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Old 02-12-2009, 02:57 AM   #1
Scooby Newbie
Member#: 178135
Join Date: Apr 2008
Chapter/Region: TXIC
Location: Texas
2006 Impreza 2.5i

Default ej257 diesel conversion

I recently got an 05 sti short block with a seized rod bearing and im not exactly sure what i want to do with it. my initial plan is to create a high HP/high TQ turbo diesel but im not sure where to start with the block, and if the block itself will even be able to handle the high temperatures and pressure. It is a project that I plan to invest quite a bit of time and money into if my desired results are achievable. My main goal is just to build something unique.

desired results = 350hp 550ft/lbs tq @ crank
realistic/acceptable = 200hp 350 ft/lbs tq @ crank

for now im trying to figure out which brand has the strongest most reliable internals.

I would like to either use this car for road racing or just to see what I can build.
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Old 02-12-2009, 04:08 AM   #2
Scooby Newbie
Member#: 158586
Join Date: Sep 2007
Chapter/Region: MWSOC
Location: North Dakota, USA
2009 WRX
Pearl White


Wait... Are you just taking a gasoline engine and converting it? No way can you make a diesel out of it. I know 14:1 compression is pretty high for an alum block but for it to handle 27:1 or more? Good luck to ya. I would suggest having one imported from overseas instead, then the hard part is out of the way.
You do realize diesels don't have sparkplugs right? I kid I kid...
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Old 02-12-2009, 09:47 AM   #3
Scooby Guru
Member#: 98961
Join Date: Oct 2005
Chapter/Region: MAIC
Location: NOVA
2003 WRX


GM tried it and failed. Taking a car engine and making it a Diesel. It was even a re-enforced iron block car engine and they still failed. Apparently, the new BMW diesels are cast iron blocks too. Considering the subaru engines are interference engines and pretty tight, I'm not sure where you're going to get the compression from.

If you think you can make it work, go for it. The weight of history and common practice is against you.
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Old 02-12-2009, 10:13 AM   #4
Scooby Specialist
Member#: 96712
Join Date: Sep 2005

although I really applaud you for trying something different, I can tell you right now that you will not find it easy in any way to make one of these engines into a diesel....

for instance, look at Subaru, they just now made a diesel boxer.....

they spend millions of dollars to develop it and it is yet to become a time-proven engine for them....

it may work fine for 30-50K miles, then, start blowing head gaskets in the real world in the average joe's cars.... no one knows for sure....

What we do know is that Subaru has hundreds of hours of development and most likely had to re-design several items as compared to what they started with.....

My recommendation is to try and buy one of these new diesel Subaru engines from overseas and then retro-fit it into a subaru here.....

As for MasterKwan's advice, please heed it.... The GM diesel he speaks of is an OLDSMOBILE 350 diesel, which has only 4 head bolts per cylinder, just like a Subaru......

and the head bolts aren't very large on a Subaru or Oldsmobile either from the factory....
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Old 02-15-2009, 10:28 PM   #5
Scooby Specialist
Member#: 45494
Join Date: Oct 2003
Location: glen rock, pa
95 impreza L awd


Now if you want to do something different you can do a miller cycle conversion or a Six cycle conversion.
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Old 02-16-2009, 07:36 AM   #6
Scooby Newbie
Member#: 203114
Join Date: Feb 2009
Chapter/Region: RMIC
Location: Clifton, Co
2003 Impreza WRX


wouldnt running e85 be a better conversion? ive read alot on it, and there are subaru guys that say its fine for your car
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