Topic: RS HP +++

[pnjunkie]

What's the best way to eek out a couple more HP's in the RS? I'm hoping there could be a way to bump it up 30, to an even 200HP. I've never done any performance mods on a car before.

[Zaider]

header-back exhaust and an intake *might* get you there... after that, aftermarket engine management and then cams

Basically, we're very restricted with the naturally-aspirated engine. The most we can do is increase the flow and change where the power comes in (visible on a dyno graph). Although, there are some that say that the NA subaru motor isn't limited by flow, especially the newer one.

Here's a little light reading: http://forums.nasioc.com/forums/showthread.php?t=1022154

In my opinion, focus on suspension and tires first. That's money better spent that you'll be able to feel more than a couple of engine bolt-ons. Your car will be "quicker" without being that much "faster".

[2008impreza2.5i]

Order here, Anything ad ons will be atleast $1/hp

http://www.canadiantire.ca/AST/browse/4/Auto/AutoCustomPerformance.jsp

sorry couldnt resist.

general consencus on the forum appears to be tuning, not necessarily parts.

[Zaider]

general consencus on the forum appears to be tuning, not necessarily parts.

Consensus.

Sorry. I couldn't resist either.

Tuning isn't going to do much on an NA motor without changing the actual mechanical parts. With the Drive-by-Wire (DBW) system of the newer subarus, the throttle can be remapped to improve the driving experience a bit better but as far as I know, there's no extra HP to be gained via just a tune.

[pnjunkie]

I'm not really interested in doing it, but I've heard adding a Turbo to an NA car is a bad idea, is that correct?

[Zaider]

You can do that... but the NA motor isn't built to take the boost... you can get about 5psi before you blow it. There is also the option of using a Supercharger... Raptor makes one for our car. Basically brings you into the WRX power range, with a bunch of other bolt-ons (intake/exhaust)

I've long since accepted that the "power" mods that I've done (cold air intake, cat-back exhaust) have given me nothing more than different sound.

[pnjunkie]

That sounds cool too. What are the options to make it sound better?

[Zaider]

That sounds cool too. What are the options to make it sound better?

Plenty more options there, but "sound better" is subjective. I've got an STI Catback exhaust that I think sounds really good. Its the perfect volume for me.

Boxer4Racing.com has a number of exhaust options if you want to go the aftermarket route. Or you can get someone's old aftermarket WRX or STI exhaust and have an exhaust shop change the flange. Just remember that just because it sounds good on a turbo car, doesn't mean it'll sound that good on an NA car.

Check out the sticky at the top of this sub-forum. There you'll find a link to the NA exhaust review thread on Nasioc.

Your options for intake are... Injen, AEM, Cobb (if you can find one), or something a little more ghetto (but the same effect) like a Ganzflow.

[Down and Dirty]

Have any "documentation" on that more than 5psi will blow your engine? Not that I'm doubting you, I'm just curious and would like to read up about it.

I spoke to Sunny about tuning mt 2007 NA and he said the most I'd get with 87 gas is 10/10 for HP/TQ...tuning a little better with better gas (keeping the rest stock). All I've done myself is change the DBW stuff and remove the CL/OL delays which actually made positive change in responsiveness. I'm looking at this car as a "spend as little as possible on it" until I dive in for an STI...so I bought the Tactrix cable and downloaded the free software .

[twinny]

you can get camshaft   

http://www.rs25.com/forums/f14/t123320-christmas-sale-2009-a.html

i read somewhere someone got 190ish whp i think but thats with  header,catless pipe, ecu flash , and the cam

[Zaider]

Have any "documentation" on that more than 5psi will blow your engine? Not that I'm doubting you, I'm just curious and would like to read up about it.

I spoke to Sunny about tuning mt 2007 NA and he said the most I'd get with 87 gas is 10/10 for HP/TQ...tuning a little better with better gas (keeping the rest stock). All I've done myself is change the DBW stuff and remove the CL/OL delays which actually made positive change in responsiveness. I'm looking at this car as a "spend as little as possible on it" until I dive in for an STI...so I bought the Tactrix cable and downloaded the free software .

Ill try to find it on Nasioc today at some point.

[silent]

Have any "documentation" on that more than 5psi will blow your engine? Not that I'm doubting you, I'm just curious and would like to read up about it.

I spoke to Sunny about tuning mt 2007 NA and he said the most I'd get with 87 gas is 10/10 for HP/TQ...tuning a little better with better gas (keeping the rest stock). All I've done myself is change the DBW stuff and remove the CL/OL delays which actually made positive change in responsiveness. I'm looking at this car as a "spend as little as possible on it" until I dive in for an STI...so I bought the Tactrix cable and downloaded the free software .

Compression ratio is too high (~10:1, varies a little bit depending on the year) to support much boost.
A little something I wrote a couple years ago:
http://www.rs25.com/forums/f7/t72808-aftermarket-forced-induction-thread-everything-you-need-know.html

[honz]

From my readings, for every PSI you add to the 10:1 NA engines, you add about 0.7:1 compression - resulting in more pressure. Another obvious thing to consider is the altitude. The higher up the lower the effective compression, this can lead to other possible dangers when traveling to lower altitudes. In any case, If you find the psi / compression references I too look forward to see them. As for all the cool people like numbers, here are some of the ones I've found...

http://wac.addr.com/auto/obs/turbo/ejcalcs.html
Also, attached (if I can... or if I cannot then I will post it on my server later tonight) is the TWE Compression Calculator excel spreadsheet.

