modifications to fit a motor made for wrx heads to sti heads?

Physics Junkie · 11-03-2005, 03:05 AM

I'm buying an ej257 shortblock that was attached to WRX DOHC heads...am I going to have a problem mating this ej257 to stock usdm sti heads? I'm going to call Axis tomorrow just wanted someone to assauge or confirm my concern tonight.

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modaddict · 11-03-2005, 11:46 AM

im thinking the pistons are different for the wrx heads. if you put the usdmsti heads on, i think you'll be way down on compression....there are some threads on here about this swap. www.crawfordperformance.com i believe has some info about this. hope this helps.

the_colombian · 11-03-2005, 11:57 AM

Im thinking that if they used wrx compression pistons that you will be down compression as well.

modaddict · 11-03-2005, 12:18 PM

i checked and crawford makes a set of 2.5 pistons for the wrx head and the sti head. the dish looks deeper for the wrx head. call them and they will tell you. Its more than likely not a bolt on or a direct fit.

sjl1614 · 11-03-2005, 12:46 PM

It's a good idea to call one of the engine builders for advice..

bboy · 11-03-2005, 02:24 PM

The volume of the combustion chamber is 51 cc with WRX heads vs. 57 cc with the STI heads. When you put the WRX heads on the 257 your compression ratio will be 8.7:1 versus 8.2:1 for the stock EJ257.

You really don't want to go any higher on the compression ratio unless you are going to run race gas all the time. So, don't 'deck' the block and don't buy pistons that raise the CR further (some aftermarket pistons are 8.5 CR).

Physics Junkie · 11-03-2005, 08:24 PM

I called Axis today--Ron confirmed that I would be running stock ej257 compression with a stock sized headgasket and usdm sti heads. The WRX heads that were previously attached gave the motor a decently higher compression ratio...so I'm in the clear. Thanks guys.

11-03-2005, 03:05 AM	#1
Physics Junkie Scooby Specialist Member#: 65609 Join Date: Jul 2004 Chapter/Region: SCIC Location: <3s me some SCIC.	modifications to fit a motor made for wrx heads to sti heads? I'm buying an ej257 shortblock that was attached to WRX DOHC heads...am I going to have a problem mating this ej257 to stock usdm sti heads? I'm going to call Axis tomorrow just wanted someone to assauge or confirm my concern tonight. * Registered users of the site do not see these ads.

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11-03-2005, 11:46 AM	#2
modaddict Scooby Guru Member#: 95840 Join Date: Sep 2005 Chapter/Region: NWIC Location: Pasco, WA Vehicle: sold to a good bud awaiting next car	im thinking the pistons are different for the wrx heads. if you put the usdmsti heads on, i think you'll be way down on compression....there are some threads on here about this swap. www.crawfordperformance.com i believe has some info about this. hope this helps.

11-03-2005, 11:57 AM	#3
the_colombian Scooby Specialist Member#: 84912 Join Date: Apr 2005 Chapter/Region: SCIC Location: San Diego Vehicle: 2003 2.5L bugeye now with 6 spd 20g!	Im thinking that if they used wrx compression pistons that you will be down compression as well.

11-03-2005, 12:18 PM	#4
modaddict Scooby Guru Member#: 95840 Join Date: Sep 2005 Chapter/Region: NWIC Location: Pasco, WA Vehicle: sold to a good bud awaiting next car	i checked and crawford makes a set of 2.5 pistons for the wrx head and the sti head. the dish looks deeper for the wrx head. call them and they will tell you. Its more than likely not a bolt on or a direct fit.

11-03-2005, 12:46 PM	#5
sjl1614 Scooby Specialist Member#: 56791 Join Date: Mar 2004 Chapter/Region: South East Location: Charlotte, NC Vehicle: 06 OBS	It's a good idea to call one of the engine builders for advice..

11-03-2005, 02:24 PM	#6
bboy Scooby Specialist Member#: 56468 Join Date: Mar 2004 Chapter/Region: NWIC Location: Seattle, WA Vehicle: 04 Improved STI Dirty White	The volume of the combustion chamber is 51 cc with WRX heads vs. 57 cc with the STI heads. When you put the WRX heads on the 257 your compression ratio will be 8.7:1 versus 8.2:1 for the stock EJ257. You really don't want to go any higher on the compression ratio unless you are going to run race gas all the time. So, don't 'deck' the block and don't buy pistons that raise the CR further (some aftermarket pistons are 8.5 CR).

11-03-2005, 08:24 PM	#7
Physics Junkie Scooby Specialist Member#: 65609 Join Date: Jul 2004 Chapter/Region: SCIC Location: <3s me some SCIC.	I called Axis today--Ron confirmed that I would be running stock ej257 compression with a stock sized headgasket and usdm sti heads. The WRX heads that were previously attached gave the motor a decently higher compression ratio...so I'm in the clear. Thanks guys.