DriftMe,
I applaud you for your enthusiasm, dedication and creativity! (I'm an engineer too!)
Here is some info I've put together over the last few years, regarding building up a 6M-GE NA allmotor setup. This has all been inspired by the great discussions that we had on the Yahoo list. Maybe it will give you a few more ideas on increasing HP (or in some cases increasing available HP by decreasing losses)... Mileage will be unknown, but most of these mods help to increase engine efficiency so they should not hurt mileage.
Building up a non-turbocharged Mk2 Supra. [numbers in square brackets are approximate gains expected from the mod as compared to the stock setup being replaced]
Rebuilt 6M [approx 190 HP stock] or 5M [approx 160 HP stock].
Port and polish the head (improves flow but also reduces compression a tiny bit). [+5 HP]
Shave head to get compression a bit higher, but not to the point of making it an interference engine if the timing belt breaks. Use 84-86 domed pistons. Try for a comp ratio of about 10:1. [+10 HP]
Headers, modified to collect into a 2.5 or 3 inch pipe, all wrapped to keep heat in. [+5 HP]
High flow 2.5 or 3 inch cat (match size to header collector). [+3 HP]
2.5 or 3 inch mandrel bent stainless steel exhaust (insulated for at least the first few feet) to a straight through muffler. [+5 HP]
Custom intake with ramair coldair intake and high flow air filter. [+10 HP]
Loosen AFM spring to richen mixture. [+2 HP]
Ported/polished AFM for now (gain a few HP) replace it with MAF sensor if possible. MAF should be good for 10-30 more HP [+2 HP]
Phenolic spacer between head and intake plenum to keep intake air cool. Should gain a few ft-lbs of torque due to longer intake air path and several HP and ft-lbs from colder air. [+5 HP]
Water bypass on throttle body to reduce intake air temps. [+2 HP]
Advance timing to 15 deg BTDC. [+5 HP]
Electric water pump (frees up 15-25 HP according to some people). [+15 HP]
Electric fan (frees up a few HP). May need upgraded alternator. [+3 HP]
Maybe some mild cams, nothing too rough. Adjustable cam gears are required with new cams. Big $$ for small gains. [+5 HP]
Coatings on chambers and piston domes to keep them cooler (if you can afford it).
Vacuum pump on the crankcase? [+5 HP]
And of course, the standard body lightening mods. I plan to get a couple hundred pounds out of the car without removing any (visible) interior parts. Lots of parts on the car that I never use or don't need.... Rear wiper washer fluid bag, broken power antenna, headlight washers, broken A/C, spare tire, rear carpet underpads, cruise, charcoal canister, etc, etc, etc. So far I've found about 200 lbs of stuff that can be removed that no one should even notice, until they race against me! 200 lbs lighter should shave 0.3 seconds from quarter mile times.
All of these mods add up to approx 80 extra HP.
Modded 5m should be putting out about 240 HP at the flywheel, 200 RWHP. 13.7 sec quarter mile.
Modded 6M should be putting out about 270 HP at the flywheel, 225 RWHP. 13.1 sec quarter mile.
Everyone, feel free to agree or disagree with anything listed here, mods or the suggested HP increases!