Supercharging small engines.

2023 small Supercharger update:

Much needed update of the current market for small engine superchargers.
Well, it has never been easier to purchase small superchargers - for as low as $200!
Several chinese companies offer replica- Aisins AMR300 and 500 and even medium sized Eaton blowers.
So, there is no excuse for people who wants to try out the effect of supercharged engines.
High-end blowers are readily available from Ogura and Eaton too.
The Ogura TX01 is the smallest of the lot and sells on special order. The TVS series
from Eaton is especially interesting offering both 3 or 4 lobe blowers aimed for a
choice of high or low pressure applications.

The market for secondhand superchargers are also bigger than ever -
just try to do a search for "supercharger" on the bigger on-line marketplaces.
Sub- one- liter superchargers are still rare, but do hit the surface once in a while!
Vintage ? Roots blower destined for Topolino Fiat 500cc.

1: What is a supercharger?

2: A smog- pump is not a supercharger?

3: Various superchargers.

4: Suck through or blow through?

5: Installation.

6: Supercharger drive.

7: The engine - how to prepare it.

8: Supercharging two- stroke engines.

9: Turbos and small engines.

1: What is a supercharger?

A supercharger is just a pump - end of story!
Then there is the little things like: A supercharger is a pump delivering more air to the engine, than it can digest!
Some superchargers are referred to as blowers. "Real" superchargers has internal compression someone once commented! Internal compression is when the air is actually being compressed before being released into the engines intake. I think that could be an issue, but then a "real" supercharger would cost more horsepower to run! Just listen to your air- supply compressor in the garage the next time you switch it on. At first it builds up rpms easily, but then it loads down when building a higher pressure! So, different types of superchargers, delivering the same volume, will very likely require different horsepower levels to be driven. Then you have to take this into that equation - does the internal compression supercharger deliver a better charge? A Roots type supercharger or blower is in fact blowing a lot of air into the engines intake, and when the intake is full, pressure builds up. So as a Roots type supercharger has no internal compression, then it is just a pump! The Roots type are the one I prefer at most cases, as it is a positive displacement pump, that builds up pressure instantaneously, but when you look at supercharger comparison- test, they are way down the list in effectiveness! A Roots type supercharger is a very simple device. An aluminum housing with two axles passing through. The rotors can be of several designs having two or three lobes per axle, along the axis they can be straight or twisted. Effiency is a matter of tolerances, and this is why you should check out a used blower! High mileage superchargers with worn bearings, will have signs of rotor to wall contact, or worse, rotor to rotor contact. Old race- blowers have seen high rpms, high temperatures as well as backfires, which necessitates them to run higher tolerances. Afterward these are unsuitable for low- rpm use. A used blower may be okay even if a few scratches are present inside the housing and on leading edges of rotors, but resistance and high spots felt whilst turning rotors by hand, should alarm you! The supercharger should be sized for the use, because it is driven of the engine via a mechanical transmission, and thus adds to the load of the engine. Using a too big supercharger will cost you horsepower - like in every other engine build- up, the right combination will give you success. The real charm of the mechanical supercharger is the way, you in minutes can alter your engines output. By simply changing the driveratio, by fitting a larger/ smaller pulley, horsepower level can be increased dramatically! Say, you are driving to the track with a 5- 7 psi, once there, you raise the boost to 10- 12 psi and enjoy yourself. Thats fully possible, but I have to warn you, its not easy to change back again :o) - t.b.c.
Easily change boostnumbers by exchanging pulley- sizes.

Supercharging small capacity engines is not a new thing!
In 1941 Ettore Bugatti designed this engine. Foreseeing the shortage
of fuel after the war, he concentrated on small engines, very
complex as usual.
A DOHC single with a Roots type supercharger sandwiched between
engine housings, this 10,66ccm cycle-engine (22mm bore) proved
to be too complicated, and thus too expensive to manufacture.

