Valve guides: Don't mess with them. The valves (especially the exhaust) can only disapate heat by the contact area it has with the valve guide. If you cut down your guides you will reduce this area and cause the exhaust valve to operate much hotter and will possibly lead to detonation. As A14Force mentioned, you'll wear the guides out much quicker and your car will blow smoke.

Bore: Each block is slightly different (even from factory) so there's no exact answer. 78mm seems about the biggest safe size for an A14/A15 providing that corrosion hasn't reduced the metal thickness around the bore. If your engine has rusty coloured water in the radiator, just bore it to 76.5 or 77.0mm

Pistons: Mazda pistons are a common swap. UC, B6 and E-series mazda motors. Some are flat top. Download the ACL catalog from their website for more info. With all suitable mazda pistons, you will need to enlarge the small end of you conrods from 19mm to 20mm.

Compression: You really need to understand how to calculate what the compression will be. Theres heaps of info on the internet. As a very rough guide, you don't want the static compression ratio to be above 10:1 in a road car.

Power Band: Your power band will depend on alot more than just your cam. Compression, Head ports, intake manifold ports, carby type and qty, exhaust headers, valve sizes, etc, etc. Again, as a very rough guide, A15's produce their best performance below 6,500rpm in street config.

i think you need to calculate carefully if you want to change flat top piston. if you have skimmed cylinder head before, better not changing flat tops.

i found i this web site saying that milling off block and piston together will increase compression ratio at lower cost than custom making piston. in Malaysia i think it is not cheap to custom make this thing...

cutting valve guide seems risky. do you have extra head?

hicam? custom make also?

Will a 78mm bore cause any trouble such as overheating?...thanks

If you cut down the valve guides, they will wear out much faster.

Hi guys..i have some questions. ( A15 )

1.) Is it advisable to grind off abt 1/2 inch from the valve guide? ( at the intake/exhaust port area )...in a way, this will minimize flow obstruction right?

2) If im running a 280deg cam, at which rpm will the power be optimum?...4k, 4k-6k, or beyond 6k?...

3) Pistons....which size shall i go for? any reccomendation from any particular engines?....and, will flat tops with decked head cause knocking due to high compression?

Advance thanks for your replies