Question:
I’m looking for a 100mm diameter dry sump oil tank because of installation issues. I noticed that the one on your site, but it says it can’t be used with a Hayabusa, why?

Answer:
The biggest problem with Hayabusa engines, in all bike engines, is the gearbox, clutch and generator areas in the engine. These can fill up with oil under different conditions e.g. cornering, accelerating, braking, etc which means that they can retain a lot of oil under these conditions and only when the area is full of oil and no longer any space, can it reach the bottom of the engine so be evacuated by the scavenge pumps. These creates 2 problems, most important of which is that you can end up with an excess of 3 litres of oil within the engine. The engine also normally retains between ½ to 1 litre when running. This means that you can end up with in the region of 4 litres of oil within the engine, so we have found the minimum capacity for oil within the dry sump tank needs to be 5 litres of oil (this excludes what is in the pipes, oil cooler and actually within the engine when running. Anything less than that will cause a problem, not just due to the lack of oil in the tank but the secondary problem which I will describe now.

The top of the dry sump tank is used to separate air from the oil, there will always be air extracted by the scavenge pumps and this can be up to 90% more air than oil. The oil is sprayed around the top of the tank and jetted as a film of oil around the wall of the tank. This helps the air to separate and by the time it is spun round the tank, the majority of the air is separated out. The taller the tank, the better this functions and the less complex the tank needs to be, the shorter the tank the less time available for separation to take place. Ideally you need a minimum of a 1½ litres of air space before the oil level is reached.

The tank we recommend for the Hayabusa engine is made taller than the original design, its first baffle has about 1.5 litres of air space, you can see the detail of the construction on the website. This tank is designed to separate air further as it passed through each level and the lowest level in the tank, in theory, does not allow for oil movement, but must be completely filled with oil only as any air left at this point would be compressed by the oil system and create catastrophic failure of the engine. This tank has an oil capacity of 5 litres, the smaller tank that you are looking at was originally designed for the Vauxhall engine in sportscars, the Vauxhall engine can run on 3 litres of oil in a tank, this meant that the tank itself has a large area for the air, it has no baffling due to its small diameter and its height. The Vauxhall engine only has small areas that the oil could congregate, so therefore would not retain as much oil as the Hayabusa.

If you do the calculations on a 100mm diameter tank, you require a tank in excess of 600mm tall and this is probably still not sufficient because you are more likely to require over 2 litres of air capacity due to the lack of baffling to allow the air to separate. Also due to its smaller diameter, you wouldn’t be able to incorporate the small internal design of the larger tank and without extensive testing could prove disastrous.