Two stroke engines were put under pressure too. When NSU and Kreidler
went out to set some 50cc speedrecords, they used superchargers for
power enhancement. Kreidler used this Engelbert Sczygiol designed
supercharger and in 1965 they reached a speed of 210 km/h at Bonneville

1978 Motobecane marketed a supercharged moped called the 99Z. Engine
was a twostroke, with a charge- piston connected to the crankshaft.
The Peugeot 125cc scooter models,Jetforce Compressor and Satelis uses a
small Roots type blower, to raise the output of its 4-stroke single.
The first production two- wheeler with a supercharger since 1978, when Motobecane
launched the 99Z. A big cadeaux to the French!
Keep them coming :o)

This modern fuel injected engine make use of an intercooler too

3: Various superchargers.

Superchargers small enough to be suited for 50cc engines are rare and
far between. You can use a too large charger, but results will not be
satisfactory. Some superchargers can be reduced in size - more about
that later! You have to turn the charger at a lower speed than the
engine itself, by reducing the driveratio, sometimes as much as 4:1!

Following pictures shows 8 of the smallest superchargers around:

The smog pump - cheap and plentiful.
Used on automobile engines since late sixties.

The Aisin AMR300.
From Subaru Kei- car - 660cc supercharged citycar.

The KF Max10- 25.
American aftermarket blower.

The Hansen V12.
Made especially for supercharging Kart- engines from 5- 20hp.

The Busch/ Peugeot
Mounted on the Peugeot Jetforce and Satelis 125cc scooters.

The VW/ Porsche smog pump.
Mounted on models destined for the American market.

The Daytona superchargerkit.
Will hit the market ???.

The Ogura TX01 and TX02.
Japanese Roots pump.

European- made Do-It-Yourself supercharger kit!
Read more below.

The Japanese based Daytona company worked to launch a
supercharger kit for their 125cc Monkeybike engine.
Their Youtube video shows a well thought out system of the suckthrough
type, and the plenum even has an intercooler added! The supercharger
itself bears a strong resemblence to the Danish- made Rotrex C15, which
uses a planetary-traction drive, to gear up the axle rpm leading to what
equals to the compressor- side of a turbocharger.
The supercharger has a built- in oilpump, and an added oiltank supplies
the high- rpm running supercharger with filtered oil.
The Daytona supercharger video:
First test drive.
Latest video.
The Ogura Industrial Corporation manufactures a line of Roots style
pumps, and the TX01 and TX02(100cc/rev and 200cc/rev) is just what
the doctor ordered!

The Ogura TX Roots blower lineup.
Dimensions of a Eaton V180 Roots supercharger. Details of the smaller series of Eaton superchargers.

Very interesting Do-It-Yourself superchargerkit manufactured
here in Europe?. A supercharger kit for 50cc-125cc stock motorcycle equipped
with the Z50/AB27(horisontal)Honda style engine. Links:

The supercharger is a vane- type and emits the most adorable
blower-whine ever heard from a moped engine! It comes in
various sizes meant to cover engines from 50cc to 125cc.
Lets hope for mass- production which will result in a
reasonable priced kit.

4: Suck through or blow through?

