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Guest Message by DevFuse

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SVX / STI Piston Swapping......

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19 replies to this topic

#1 Guest_soloracer951_*

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Posted 17 June 2003 - 08:05 PM

I just noticed that the bore and stroke for the 3.3 SVX engine and the 22B-STi engine are the same. Could one use the pisons from the 22B-STi in an SVX engine to lower compression and then turobcharge it to get safe reliable power? Anyone know of any links or websites where this has been done?

#2 Guest_wrxsubaru_*

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Posted 17 June 2003 - 10:13 PM

the eg33 or svx engine is basicly a ej22 or the 2.2 liter with 2 more pistons. Both engines have the same bore and stroke, so you could take those pistons and rods and have safer more relible turbo charged eg33. You could all so get a good shop to put some more metal in between the cylinder wall and block , so its not a open deck. The bigger problem with the svx and more power is usally the tranie not being able to hold it.

#3 Guest_Legacy777_*

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Posted 18 June 2003 - 06:16 AM

The eg33 is not just an ej22 motor with two more cylinders.

If you want to lower compression, just look for some aftermarket pistons or custom ones. I don't know enough about the differences between the svx motor and the sti one to know whether that would work or not, but it's probably likely you can find something if that's the route you want to go.

#4 Guest_LeoneTurbo_*

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Posted 18 June 2003 - 09:08 AM

I believe the EG33 engine uses the same pistons as the n/a EJ22 engine. Speaking of EJ22 engines, there have been 2 versions: 1 open deck n/a engine with high compression pistons, and 1 closed deck engine with turbo pistons, the latter was used in the US-only Legacy 2.2 Turbo (non intercooled 165 hp) and possibly also in the storming 300 hp 22B. MInd you, the Legacy 2.2 Turbo uses SOHC heads, the 22B uses the MY98 EJ20 WRX STi heads (DOHC). The 22B also uses the same turbo charger as the 'normal' WRX STi.

So find yourself a dealer with a Legacy parts book, order 6 Legacy 2.2 Turbo pistons and put them into an SVX engine.

BTW, the SVX uses the same injectors (according to my parts CD-ROM) as the n/a EJ22 engines. They're good for up to 250-260 hp (on 6-cylinder engines). If you want more power, use early EJ20 turbo (Legacy Turbo, Legacy TwinTurbo or Impreza WRX) side feed injectors. MY99 and after WRXs have top feed injectors which do not fit the pre MY99 fuel rails.


#5 Guest_Legacy777_*

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Posted 18 June 2003 - 11:25 AM

Only thing you need to be careful of is there are different injector types for the EJ22 n/a motors.

First, there is a difference between manual & auto trannys. Second the injector type in the 90-91 autos are definitely different then the 92-94 models. I can't tell you for sure whether the manuals had a similar change or not.

#6 Guest_LeoneTurbo_*

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Posted 19 June 2003 - 02:02 AM

92-94 injectors (red plastic connectors) are identical to the ones used on the SVX.

#7 Guest_Greg Donovan_*

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Posted 20 June 2003 - 10:09 AM

i was thinking of putting svx pistons into an ej22 to get the higher compression ratio. i believe the piston is the same everywhere except the volume of the top. this info is from a chiltons manual that lists engine specs.
we are also thinking of putting ej22 heads on a sohc ej25 block. anyone tried this?

#8 Guest_Legacy777_*

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Posted 20 June 2003 - 11:34 AM

putting ej22 heads on an ej25 block will increase compression quite a bit, I don't know the exact amount. But I was told it would be enough where you'd have to run premium to make sure you don't get any detonation.

#9 Guest_Greg Donovan_*

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Posted 20 June 2003 - 08:10 PM

we would run premium (which i allready do anyway) and an aquamist water injection system to reduce the temps in the combustion chamber and stilll keep the comp ratio up there.
any one have an idea if the timing would still be right w/the different heads? cuz there are no adjustable timing gears for the subaru motors as far as we know.

#10 Guest_LeoneTurbo_*

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Posted 23 June 2003 - 01:05 PM

As long as you will use the EJ22 SOHC heads and the SOHC camshaft, timing can't be wrong. EJ22 heads will fit the EJ25 short block.

Regarding compression ratio: the EJ25 engines that I have seen, all have dished pistons to reduce compression ratio, probably because the volume of the combustion chamber in the cylinder head is the same as with the normally aspirated EJ20 and EJ22 engines. However, I have no hard evidence of that.

Please be aware that (early) SOHC EJ22 heads have smaller valves than the EJ25 DOHC heads. I have no information on EJ25 SOHC heads at the moment.

#11 Guest_Greg Donovan_*

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Posted 24 June 2003 - 02:51 PM

so you think the volume of the combustion chamber volume is the same on the 25 as the 22?

#12 Guest_wrxsubaru_*

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Posted 24 June 2003 - 07:01 PM

I thought the ej 25 has a longer stroke than the ej 22?

#13 Guest_LeoneTurbo_*

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Posted 25 June 2003 - 03:46 AM

Stroke is longer but block width is the same. I guess they use shorter con rods on the 2.5. I know EJ20 and EJ25 manifolds (for DOHC versions) can be swapped, so that more or less proves the similarity in block width.

#14 Guest_Legacy777_*

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Posted 25 June 2003 - 06:45 AM


EJ25 either has shorter rods or change on the crank. One of the two.

#15 Guest_Greg Donovan_*

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Posted 26 June 2003 - 12:04 AM

we are palnning on using the pase II sohc block w/the flat pistons. i am doing this w/a sbuaru tech. actually he is going to do it first and then he will help me w/mine later. yea the valves are smaller on the 22 but e want more low end torque. my engine will be used for rallycross.

#16 jvaughn


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Posted 09 September 2009 - 04:18 PM

Check out this site i found. It might be better to buy there pistons (and everything else they have too):


#17 Durania


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Posted 09 September 2009 - 04:21 PM

Way to bump a six year old thread.

#18 Suzam


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Posted 09 September 2009 - 04:30 PM

:lol: :lol: :lol: :lol: :lol: :lol: :lol: :lol:



#19 ericem


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Posted 09 September 2009 - 05:16 PM

its a awesome way!!

#20 EVOthis


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Posted 09 September 2009 - 06:09 PM

The whole time I was reading it I was thinking this.. fore the date said 03' ...:lol:

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