Jump to content
Ultimate Subaru Message Board

Frankenmotor: 2.5<2.2 heads single port vs dual ports


MilesFox
 Share

Recommended Posts

I have an ej25d block. I have dual port heads from a 1st gen legacy, and a 1st gen intake to swap components to.

 

My current car 96 legacy brighton 2.2 single port heads.

 

I was going to use dual port heads on the ej25 block, but if there is an advantage to using single port heads, i can consider them,but at the expense of a functioning engine for parts.

 

I read that the single port head has bigger valves. Is there an advantage with single port heads in regards to valves or cam options vs dual ports?

Link to comment
Share on other sites

Valves aren't any bigger in 96 single port heads.

 

Although I do think the cams in that year are roller follower, and make better low end torque than the 90-94 dual port heads.

 

The only down side to the singles in my mind is the lack of interchange of exhaust manifolds. 

Link to comment
Share on other sites

The only difference in availability to me is either using heads off the shelf (dual port) vs taking heads form a complete motor (single port)

 

Perhaps i'll consider swapping the roller assemblies to the dual port heads essentially making '1995' dual port heads of them.

 

Now, this sparks eanother question, so that i can still have a complete spare engine: Will the standard dual port rocker assemblies swap onto a single port head?

 

And another thing to consider, the car currently has a straight pipe all the way back, so if i want to keep that, i;ll have to stay with single port. But this will require my hybriding or swapping heads. Otherwise, i already have a complete dual exhaust system to swap over with factory cats.

 

I guess i could go either way if there is nothing to gain or lose other than the exhaust pipe itself. My car will have to be emissions legal as it still has yet to pass.

Link to comment
Share on other sites

Swap the Cams to match with rocker assemblies.

 

All intechangable but you want to keep the cams with their matched rockers.

 

 

Single port heads I do think make better low end torque.  The single port equalizes the port length in the head.  This plus the 95+ equal length header pipe helps scavenging at low RPMs.  Loses some of the nice boxer rumble though.

Link to comment
Share on other sites

Yeah, i cpuld do that as well, least amount of work using shelf parts, without having to disassemble a good motor. I wouldhave to steal the header off the forester, though. I think i'll stick with the dual port for simplicity and labor as i had originally intended. I would probably need a 1997 and later single port head for any potential gains anyway. I'll just swap the cams and rollers from the single ports as long as the lifter style swap onto the single ports to keep a complete spare engine around.

Link to comment
Share on other sites

  • 2 weeks later...
  • 2 weeks later...

Formula I saved years ago, not sure if I helps you any:

 

Originally Posted by grafton viewpost.gif
simple version of franken motor combos:

engine block + heads=

"best"
p2 2.5 + p2 2.2: highest compression ratio (stock gasket) better manifold options, decient heads

good
p1 2.5 + p2 2.2 again good manifold options and decient heads
p2 2.5 + p1 2.2 dual ports (header options & possible better flow than single ports) 
p1 2.5 + p1 2.2 dual ports 

ok 
p2 2.5 + p1 2.2 single ports
p1 2.5 + p1 2.2 single ports

thats for running completely stock, aka slaping it together and going.

if you can port & polish, do cams, or a valve job you'll be much better off
Link to comment
Share on other sites

The thing is, p2 ej222 heads and p2 ej251 heads have the same combustion chamber volume, so you really aren't making a frankenmotor with them.

 

Source? Everything I have read or researched begs to differ. Unless not all p2 ej22 heads are created equal.

 

 

"The phase 2 2.2 heads do have the same combustion shape as the phase 2 2.5 heads from 99 to 05. However, the combustion chamber volume for the phase 2 2.2 heads is 41 cc's where as the chamber volume for the phase 2 2.5 heads I believe is 51 cc's."

Link to comment
Share on other sites

Side by side comparison is my source.

 

That and simple math that this ej222 piston IMAG0131-1_zpshp8ethps.jpg

 

Which has a 10cc dish at -.4mm piston to deck height, with a. 8mm gasket and a 41cc combustion chamber would have over 12:1 compression.

 

I don't have any pictures, but I bought a 99 L wagon a few years back that had bent valves because the timing belt went. Used ej251 heads on it and compared the two while it was apart.

 

Btw Brian, the twe compression calculator has absolutely no information on the ej222 or the ej22e for that matter.

Link to comment
Share on other sites

12:1, yep. Hence the whole idea of a high compression frankenstein, I stand by the numbers I quoted. The heads have the same shape, but different volume. I'll go pull some PaP heads and CC them, if you really want.. But there is plenty of info out there if you search nasioc.

 

Good read:

http://forums.nasioc.com/forums/showthread.php?t=631527

 

 

Side by side comparison is my source.

That and simple math that this ej222 piston Which has a 10cc dish at -.4mm piston to deck height, with a. 8mm gasket and a 41cc combustion chamber would have over 12:1 compression.

I don't have any pictures, but I bought a 99 L wagon a few years back that had bent valves because the timing belt went. Used ej251 heads on it and compared the two while it was apart.

Btw Brian, the twe compression calculator has absolutely no information on the ej222 or the ej22e for that matter.

 

Link to comment
Share on other sites

I've read it all, and the pistons I showed are ej222, it doesn't have 12:1 if you could read you'd understand what I was saying. There is no way possible with a 10cc dish piston, and a .8mm head gasket and a 41cc chamber that you can get the 10:1 compression ratio they came with stock. It is physically impossible.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...