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Old 10-15-2001, 07:42 PM   #1
Scooby Newbie
Member#: 6553
Join Date: May 2001
Location: Lima, OH
Default 99 2.2 vs 2.5 heads on EJ22t block

I am planning an engine build starting with a new ej22t block adding forged pistons, etc. I want to use either 2.2 or 2.5 SOHC heads. I have a chance to buy a 99 2.2 engine with ecu and wiring. Are the heads the same as a 2.5? What changes were made to the heads from Phase I to PhaseII?
My theory is that the 2.2 heads and ecu will calculate mixture correctly under mild boost, but the 2.5 heads will give a rich mixture expecting more air in the cylinder. But, they must bolt up and match coolant passages, etc. (I know 2.5 heads will work)
Any info is helpful- like a head flow comparison graph
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Old 10-16-2001, 12:28 AM   #2
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Member#: 689
Join Date: Dec 1999
Chapter/Region: NESIC
Location: Lebanon, NH, USA
2005 Outback 2.5 XT
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N/A 2.2L heads are single port exhaust (although I'm not entirely sure about MY99-MY01). Strikes me odd how the bean counters got away with this one, when the EJ18's, EJ22T's, and EJ25's all have dual port exhausts. Also, I am not aware of anyone who has figured out what the CR will be on an EJ22T short block and N/A EJ22 heads. My guess is it's either going to be 8.0:1 or 9.7:1 (there were rumors about 10:1 for MY99-MY01, but little is known).

Get EJ25 heads unless you have no other option.


Last edited by wac; 10-16-2001 at 12:53 AM.
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Old 10-16-2001, 12:17 PM   #3

i can remember reading somewhere that the 2.5 is really close to same design as the WRX where the 2.2 is significantly de-tuned..

exact differences i'm not sure, it might be the exhaust port design that some one mentioned.. the flowing might be smoother too..
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Old 10-21-2001, 12:36 AM   #4
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Member#: 6553
Join Date: May 2001
Location: Lima, OH

Thanks for the input.
Now a different question. 2.5 SOHC heads vs 2002 WRX heads. I'm planning on using this build up in an experimental plane I am building- a /van's RV7. Low end torque and spool time is insignificant. Dependability at 200 hp+ continuous is CRITICAL at between 4250 and 5500 rpm. Therefore, my thoughts are to have the best flowing heads, which translates to lower boost pressures and better intake temps. Maybe o-ring the heads for less chance of head gasket failure? What I need is absolute reliability and 200 hp output at 10,000 ft altitude. I want to think this through carefully and execute the build even more carefully for obvious reasons.

Any and all input is appreciated
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Old 10-21-2001, 01:28 AM   #5
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Location: Seattle, WA, USA
2000 Impreza 2.5RS
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The numbers I have seen indicate the EJ25 heads have very high flow. Cobb tuning has put them on a flow bench: Trey rules!

Having the heads ported and installing appropriate performance cams would also really up the power. If you are trying to maximize flow, also consider having your throttle body bored.

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