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Old 11-28-2004, 03:53 AM   #1
TooSlow
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Question Pros/Cons of 2.0 JDM STI vs. 2.5 USDM STI engines

Sorry if this is the wrong area or if I'm beating a dead horse, but I searched for about 1.5 hours and could not find the info that I'm looking for.

From what I've read it seems the JDM 2.0 STI engine is slightly stronger and built/tuned to run on higher octane fuel. But beyond that I'm a bit puzzled as to why Subaru would run a 2.0 as opposed to tuning a 2.5 comparitively to run on higher octane fuel in the JDM STI. Wouldn't they want the additional torque from the larger displacement? Or is the gain small enough that maybe the f/r weight ratio and weight savings might become a factor? I almost feel as if I've answered my own question, but I'm hoping that someone could reply back with a more definitive answer.
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Old 11-28-2004, 04:10 AM   #2
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rally homologation for impreza wrx with 2.0? JDM they get good 98 and 100 octane gas too the buggers
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Old 11-28-2004, 04:14 AM   #3
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Taxes in japanland on 2L+ engines are through the roof
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Old 11-28-2004, 04:17 AM   #4
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Im in search of similar info. All that I know is that the JDM 2.0 is forged internals, crank, rods, pistons everything. I saw a vendor make a comment that it could handle 30psi. I am in the market for a new block to put a GT30r on and im thinking the JDM 2.0 is the better option, it revs to 8k and that block with ver. 8 heads seems to be a pretty sweet setup.
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Old 11-28-2004, 01:20 PM   #5
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Quote:
Originally Posted by ncarn8
rally homologation for impreza wrx with 2.0? JDM they get good 98 and 100 octane gas too the buggers
I never thought about the rally issue. You're probably right, they likely needed to make a 2.0 for the competitive advantage in WRC, maybe for the reasons I tapped on earlier (f/r weight dist. and weight savings). The tax issue is likely a good one too.

On a second note, I'm really interested in what cubuff is doing too. However being the shade tree mechanic that I am, I'd likely do an early 90's JDM 2.0 swap into an identical year USDM impreza to save me a lot of trouble on wiring. Can you run a ver. 7 or 8 head on an older 2.0 JDM engine like that? I'll have to do more reading, as you guys can tell I'm a bit new to Subarus, I came over from Supras and Rx-7s. Can't wait to finally get some traction
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Old 11-28-2004, 01:54 PM   #6
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Look into a JDM with a Twinscroll setup and AVCS.

We USDM motors can only dream about these things....


oh wait... I can only dream about AVCS.... the other one i got covered

-J
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Old 11-28-2004, 08:51 PM   #7
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Want ot run 30PSI. 2.2 engine and replace rods and pistons. Crawford and Axis sells them.

Want ultra smooth high rpm power use JDM 2.0 and when coupled with a JDM 6mt, the engine becomes magic. I have one and I would swear the engine is balanced and blue printed. The level of smoothness puts you to sleep at 4K on the highway.

Want torque to kill Camaros use US 2.5,. Not balanced and are rough. Kinda like the US 2.0 but make power and no need to rev past 6.5K so balance is not an issue. I have heard of the rngines being as much as 34 grams off when undergoing balancing. MAn that is alot. They do make power though.

In the end, the JDM motor is stronger. The US 2.5 will always make more power and take bigger turbos when outfitted with JDM Ver 8 heads. It is afterall 25% bigger but the cylinder walls are thinner so if you actually want BIG boost go with 2.2 variants like the 2.35.

Either will take 20# all day on the street.
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Old 11-28-2004, 11:20 PM   #8
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the reason jdm sti don't come in 2.5 liter is becasue in rally racing engine displacment is limited to 2.0 liters, and that is huge selling point for japanese buyer. At lest thats what I read in a mag.
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Old 11-28-2004, 11:29 PM   #9
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Great info thanks to everyone for putting in their own 2 cents. Hey ebeck, the JDM 2.0 sounds like the path I'd like to go, what do you recommend for a head/turbo/driveline setup for someone who would like excellent road course performance and hard launch abilities (read "best 0-60 times")?

