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Old 08-20-2003, 08:48 PM   #1
Scooby Newbie
Member#: 37417
Join Date: May 2003
Chapter/Region: MAIC
Location: Baltimore, MD
2003 Impreza RS 2.5
Blue Ridge Pearl

Default 2.5RS to new 2004 STI

is there anyway to do an sti conversion from a 2003 RS to an STI since they both have 2.5l engines. the only big difference i know of is the sohc of the rs and dohc or the sti. are there anyother major differences? what would i do replace the cylinder heads get a some guy who is seriously redoing his sti and take his piping and turbo and stuff and put that all in my car? any ideas or suggestions?

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Old 08-21-2003, 12:03 AM   #2
Scooby Specialist
Member#: 1305
Join Date: Apr 2000
Chapter/Region: AKIC
2000 Impreza


SOHC/DOHC? No, there's a lot more than that.

You're better off just selling your 2003 RS and getting an STI.
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Old 08-21-2003, 07:14 AM   #3
Scooby Guru
Member#: 36080
Join Date: Apr 2003
Chapter/Region: South East
Location: Raleigh, NC
2005 Volvo V70R


I agree.... But good on ya though for wanting to be adventrous!!! :COOL:
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Old 08-21-2003, 07:51 PM   #4
FuJi K
Scooby Guru
Member#: 3687
Join Date: Jan 2001
Chapter/Region: MWSOC
Location: St. Paul, MN
MY99 GF4 JDM 6spd
NF Performance


Since no one answered well enough...

...looks around...

Let me answer some questions.

The STi has completly different interenals in the engine. It runs stronger internals with a compression ratio of 8.2:1, which is why it can run well with the turbocharger. It also has Subaru's AVCS with is another type of variable valve timing which changes the degree of the camshaft via engine RPM. The other biggy is the transmission driveline. The STi, as you may know sports a 6-speed with DCCD.

Depends HOW MUCH of a STi do you want to impersenate. I'm guessing the power output. You can do that with your engine but you'll have to open it up and put stronger parts in so it can HANDLE the boost, that's if you're going to boost it.

I'm sure you can replace your pistons, and rods with the STi ones. Then you'll have warrenty on the parts too! Then you can turbo it.

You just have to worry about the block. If you don't run high boost say 1.5bar or more then you'll be safe. STi's block is semi closed, yours is open.
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Old 08-21-2003, 11:15 PM   #5
Scooby Specialist
Member#: 1305
Join Date: Apr 2000
Chapter/Region: AKIC
2000 Impreza


Subaru isn't going to warranty STI pistons and rods in a 2.5rs block. May be the same dimensions, but it wasn't OEM for that engine.

Like I said, he's better off just getting an STI. With the money you'd spend converting an 03 RS into an STI you could have just sold the RS and bought a new STI(assuming mofong would be paying someone to do the work). Even if you did the work yourself it'll still be expensive because the parts are in high demand now. Plus the resale on an 03 rs converted to an STI would be horrible compared to an actual STI.

So like I said, just get an STI.
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