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Old 03-27-2004, 09:59 AM   #1
Scooby Newbie
Member#: 19562
Join Date: Jun 2002
Chapter/Region: NESIC
Location: VT
93 Impreza wagon L

Default 2.5L rebuild questions

I'm picking up a high milage DOHC 2.5 to swap into my 93L. 140,000. I would like to replace pistons/rings, bearings, cams. I have rebuilt many engines but not in the last 25 years. My only aluminium blockexperience was with Chevy Vega's, I have also done many TR3/TR4's, MG's V8's and Willy's Jeeps.
Besides the wierd head torque proceedure is there anything else that is much different ? Some questions.
1. Can you/should you mill the heads, How much can you get away with without negativly impacting cam timing, also what about thin head gaskets. I've read about the 4 layer improved gasket for the DOHC. We used to do three angle valve jobs to improve flow, do they still do this, or are valves and seats cut good from the factory?
2. What is the largest standard oversize piston you can get? Will these raise the compression or have they increased the "dish" to keep the compression the same? This will be a street engine but I would like to increase the compression a bit, should I go with something from TWE? ($700+ ouch)
3. How much compression works well with the street grinds available (the three I've looked at seem about the same). Has anyone sent their cams out to be welded and ground?
4. Bottom end, any weak spots there. Looks like a nice solid crank compared to a MG or Triumph. How is the balance from the factory? Anyone still knife edge their cranks? How about hi flow oil pumps??

And lastly, It seems the concensus is that these engines run rich on the 1.8 ECU. What if you put a controlled air leak upstream to the MAF?
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Old 03-27-2004, 05:13 PM   #2
Scooby Guru
Member#: 5218
Join Date: Mar 2001
Chapter/Region: MWSOC
Location: SAUL'S Motorsports
96L Most Over-
Developed Beater


Since I'm doing the same thing, I'll answer what I can.

1. The heads should only be milled to SOA's limits. I think .010" is that limit. The motors are interference already, milling may only make it worse. I don't know where valve timing would become an issue, but Fidanza should release an adjustable cam pulley set in the not too distant future. (they have my pulleys as patterns)

2. SOA says +1mm for overbore limits. Pistons will be dished, but I don't know if the CR will be reduced or what. Not too much out there by the aftermarket, so prices reflect that.

3. Depending on what your goals are, custom cams can be made for whatever CR you run and RPM range you want. Most if not all aftermarket cams require yours in trade as cores, so I guess everyone is essentially doing the same thing. Getting accurate numbers is another story. Short of doing your own measurements on a set of reground cams, you have to choose between "mild/spicy" or "stageI/II"etc...

4. Phase I blocks have the crank thrust bearing in a different position than phase II blocks. An STi block (EJ257) would be strongest of all, but also the most expensive. Balance is good from the factory, but some folks have knife edged anyway. Subies crank is already well away from the oilpan, so I question the need for this other than "on-paper HP" Using a oil pump for the turbo motors is about the best you can find off the shelf. Same with the water pump.

Lastly, browse the "conversions" forum for more detailed info from folks running EJ25s on 1.8 and 2.2 ECUs. This is also what I'm in the process of doing.

Jay Storm
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Old 03-28-2004, 12:50 PM   #3
Scooby Newbie
Member#: 19562
Join Date: Jun 2002
Chapter/Region: NESIC
Location: VT
93 Impreza wagon L


Thanks for the detailed response. Can you recommend a Cam grinder? Thanks
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