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Old 08-01-2011, 11:58 AM   #1
Highflyr
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Default Ej251 Dohc?

Few questions:

Is it possible to fit the Heads from a EJ25D DOHC to the EJ251 SOHC?

Is the EJ251 considered the Phase 2? Or was there an EJ25D Phase 1 and Phase 2?

I'm basically looking for the best short block for the DOHCs. I have 2 newly reman from an engine I bought and need to get a bottom end for them. Of the 2 blocks that I have 1 needs to be rebuilt the other is cracked. I can use the Phase 1 block that I have but will need to buy a crank since I only have a working Phase 2 crank. Thanks for the help in advance.
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Old 08-01-2011, 12:37 PM   #2
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You can bolt DOHC heads to the Ej251 bottom end without issue. It bumps the compression ratio a touch and may require that you run higher octane gas than you run now.
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Old 08-01-2011, 01:35 PM   #3
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I've run the DOHC heads on a phase II bottom end. I was able to get away with regular gas....but as always, YMMV. You can use SOHC or DOHC headgaskets, but only when using a phase II bottom end.

For others benefit, when using a phase I bottom end, you MUST use phase I or DOHC headgaskets, as the pistons clear the deck at TDC.


OP, pay attention to journal sizes, thrust bearing placement and rod length when debating which block to use with what rotating assembly. There are differences that make this an expensive option....

Jay
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Old 08-01-2011, 03:08 PM   #4
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So is Phase II another name for the EJ251?

Is there a better HG to use? Like DOHC vs SOHC? Is one thicker than the other.

Lastly what kind of compression increase are we talking about? Is it mroe than 1 PSI? I don't want to increase it to where I have to run Sunoco DP13 as this will be my daily beater. Thanks again for the anwsers.
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Old 08-01-2011, 06:34 PM   #5
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Will the heads bolt on an EJ255? Just found a good deal on one.
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Old 08-01-2011, 07:26 PM   #6
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Quote:
Originally Posted by Highflyr View Post
Will the heads bolt on an EJ255? Just found a good deal on one.
They will but because it's a turbo engine you will lose compression. Unless you want to turbo charge your car at a later date or the engine is almost free, pass...
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Old 08-01-2011, 08:53 PM   #7
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Yeah that's not going to work then. This is going to be a daily driver so I'm looking more for MPG than HP. Thanks for the input. I'll keep looking for a 251/3.
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Old 08-03-2011, 04:38 PM   #8
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Would an EJ254 short block work with the DOHC heads?
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Old 08-10-2011, 11:19 AM   #9
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Anyone know deck clearance for the EJ254?
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Old 08-10-2011, 01:23 PM   #10
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It is my understanding that the deck height has not changed since the EJ251 was introduced. That's not concrete info, but I haven't seen anything pointing to changes.


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Old 08-10-2011, 03:53 PM   #11
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The deck height isn't a concern as much as piston shape. Some of the later engines they've produced recently have some pretty funky piston shapes that might not be "compatible" with earlier heads.

Pardon my ignorance, but what year and model came with an Ej254?
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Old 08-13-2011, 12:45 PM   #12
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I'm currently trying to find more info on this too. My current engine is a Phase I EJ25D. I want to put in a Phase II EJ25 (not sure about all the numbers on the end) engine block and put my Phase I heads on it.

From what I understand, it doesn't matter what engine block you use and all EJ subie blocks bolt into any EJ Subie (whether it's a 96,04,auto, or manual). It also seems that you can almost put 2.2 or 2.5 heads on any block, but then you get wiring compatibility issues. Please correct me if I'm wrong. There's so much info out there it's hard to keep it all straight.
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Old 08-14-2011, 01:42 PM   #13
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The EJ254 is the PZEV motor. Single exhaust port that looks like a twinkie mold, but still uses the same 3 bolt exhaust flange. I believe the piston shape on that motor may be domed a bit, but I can't confirm it.

Jay
Quote:
Originally Posted by Matt Monson View Post
The deck height isn't a concern as much as piston shape. Some of the later engines they've produced recently have some pretty funky piston shapes that might not be "compatible" with earlier heads.

Pardon my ignorance, but what year and model came with an Ej254?
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Old 08-15-2011, 10:14 AM   #14
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Quote:
Originally Posted by Storm View Post
The EJ254 is the PZEV motor. Single exhaust port that looks like a twinkie mold, but still uses the same 3 bolt exhaust flange. I believe the piston shape on that motor may be domed a bit, but I can't confirm it.

Jay
The pistons in the one I just got look dished not domed. The center looks higher than the rest, but almost half the bottom portion of the piston looks dished. I took some pictures yesterday I'll try to get them up tonight.

As for the the DOHC heads on the newer block I'm planning to run the stock EJ253 HGs everything else should be stock EJ25D gaskets. I'm planning to build this weekend so I'l be updating with pics within the next couple weeks.

Last edited by Highflyr; 08-15-2011 at 10:21 AM.
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Old 08-15-2011, 11:19 PM   #15
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Highflyr: an EJ251 block with EJ25D heads will result in:
- a 9.6 CR with 11044AA610 HGs which are 1.37mm thick.
- a 10.4 CR wiith 11044A642 HGs which are 0.56mm thick

You can also use heads from EJ20G, EJ20K, EJ20R and EJ22T . The first three will yield the same CR / HGs numbers as posted for EJ251 heads; whereas for the EJ22T heads you will have respective compressions of 11.4 and 10.4. Again, same head gaskets.

