in
>efficiency).
>
>--
>Christopher Bruno
>Teradyne

Where supercharged snowmobiles get their gains are when the pumping
action of the cases aren't at their most efficient.  Tuned pipes only
work at certain rpms, and they stuff as much fresh charge into the
cylinder as possible, but charge purity is only like 80% in the tuned
range.  Turbos can get 90% or more all the time.  So you get the power
by blowing tons of fresh charge out the exhaust.  Peak cylinder
pressure won't get a lot higher like it does in four strokes.  That is
why turbo two strokes don't really "work", you can't double or triple
horsepower by the same multiple of boost pressure over ambient.  The
most that can be achieved is what normally aspirated race engines do
today (sometimes not even that much).

John Bucknell is jb24 at chrysler.com



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