To rebuild [with 2.5L block] or not to [rebuild with 2.5L block]

View Poll Results: Do I go Hybrid?

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This is a discussion on To rebuild [with 2.5L block] or not to [rebuild with 2.5L block] within the Engine Modifications forums, part of the Tech & Modifying & General Repairs category; Alright folks, I have been contemplating the next move I take power-wise and have considered the options. In the spring ...

  1. #1
    zax
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    To rebuild [with 2.5L block] or not to [rebuild with 2.5L block]

    Alright folks, I have been contemplating the next move I take power-wise and have considered the options. In the spring of next year, I will be making the step to an upgraded turbo. Now the question arises (when I select the turbo), do I gear more towards a future 2.5L rebuild or do I work to reinforce and build a stout high-revving EJ205. Here is my argument:
    For the EJ25x block:
    - Semi-closed reinforced
    - More torquey, better for daily driver
    - Bigger turbo spools quicker
    - USDM 5-speed is better geared for the torque-spread of the 2.5L block to a high-revving 2.0L

    For the EJ205:
    - thicker cylinder sidewalls
    - open deck weakness can be mitigated by stronger ARP headstuds (better clamping force)
    - Rod to Stroke ratio is 1.74 compared to 1.65 of EJ25 (1.75 is considered "ideal" for a high-revving road car)
    - I don't have to worry about spacers or machining to achieve the correct CR

    So I could take two paths with the $2K:
    1. Spend the money on the 2.5L block
    2. Spend the money on balancing and valvetrain enhancements

    I'd like to hear arguments on either side... hybrid build or no. I've seen many other threads just like this one, but I'd like a fresh outlook from those of you that have taken one path or another.
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    Administrator RayfieldsWRX's Avatar
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    I certainly can't make the decision for you; some people just love their high-revvers....

    For me, I'd had nearly 7 years of 2.0 goodness (with TD04 and VF34) and wanted to get in on the nice driveability that 2.5 owners had been reporting ever since the 2006's came out.

    I'd never go back. The combination of the 2.5 and a moderately sized turbo is just the greatest. Good power is just, well, always there, at any engine speed above, oh, say 2500 rpms. I'm a 75% throttle kind of guy when I'm accelerating briskly on a normal basis these days...last night I was carting the kids home and for a lark put the wot smack down on a side road to get up to the speed limit in a hurry...glorious...my kids got really quiet.

    edit:
    I won't address the durability issue between the blocks...I think you're better educated on this than I am by a long shot!
    Last edited by RayfieldsWRX; 11-12-2010 at 12:21 PM.
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  4. #3
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    I hear your argument, Ray. I do like the sound of having that extra torque on tap for my daily driving. Furthermore, the 2.5L is capable of producing just as much power at lower revs than a high-revving 2.0L. However, there is something fun about wringing out a low-displacement engine at 8K. That is the one thing I absolutely loved about my driving my friend's RSX type S...
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    Administrator RayfieldsWRX's Avatar
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    There are situations where I've enjoyed that feeling...revving my CBR600F2 to 13,500rpms was insane fun, but it felt like an engine that was supposed to be doing that. (I suppose the Acura/Honda car engine is in the same category)

    For some reason I've never gotten the same enjoyment out of pushing my Subies to the stratosphere. Personal preference; YMMV.
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    I can't speak from experience here as far as a Subaru 2.5 vs a Subaru 2.0...my only contribution to this is that, in general terms, I think torque is way more fun than horsepower.

    If you're building a racecar, by all means the high revving motor will be a lot of fun. But for day to day and the occasional track day, I'd take the 2.5 any day.
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    Luke Skywalker Mikie13's Avatar
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    Why can't you build the 2.5 to high-revving?
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    Registered User Crb03's Avatar
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    I'd say build a 2.2 stroaker. Buddy in my class is building one with forged internals. Should be nice.
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    Quote Originally Posted by Mikie13 View Post
    Why can't you build the 2.5 to high-revving?
    There's no reason that you can't. But money is an issue... it's either spend the money on the shortblock or spend the money on valvetrain upgrades. When you really nitpick, the 2.0L will be smoother in the upper revs thanks to the better R/S ratio, but I've seen 2.5L STis balanced to 8K no problem.
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    2.5 > 2.0 /thread.
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    God call me old-fashioned but there is something about the 2.0L (WRC pedigree perhaps?) that has always attracted me. I'd hate to part ways.

    That being said, I think that I would enjoy driving the 2.5L hybrid more. I rarely take the car past 4000 RPM and enjoy the low end torque it allows.

    Still, there is something about building a stout 2.0L that attracts me...
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    Quote Originally Posted by Crb03 View Post
    I'd say build a 2.2 stroaker. Buddy in my class is building one with forged internals. Should be nice.
    The problem with this is that a 2.2 stroker will increase the stroke to 82.5 mm from 75 mm. This effectively reduces the R/S ratio from an ideal 1.74:1 to 1.58:1 (the EJ series uses relatively short rods). This would increase sidewall loading and perhaps compromise the durability of the engine in the long run (though the cylinder walls in the EJ205 may be thick enough to handle this IDK). Either way, it would increase the harshness of the engine at high revs. Unless your buddy is using longer rods with the pivot drilled deeper into the piston, which I don't know if I want to risk tons of friction so close to the oil seals
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    Quote Originally Posted by Sasquatch View Post
    2.5 > 2.0 /thread.
    As a driver of a 2.5l car ...

