I got interested in turbo charging when I read about a guy, Lennart Zander in a
Swedish bike magazine. He had just finished charging a Yamaha TZR125,and proved
that it can be done. This was in autumn 1993. I called him up and asked him if
he could help me, if I would start up a project with my RGV. As he had
experimented with this at Chalmers institute of technology for a couple of
years,he had the empiric knowledge, so I didn't have to do it the trial and
error way. I did some volume measurements on the engine and send a cylinder,a
reed valve and one pipe down to him to do some more.He then finished a report
based on measurements, experience and Gordon Blair's engine simulation program,
and came to explain it to me in person. Then it was on the go! In the spring of
'94 I was saving money to buy some parts needed like the oil cooler, a tank
that has to be modified, a set of new cluth springs and much more, AND of course
the turbo charger. It was a Japanese IHI RHB5. It costed about 1000 USD at this
time, including air filter (K&N) and gaskets. Then of course it was a million
things that had to be solved and manufactured by me or by my helpful friends
with the right knowledge, for example:
Complete oil system with oil pump, cooler and oil tank.
Air box between the turbo and the carburators.
Fuel system, I choosed not to use a fuel pump and regulator, instead we
constructed a fuelpressuretank which would be under pressure from the air
box.
It was always the same question; Where the hell will I fit in this one? The RGV
is quite a compact bike. I thought a long time before I placed the turbo itself
under the saddle, a little aligned to the left. As you can see at the top of
the page I had to cut off a tube of the rear frame, this was later rewelded and
bolted back as in this picture
At this instant I had the whole electrical system in the little plastic bag
that you can see where the turbo should be. As it is a very long way before the
exhaust gases reaches the turbo, (and the gasses are colder then on a 4stroke-
engine), the chambers has to be isolated to keep some of the heat. I bought
(but didn't use) some ceramic heat coating which should be extremely good at
this.They claimed that they had 10% increase in power on a raceV8-engine, and
that you could lay your hand on the headers afterwards. I don't know if this is
true but it was a really expencive bottle.In the summer of '94 mostly of the
stuff was in my garage and ready to be put together, we were welding the new
pipes from the expansion chambers to the turbo (the stock chambers worked fine
for this) and had some small problems left to solve. Then suddenly I got myself
a place at this school, and had to move very quickly. Soon I realized that I
had no time (and no place for the bike) for a project like this, so I began
thinking about selling or trade it for one that was turn key ready.And that is
how I became a proud gamma owner.For those of you who speaks Swedish,the report
is to read here All you others can read this freely translated (by me) version:
SUZUKI RGV 250 TURBO
Summary
Suzuki RGV 250 has been simulated in a non supercharged condition in professor
Gordon Blairs simulation program for reedvalve using 2stroke engines.The
meaning was to decide the power,average pressure, consumption, efficiencies
and pressure history in the exhaust port for the engine, then to choose a
suitable turbo charger.The engine gives in its initially condition almost 70
HP @11000 rpm and shows some good efficiencies. Of special interest on a turbo
engine is that the DR (Delivery Ratio), or gross flow through the engine is
high enough to avoid too high piston temperatures. This could be the case on
a 2stroke stock engine with optimized consumption and the efficiency is needed
before you can calculate on the compressor and turbine parts. The exhaust
system is extremely important on a ordinary 2stroker and even more important
on a turbo charged one. If you want more power, and at a higher rpm you can
use the other exhaust system wich i have calculated for you. It's marked in
the diagrams with an "R".
Diagram explanation
The power diagram for the stock engine needs no explanation i think; It's
right from the program. The turbo power is calculated under the assumption
that the power increases proportional with the load pressure. The maximum
load pressure is 1.0 bar, and it will be reached stationary at 9500-10000
rpm. Under charging the exhaust temp will increase and the chamber is
tuned for a higher rpm. You could say that the turbo engine stretches its
register in rpm meaning.The next diagrams shows the three different
efficiencies of the stock engine; DR, TE (Trapping Efficiency) and CE
(Charging Efficiency). DR is the gross flow through the engine and the
flow that the turbo will know. TE is a measure of how big part of DR that
stays in the engine and takes part in the combustion and CE is the proper
net efficiency wich is the product of the both previous and it's towards
this that the power is proportional. We realize that we can compose our
efficiency a little bit as we want between DR and TE. Usually you prior
TE on a stock bike for a lowest consumption while racers have higher DR
for a lower exhaust temp. SE (Scavenging Efficiency) is a measure of the
wash effect or how much exhaust there is left in the cylinder from the
last cycle.BMEP is the braked average pressure on the stock engine. The
pressure inside the cylinder varies extremely in a cycle,and to describe
the status on a engine you integrate up the area in this so called
pV-diagram and divide with the stroke of the engine and in that way we
get a average pressure. BMEP is proportional to the torque and is
therefore the thrust you will feel when you drive. As we can see, we
have a rather peaky character!With a max-BMEP of 11 bar you should be
rather satisfied. The last rpm-curve shows BSFC and is a measure of the
fuel consumption. Note that the consumption comparative to the power is
best when the engine gives the most power! There are also two
crankangledissolved pressure curves of the pressure in the exhaust port.
This subject could take up a entire book, but in short; the radical
power difference between 11000 and 12000 rpm depends only on the
difference in pressure history that we can see in the exhaust port at
each rpm.
Turbo choice
The turbo choice must unfortunately still be done with calculating by
hand and already known connections. The problem is that we are dealing
with related functions; The engine gives unloaded a certain flow wich
i can get with the program. If we just increased the denseness off the
air everything would be simple, but since the engine is "short
circuited" this long part of the cycle (scavenging ports and exhaust
port open at the same time) the flow is highly affected by the
difference pressure between air and exhaust side. You may see the same
peculiarity on a highly tuned 4stroker. If you are able to keep higher
load pressure then exhaust pressure you may reach about 35% higher flow
because of this. Higher load pressure then exhaust pressure is a
condition for the function on a 2stroker; Otherwise it will be filled
with exhaust gases and "spike" apart. To succeed with this the turbine
must be choosed so big that it won't start the turbo until the chamber
starts to assist. You will then be helped under the scavenging period
by the vaccum wave from the sip cone in the chamber. A large turbine
also brings with it that the wastegate-valve doesn't have to handle
that big part of the exhaust gases and that keeps the exhaust pressure
down.I have found out that the turbo will have reached a pressure
condition of 1.2 at the rpm when the chamber starts to assist. By
formuling the equation for the mass flow of the turbine as a function
of load pressure and the mass flow of the engine as a function of load
pressure and then study their common points you can find a turbine area
that will fit.The choice of turbo is a IHI RHB52-393-P12.
This report was written by Lennarth Zander 940126, ordered by me.
The handmade calculations and the parts including the race pipe
mentioned has been left out on this page.
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