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Old 08-14-2012, 04:39 PM   #1
neko
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Default Ambitious n/a project.. opinions? advice? 200hp ej25 on wrx ecu?

Ok, so in my head my next (and perhaps final) Impreza takes shape...

Requirements.
Want something fairly light, somewhat powerful, but not so much that i lose lots of fuel economy over it. (have more powerful cars, and my last 5 imprezas have been 3 WRX's and 2 STi's. i don't find them as fun anymore.) Which makes my answer n/a basically.
1. Weight benchmark: 2700lbs (or somewhat close, say within 100 or so)
2. Power benchmark: 200chp or more. (Lets say 165-175, if we have to talk whp, but its not like i'm gonna bother to dyno it...)
3. Mileage benchmark: 35mpg hwy. (or at least low 30's) And hopefully 25+ city

These goals are similar to cars like the RSX, and the BRZ.

Step 1. GF wagon. Never owned one, one of the few Imprezas i haven't. Love the styling, easy to come by. Any years that are the best to get? Newer usually means better options (std PW/PDL/easy to install keyless/etc) OR will i not meet my weight goal without sticking to an older car? This will be a daily/winterable car, so i'd prefer some creature comforts.

Step 2. 4/2pot brakes, good adj struts n mild lowering springs, sways, etc. Driveline i think should remain R160-based for lightness. Could use a Std 4.11 RS setup with oem rear V-LSD and front obx helical. Or perhaps look into the new R160-based 6spd from the new legacies? 4.44 LSD rear diffs are pretty unloved n easy to come by... Wonder if it will take an aftermarket front LSD like the older R160's...

Step 3. The engine... Will any 6cyl make 30+ mpg hwy, 25+ city? Also leaves no cheap tuning/EM options. So most likely out, tho i'd love the power.
So most likely a sohc 2.5L. Easy motor to get and work with. Considering i only need about an additional 40-50hp or so to come near my goals, i would assume a stock compression with cams perhaps, and full exhaust would make it on a good tune? (tho i wouldn't mind stuffing higher comp pistons in, can i cheaply get 11-1? more?) So that brings the last an most important question up:

Tuning: What is needed for me to simply wire in a harness that would mate to the ej25, but work with a ej205 ecu? Fully programmable, does everything i need, i think. Could i easily run the stock 440 topfeed wrx injectors on the ej25 somehow for simplicity in ecu tuning? If i can swap a few sensors, at the most, and at least get the block running on a 205 ecu, that should give me all the tuning i need to hit my 200hp mark i would think?

Ok, so now everyone school me, tell me where i've made bad ideas...Is there a better path to my goals?
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Last edited by neko; 08-14-2012 at 04:46 PM.
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Old 08-14-2012, 07:05 PM   #2
cal_look_zero
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The simplest way to hit your goals (MPG aside) will be a NA hybrid/frankenmotor. 2.5 block with 2.2 heads; whatever other goodies your heart desires. Stock ECU. Simple and cheap, makes around 175 whp. Don't bother with 4/2s; earlier WRX discs are more than enough (Unless you have gobs of money or a set of them laying around, then go crazy)
I get a lot of naysayers, so PM me if you want more detail on the engine.

Stock curb weight of an L wagon is around 2800, so your weight goals can be met without having to go to a fully stripped interior (Small battery, no spare, lighter rims, no back seat, and you're there)

I say MPG aside based on my MPGs, but even with the stock 2.2 I never got good econ. I probably have fouled cats or some crap. I have gotten 25mpg at 75 on the freeway with a/c on in flat terrain if that means anything.
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Old 08-14-2012, 10:17 PM   #3
neko
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Couple simple things then:
Why the ej22 heads? Aren't sohc ej25's about some of the best flow? Or do the 2.2's offer higher comp?
As far as the brakes, I've used just about every Subaru setup, and I like it the best. Feels as good as the brembo's and way better wheel fitment. And yes I already have a full set lying around.
As far as mpg's? I've had consistantly 26/33 from my old 2.5L RS's. I would think a bit of tuning could get me a few more mpgs...
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Old 08-14-2012, 10:33 PM   #4
Pickler
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what year impreza is this? i get about 32mpg on highway or 40mpg if i try hard. city wise mileage is down to about 23-24mpg. i have video if you not buying it lol.

as far as mpg with power goes, im sorry that's just not possible. you cannot improve your brake specific fuel consumption dramatically. that requires a whole engine overhaul or hybrid conversion. in a lightly modified engine, more fuel burnt = more power. now to power, NA cars your best bet would be to run richer down low and lean it out a bit at higher rpms (+5.5k rpm) while keeping the midrange (4.5k rpm) at around ~13:1. E85 tune, performance EL headers, straight pipe, lightweight pulley and delta cams set my buddy's 06 2.5i to 150whp vs 125whp stock. i doubt going any higher is reliably possible. i say just go turbo, avo turbo with bigger injectors and fuel pump. a 09 legacy 2.5i that i know with avo turbo kit does about 175whp on the dyno @4.5psi.
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Old 08-14-2012, 11:29 PM   #5
Steve2.5i
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Quote:
Originally Posted by Pickler
what year impreza is this? i get about 32mpg on highway or 40mpg if i try hard. city wise mileage is down to about 23-24mpg. i have video if you not buying it lol.

as far as mpg with power goes, im sorry that's just not possible. you cannot improve your brake specific fuel consumption dramatically. that requires a whole engine overhaul or hybrid conversion. in a lightly modified engine, more fuel burnt = more power. now to power, NA cars your best bet would be to run richer down low and lean it out a bit at higher rpms (+5.5k rpm) while keeping the midrange (4.5k rpm) at around ~13:1. E85 tune, performance EL headers, straight pipe, lightweight pulley and delta cams set my buddy's 06 2.5i to 150whp vs 125whp stock. i doubt going any higher is reliably possible. i say just go turbo, avo turbo with bigger injectors and fuel pump. a 09 legacy 2.5i that i know with avo turbo kit does about 175whp on the dyno @4.5psi.
His last cars were wrx's and sti's and he wants n/a.
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Old 08-14-2012, 11:48 PM   #6
Counterfit
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I think 30+mpg on anything shorter than 3.9 is not going to happen.

