ej25 SOHC Heads vs ej25 DOHC Heads?

dropdfocus · Post by **dropdfocus** » Wed Feb 13, 2008 9:41 am

If you're looking for a set of EJ25D heads (2.5 DOHC), I have 2 sets available. I also have a pair of EJ25D intake manifolds too. I just cleaned out my buddy's garage & he's giving me everything to part out for him. By Wed/Thur I'll have pictures snapped of everything.

As for what has been said about the head swap & such, going with the EJ25D heads allows you to use the EJ20G/K/H intake manifold. Pure JDM goodness!

I did manage to pick up a JDM EJ20G intake manifold for my hybrid motor ($150 from a fool on NASIOC). Before I have everything installed, I plan on doing a mild port & polish on the intake. The only real problem with the JDM vs. USDM intake is that the original set up over in Japan was coil over plug design. So I need to make a braket to hold the coil pack where it would normally have mounts on the US model.

Post by **Legacy777** » Wed Feb 13, 2008 4:47 pm

I'd also suggest searching the archives and the board. There were some threads a long while ago where larry witherspoon was doing some research on what heads to use. I think there's a few other threads as well. Most give similar info, but may have some addition details.

smh0101 · Post by **smh0101** » Wed Feb 13, 2008 4:49 pm

Um... Whats exactly is a td04hl?

smh0101 · Post by **smh0101** » Tue Feb 19, 2008 2:58 am

PhyrraM wrote:Niether is 'better'.

Beyond simply saying SOHC or DOHC you need to where each one comes from.

SOHC is commonly refered to for both early BC/BF heads such as the stock Ej22t heads and also the heads on later (phase 2) Ej25s.

DOHC is really a bit of a cluster f**k. Ej20g, Ej20k, Ej20h are all DOHC. These are the most commonly discussed here. Ej205, Ej207, Ej255 and Ej257 are all newer (different ECU signals) and basically ignored on this forum. The early (phase 1) non-turbo USDM Ej25s also have DOHC heads.

Ej20g is BC/BF Legacy and early WRX (v1&2). Legacy heads have stub rockers while WRXs have cam-over-buckets. Both of these engines have the 'elbow' turbo inlet like our Ej22ts.

Ej20k is later WRX (v3&4) and is also cam-over-bucket. These engines have the under the manifold turbo inlet. There is also engines in these years Subaru labeled as Ej20g, but should be treated as Ej20ks because electrically and installation-wise that's what they are.

Ej20h is Legacy twin turbo. Electrically these are way out in left field from most other Subarus. But used just for the hardware, not the electrics, it's basically a Ej20k.

USDM phase 1 Ej25 heads are losely based on Ej20k heads. They only need existing bosses drilled and tapped for turbo oil and coolant lines.

The above heads are mostly interchangable because they all accept the same intake manifolds. The 'bolt in/plug-in" deal would be any of the above heads with an Ej20g intake manifold. For our cars the Ej20g intake manifold is prefered becasue it uses comapatable sensors and IAC. It is by all means not the only option.

The Phase 2 SOHC Ej25 head is a very good flowing head, but because it has no provisions for a turbo it seems mostly avoided.

The phase 1 SOHC head is what you have already got on a Ej22t.

Phase 1 and 2 refers to a mild redesign of the block by Subaru about '98. It appears mainly to adrress some problems that cropped up when Subaru 'factory stroked' the Ej20/22 series into the Ej25. Headgasket problems are the most notable. There are numerous improvements but the major ones were a change in the position of the thrust bearing on the crank, the size of the rod journals on Ej25s and structural improvements. As far as heads go there is little to concern yourself with as far as phase1 or 2.

So basically any jdm 2.0L DOHC setup is fine (minus twin-turbo) as long as I have the Legacy RS/V1/2 WRX ej20g intake manifold?

PhyrraM · Post by **PhyrraM** » Tue Feb 19, 2008 3:10 am

Up to a point, yes. Once they started calling them Ej205/Ej207 they are no good. Those are the ones with the newer cam sensor timing.

If it's Ej20x (where 'x' is a letter) then you can slap on:

1) an EJ20g intake manifold.
2) an EJ22t engine/intake manifold harness on said manifold.
3) an Ej22t coil pack and plug wires.

Then plug her in and go.

smh0101 · Post by **smh0101** » Tue Feb 19, 2008 3:16 am

Sweet! Thanks...

Is there a difference between the different heads? I mean, which flows the best?

Arctic Assassian · Post by **Arctic Assassian** » Tue Feb 19, 2008 4:43 am

the td04hl is a turbo that came on certain JDM wrx's and is capable of almost vf39 territory. Its got a bigger compressor housing than the td04l that came on the USDM wrx.

smh0101 · Post by **smh0101** » Tue Feb 19, 2008 4:47 am

So... how is its spool?

BXSS · Post by **BXSS** » Tue Feb 19, 2008 4:16 pm

Here is a long read on JDM TD04s.
http://forums.nasioc.com/forums/showthr ... ?t=1213890

smh0101 · Post by **smh0101** » Tue Feb 19, 2008 5:31 pm

Wow... That was a long read! Bu very informative...

Matt Monson · Post by **Matt Monson** » Mon Feb 25, 2008 5:10 am

smh0101 wrote:
PhyrraM wrote:Niether is 'better'.

