Selection of Suitable Parts

When you start to design and create track motorcycle, you have to first think, which parts you intend to design and manufacture yourself and which you intend to acquire from elsewhere. Before you can start actual design you have to decide for example what kind of engine is best to help you to reach your goals. Also best suitable shock absorbers are good to think as soon as possible.

Engine

First little bit about which kind of engines is used in track motorcycles and little bit about their pros and gons. So engines which are mainly used in track motorcycles are inline-4-, V2 and V4 in 4-strokes. In 2-strokes there are V2-, inline-2- and one cylinder -engines.

2-stroke engine

2-stroke engines are lighter compared to same size 4-stroke engine, that because 2-stroke function is simpler than 4-stroke. 2-stroke engines are also more powerful than same size 4-stroke engines, because in 2-strokes every cycle of crankshaft is power stroke and in 4-strokes only every second. I think that weak points in 2-stroke engines are availability, durability and price. Example in track use piston / pistons have to chance after about 10 hours of driving. Also over 100 hp series-produced 2-stroke engines aren't exactly produced, so if you want to get such kind of engine it would come very expensive.

4-stroke engine

The most common 4-stroke engine is inline-4 it's top rated and most produced. This is probably result of cheaper manufacturing than V2 engine. Inline-engine is easy to manufacture with higher rpm range than V- engine and under these circumstances inline-engine produce more power than V2. Example in new Suzuki GSX-R 1000 is 185 hp on 12000 rpm and in new Ducati 1198 is 170 hp on 9750 rpm. There has manufactured also V-engines which are with high rpm range, example new Aprilia RSV4-R, which is V4-engine and have power about 180 hp on 12500 rpm. So in V-engine there could be almost equally same power than in inline-engine, but powerful V-engine is little bit more expensive, than same power inline-engine.

Now I have told little bit about engine alternatives and next I will tell you what kind of engine we decided to choose to our project.

Most important criterions for choosing engine were:

- Price
 o Engine acquire and maintain expenses as low as possible
- Power / weight
 o Motorcycle power / weight ratio as good as possible
- Parts
 o Engine control parts as new as possible

First was good to think which one 2-stroke or 4-stroke is better to reach our goals on criterions. We think that 4-stroke was better for us, because largest 2-stroke engines which are available are little bit too small of their engine capacity. It's about 300 cc – 400 cc and it’s not enough to reach as good power / weight ratio in our motorcycle as possible with 4-stroke engine. This selection is based on series-produced engines, exception for example in MM-series middle class GP2 has used 250 cc 2-stroke engines, these had power about 110 hp.

So we decided to acquire 4-stroke engine and next we needed to think which one is better inline- or V-engine.

While choosing the right engine we had a tight budget to follow so we wanted to find a suitable engine as cheap as possible. We decided that: the engine displacement should be 600 cc - 1000 cc, powerful inline-4-engine and model should be newer than 2003. Also a slipper clutch would had been nice but not necessary. Slipper clutch is useful when you’re breaking with the engine brake because tires can’t lock but the clutch starts to slide if the breaking moment is too high. We wanted to have the 600 cc - 1000 cc inline-engine because many different manufacturers manufacture just those engine capacities which are suitable for track use.

We ended up buying a crashed year 2004 Suzuki GSX-R 750 cc motorcycle from damaged vehicle center. Fairings were broke from the other side and the back frame was split. It was ok to us because we were going to make them however by ourselves. Engine, shock absorbers, exhaust pipe and rims were fine and suitable for our project so we had a lot of executable parts from the motorcycle.

Pictures of motorcycle and engine which we bought is at the end of the Finnish version of this post, below.