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CASE STUDY: NITROUS DRAGSTER

STAGE 1:
 
The engine was sourced, a low mileage 125cc unit which are better for tuning. The outside casings were cleaned before everything was stripped from it. Crankshaft and the gearkit were removed leaving the four aluminium castings that make up the engine.

New Parts at stage 1:
 
- Malossi full circle crank
- Malossi 172 kit
- New bearings and seals
- Oversize reed block
- Gasket kit
- Nitrous oxide kit - courtesy of SCCC

Jobs to be done at stage 1:
 
Remove old bearings and seals. Plug all threaded holes and tape machined surfaces ready for bead blasting. Bead blast crankcase castings.

Considerations 
Seeing some engine crankcases fail when the engine has been tuned to high levels we have decided to look into strengthening the crankcase, there are three methods ranging from the simple to the very hi-tech. The crankcase halves are being drawn on CAD so any future parts that have to be made will be a lot simpler to make, a full crankcase or parts of it maybe CNC machined from alloy depending on the levels of nitrous used and what the crankshaft will take.

Unfortunately the Dragster battery just doesn't hold enough 'ah' so it looks like a bigger one will have to be used and re-housed under the seat with the solenoids, the nitrous tank will have to be mounted above the front shock absorber or on the rear panel.

The nitrous system used is a NOS single stage - soft hit, the reason for this is we don't want the engine going BANG on the first run. With other systems being developed at this time and having fuel problems i.e. Nitrous fuel pump starving the carb supply - we have opted for the easiest option and are going to convert the oil tank and therefore run on pre-mix.

Nitrous and corrosion 
Concerns about corrosion were looked into, it seems that sulphur-dioxide is produced during the combustion process and then mixes with other by-products to make sulphuric acid when using nitrous and that some feel that it will cause increased corrosion. The normal combustion process already makes as a by-product sulphuric acid in small amounts so the risk of running increased corrosion is very small indeed more likely parts will wear away than corrode away.

STAGE 2:
 
With all the engine castings cleaned we have heli-coiled all the threads - the reason? This engine is probably going to be taken apart a lot and most threads cut in to aluminium just give up after a while, the stainless coils allow for repeated use and higher torque settings.

This is how the engine looks now:

The Malossi 172 kit has been ported slightly along with the engine cases which were also machined to house a larger reed valve, this now sits below our NOS manifold.

You can see the manifold below the Malossi rubber intake manifold, it still has to be drilled and tapped to take the NOS 'Fogger' and also the connection for the 'Boost Bottle' (which is still under development).

Now this engine is running on pre-mix we have done away with the oil pump, however we have decided to keep the water pump as it makes life simpler to use it on the road. Some tuned engines run with electric water pumps but as we intend to use a NOS system we don't want any more current being drawn from the battery, we have redesigned the water pump drive sprocket and it is nearly a 1/3 the weight of the original.

All we have to do is put the engine back in now and get some miles under our belt while we fit the NOS kit and other mods needed to be able to use it.

Words: Ian Sim.