I'm guessing that I'd also be looking at a front clip from a JDM WRX... does the transmission usually come with them?
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Old 11-28-2004, 11:42 PM   #10
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After reading my thread I realized most of this info could be easily obtained by doing a search, so if you feel like answering, great. If not that's fine too.
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Old 11-29-2004, 12:01 AM   #11
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Look up East Coast Suby. He's got some of the best prices on JDM engine and drivetrain components. He hooked me up with my twinscroll setup and it was in almost perfect condition - the shop that installed me asked if i got a brand new turbo.....

his shop web page is IA performance

E-mail him and ask him prices... he's normally a little friendlier to nasoic people and might give you a break if you order all your parts as once.

-J
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Old 11-29-2004, 06:57 AM   #12
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ive driven both v7 cars and the 2.5's. I even had a v7 block w/ v8 ra heads right here and traded em off for a usdm 2.5. the v7 is an unbleviable motor for sure, but i love the low end of the 2.5. I guess im kinda over my whos got the biggest wang days lol, now im much happier w/ the area under the curve. i also feel that the us short block has proven that it can hold a substantial amount of power w/ proper tunning. hell, i remember when i got my rex in 01, people was afraid to boost that thing past 16 psi. IMO cant go wrong w/ either one though.
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Old 11-29-2004, 08:48 AM   #13
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the EJ207 isnt SLIGHTLY stronger than the usdm sti 2.5.
its a LOT stronger than the usdm 2.5
I am buying a short block very soon, and in my research I have discovered one thing, the usdm 2.5 breaks at right about the same hp level as the stock WRX motor. Maybe 30whp higher.

The 207 will make 400whp forever if tuned right. If you want SERIOUS power, and dont want to spend the money on a built block, the 207 is the only way to go.
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Old 11-29-2004, 09:53 AM   #14
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Default so...

if your obsessed with a wrx, but want the HIGHWAY power... then the ultimate way to go is a built 2.5 and a big turbo...

thats for me baby... just saving and saving... if i go that route... recommend the best street driving tranny... probably the sti 6mt... of course, for that money, i don't wanna brake it... will it hold the power of a built 2.5 and a green... (on the street, not launched at 5k rpm at the track?)

wow... doing the math.. i'm gonna be saving up for a LONG time! may as well just buy a magnus 2.5 and have my wrx heads worked to fit with it (this can be done, correct?), since i'm already waiting this long to save the money, may as well wait another yr to get ahold of the darn block.
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Old 11-29-2004, 10:24 AM   #15
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I would say an EJ257 with forged pistons would be the best motor to get. It's the only real weak link in the block unless you are planning on making 500+ whp, which most aren't. The pistons can be swapped in an afternoon with the right tools and it's about a $600 initial investment. The V8 JDM STI doesn't used forged pistons, it uses the same hyperutectic pistons as the EJ257, so if you want forged pistons buy a V7 shortblock. The only real failures I've seen in EJ207s is spun bearings, but if you aren't road racing the car that probably won't be an issue.

All the engines are balanced from the factory.

I would never go back to running a 2L engine at this point, and I ran my EJ257 to a 7500 redline with no problems.
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Old 11-29-2004, 11:08 AM   #16
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I think a Ver 7 or Ver 8 engine with the complete drivetrain, you would have an extremely nice machine...then you could always swap the blcok if you want more displacement
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Old 11-29-2004, 12:14 PM   #17
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Quote:
Originally Posted by Homemade WRX
I think a Ver 7 or Ver 8 engine with the complete drivetrain, you would have an extremely nice machine...then you could always swap the blcok if you want more displacement

so you have DEEEP pockets? why would you buy a complete v7/v8 and then decide to 'swap the block' for more displacement... ????

