whiteyisback

Advice on this would be much appreciated. C
urrently I drive a MY03 WRX with a full decat , ITG Panel filter and Ecutek 3 remap. So far so good as the car now chucks out 280 bhp.....however, like everything this power now doesnt feel as quick as it once did, so.......wondering what would be the next stage ? Seen some people on here getting hold of either OBX or Gruppe-S headers for what seems like relatively little outlay (£400'ish), will this do the job to get me to 300 bhp? I get a free remap from the firm (Xtreme) that fitted the decat and did the Ecutek so the headers option would be the most cost effective for me by a long way. My worry is that the car will need a bigger turbo and injectors/fuel pump to match the headers and then this all starts getting too expensive for me.

So 2 questions : could i just put the headers on and remap the car and get 300bhp ? what headers would people recommend, OBX or Gruppe-s (or Hayward and Scott as they provided my exhaust, which i'm pleased with) ?
So wadya rekon, any help as always much appreciated fellas.

Beefy

Just as a matter of interest the STI8 engine develops 300 BHP in PPP form. Is it vastly different to the 03WRX engine (if at all) or in theory could you "double PPP" the engine and take it from 265BHP to 300BHP?

hades

The STi engine is very different. Variable valve timing, bigger injectors, bigger turbo being some of the obvious points.

The most I've ever heard of out of a standard TD04 turbo as fitted to MY01+ is ~310bhp. To get 310bhp, I'd suggest: uprated Top Mount intercooler (eg APS), induction kit, uprated inlet hose and intercooler hoses, uprated fuel pump and regulator (maybe fit STi injectors), and either change the headers or port the OEM ones. With this little lot, 320 on the right day on the right rolling road might just be possible. Most people after 300bhp+ will go with a bigger turbo. Much over 300, you start getting into clutch and gearbox mods too. See RB5Scott's post in the general forum if you want to see what can be achieved, and the pitfalls of doing so!

Re: headers I've heard of one or two people with tubular headers, they demanded more fuelling and therefore required injector or pump and regulator change, gave perhaps 15lbft torque lift. I'd be tempted to just port the OEM ones.

Beefy

Thanks for the info, I wondered where all the extra money was spent on the STI.

whiteyisback

cheers guys, thnx for the info but it doesnt really answer my questions:
could i just put the headers on and remap the car and get 300bhp ? what headers would people recommend, OBX or Gruppe-s (or Hayward and Scott as they provided my exhaust, which i'm pleased with) ?

Anyone been down this route ? as in just performed the mods I've listed already to my car and then just put the headers on ?

whiteyisback

any help much, much appreciated as i'm close to reaching for the credit card to order some headers.............help !

greasemonkey

No, in a word, although the full answer's a little more complex than that. Could even be that changing the headers could lose you power if the ones you get don't suit your setup.

It would be worth searching though Edcase's posts as he's recently changed his headers and his experience may be useful to you.

Silly question maybe, but why the fixation on 300bhp, apart from it being a nice round number? It's only 7% more than you've currently got, and unless matched by a similar percentage increase in torque, you'd be unlikely to feel the difference.

The TD04 turbo is the biggest limiting factor on your car. If you want noticeably more usable performance than you've currently got, I'd suggest that an alternative, plus bits like fuel pump, pressure reg and injectors, should be in front of new headers in the shopping list.

Pete Croney

I agree with greasmonkey.

The injectors will be close to 100% at current power, as well as the turbo being maxed.

New fuel pump, FPR, injectors and turbo will be good for 330-340bhp and cost £2.0k to £2.5k depending on the turbo used.

MikeWood

As stated above, you will now be at the limit of your std injectors, possibly even slightly beyond the point where they are working efficiently. The next step must be bigger injectors and a fuel pump that can support them. I know you aren't a fan of our (legal as it's got a cat and quiet as well as not being restictive, although it is handbuilt!) exhaust but with basically the STi PPP exhaust, injectors and fuel pump fitted we can quite easily get to 300/300 but there are several major concerns. We've also tried a manifold but it didn't sound like a Subaru and was too expensive for the gains that it made at this sort of level of performance.

The turbo is really too small to cope with this sort of flow rates and is working far too hard and therefore inefficiently. The WRX intercooler and scoop are also not really up to the job of coping at high speed/load for any length of time due to the extra heat produced.

Other things that will start to struggle would be the brakes and possibly transmission. That's without upgrading to larger wheels and tyres to get all the extra grunt onto the tarmac!

whiteyisback

nice one guys, especially Mike Wood. Mike - feel really bad now that I moaned about the ppp kit (especially exhaust) on another thread...lol.
So the bottom line is save my pennies, get a bigger turbo/injectors/fuel pump and then blow my transmission, etc....damn!
I only really considered the manifold option as i've been offered one for about £300 and thought it might be a cheap route to push me over the magic 300 number. Thought it might be too good to be true!
Actually seriously considering selling the WRX and getting either an STi8 Group C jobbie or a 2 yr old skyline R34, it's gotta be the only way of squeezing a "reliable" 350/400 bhp figure whilst remaining an everyday drivable car.

greasemonkey

The problem with being fixated with "magic numbers" is that there's really no such thing. Once you're through 300, you'll be after 350. Once you've got that, 400 and so it goes, until cost/reliability/driveability/speeding convictions get in the way.

The recent Spec C's will get to 350bhp without too much work/component switching, but 400 will again cost you a bit, and unless you're into 1/4 mileing in a major way, for nebulous gains. I get much more enjoyment from driving a car (albeit a lightweight classic) with 300/300 and excellent throttle response than I would from a car with an extra 100 of each and loads of lag.

If chasing figures is what turns you on, the Skyline will probably provide a better platform than any Impreza. However, whether the bigger, heavier car's combination of strengths will prove as satisfying as a good Scoob is another question altogether.

Jza

Think the next step must surely be to buy an STI asap and start upping from a more "stable" base ?????

Jza