how to achieve 300whp?

[RallyCulture]

hello im new to subarus and to to this fourm so please bare with me. I have a stock 02 wrx with koyo radiator, sti exhaust, and cobb flash (making from what im told 250hp) with 105k on motor, I wanted to know what would be the most cost effective and reliable way (daily drive) to achieve 300whp? Ive never owned a turboed car before so im pretty lost as to the do's and donts. I heard with turbo cars if you chang anything stock then it needs to be tuned in order to run properly. obviously im going to have to tune it in order to achieve that kind of power but i didnt know if i need a bigger turbo, injectors, piggy back, forged internals or whatever else. I dont want to blow money on things i really dont need or over priced parts if others are just as good. please point me in the right direction im clueless, of course ill start doing my own research but im hoping the vets can give me some sound knowlege thanks so much

[SD_GR]

Have you done the 105K service? That's lots of money and great fun. I'd start there.

Then I'd follow the link in my signature. Incidentally, you don't need a tune for an exhaust on your model. However, given what the car is worth I'd not go further than up pipe, down pipe, map (not piggyback) and call it a day.

[RallyCulture]

whats the 105k service? like i said im new what does that entail exactly? spark plugs nd fluids, belts nd all that jazz?

[EJ257]

You set a goal of 300whp, but don't list what you'll be measuring that "300whp" goal on. Every dyno reads differently, and will require different mods to get there...

whats the 105k service? like i said im new what does that entail exactly? spark plugs nd fluids, belts nd all that jazz?

https://www.subaru.com/my-subaru/mai...edule2002.html

[MainFrame]

Start with the scheduled maintenance..



Do you want to know the most cost effective way? Or the reliable way? You said both, but those are two very different things. You need to decide what you want first.. and as Mat said, how are you going to be measuring the power? Dynos vary drastically, so what may be 300whp on one dyno could be 250whp on a different dyno.

[RallyCulture]

I see i never knew, at the very min i want 300whp no matter what dyno im on nd reliablity is the up most importance then cost effect. i guess i need to do my research i just check the maintenance schedual, thanks for the link, and yes all of it has been done and then some.

[MainFrame]

I'm going to assume you will be using 93 octane pump gas? What fuel you are running also makes a big difference.



To make sure you can hit 300whp on any [reasonable] dyno here are some options..


More cost effective route:

OEM ej257 shortblock
11mm oil pump
ej205 heads rebuilt and CnC'd to match 2.5L combustion chambers
OEM 2.5L headgasket
ARP head studs
04-05 STi cams
Process West TMIC
Walbro 255lph fuel pump
750cc injectors
aftermarket uppipe
turbo back exhaust
GM 3-port EBCS
Blouch 20g-XT


I'll post other options in a min..


You could also consider reusing your existing ej205 case halves and building a 2.1L stroker. The advantage to this would be you could save the cost of buying an ej257 block and machining the heads. The down side would be you'd have to pay for someone to build the shortblock (which likely won't be as reliable as an OEM block), and I would imagine that it won't spool the turbo quite as fast, will make considerably less torque, and less hp over all than going with a 2.5L block.



A better (more driver friendly) route, albeit more expensive:

OEM ej257 shortblock
11mm oil pump
ej205 heads rebuilt and CnC'd to match 2.5L combustion chambers
OEM 2.5L headgasket
ARP head studs
*port and polished intake manifold
*composite TGV deletes
*GSC S1 cams
Process West TMIC
Walbro 255lph fuel pump
750cc injectors
*aftermarket EWG uppipe
*external waste gate
turbo back exhaust
*equal length headers
GM 3-port EBCS
*MBC (for hybrid boost control)
*Blouch 18g-XT



You also might want to consider installing forged pistons, but at 300whp they shouldn't be needed (and tampering with the shortblock may decrease reliability). If you were ever wanting to go for more power in the future I would say forged pistons is a no brainer. The pistons are the weak point of the block. There are other parts you may want to consider upgrading while you have it all apart for reliability sake as well, such as a KillerB ultimate oil pickup. The OEM oil pickup is known to fail, so if you can afford it I would definitely upgrade to the KillerB unit. It is also a good idea to have everything balanced that you can. If you're not pulling the shortblock apart you can still have the crank pulley and flywheel balanced.




Most people will probably consider such extensive mods over kill, but it will be needed to ensure 300whp on a real heart breaker dyno. I've seen hybrid builds with 16g-XTs only put down 240-260whp, so you really need to go up to a 47-49lb/min turbo if you want to make sure you're going to hit 300whp where ever you go.


Keep in mind that your stock clutch, transmission, suspension, and brakes are likely not up to the task of handling 300whp reliably and safely.