EDIT:  I had to up-save it to excel '07/'10 format as the '03 version is 131kb which cannot be attached. AND rename it to .xls so that it could be attached. (Excel will complain and try to persuade you that it's got the infektion) Sooooooooo... Download it and if you have troubles opening it - rename it to .xlsx. sorry, but at least here it is

[attachment deleted by admin]

[honz]

OP: Some additional points:

As Zev said:
 - STI Exhaust is plenty good (I have one too, love it!)
 - Headers, Equal lengths help a little with flow. Just remember, these modifications do not _make_ horsepower, they simply _recover_ horsepower that is lost by a restriction somewhere.
 - Intake, I guess it could help ever so slightly by removing the obfuscated intake baffling. It makes the car growl more too.
 - ECU: since you have an 04, the computer isn't really reflashable(?) with romraider, 05+ only.

As Twinny said:
 - CAMS: Delta reground cams can be had for a cheap price, but my understanding that an aftermaket ECU with a tune is then best to take full advantage of them.

- Head work is not cheap but can help with flow (port & polishing of the intake/exhaust ports). It would cost about twice to three times as much as buying a fitting up/down pipe, TD04 and standalone ECU to turbo the NA.

- Throttle Body spacer I found helped (again, ever so slightly) with initial throttle response. It is a 1" tall spacer that sits after the throttle butterfly valve. My understanding is that it just increases the air volume before the intake so that the air is there when needed (initial response) before it has a chance to start flowing through the intake baffling.

- Cheapest HP/$ for the NA is to reduce the car's overall weight. Decreasing the overall weight of the car can help quite a bit and makes it feel significantly quicker. Couple that with some suspension modifications and it will become an absolute blast to drive. The 2.5 will become fast enough when you're having a good time bombing around corners and such.

There is also something that can be said for suspension modifications. I replaced pretty every piece of rubber with polyurethane which stiffens it up a bit (also increases road noise a little). But the idea here is not only do things stay where they're supposed to, your engine power isn't being used to move the cars components around - but instead it uses that force to move the car around.


But... In the end, if/once you get into it, you may just end up swapping in a STI engine (or a WRX engine if you're lame like me).

[twinny]

i wouldn't spent too much on N/A but suspension mod is fun

so it is depending you want to have a fast car  or be a fast driver 

[eric92]

First things first, suspension upgrades: 18-20mm rear sway bar and short throw shifter is a must (They should come that way from the factory).

For power: full exhaust system (headers, mid pipe high flow cat etc) with cams, and high compression pistons.

Or forced induction.

[reeskm]

How much could I gain if I retuned my 07 Impreza 2.5i to use 91 Octane?
I can't wait until my warranty expires in 8 months because I feel better about tuning my ride then...

I haven't done it yet but agree: suspension mods and a short shifter are a must! my car rolls around way too much and i'm sick of it. The long shift throw is so nasty. I'm going to have to order those parts soon...

[smrt_ass_engr]

How much could I gain if I retuned my 07 Impreza 2.5i to use 91 Octane?
I can't wait until my warranty expires in 8 months because I feel better about tuning my ride then...

I haven't done it yet but agree: suspension mods and a short shifter are a must! my car rolls around way too much and i'm sick of it. The long shift throw is so nasty. I'm going to have to order those parts soon...

i doubt you would see any realistic gains from just going to 91.  at first you will notice a tad more get up and go combined with a tad more fuel efficiency.  But once your ECU becomes familiar with the new gas, the thrill is gone. 

[Airboy]

i doubt you would see any realistic gains from just going to 91.  at first you will notice a tad more get up and go combined with a tad more fuel efficiency.  But once your ECU becomes familiar with the new gas, the thrill is gone.

What exactly does that mean?  What happens when "your ECU becomes familiar with the new gas"? 

[silent]

What exactly does that mean?  What happens when "your ECU becomes familiar with the new gas"?

Kind of like when you meet a new girl.  At first you're really patient dress well and take good care of yourself.  After a while, you start rocking sweats, stop doing your hair and becoming a little less patient.  Your ECU does that with 91 octane.

[ultimatt]

Kind of like when you meet a new girl.  At first you're really patient dress well and take good care of yourself.  After a while, you start rocking sweats, stop doing your hair and becoming a little less patient.  Your ECU does that with 91 octane.

Best

Post

EVAR!

[smrt_ass_engr]

Kind of like when you meet a new girl.  At first you're really patient dress well and take good care of yourself.  After a while, you start rocking sweats, stop doing your hair and becoming a little less patient.  Your ECU does that with 91 octane.

LMAO YES! that is the best guy answer to that ever

and to the OP, check out crawford's SRS tunes.  If you modify your intake, headers, HFcat, CBE (optional), and go to 91 get SRS-19/20.  Good 10-15hp gains ontop of what the exhaust will do for you.  Under perfect conditions its possible to hit 190-200hp with that, makes everything smoother on top of that.  Search rs25.com for numerous threads on this.   

[Triple T]

Here's some reading on what can be done for N/A hp....
http://sl-i.net/FORUM/viewtopic.php?f=11&t=11403
Biggest addition to what has been previously mentioned - bump the CR to around 11:1.  Though this now means 91 gas.
Good luck!

[Way-do]

TechWorks makes (sells:  they are CP castings) drop in 11.2:1 pistons.  Haven't looked into valve clearance if going up to a hot cam though.