I often get emails from fellas wanting more hp
and I would like to help them all but engineering laws
and cost of parts all play a role.

Any advice to these fellas looking for budget hp?

I reckon shaving the head to bump up comp is the easiest

after that engineer is needed as boost is hard to beat

Yes, shaving the head to bump up compression will gain one hp. But more importantly, it gains at all RPMs, unlike cam, carbs, etc that only gain at high RPMs

Budget HP requiring only self-certification (no engineer needed) is to replace the A12 with an A13 (1270cc). Under NCOP, up to 1346cc is allowed without engineering. Better yet, keep the A12 and fit Mitsubishi 4G32B pistons, milled flat, for 1300cc. A set of 4 new Mitsu pistons can be found on eBay for $75 from time to time

Its great if rebuilding the A12, Mitsu pistons like that are an awesome option and the revs of the 70mm A12 is proven. There is also the sneaky A14 inside the A12 but needs A12 rods machine to suit, bored for A15 pistons (which are milled 1mm) and A14 crank machined counterweights to clear and rebalanced. Rowland manifolds are a good option for bigger carbs.

Simon seems to be the budget master for power.

So do we have a compiled list or wiki of what is optional for power under the engineering radar?

for Australia (NCOP), yes, see article National Code of Practice and State Rules for Engineering

The big problem from what I've heard is that the state just refers you to an engineer (they won't answer specific questions), and some engineers want to add their own pet preferences to your list of requirements. For example, several engineers want you to add power brakes, but one of our club members pointed to the relevant section of the Rules then the engineer tested his car and found it stopped well enough w/o power brakes, so he engineered it

I often wonder why our country doesn't have safety tests, but then again I've never heard of any accident because of user modifications ...

With the comment about shaving the head to increase compression, at what point is it recommended to use higher octane fuels (95 and above) in a high compression NA engine, lest you harm the internals?

If you shave the head to gain more compression, then Premium is suggested

Regular A12: ULP (regular fuel)
10:1 GX A12: PULP (premium)
9.5:1 GX A12: mid-range fuel

The GX could take more compression because it had superior flat-top pistons. With dished pistons and shaved head, you'll need higher octane fuel sooner. For more information, see Quench

DD always to the rescue! great stuff mate.

14.1 comp is possible and will go well with e85
A buddy of mine in the corolla scene with inferior
K series 1.3 similar to A12 datto engine used
14 to 1 comp ratio with E85 and recurved dizzie
and went up to almost 18-20% difference on a dyno
from one year to the next throughout the rev range.
He is going to use Singh grooves next which are
even recognised by German enthusiasts quite remarkable
and possibly the best mod anyone can do to their stocker
https://www.youtube.com/watch?v=5YbcOhiwmkE

another weird groove trick

http://peswiki.com/directory:gadgetman-groove

That reminds me, the Mazda skyactiv-g is 14:1 compression on premium gasoline

with the German Interviewing team in the vid @ 2.23
car idles at 500 rpm instead of 750-850 factory norm
and they shift from 1st to second at 20kmh to 4th and
it doesnt stall keeps going at 200km and a guy asks
"is this a diesel" reply is "no its gasoline...

They also start the car in second and it takes off
without accelerating just ignition and torques away!

The big wigs hate this little guy as he has so many
customers and other people using his tech online and
many of their own vids to show the gains