Totally agree for an NA application but I have a high comp. boosted application in mind. That requires heavier duty pistons for the extra heat and occasional ping.

An old thread I know, but I was thinking about it again. I reckon you could use the Daihatsu HD-E piston without modification, if the crown is 0.5mm above the deck it's still within the gasket height. Should get some good compression, I calculate 12 and a bit with a stock head and gasket.

I don't have a thermostat (in the traditional sense) in my A15. I replaced the mechanical pump and thermostatic throttling valve with an electric pump, temperature sensor and controller. I've had no issues flogging it or driving interstate. Always sits on the middle of the gauge.

I can't think of any good reason to get rid of temperature control. If you're not getting enough flow and hence overheating drill a hole or two in the thermostat. It'll take a bit longer to warm up but maximum flow will increase.

An A series T5 conversion kit would make this gearbox more attractive. Sounds like a good little project for someone with more spare time than me.

Mine's standard Orange. I've come to love it.

Is that the right link? Looks like a drag car to me...

Ok, by contraction or expansion angle I mean the cone angle. Imagine you're using a piece cut out of a cone to join two pipes of different diameter, the cone angle is the angle between the sides of the cone. Basically you just want smooth, gradual changes in runner cross section. Steps or abrupt changes restrict the flow.

If you want the maximum power, make them match. Sudden steps in the pipe are bad for flow. I'd recommend doweling the manifold to the head and then port matching. Whether you add to the inlet or take off the head is up to you, just keep the transition smooth and gradual. Think 15° included angle for contractions and 10 for expansions like a venturi tube.

H beams are more efficient with material and hence lighter for the same strength. Any weight saved is less stress on everything at the same rpm. Reciprocating mass is the main source of stress in a piston motor.

I was under the impression the standard con rods are forged.

Shot peening introduces compression stress at the material surface and effectively increases the resistance to fatigue crack formation. That means you can stress them more (i.e. increase RPM) before running into fatigue issues. Forced induction has less of an impact on rods than rpm does.