S2K Bolt-On Power

For 300 naturally aspirated horsepower at the wheels, you'll need increased compression and, ideally, larger displacement. Cams, head work, a long-tube header, ECU tuning, dyno tuning, etc., will also be required. Unfortunately, it isn't going to be found with just a series of bolt-ons.

Affordable Boost

My friends say to go the forced induction route, and so far the best solution I found is the Power Enterprises twin-turbo unit, but it's a bit pricey. Plus, I know I would eventually have to build the engine's internals to handle boost. Others have suggested the Vortech supercharger, which is more within my price range than most turbo kits on the market. I want 350-400whp. What should I do?
-Chris M.
via importtuner.com

To be honest, a big-power, naturally aspirated build is expensive, can hamper street drivability, and is generally loud without turbo(s) to silence the exhaust. To make 400hp naturally aspirated, you'd need camshafts, head work, high compression pistons, and bigger displacement, all which will add up to big bucks. Back in '08, Cosworth built an engine for the Castrol Syntec Top Shop Challenge that made 439 naturally aspirated bhp, but the parts alone cost nearly $16,000-without labor. The PE twin-turbo kit uses IHI turbos with the capability of delivering 500whp while offering excellent boost response. But like you said, it would be ideal to build your engine first. Another option is to keep the boost down on stock internals, and the power at or below 400whp with good tuning. The Vortech kit is a good option for this. Unfortunately, it all comes down to how much your wallet can handle, before your engine.

Old School Transformation

1. No, what's the point? Why not just buy a S13? An S13 doesn't cost much more than an '88 Sentra. 2. You can swap in anything that will fit if you have the money, but it probably isn't worth it. 3. See answer #1. 4. It's usually only the larger mail-order warehouses that offer military discounts. The smaller shops that do engine swaps probably won't have the budget to offer "hook-up pricing", but it doesn't hurt to ask.

Induction Suction

I would suggest looking into a K&N Typhoon or an AEM Cold Air Intake. The K&N Typhoon intake plenum isn't as long as their competitors' and might be good for your application if water is of concern. K&N claims to deliver a 7.5hp gain at 6,400rpm over the factory intake.

Backpressure

A well-designed 4-2-1 header will provide gains in both torque and horsepower, but it's the 2.75-inch exhaust that I think might be a little too big for your naturally aspirated engine. Even near-stock road-racing Hondas-such as NASA's Honda Challenge H3, H4, and H5 class cars that spend their lives above 6,000 rpm-don't usually use exhausts that large. Of course, it all depends on the mufflers and silencers used in your 2.75-inch system, but I think a 2.25-2.50-inch exhaust would yield more usable power.