A term often used when dealing with carburetted engines, which describes
the placement of the carb in relation to the supercharger. If you mount the carb
between the supercharger and engine, you have a blow through arrangement.
Leaving the carb in its original mounting seems easy, and attaching a hose from
the supercharger to the airfilter flange. A troublesome configuration in most cases, because in a blow through setup the carburetor sees both vacuum and boost, and the transition which takes place when opening the throttles, makes carburettor tuning very tricky! Sometimes its necessary to encapsule the carburettor completely, to avoid fuel bowl getting emptied by boost! Another issue is the dry- running supercharger, which in my experience is a bad thing. Running mixture through the supercharger does have several advantages, as it "seals" the rotors at ends and tips, making it pump more efficiently, and another bonus is a reduction in the charge- temperature. And I have to mention that I in several cases have seen an increased mileage in no- boost situations, when running the blower "wet", which leads me to think that the whirling rotors have an effect too, as they "atomize" the charge into smaller particles.
Advantages when using the blow- through setup are that boost- pressure
regulation can be handled by a simple spring loaded valve, which just dumps excessive pressure to the outside. Those adjustable wastegates that are mounted before the turbo, in a turbocharged setup, will work just as well in a blow- through supercharging setup.
A necessity in any suck- through installation is a pop- off panel or valve. A spring- loaded device opening a window big enough to let out excess pressure, in case of a backfire. It is neither a wastegate nor a BOW (blow off valve) and is a serious matter due to the amount of mixture present in the intake system, which now has a much larger volume. On a normally aspirated engine a back- fire will ignite the charge present in inlet passage only, (you hear a slight pop from the carb) but in a supercharged engine the charge in the volume of the supercharger and plenum must be added, and when it happens - well, you will know!. I have seen pressures as high as 60bars in a backfire, and that will do short work on gaskets, seals, airfilters and throttle valves, which occasionally turns into artwork! Adjust the pop- of valve to open 0,5bar above your boost setting. I usually make the outlet roughly the same diameter as the carburettor bore, cover is a piece of aluminum with a o- ring groove sealing outside the outlet. If you glue- in the o- ring, there is a big chance it will stay in place during a backfire and this will allow you to drive on. If the pop- valve dont re- seat after a backfire, your engine will have a major vacuum leak, and behave erratically until fixed.

5: Installation.

Around installation one should mention, that this picture is all wrong! Those who have driven
a supercharged motorcycle knows that installing a supercharger, that are bigger than your
brakes, is a no- no!!!
One thing is correct though, namely the placement of the supercharger. Compressing air means
heating it, and placing the supercharger in front of the engine is a very good way to cool
down the intake charge. If this is not an option that will work for you, second- best solution
is to mount the plenum/ intercooler in the airstream.

6: Supercharger drive.

There are many different ways to drive your supercharger, but these
small pumps do not require that much to be turned. The biggest load
takes place during acceleration/ deceleration, and that is mainly
down to the rotating mass inside the pump.
Superchargers has been known to be driven by:

Gears: Mostly seen on factory installations where a cast- in
supercharger ran at a pre- calculated rpm.



Toothed belts

Multi- rib belts

Hereby follows examples of above

Examples of chain- driven superchargers:

V- belt driven superchargers:

Toothed- belt drives:

Poly- or multi- rib beltdrives:

7: The engine - how to prepare it.

The engine which is about to be supercharged must be in good condition,
preferrable rebuilt to factory tolerances. If your engine has a problem,
be it overheating, oilconsumption, or a slipping clutch, then that
problem will be multiplied in supercharged form. A stock engine will
respond really well to low- pressure supercharging (below 9psi), if
following demands are met:
a compression ratio below 9: 1
a strong crank and conrod
a strong clutch
a good cooling system
a powerful ignition system
a free flowing exhaust.

This list will be longer if you move on to high pressure supercharging.