Unless you feel like finding and running some crazy tall 5th...
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Old 08-15-2012, 10:25 AM   #7
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Quote:
Originally Posted by Counterfit View Post
I think 30+mpg on anything shorter than 3.9 is not going to happen.

Unless you feel like finding and running some crazy tall 5th...
a 3.90 will get you there the problem is the engine setup, with pure tuning he can get 190 at the crank but that doesnt suit the whp rqmt. Even a bump in CR and more fuel wont get him to reliable 30+ MPG and 180 whp with a EJ253. If he wants pure N/A, high power and 30+ mpg then

He can get more power with fueling and a bump in CR and still be reliable but not 30+ MPG avg. He can get 30+ MPG avg and reliability but not much over the 120 whp the EJ253 puts out currently. A EJ222 is lower power than than in stock trim and the heads dont flow better than a EJ253 so that wouldnt make make sense unless you going for high CR but again reliability is at stake.

Quick answer build a EJ253 with a target 11:1 CR , 93 oct and a GREAT tune! You could find a set of those Rallitek heads (terrible idea to build heads for a EJ253) and PnP the IM for optimum power output but youll be into the engine around $6K when its said and done.

Weight is easy strip all that **** out that you dont need
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Old 08-15-2012, 10:37 AM   #8
neko
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Quote:
Originally Posted by Counterfit View Post
I think 30+mpg on anything shorter than 3.9 is not going to happen...
did I mention above that I get 30mpg on 100% stock RS's (with 150k) on the hwy at 75, and my old sedan w/intake and catback would get a constant 33. Heck, my last GC coupe with a ej20g would get 27mpg in daily driving.
So I think 2mpg more from a tuned n modified 2.5 block ought to be doable.

As far as boost, yes, that's out. I get 21/26 in my GD STi, and I think I'd like to go back to n/a for a bit, since I have multiple other boosted cars still. (the STi will probably get sold when this runs) plus, if I feel the need to make it faster, Ill probably go with a v7 207 block. Now I could stick with high comp/low boost, but that's usually a big headache for reliability and low grade fuel issues. I'd actually even like a motor that will run on regular. Helps gas mileage even more...

So on my other big issue: engine management... I could use a stock 00-01 ecu, even have it reflashed, but I'd prefer a full programable. Standalone costs a ton more, and they never seem to run smooth like stock em no matter how much time ya put in. So that leaves either a 05+ RS ecu that is programmable, or a 02+ WRX ecu that's programmable and could easily be setup to run an n/a ej25 (ecu wise, not sure how tough wiring/sensor compatibility would be).
Lastly, any options for higher comp 2.5L pistons out there?

Last edited by neko; 08-15-2012 at 12:37 PM.
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Old 08-17-2012, 10:00 PM   #9
T Wrex--OH
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TWE offers high compression pistons for the EJ251/3, but you have to use STi rods with them.

Call me a doubter, but no motor, franken or not, is gunna get you 160whp without upgraded camshafts.

A 2.5 with 2.2 heads will probably not meet the goal. I just don't think the bump in compression alone with tuning will get to the 200chp.

Throw some deltas 2000s in there, good EL headers, and I think it'll fit the bill.

As far as tuning, a piggyback would be much easier than wiring for a denso wrx ecu.

Greddy eManage is one that comes to mind.
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Old 08-18-2012, 09:48 AM   #10
neko
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Quote:
Originally Posted by T Wrex--OH View Post
TWE offers high compression pistons for the EJ251/3, but you have to use STi rods with them.

Call me a doubter, but no motor, franken or not, is gunna get you 160whp without upgraded camshafts.

A 2.5 with 2.2 heads will probably not meet the goal. I just don't think the bump in compression alone with tuning will get to the 200chp.

Throw some deltas 2000s in there, good EL headers, and I think it'll fit the bill.

As far as tuning, a piggyback would be much easier than wiring for a denso wrx ecu.

Greddy eManage is one that comes to mind.
and yes, it doesn't have to be a stock block, cams were probably on the list of acceptable. Full exhaust from exhaust ports back, definitely.

As far as EM in the form of greddy eManage, thats not toally out. I'm not a big fan of black boxes + factory ecu versus just a real ecu, factory or not, but sometimes it works. The emanage isn't super expensive, and doesn't lose the factory-smooth ecu operation, unlike expensive aftermarket full-ecu's, so its a possibility.
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Old 08-21-2012, 09:16 PM   #11
jackolafedon
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My 07 2.5i dyno's at 166 whp with a twe header and the delta regrinds w/ stock ecu retuned. I get 27-28 mpg if I stay below 70 on the highway. saw one of these engines on rs25 for 1g for the long block a few moths ago so not a terrible option
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