I got a great email from Martin which was a copy of a thread in the AJP newsgroups (a thread is a conversation - where people have sent messages, replies to the messages, replies to the replies etc).

There was debate about how you could take the new AJP PR3 and make it much, much faster. Apparently, some guy was claiming (and the guy seemed to have an awful lot of knowledge about AJP engineering) it is possible to increase the capacity by 35% - from 200cc to 270cc.

This wouldn't automatically translate into a 35% increase in power, but would definitely make a huge difference. The top speed of the bike would go up into the 80mph+ mark, and the torque (the amount of power you have at very low speeds for getting up hills and/or out of sand) would also go up.

You do this by boring out the cylinder. Since I know that some of you aren't really into the detailed engine stuff, I'll avoiding engine geekery. But you need to think about how an engine works, so let me use a really simple analogy.

Imagine a syringe with a plunger in it (no needle). You have the syringe itself, the round barrel part, and you have the plunger (the part that moves). The syringe has got numbers on it telling you how much of a particular thing you have in it. The maximum amount of stuff you can fit in the syringe, when the plunger is all the way back, is its maximum capacity - measured in CC.

Imagine you stick the end of your syringe in some petrol, and you start pulling the plunger back - the syringe starts to fill with petrol. Then you remove the syringe from the petrol and pull the plunger back some more. The syringe will now contain both petrol and air. Give a little shake to mix them up a bit, put your finger over the end of the syringe and push the plunger in. You'll feel pressure on your finger as the stuff in the syringe gets all compressed. Just when you can't compress it any more and your finger is about to fall off, you create a little spark inside the syringe - this causes a mini explosion because of the petrol and the air that is in there.

This explosion makes the plunger shoot all the way back and go POP! out of the end of the syringe. It was such great fun that you do it again. And again. This is exactly what an engine does: suck --> squeeze --> bang --> blow.

The bit moving up and down (with the pointy bit at the top) is the piston. The bit where the colours change from orange through blue is the chamber. Each step is numbered:

1. Suck: Suck fuel and air into the chamber
   
   
2. Squeeze: Compress this little lot to make it explode better
   
   
3. Bang: Spark plug sparks, creating an explosion - the piston gets pushed all the way down because of the explosion, and this is what turns the engine
   
   
4. Blow: Get rid of all the smoke and nasty bits left after the xplosion. This comes out of the exhaust

So you can see, it's just like a big syringe.

When the plunger is all the way back in the syringe, and you've got it as full of petrol and air as you possibly can without the plunger falling out the end, that is the maximum amount of stuff that the syringe can hold. It is measured in cubic centimetres (cc). If you need more cc, then you need a bigger syringe.

Sticking with this for a second, the syringe is like the cylinder in the engine (basically just a round pipe). The plunger in the syringe is the piston (the bit that moves). The seal between the cylinder and the piston is airtight, just like the syringe. At the top of the pipe, where the needle would be on the syringe, is the spark plug. Just like the syringe - the total amount of air that the cylinder can hold when the piston is all the way out is the capacity of the engine. Just like the syringe, it's measured in cc.

When the piston goes all the way back, fuel and air is sucked in. The piston comes up to squeee this little lot. The spark plug creates a spark, which causes the bang and the piston shoots all the way back (which is ultimately what turns the engine). The smoke from the xplosion is blown out of the exhaust. Lots of times a second.

So, a 200cc engine basically means that the amount of fuel and air you can fit inside the cylinder when the piston is all the way out is 200cc. A 200cc engine is really just a big syringe without a needle.

The more fuel and air you can fit in the engine (i.e. the more cc), the bigger the explosion and the more power you get.

You get a huge drill, and you drill the cylinder out so that it is a much much bigger hole. Then you get a much much bigger piston (because it needs to be airtigh for it to work). The size of the hole you can drill really depends on the size of the engine itself - you have to leave enough of the engine to make sure that the sides of the cylinder are thick enough to handle the explosions.

So, by increasing the size of the cylinder and piston, you are dong exactly the same thing as getting a bigger syringe - all you're doing is creating a much bigger chamber in which to explode fuel (more fuel means bigger explosion means more power).

Martin, who has been dismantling engines since he was still wearing shorts to school, thinks that 270cc may well be possible but he's got some doubts about whether the cylinder head (top part of the engine) is big enough to allow the hole to be this big. If anybody can do it, Martin can.

The best thing about doing it this way is that you keep the original engine. This means that the frame of the bike (and suspension and stuff) isn't having to cope with carrying a shape and size of engine that it wasn't designed for.

AJP have spent an awful lot of time, money and skill engineering the PR3 and some very clever engineers have done some very hard sums to make sure that all of the bits can cope with all of the stress and strain of carrying all of the other bits. Not replacing their well-engineered bits
with other bits makes sure that you are staying within the tolerance levels of their sums.

Simply put, this gives much less chance of breaking the bike (apart from falling off, which I do rather a lot of). Which means more chance of making it to Dakar.

It also keeps the weight at that simply elegant 89kg. Lighter bike. Better fuel consumption. We've done this already.

It's also going to be much more fun to bore out the 200cc engine into something much faster than it will be to just replace it with a bigger one.

The AJP PR3 is going to be available in December. I have been a very good boy and have already written a letter to Santa saying so.

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