you would end up with v7/v8 heads and that's it by the time you were done.... pointless to pay all that money and then get rid of the best part... the solid internals... 'course the valvetrain is great too... but that seems rediculous to me if that's what you're saying...

bottom line here... i would take any of these mods... anything is better than the stock 2.0 block i have now... but until its blown to bits and doesn't run anymore... or only makes 200hp... its gettin' used... hey... look at it this way... it handles more boost than a honda! somehow though, that just doesnt console me too much...
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Old 11-29-2004, 12:43 PM   #18
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Axis Racing Stage 2 shortblock is a 2.5L with Ron's spec'd CP pistons. I have well over 10k miles on the motor, run a GT30R on it and it spools up about as fast as a 2.0 does on a VF22. Pulls HARD to 7k RPM, and with the right head work, hardware components, can spin higher... though there's no reason to without properly selected cams.

I've tuned spec c motors, as well as several built 2.35/2.5L's. I have become a junkie for the bottom end torque and usable application of power (I.E. you're not being beat by tercels across an intersection) that the 2.5 offers.

But if you are road racing, then I'd very much recommend the 8000+ redline of the spec c motor with a properly setup turbo system.

Jorge (RiftsWRX)
www.ProjectWRX.com
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Old 11-29-2004, 01:58 PM   #19
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Quote:
Originally Posted by RiftsWRX
Axis Racing Stage 2 shortblock is a 2.5L with Ron's spec'd CP pistons. I have well over 10k miles on the motor, run a GT30R on it and it spools up about as fast as a 2.0 does on a VF22. Pulls HARD to 7k RPM, and with the right head work, hardware components, can spin higher... though there's no reason to without properly selected cams.

I've tuned spec c motors, as well as several built 2.35/2.5L's. I have become a junkie for the bottom end torque and usable application of power (I.E. you're not being beat by tercels across an intersection) that the 2.5 offers.

But if you are road racing, then I'd very much recommend the 8000+ redline of the spec c motor with a properly setup turbo system.

Jorge (RiftsWRX)
www.ProjectWRX.com
Jorge...

thanks for the input... when i test-drove the STi, i did instantly fall in love with the immediate response of the engine in the lower rpm ranges... so you basically have a 2.5 with forged piston upgrade, and what heads??? stock wrx heads worked to fit the 2.5 and more agreessive valvetrain work or not???

How is that on the highway??? that's mostly what i'm looking for... something with more on top when you're already going 65mph AND more rarea under the power curve for overall ease of driveability around town... no racing here, but would like to WI and run 22-24psi on 94 octane pump... would you suggest the 2.5 block w/piston upgrade alone would suffice for that setup... maybe a 20G or green turbo... (of course in a 2002 wrx w/utec/fmic/etc)

thanks for your input... just trying to tie down the direction i'm going to go... oh yeah-- what tranny are you running-- not the stock wrx?
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Old 11-29-2004, 02:02 PM   #20
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if your looking for top end go w/ the v7, you can easily rev them to 8K+
the torque is nice but even w/ a green the 2.5 is gonna fall off up top.
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Old 11-29-2004, 02:06 PM   #21
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Quote:
Originally Posted by pux888
if your looking for top end go w/ the v7, you can easily rev them to 8K+
the torque is nice but even w/ a green the 2.5 is gonna fall off up top.

so you're saying the v7/v8 will pull harder on the highway from say a 65 roll or so than a USDM 2.5 w/forged pistons .. all else equal.. .same turbo, same boost, same 94oct pump gas... ?
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Old 11-29-2004, 03:24 PM   #22
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I have a Version 8. I make 300 ft pounds of torque at the wheels and over 300whp at 4K with an AVO450. It peaks at 332 whp or 450 hp which is the rating of the turbo. all on 91 octane. The 2.5 is more grunty. Like a Viper. With the JDM 6mt and the JDM R180 the power and tractability is more than adequate.

In roll on accelleration on the highway V8's will still win even against 2.5's running large turbos. So those guys tell me.

Oh and No Tercel or Z06 beats me across an intersection.