    YES you want the torque. You cant rev out all the time, but you can enjoy grunt any time you need it.

    The rod/stroke ratio is super important.. the 2.5 has a good r/s ratio (compared to other 2.5l I4 cyl mills) as well as torque. Why stroke a 2.0 when its easy enough to build a really solid and reliable yet more powerful 2.5? You could always build the 2.5l with different rods/pistons to put the r/s ratio back up toward 1.7-1.8 ... but at a drawback of cost and possible oil consumption if the oiling ring is too near the wrist pin opening.

    Dooooo eeeeet.. you know you want more than a soda bottle worth of displacement lol
    Last edited by mangostick; 11-12-2010 at 03:33 PM.
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  14. #13
    Registered User Crb03's Avatar
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    Quote Originally Posted by zax View Post
    The problem with this is that a 2.2 stroker will increase the stroke to 82.5 mm from 75 mm. This effectively reduces the R/S ratio from an ideal 1.74:1 to 1.58:1 (the EJ series uses relatively short rods). This would increase sidewall loading and perhaps compromise the durability of the engine in the long run (though the cylinder walls in the EJ205 may be thick enough to handle this IDK). Either way, it would increase the harshness of the engine at high revs. Unless your buddy is using longer rods with the pivot drilled deeper into the piston, which I don't know if I want to risk tons of friction so close to the oil seals
    My tuner actually suggests doing a 2.2 over doing a normal 2.0 rebuild. He says it's cost is exactly the same as it would be to rebuild the 2.0. He actually just rebuilt his 2.2 with a 42r in his GC8.

    If you are a little interested call this number and talk to kevin. He's a stand up guy that will talk and explain everything to you. But careful of his sales men side, he'll get you all excited and you'll be sprinting to give him your cc #. He's in california so you should be able to reach him.
    (714) 288-2887
    Also his website where he has some info on the 2.2 kit.
    www.garagetuning.com

    Edit - from their site

    Includes 79mm forged crankshaft, lightweight forged Eagle rods, 92.5mm forged Mahle Pistons, and custom Cometic headgaskets.

    This engine is a Garage Tuning favorite. The 2.2 Stroker engine is the perfect solution for the 2.0 liter WRX engine replacement. While adding a 2.5 STi block seems quick and easy, it is flawed in many ways for the WRX. The size of the combustion chamber is designed for 92mm bore. The STi bore is 100mm. This leaves a 4mm step all around the edge of the combustion chamber. This flaw cuts power at about 5000 rpm. Many people think changing cams or porting solves this problem, but it does not. The other problem with the STi block is the piston material. These pistons are prone to failure with mild detonation or high boost.

    The 2.2 stroker is a simple solution that easily adds 30-40 horsepower and torque with no additional modifications. This engine coupled with the Garage Tuning GT30R Twin Scroll Turbo Kit has made 430 whp on our dyno. This engine is built with Mahle pistons, Eagle rods and ACL Race Bearings. All remaining gaskets required to finish the engine are included.
    Last edited by Crb03; 11-12-2010 at 04:05 PM.
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  15. #14
    zax
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    Quote Originally Posted by Crb03 View Post
    My tuner actually suggests doing a 2.2 over doing a normal 2.0 rebuild. He says it's cost is exactly the same as it would be to rebuild the 2.0. He actually just rebuilt his 2.2 with a 42r in his GC8.

    If you are a little interested call this number and talk to kevin. He's a stand up guy that will talk and explain everything to you. But careful of his sales men side, he'll get you all excited and you'll be sprinting to give him your cc #. He's in california so you should be able to reach him.
    (714) 288-2887
    Also his website where he has some info on the 2.2 kit.
    www.garagetuning.com

    Edit - from their site
    Actually it would be interesting to talk to him. I wonder why he suggests the stroker? I'd trust the word of a professional rebuilder over my own amateur analysis.

    EDIT:
    I see what he's done. He's increased the stroke to the same as the EJ255 (79 mm) perhaps by using the STi crankshaft. This actually comes out to be about 2127 cc, I assumed that 2.2 was 2.2 on the dot...
    Last edited by zax; 11-12-2010 at 04:13 PM.
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  16. #15
    Registered User Crb03's Avatar
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    Quote Originally Posted by zax View Post
    Actually it would be interesting to talk to him. I wonder why he suggests the stroker? I'd trust the word of a professional rebuilder over my own amateur analysis.
    Its pretty funny my buddy in my class was in the same boat. He was going to rebuild his 2.0, then i hooked him up with kevin... Three days later do took him a check for the stroaker kit. He just got the parts on monday, they shine all purrdy like.

    I'd sure suggest talking to him. It never hurts.
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