Supercharging small engines.


Supercharged scooter engine.

I would like to make an enquiry amongst those who has an interest in a DIY- supercharger kit, for
small Honda engines or replicas hereof. My reason for doing this should be obvious, when searches
for something like that usually end up with heavily over-priced kits suiting no- one and withdrawn
before even hitting the market!
I am contemplating a kit consisting of a small (very small) Roots blower along with a mounting kit
for various models.
If YOU think that could be vaguely interesting, drop me a line explaining your thoughts - I will
probably not answer your mail, but include it in a survey, that will run the year out.
To be more precise I envision a max 20hp setup, which anyway would be outer limits on the chassis
of most small bikes carrying these engines of 50- 125cc.

Mail to Subject: DIY supercharger kit.

Looking forward to hear from you.

UPDATE! Due to my involvement in a national championship, the supercharger- fabrication has been
postponed for a year. That means that your input in this survey are as important as ever!

As of June 2013 requests has been made for following models:
Honda Dax (3)
Honda CT90 (4)
Aixro XR50
Suzuki SP370
Honda CT110 (3)
Honda XR80 (3)
Sachs Madass 125 (2)
Yamaha TW200 (3)
Honda Ruckus/ Zoomer (4)
Lifan 125
Honda CB77
Yanmar diesel 220/ 330/ 420cc
Honda CBX250
Yamaha TW200
Honda CB50
KLX 110 (2)
Honda Ruckus 150
Honda SS50
Honda XL125
Honda GX35
Honda Chaly
Smart 451 ?
Honda SL70
YX 140
Honda CL90
Yamaha TMax 500/ 530 (2)
Honda XR100
Derbi 250GP1
Briggs&Stratton OHV
Yamaha XVS125
Honda CG125
Honda Aviator 109
Scooter GY6
Sachs Madass 50
Motom 48
Kymco Agility 50
Honda XL650
Laverda 100 (1955)
Suzuki DR/VanVan 125
Kawasaki Ninja 250R
Ducati 600
Kinroad Sahara 150
Honda GX200

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 TITLEer 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.

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

2: A smog- pump is not a supercharger?

Well, the smog pump is an airpump, a supercharger is nothing but an airpump, so of course a smogpump can be adapted as one! My experiences with this cheap and plentiful smogpump is all good! But like everything else, the equation must sum up. Pumps have different sizes, and maybe not the size needed! The most trouble I have had with a smog pump supercharger was a wrong sized pump! Intended use is important too! I have used the smog pump as a supercharger on a racebike for short distance races. I have not used the pump as a part of a daily transport vehicle. Unlike the situation of a racebike, which is "supposed to be" taken apart and inspected, before next racemeeting, a daily driver would present other problems. Will the five roller- bearings inside the rotating drum be washed out, by the fuel- mix present?
The most common, and cheapest, smog pump is the one mounted on GM and Ford V8 engined vehicles from 1969- onwards. Also known as an A.I.R. pump, this device can be found attached to the front of the engine, driven by a v- belt. These pumps gave a steady 5psi reading, when tested for functionality, and their mission was to ingest air, via small tubes to each exhaust manifold, just outside each exhaust port. This air- injection helped igniting the catalytic- converter, reducing emissions emitting the exhaust pipe.
Converting your smogpump into a supercharger goes like this:
Unbolt the rear cover, and pry it apart, but very gently! These are delicate thin- wall castings and you dont want a leaking supercharger. A little trick here is to drift out the two dovels, which lines up everything. After loosening the cover, you have to wiggle it from side to side to extract the cover-mounted axle from the vanes rollerbearings. Once out, you can see the internals. Most significant is the large metal drum, with two vanes protruding 180degrees apart. You can also note the rollerbearing which supports the barrel. If You want to change the direction of rotation, you must pull the bearing support from the drum. A simple special tool must be made for this operation. The support is a casting, and a bit fragile! Once the bearing support is removed, you can see the two cages containing the seals. These cages are asymmetrical because one of the seals has a spring behind it. If you try to run the pump counter- clockwise as is, this spring will be compressed. Result will be a major leak, and at high rpm, the seals can move around and break! So it is vital that the cages are loosened, turned around, and welded back in! If the six? spotwelds are carefully removed, the cages can be loosened without getting out of shape. When re- installing the bearing support, take care not to squish the curved end- seals
As an alternative you can run a jackshaft, allowing you to run the smogpump as is - see drawing!
Most smogpumps has its air- intake in front, behind the plastic-fan, which also acts as an airfilter. This is no good since its quite impossible to fit a carb or much needed airfilter here. This intake can be closed by applying Devcon, or similar, into the hole.