The WRX gear box, front diff and rear diff all suck. The engine is half of the battle. IF you are looking for most hp bang for the buck the 2.5 is the ticket. It is simple. It is bigger, Slap on between an 1820-Green and have fun.

Personally I like track days. Road racing track days not Drag racing track days so Full 2.0 driveline for me. Version 8 are sweet motors.
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Old 11-29-2004, 03:39 PM   #23
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Default ...$

and what did it cost you to get in the seat of a full v8 (i assume avcs heads and whatnot) engine swap??? $7000-8000 just for the crate engine, right?
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Old 11-29-2004, 04:04 PM   #24
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Quote:
Originally Posted by RexRonald
and what did it cost you to get in the seat of a full v8 (i assume avcs heads and whatnot) engine swap??? $7000-8000 just for the crate engine, right?
I can't speak for ebeck, but most people get a used motor for around $4500.
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Old 11-29-2004, 04:12 PM   #25
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Quote:
Originally Posted by RexRonald
Jorge...

thanks for the input... when i test-drove the STi, i did instantly fall in love with the immediate response of the engine in the lower rpm ranges... so you basically have a 2.5 with forged piston upgrade, and what heads??? stock wrx heads worked to fit the 2.5 and more agreessive valvetrain work or not???

How is that on the highway??? that's mostly what i'm looking for... something with more on top when you're already going 65mph AND more rarea under the power curve for overall ease of driveability around town... no racing here, but would like to WI and run 22-24psi on 94 octane pump... would you suggest the 2.5 block w/piston upgrade alone would suffice for that setup... maybe a 20G or green turbo... (of course in a 2002 wrx w/utec/fmic/etc)

thanks for your input... just trying to tie down the direction i'm going to go... oh yeah-- what tranny are you running-- not the stock wrx?

Well... stop to think about what PSI represents... an excess of compressor effort not being used by the engine, and bottled up in the intake system.

Case in point.... My turbo outflows my SR40 at 22 PSI with 4 less PSI of effort. Which means that the sum of all parts can process the air fast enough for my goals..

In short.... who says you can't make 100 more WHP at 14 PSI on a GT35R, vs. 28 PSI on a GT30R. Don't make the mistake of being caught up on "boost" targets, to make a goal.

This is what I'm using for an engine configuration right now.

Powerplant:

Axis Racing Stage 2 motor
-Subaru EJ257 2.5L
-CP forged pistons
-Subaru forged rods
-Subaru forged crank
-ARP head stud kit
-Cometic 3 layer head gasket

Ultimate Racing heads
-Reformed combustion chambers
-Valve job
-Extensive porting

Shimless bucket conversion
Axis racing titanium springs and hardware
USDM EJ257 cams
JDM STI timing belt
Re-shimmed high flow EJ257 oil pump
EJ257 water pump
Zerosports thermostat
Perrin fuel rails
Ultimate Racing 785CC injectors
Walbro 255 l/hr. fuel pump
DIY water/alchy injection kit

Aspiration:
Slow Boy Racing
-GT30R-11

GTspec v.III header
IA performance tumbler valve deletes and porting
Ported and knife edged throttle body
Samco turbo inlet hose
TurboXS hyperflow FMIC
TurboXS short ram
TruboXS TBE

That's what's worked for me so far. Has given me the best of all worlds in light of my goals.

As for how is it on the highway? Well... I have relatively inefficient gearing, and have NO issue tearing through 3rd gear (70-115 MPH). 4th slows down a touch (but that's relative I guess), since it's a .64:1 gear ratio. By slowdown, it still only takes about 10-15 seconds to peg the speedometer at 140MPH from 115, and still keep accelerating to 155 (my hard limit in flash).

But I don't do that often at all, due to the simple inefficiency and tremendous loads that the trans goes through at that gear ratio in 4th. Not a bad thing... as it limits my damages on a ticket to the top of 3rd heh.

Jorge (RiftsWRX)
www.ProjectWRX.com
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