Ej20h is Legacy twin turbo. Electrically these are way out in left field from most other Subarus. But used just for the hardware, not the electrics, it's basically a Ej20k.
So basically any jdm 2.0L DOHC setup is fine (minus twin-turbo) as long as I have the Legacy RS/V1/2 WRX ej20g intake manifold?

Two corrections here:

PhyrraM,
Even the twin turbo heads and manifold are fine. Just ask Douglas Vincent.

smh0101,
The Ej20H heads are actually HLA heads most similar to the Ej20G heads. The Ej20R heads, which were left off the list, are the last twin turbo heads and they are essentially the same as Ej20K heads.

Lastly, as for the comments about it potentially costing a fair bit more to make Ej22T heads flow for the desired power level, I don't know that I agree. The old Cobb flow charts that get passed around show the Ej22t heads to be about +/-15% less flow than Ej205 heads. A good port job will usually net you about +/-15% in flow. If you can get your ej22t heads ported and rebuilt for less than $500, then it's probably a cost effective approach worth considering.

Oh, one last thing. I have had several of those JDM td04's good little turbos. That's what's on my '91 SS that I sold at Christmas time. The car was putting out 240chp at 12psi on an Ej20G 2.0l engine. I don't know if Jeff has fiddled with it since he took the car home to Seattle, but I imagine that at around 1 Bar, that turbo could probably put out somewhere around 275-295chp depending on intercooling and ambient temps...

smh0101 · Post by **smh0101** » Mon Feb 25, 2008 5:22 am

Thanks Matt...

So how would the stock heads PnP be with a 2.35l stroker, a vf-12, and 440cc injectors be? With a Perfect Power, exhaust, ic etc. of course.

With say 16lbs of boost?

Any idea as to hp?

PhyrraM · Post by **PhyrraM** » Mon Feb 25, 2008 5:27 am

Matt Monson wrote:
PhyrraM,
Even the twin turbo heads and manifold are fine. Just ask Douglas Vincent.

So the Ej20h/r TPS and the IAC is compatable with EJ20g/Ej22t ecus? If so, that is nice to know.

BXSS · Post by **BXSS** » Mon Feb 25, 2008 5:35 pm

I have a JDM 90* TD04 on my EJ20G'd SS, I'm not sure if it is the same as the turbos listed in the above link (I saw a pic with a straight inlet) but it works way better than I thought it would.

I thought I was going to swap a TD05-16G on right away, but I was so surprised that I have not swapped a 16g onto my car yet.

I want to track the car as is with the TD04 to see what it could do.

dropdfocus · Post by **dropdfocus** » Mon Feb 25, 2008 5:42 pm

You'd have a bit of noticeable lag with the 16g vs. the quicker spooling TD04. Obviously the peaks out where the 16g keeps making power for the motor.

Of course if you have a 16g you don't "want" to use, I'd be glad to "use" it for ya Carlos.

BXSS · Post by **BXSS** » Mon Feb 25, 2008 8:01 pm

Yeah, I figured that the 16g would have some more lag.
I like the response of the TD04, but would like some more top-end.

I'm going to put a 16G on eventually, but I have to see what the TD04 can do.

As for 16Gs I now have 4, 3 Good 16s + 1 POS parts donor.
1 is pending sale & I'm going to keep the 2 other good ones (1 for use + 1 spare).
The parts turbo has a bent compressor blade + shaftplay like a mo-fo so its more or less a paperweight.

My friend/fabricator wants me to skip the 16G all-together & go straight to my t3/t4e - he says the 16g looks like a cookie (he runs a GT45R) & is a waste of time.

Post by **Legacy777** » Mon Feb 25, 2008 8:05 pm

I don't know about all 16G's, but I wouldn't say the ported 16G I have on my car with associated mods spools that much slower then stock.

BXSS · Post by **BXSS** » Mon Feb 25, 2008 8:09 pm

Funny, the one pending sale has a very nice up-pipe match port (took about 30-45 minutes with a new carbide porting bit).
When I put one on the SS it will definatly get ported too.

Post by **Legacy777** » Mon Feb 25, 2008 8:10 pm

I had the turbine section ported, and the 90 deg inlet section ported.

The compressor outlet for the most part should be alright, at least that's what I've been told.

chochocho · Post by **chochocho** » Sun Mar 09, 2008 7:53 am

bxss, the turbo looks good. i am looking to get some porting done by a shop here in cali.

i hope to have the turbo installed in a few weeks. thanks.

smh0101 · Post by **smh0101** » Sat May 10, 2008 5:12 am

Can you use a 20g intake manifold with the 2.5l dohc heads? Or do you need the ej25d intake mani?

Can you use the 22t electrics with the 25d manifold?

PhyrraM · Post by **PhyrraM** » Sat May 10, 2008 5:23 am

Yes, you can use the EJ20g intake manifold with EJ25 DOHC heads.

I don't know if the IAC or the TPS on the EJ25D is compatable with EJ22t electrics. Also, EJ25D has EGR, the EJ22t does not.

smh0101 · Post by **smh0101** » Sat May 10, 2008 5:29 am

Um... EGR?

But if I used a 20g manifold everything would be fine?

asc_up · Post by **asc_up** » Sat May 10, 2008 6:16 am

EGR=Exhaust Gas Recirculation.

dropdfocus · Post by **dropdfocus** » Sat May 10, 2008 6:19 am

You make a block off for it. I'll be doing that for my setup (EJ20G intake, EJ25D heads, & EJ22T block). Since it's not required on the older cars, it can be blocked.

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ej25 SOHC Heads vs ej25 DOHC Heads?