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.

NEW KIT: 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!

Follow this link for more info:

New DIY kit!

Very interesting new Do-It-Yourself superchargerkit manufactured
here in Europe about to be launched. A supercharger kit
for 50cc-125cc stock motorcycle equipped with the Z50/AB27
(horisontal) style engine. Video 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.
Dr. Kosta and his team presented their product and future
plans at the SETC 2013
(Small Engine Technical Conference).

Here is an excerpt of the presentation:

The article presents a theoretical basis on how to improve
high performance characteristics of a motorbike by supplying
a working cylinder with additional compressed air under
certain conditions. A few versions of a positive displacement
air compressor (supercharger) have been developed, built, and
used for engine boosting. Road tests of the pitbike motorcycle
equipped with our small rotor-vane compressor were performed.
The results exceed expectations of the supercharger's
performance and efficiency. Thus, to reach 50km/h for the
motorcycle powered by the 50cc four-stroke engine equipped
with the supercharger, 40% less time is needed than for the
same motorcycle powered by a naturally aspirated engine.
1. We have developed the detailed specification of supercharger design
which could provide corresponding air productivity required
for the engine under different backpressures. According to this specification this kind of supercharger
was designed and manufactured.
2. Here you can see air productivity graphs of the super-
charger - predicted and actual provided at different back-
pressure of 0.0bar (with no backpressure) up to 0.8bar.
3. Please, pay attention to the fact, that supercharger
air consumption values under backpressures are almost
straight lines. By the way, this feature was observed on
every in-house compressors of Vane type.
In order to evaluate acquired data on acceleration dynamics we have
conducted the following experiment.
We have purchased stock model of the prototype bike and
conducted 3 experiments:
1. Standard equipped most common stock model
2. The same stock model equipped with our supercharger kit
3. The same stock model with the most common tuning to
a 75cc big bore kit
2. We have tested three variants for acceleration and
speed performance.
3. As it can be seen from the diagram, supercharged motor-
bike has the acceleration time of 8.5 seconds to reach the
speed of 50 kilometers per hour, which is comparable with
75cc model and much better, than stock model has. Time of
acceleration stock model up to 50 kilometers per hour --
14.5 seconds. Thus time to reach maximum allowed speed
for supercharged motorbike is less than naturally aspirated
stock motorbike by 40%.
4. Allowed by technical certificate maximum speed of the
target bike - 50 kilometers per hour.
This joint diagram gives air-to-air ratio of engine and supercharger.
1. This diagram shows theoretical and actual capacity of
the supercharger at different backpressures and also theo-
retical and actual curves of air consumption by the motor-
cycle engine. Projection of intersection of backpressure
value points in plenum at defined (chosen) rpm on Y axis
shows actual engine air consumption at chosen rpm.
2. In the result of conducting numerous tests we have
defined optimal backpressure at defined rpm of the engine,
notably: 0.4bar @4,000rpm, 0,6bar@6,000rpm and 0,8bar @8,000rpm.
3. Comparisons show that in total of all vehicle parameters
especially on its acceleration characteristics, reliability
and other, less important, the shown values of backup
pressures on diagrams are optimal.
4. We have tested also other versions of backpressure, for
example: 0.3bar @4,000rpm, 0,4bar@6,000rpm and 0,55bar@8,000
rpm and even maximum possible from our point of view: 0.6bar
@4,000rpm, 0,8bar@6,000rpm and 1,0bar@8,000rpm.


Download and read the VERY informative study of super-
charging small engines:

This is a SAE paper (Society of Automotive Engineers)
and is downloadable against a small fee.
Now they are planning to set up a plant mass- producing
these small superchargers weīre all waiting for!

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 havenīt tried it and probably never will -
these small pumps donīt take that much effort to turn, but the
strain lies in the accelleration/ decelleration of the pump
when throttle is activated, and thatīs 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.

Interesting file on two- stroke supercharging
from Dr. Kosta and his team:

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 Iīm trying to say is that you actually dont feel the loss.