How to Build a 300whp 2022+ WRX

Ethanol does the work, not the hardware

Compare two rows of that ladder and the whole build strategy falls out. Stage 2 on pump gas: 274.7 whp. That is a full hardware package - intake, intercooler, charge pipe - plus a custom tune, and it sits about 14 whp above a Stage 1 car that had none of it. Stage 1 on ethanol: 289.4 whp. No hardware at all beyond a fuel sensor and a pump, and it beats the pump gas hardware build by 15 whp. The conclusion is not subtle. On the FA24 the fuel is worth more than the parts, and a 300whp build is fundamentally an ethanol build with supporting hardware attached - not a hardware build that happens to run ethanol. If you have no E85 near you, this guide's target is the wrong target; a Stage 1 car on 93 with good tires is the better car for your money.

The parts list

Tuning device, roughly $770. The gate for everything else. Intake, roughly $400 to $500. Required for a Stage 2 tune. Tell your tuner exactly which one you bought, because MAF housing diameter drives the map. Intercooler, roughly $750 for a quality top mount. At 300whp on ethanol you are making real heat, and this is what keeps the third pull as quick as the first. It buys sustained power rather than peak numbers. Charge pipe, roughly $265. Not for the power - for the leak-free charge path at the boost levels this build runs. The factory couplers are the usual failure point. Flex fuel sensor kit, roughly $440, and a 340 lph fuel pump, roughly $190. E85 needs around 30 percent more fuel volume than pump gas and the factory pump runs out before 300whp on ethanol. Custom flex fuel tune, roughly $575. Not an off-the-shelf map. At this power level on a variable fuel you want a tune written for your car. Parts total lands near $3,390, plus labor if you are not doing the install yourself.

The parts that define this build

The two limits that matter

The first limit is torque, not horsepower, and it belongs to the transmission. Tuners generally hold the FA24 near 350 lb-ft to keep the factory gearbox intact, and a Stage 2 ethanol car already sits at roughly 348 lb-ft. You are not approaching that ceiling at 300whp - you are sitting on it. This is the single most important thing to understand about this build. The horsepower number has headroom. The torque number does not. A tuner who chases a bigger peak figure by adding midrange torque is spending your transmission's life to do it, and a good one will tell you so. The second limit is the turbo itself, which is comfortable into the low 300s on ethanol and falls off past that. Beyond it you are buying a turbo, and a turbo drags injectors and a high pressure fuel pump behind it, and the added torque drags a clutch. That is a different build at several times this cost. Together these make 300whp a genuinely sensible place to stop. It is the most power the stock drivetrain is comfortable with, reached with the cheapest possible combination of parts.

What this costs to live with

Fuel economy drops 20 to 30 percent on ethanol. If you commute, price that honestly against the fun - it is the running cost people forget when they budget the build. Maintenance gets slightly more attentive rather than dramatically harder. Ethanol is hard on some fuel system components over long periods, plugs live a harder life at higher cylinder pressure, and oil changes want to be on the shorter end of the interval rather than the longer. Warranty risk is real and worth stating plainly. A flex fuel system is not something you flash away before a dealer visit. This is the tier where you should assume powertrain claims may be contested and decide whether you are comfortable with that. None of this makes the build a bad idea. It makes it a decision rather than a purchase, and it is the tier where being honest with yourself about how you use the car pays off.

The verdict

Build it with ethanol or do not build it. That is the whole guide in a sentence. With E85 available, roughly $3,400 in parts and one good custom tune produces a VB that is quick everywhere, comfortable in traffic, and running inside the limits its drivetrain was designed around. It is the most satisfying stopping point on this platform. Without E85, the same money buys about 14 wheel horsepower over a Stage 1 car and a set of parts that mostly exist to support a fuel you are not running. Spend it on a Stage 1 tune, tires and brakes instead, and you will have a faster car on any road that has corners in it. And once you are there, stop. The next real step past 300 is a turbo, and everything that step drags behind it costs more than this entire build.