What happens when you supercharge an engine? The engine will no longer
have to suck in the mixture by itself, and therefore becomes very
responsive - xtremely responsive! A missed shift could result in over-
reving the engine - meaning bent valves, so if it is possible to add
an rpm- limiter, this might be a very good idea! The increase in power
will make the engine run hotter, so its important that you find ways
to keep it cool.
Low pressure supercharging is not a bad thing. As you can see from
chart on the left, the knock- threshold comes real close, when
you exceeds 9,5: 1 CR! However, the higher the compression, the
higher the effiency of the engine, so retaining the initial high
CR and adding a little boost, will result in a wide torque- band.
Good planning is a must - and some technical insight! Many have
asked me if the crank- mounted supercharger drive- pulley could
be attached on the outside of the flywheel, making installation
much easier? Well, I haven´t tried it and probably never will -
these small pumps don´t take that much effort to turn, but the
strain lies in the accelleration/ decelleration of the pump
when throttle is activated, and that´s where you would want the
load as close to the big main bearings as possible!
So, room must be made for a pulley inside of the ignition, and
an extra keyway must be made in the crank.
If, and only if, you got a steady hand, it is possible to use
a Dremel- type tool, to cut the keyway. Wrap entire crank in
several layers of cloth with axleshaft poking through, before
any grinding. When the correct depth has been reached, square-
off grinder disc against a hardened piece of metal, to get the
sharp corners needed.
Works for me!
As you can see, the pulley location will be outside the oilseal
which is mounted in the ignition- baseplate, and if crank-
pulley was mounted outside of flywheel, the distance to the
bearing would be nearly doubled! That could lead to a breakage
over time.
Later type engines (12Volt) has a longer axleshaft making room
for an electric start arrangement, and some even has an out-
ward facing flywheel. These wide engines has a cover- mounted
stator, and in one instance, I placed a supercharger- drive
instead of the starters clutch- unit.
Original CD50 cylinderhead. Biggest issue with these heads are
the rather flat valve- angle caused by the 39mm bore. This wide
angle have caused me a lot of trouble - even the slightest
valve- float (above 12500rpm) and the valves touch each other!
Took me some time to understand what was going on here! Upon
disassembly small marks in piston showed contact with
exhaust- valve, but only because exhaust valve were delayed
in its motion by opening intake valve! I dont believe the
larger heads (65cc and larger) have the same problem as the
valve angle are steeper.

8: Supercharging two- stroke engines.

What happens when you add a supercharger to a two- stroke engine?
Will horsepower and torque be increased? YES, but if we are
talking about a symmetrical two- stroke, the supercharger will
just work as a scavenge pump! The raise in output comes from
the pumps ability to flush all remains of the former combustion
and leave the chamber filled with a hundred percent fresh
charge mixture. Some low boost- pressure can be achieved in
some cases, but hardly recognised as a "supercharge" due to
the fact that the exhaust port remains open after the transfers
closes. And that is the downside of supercharging a symmetrical
two stroke engine as throughout the rpm range, a lot of this
fresh charge will continue right through the exhaust unburned,
and leave you with a horrendous fuel consumption.
Fitting a well designed expansion chamber to such a setup will
remedy the situation to a certain degree. That is when the
arrangement of cones and reverse cones will form a pressure-
wave, that at the right moment will reverse flow into the port
just before its closed by the rising piston. Some people do
in fact regard the expansion chamber as a "back- door" super-
charger, but as it only functions properly in a certain rpm-
range, it is not really comparable to a scavenge- pump/
supercharger. Those two in unison however, will reward you
with a strong setup.
If we look back in history, we will detect some very
succesful supercharged two- strokes like DKW and Puch,
and these had engines of the asymmetric variety. A seperate
valve controlling intake timing is what is needed to really
get going.
DKW twin-piston 250 with scavenge- piston.

8: Turbos and small engines.

As for the comparison of turbos to mechanically- driven superchargers, one must keep in mind that there is different types of superchargers. The positive displacement type (my favorite), and the centrifugal ones. I favor the brute force Roots type delivering boost on demand, instant power breaking the tires loose, snapping chains, and wrecking transmissions! It is really difficult to achieve that kind of response from a turbocharged engine - it can be done, but its hard! More popular is the slower, controlled boost- rise of the centrifugal blowers, making them much easier to map and emissions are thereby lower.

I dont agree to the popular belief that turbos doesnt rob any power off the engine. If you ever get the chance to take a look inside the turbine- housing, you will notice a cross- sectional area which is almost one third of the normal exhaust id! That explains the sensation of torque you feel, when the turbo has spooled up. Before that the turbo was just a cork!

I remember a dyno- session with a Roots blown big-block Chevy, where frictional losses was measured to 330hp, but who cared when engine output was 990+hp! What I´m trying to say is that you actually dont feel the loss.