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#6: 08-11-2011, 05:52 PM
 
 broknindarkagain
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HYBRID BUILDS / FRANKENMOTOR FAQ
under construction

What is a hybrid build / frankenmotor?
It is a term used for using the heads off of one Subaru engine and the bottom of another.
Can you give an example?
A popular hybrid build is an EJ257 (STI 2.5L) bottom end (block/crank/pistons) and EJ20 (WRX) heads / intake.
What is the advantage of a hybrid build?
One of the biggest advantages is compression. Some decide to do hybrid builds to get higher compression then stock.
So what heads can I combine with what block?
Pretty much any head intended for any EJ engine can bolt up to any EJ block.
So whats the catch?
Most EJ engines are interference engines....meaning when the valves open they drop down into the cylinders. This is why when a timing belt breaks, you have to rebuild the heads.

Back to the point...

Some heads have valves that drop down into the cylinder further then others. I can't provide a complete lists of everything, however some builds require thicker head gaskets to avoid high speed valve interference....meaning the valves slapping the tops of the pistons at higher RPMS
All the hybrid builds I have seen are for turbo engines. Can I do this with a non-turbo engine?
Of course you can! The reason hybrid builds on N/A Subarus is not well documented is because most decide to do turbo builds.
Can I use my USDM EJ25D heads on a JDM EJ20K block?
Yes. I don't know what kind of benefit it would give you though. Usually people like to pair heads off a smaller engine onto a bigger block.
What transmission can I use with my hybrid build?
Just about anything. Any transmission that was meant to be paired with any EJ engine will bolt up just fine.
Can I use my stock ECU?
It depends on how big of a change you make. There is no concrete answer to this question.
Should I have some kind of after market engine management?
Of course! I actually suggest even those running stock to have some form of engine management. Stock ECUs suck.

Last edited by broknindarkagain; 08-21-2012 at 11:19 PM..
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