Whilst your friend's math isn't 'wrong' by any means, it does however come across as if he thinks it has to be a big dollar perfect match or it just won't work.

In real life, especially 'the ghetto' - you will find you can actually get away with a lot. fwiw I think you should be looking for another turbo - and if possible one off a nissan exa or et pulsar (same engine/spec afaik). I had one of them on a 3k corolla motor and got it into the high 14s (with absolutely EVERYTHING done wrong - smaller motor, crappy flowing pollution era head (you have a bigger motor, and a much better flowing head) and a j pipe that was nothing short of an abortion (the funnelling down from the twin outlet cast iron exhaust manifold was atrocious,the j pipe itself was 2 1/4 inch diameter - too big (slightly smaller keeps the velocity up) and the flange welded on the other end to mount the turbo to - since it had to sit over a 2 1/4" pipe (whereas a 1 3/4 or maybe 2 inch j pipe absolute max will be easy to gently funnel into the flange without an obstruction) - well it was like a big parachute, horrifically inefficient).

despite all that, it ran hard. If you ran a similar turbo on your a14 it would surely be able to run a low 14 without spending stuff all.

I'd like to make a point 'against' laggy turbos. Obviously it is all relative, so there's 'a little bit' of lag that might not be a problem, then ther is a ridiculous amount. as an example - in the US there were 2.3 litre 4 cyl turbo fords (mustangs) from about the mid 1980s. They were discussed a lot on the jyturbo list. Anyhoo, they mostly ran almost identical turbos, but some had 0.48 a/r exhaust housings and some had 0.63 a/r . the larger 0.63 ones produced more power, due to less exhaust restriction overall. However, despite that, on the street, the vehicles with the tighter turbo would always get a few lengths ahead (and maintain it) taking off from a standstill. The reason is simple enough - they spool quicker and get into 'big power' (relatively) sooner and start accelerating hard sooner. The others spool slower so even though they eventuall make more power, they spend more time 'getting into the swing of it' and get left behind so to speak. On the street, better spool (well not so tight on the exhaust that you can spin the motor up to 4500rpm or something!) will be king. It's not just good off the mark, but things like overtaking - the quicker you can access boost/big power the better the outcome. Another place you can see it is some of the 'flagships' of certain turbo workshops. They have a car - once upon a time the VL commodore was the big one here - that they have one of their top of the line engine/turbo combos in. And there's footage of it at the dragstrip and the car runs some absolutely exceptionally quick et/high mph. Which is admirable. But if you look at it closely, they are just running to get a good time (and remembering the 1/4mile et timer only starts once the car actually starts moving and breaks/passes the beam under the front wheels, so they can sit there forever and not be 'running up the meter') - and they'll often spend 5 seconds or so spooling the turbo up so they can launch optimally and run hard. that's all well and good, and whilst it produces a quick time, in a 'real' drag race, a car that spools better can launch harder (and in drag racing the winner is the first one to the finish) will launch, and beat the 'quicker' car to the other end. The 'quicker' car - the driver either needs to launch earlier (than optimal, but I don't mean red-lighting by leaving too early) and without full spoolup, and therefore run slower, just to get off the line in time. He could wait and spool it up so it launches harder, but all the while the 'slower' car is charging further and further away.

So how much lag (or lack of it) is acceptable or not. Well - it differs from engine to engine and car to car. Since we are dealing with smaller engines (that can handle ok rpm without much work) 'ok' spoolup rpms can actually be a little higher in the rpm range than a turbo you might put on a much bigger engien that revs lower overall. So that in mind, I'd suggest that if you can get it starting to spool just prior to 3000rpm, and getting to useful boost (or nearer full boost) by about 3500 you'll be pretty happy with the result.

I absolutely agree that e85 (or e-flex which I think varies down to around 75% at times, but don't quote me on that!) would be perfect for this. But if 98 it has to be, then it's still going to get a good result. Water injection is your friend, and works exceptionally well. You can read about early work on water injection if you look up 'naca reports' (NACA was the forerunner of NASA, and was a tech/research sort of thing for all things aircraft development related). They tested various engines (often to destruction) with higher and higher boost levels and ever increasing water levels. water injection was used on ww2 fighter aircraft (when combined with higher than normal boost levels, for short during emergency high power for stuff like dog-fights) fairly extensively. They (NACA) went as far as actually exceeding a 1:1 ratio of water to fuel (i.e. for every litre of fuel being fed into the engine at full boost/power, they actually were feeding in MORE than 1 litre of water) - and it was still effective up at those levels. On most automotive applications, you'd rarely find anyone going beyond maybe 4:1 (for every 4 iltres of fuel used, and yuo can calculate that based on power output - anyhoo for every 4 litres of fuel, 1 litre of water is added).

They say you need a richer mixture under boost to help prevent detonation. This is certainly true. what not everyone knows is 'why'. It's not because the fuel burns dramatically differently. Run richer and there's going to be some unburned fuel going out the exhaust. It's actually the cooling effect of the extra fuel that cools the intake charge a little bit that helps prevent detonation. This is where it gets interesting. Since it is the cooling effect, and testing has backed it up 100%, well if you added water injection, then that water could take the place of the extra fuel, and it would take care of the cooling effect. I'm not suggesting you should lean it out way too far and then run water and hope for the best. What i am saying is that instead of (hypothetically) going as rich as perhaps 11:1 as you run more and more boost, you could run around 12:1 a/f ratio and add as much water as is needed to handle whatever boost level you are going for.