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dazmatic · # 6 22-08-10, 11:17

I'm a long way off before I start engine mods im afraid.

Quite simply don't have the funds. I do know of a company locally to me though that can machine out the cylinder and possibly plate it so its all possible.
I have other projects I need to attend to first.

I believe a 700 system on these is a 102mm piston? So that would require a 102mm head gasket and if possible, blending of the head to the cylinder.
Thats if you stick to the standard cylinder and bore it out.

If you do like kev and fit a cylinder of a raptor 700, there are a few extra mods you need to do, including fitting a different base gasket.

I'm not sure if its possible to bore the standard 100mm to 102mm without removing to much material, remember, if you start removing material reliability would be degraded but it would make for an easier job unless you swap the liner for a 2mm larger one.

Flat top piston with this style of engine is hard to come by.
The reason a piston would have groves in it is to make room the for the valves. Some cylinder heads are designed so that the valves sit proud of the machined base of the head. Because they sit proud, they enter the top of the cylinder, only by a few MM mind when closed. As the piston rises during its Cycle, it'll come very very close to the top of the cylinder, if it was a flat top, it'd likely collide with the valves, even when closed!
With the grooves it allows for the piston to come ever closer to the valves during the compression cycle, the deeper the grooves the closer it can get increasing the compression ratio.

There are of course other factors to take into account of compression ratio such as the height of the pistion, centre of the gudgeon pin, crank height, con rod length, even the thickness of the valves.

There is a resonable amount of power that can be had from decent head work. I used to have a VW Polo, little 1.3 where the head gasket had gone and struggled to start because of water getting into the cylinder.
I removed the head, took it to work and skimmed off an unknown amount (cowboy, yeehaw!) to remove some pitting, new stem seals and relapped the valves into the seats.
No gas flow, or port and polish. Just a small skim and lapped valve seats!
After refitting the head I took the car for a drive and there was so much more go in it. It picked up speed quicker and red lined in every gear whereas before, it struggled, was like a little go-kart!