An EJ255 block will take any heads (EJ20G to EJ257) except for those an from EJ251.

Not pulling this from my derriere - I have in front of me a page from "br engine technologies" which is basically a chart of heads vs blocks, from EJ20 to EJ257, stating which fit on which, and giving the CR based on the headgasket used. 15 distinct HGs are also listed with their respective bore, thickness, and material. For some reason the PDF disappeared from the website recently, but I will scan it later this week and post/send it - seems it could be VERY useful for you guys. I actually used to change HGs on my EJ251 for thinner ones. No info on EJ254 or EJ253 block/heads though.


Edit: after months, the file is actually back. Enjoy!
http://www.b4et.com/docs/cr_matrix.pdf

Last edited by Bluefoton; 08-15-2011 at 11:38 PM.
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Old 08-16-2011, 07:21 AM   #16
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Quote:
An EJ255 block will take any heads (EJ20G to EJ257) except for those an from EJ251.
I wonder how they came up with that?

Jay
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Old 08-16-2011, 09:11 AM   #17
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Quote:
Originally Posted by Bluefoton View Post
Highflyr: an EJ251 block with EJ25D heads will result in:
- a 9.6 CR with 11044AA610 HGs which are 1.37mm thick.
- a 10.4 CR wiith 11044A642 HGs which are 0.56mm thick

You can also use heads from EJ20G, EJ20K, EJ20R and EJ22T . The first three will yield the same CR / HGs numbers as posted for EJ251 heads; whereas for the EJ22T heads you will have respective compressions of 11.4 and 10.4. Again, same head gaskets.

An EJ255 block will take any heads (EJ20G to EJ257) except for those an from EJ251.

Not pulling this from my derriere - I have in front of me a page from "br engine technologies" which is basically a chart of heads vs blocks, from EJ20 to EJ257, stating which fit on which, and giving the CR based on the headgasket used. 15 distinct HGs are also listed with their respective bore, thickness, and material. For some reason the PDF disappeared from the website recently, but I will scan it later this week and post/send it - seems it could be VERY useful for you guys. I actually used to change HGs on my EJ251 for thinner ones. No info on EJ254 or EJ253 block/heads though.


Edit: after months, the file is actually back. Enjoy!
http://www.b4et.com/docs/cr_matrix.pdf
Thanks for the great chart!
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Old 08-16-2011, 12:28 PM   #18
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I'm not sure why you want to run the DOHC. It is technically a worse head. Despite the top end performance stock, it has a LOT less mid range torque. As well, the SOHC only needs sport cams to get the top end the DOHC has. The actual design of the SOHC is superior. I would seriously just stick with the SOHC heads, toss in some Delta 2000 cams decently cheap, and call it a day if all you're looking at is a little more power and top end. If you're really compelled, TWE does have high compression pistons if the block's out, and you don't mind popping in some new pistons. You could grab the exhaust header too and Crawford's SRS-30 ECU flash too and make a good chunk more power, if you don't mind sitting at 91 octane from now on.

There are a lot of things you can do, but stepping back to the old DOHCs isn't exactly a good route.

p.s. Cobb wrote up a tech article a while back investigating the SOHC and DOHC cams and their differences. I'll attach a Word document copy of the article they wrote. This is a ZIP file. I will repeat this. It is a ZIP file. It is merely .pdf only because RS25 has size restrictions on file types. PDFs could be bigger, so I just wrote .pdf to have it accept the file size. However, this is a ZIP file of the compressed Word document, just so there's do confusion when trying to open it and Adobe Reader is telling you it's not a PDF.
http://www.rs25.com/forums/attachmen...0&d=1307648934
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Old 08-16-2011, 01:21 PM   #19
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I'm using the DOHC heads because that's what I have and that's what the car came with. I don't have any SOHC heads and don't want to deal with rewireing half the car to get the heads to work. I'm just replacing the block with an updated one and maybe get a little extra out of it.
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Old 08-16-2011, 02:20 PM   #20
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Quote:
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I'm using the DOHC heads because that's what I have and that's what the car came with. I don't have any SOHC heads and don't want to deal with rewireing half the car to get the heads to work. I'm just replacing the block with an updated one and maybe get a little extra out of it.
You're a smart man.
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Old 08-16-2011, 02:39 PM   #21
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Ah, I misunderstood. I assumed you had a SOHC engine and wanted to toss on DOHC because of the "mad top end yo." I didn't realize you were just grabbing a shortblock to replace a damaged one.
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Old 08-17-2011, 09:55 AM   #22
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Here's a picture of the pistons in the engine I just picked up.

https://picasaweb.google.com/lh/phot...eat=directlink

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Old 12-13-2013, 07:49 PM   #23
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Bringing this back from the dead.

Tossing around the idea of a 251/25D heads w/ STi HG's. Is it worth it over a 251/22E heads (delta cams)?
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Old 12-17-2013, 12:24 PM   #24
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Quote:
Originally Posted by Baddog909 View Post
Bringing this back from the dead.

Tossing around the idea of a 251/25D heads w/ STi HG's. Is it worth it over a 251/22E heads (delta cams)?
Not really. It would pull a bit more up top compared to a full ej251 block though. Do you already have the ej25D phase 1 heads? Any particular reason for wanting to do this?
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