Supercharging small engines.
|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.
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|
|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.
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 7 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 2011.
NEW KIT: European- made Do-It-Yourself supercharger kit!
Read more below.
The new kit on the block, the Japanese based Daytona company (sudden-
ly my favorite Honda aftermarket supplier :o)) are going 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 planetarytraction 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.
|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.
|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.
|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.|
|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.
|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.
Multi- rib belts
Hereby follows examples of above
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 it will
be multiplied in supercharged form. A stock engine will respond really
well to low- pressure supercharging (below 9psi), if following demands
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 intire 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 outward 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.
|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" supercharger, 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.