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Old 12-18-2005, 10:05 AM   #1
FuJi K
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Default Head ports comparison

Here are pics of different heads from USDM to JDM variations old skool and new skool.

The REST of the head pics are all on PAGE 6 on post # 135 and down.
http://forums.nasioc.com/forums/show...1#post20924511


The MUCH TALKED about BIGport and SMALLport port runner casting style found in USDM/EURO/AUS WRX STi's
bigport

smallport



USDM WRX/STi/STI/FXT/LGT turbo models as of current PHASE 2 head


JDM STi PHASE 2 head





JDM Version 6 big port gallery
http://forums.nasioc.com/forums/show...1#post26035191

Head tech talk
http://forums.nasioc.com/forums/show...t=springs+sohc

EJ20G and '96 EJ25D pics
http://forums.nasioc.com/forums/show...5#post21618155

Combustion Chamber comparison EJ205/EJ255/EJ257
http://forums.nasioc.com/forums/show...1#post25994221

Last edited by FuJi K; 06-24-2009 at 01:36 PM.
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Old 12-18-2005, 10:41 AM   #2
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Yes the RS DOHC heads are better then the WRX heads but they still dont compare to a RA STi head. With a nice turbo like the GT30 the STi heads will make much more power then the WRX heads. Another plus with STi heads are the cams. A drawback to the RS heads is the intake mani, it only fits the NA DOHC heads.

Get rid of the wrx heads, they are only slightly better then the EJ22t heads
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Old 12-18-2005, 11:20 AM   #3
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we're just looking at the ports, cams and other things can be delt with (JUN 272* on these phase I DOHC; same as STi I-IV. I'm looking at a custom intake manifold.). So to speak these Phase 1 2.5L NA heads seems to flew very well. The SOHC flow at around 240cfm in 25" water on the intake port side from Cobb's site. The Spec C heads supposely flow 260cfm in 28" of water on the intake port side from what I've read. The DOHC 2.5L shouldn't be much different. The cams are a bit different in lift from the DOHC and the SOHC in numbers, the SOHC had slighty higher lift thus like somewhere like 7cfm more in the higher revvs IIRC.

some pics from another thread.


USDM STi head port

Last edited by FuJi K; 04-09-2008 at 12:00 AM.
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Old 12-18-2005, 01:12 PM   #4
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here's a few more comparison pics


Quote:
Originally Posted by Hurley 2.5 WRS
ill look. you want width and lenth? i know the divider looks like the version 6 did.

these are Version 4 STi type RA heads

EDIT: all measurements done with a digital caliper.

length in bolt direction: 58mm

width including injector boss: 48mm
my RS 2.5L DOHC measures
length in bolt direction: 59mm

width including injector boss/tongue: 44mm

Now we go back up and look at the ports on my heads. *hummmmm....*

Last edited by FuJi K; 12-18-2005 at 01:47 PM.
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Old 12-18-2005, 06:04 PM   #5
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Rac's Ver 3 heads look alot like DOHC NA heads and even have the inline bolt pattern. I think its safe to say these heads are from the same or very similar casting. I wish I had dimensions for this head port, it might be slightly larger then the NA DOHC.

The NA heads really need some port matching!
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Old 12-18-2005, 06:33 PM   #6
FuJi K
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The JUN cams for the STi Ver 1-4 fit the DOHC 2.5L NA heads. So to speak these 2.5L NA heads are pretty big. flowing approx up to 240cfm@.3xx" lift (SOHC 2.5L flow 240cfm, I don't see how the DOHC would flow differently) compared to the Spec C's 260cfm@.4" lift. it's not too far off on the intake ports.
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Old 12-18-2005, 10:41 PM   #7
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Flow benches are like dynos, they shouldnt be compared. It is very hard for me to believe that a Spec C only flows 20 cfm more then a NA head. But I dont have any info on valve size. If the valves are they same size then it might be possible. The Spec C has a HUGE intake port compare to any NA head but maybe that doesnt help flow that much.
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Old 12-25-2005, 08:21 PM   #8
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Quote:
Originally Posted by Scoobie Steve
Flow benches are like dynos, they shouldnt be compared. It is very hard for me to believe that a Spec C only flows 20 cfm more then a NA head. But I dont have any info on valve size. If the valves are they same size then it might be possible. The Spec C has a HUGE intake port compare to any NA head but maybe that doesnt help flow that much.
but they arn't dynos. They where flowed on water based flow benches in the same 25" of water. But this is just the intake side, remember. 20cfm is a bit. BUT LOOK at the port though, and look at the USDM WRX and the Spec C or the Type RA ones, the DOHC NA 2.5L has a very large port as well.

The pictures are there..... the 240cfm is from Cobb's flow bench. the 260cfm Spec C is from off NASIOC here from researching.
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Old 12-25-2005, 09:16 PM   #9
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Your numbers are from two different test pressures and CANT be compared. They are even two different lift heights. If the same test pressure and lift was used it would be less then 20cfm, probably showing the NA head to flow more then the STi. You can measure flow at many different pressures. To compare they have to be the same pressure and really should be the same flow bench. Also many people flow heads without using a simulated cylinder. Flow benches are like dynos they are good for a before and after number, not for comparing. There are just to many varibles in the setup to accurately compare numbers.
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Old 12-25-2005, 10:14 PM   #10
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is it hard to believe an NA head flowing pretty well?

Here are some V8 heads. The inlet where the intake manifold bolts onto seems larger but look at the splitter, very similar to the NA heads. The port entry on the NA 2.5L head looks like the older heads because it's a phase 1, but the casting on the inside looks a lot like Spec C and the V5/V6 Type RA
http://forums.nasioc.com/forums/show...jdm+head+heads

isn't testing on H2o just water pressure with gravity? Cobb's is in 25" of H2o


http://forums.nasioc.com/forums/show...jdm+head+heads
Quote:
Originally Posted by Ver.III
The 98 RS DOHC heads looked identical to my V3 and a set of early EJ20G heads from a 96 Sti RA . That includes the combustion chamber. Only difference with the NA heads was the valve gear and the oil drain hole that was used for the turbo was blocked.

Last edited by FuJi K; 12-25-2005 at 10:34 PM.
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Old 12-26-2005, 01:44 AM   #11
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good info guys.

now anyone want to let me have there V6?
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Old 12-26-2005, 04:22 PM   #12
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Its not hard to believe NA heads flowing well. It is hard to believe they flow better then Spec C. I am not questioning the fact that DOHC 2.5 head are very similar to early JDM heads. They are not like Ver 6 RA heads or Spec C heads.


What we need are flow numbers from a NA DOHC head (which i have never seen) and flow numbers of a Spec C head on the same bench pulling the same Inches of water. You can not compare 25" and 28", there is a formula to convert them but i dont know how.
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Old 03-25-2013, 09:13 PM   #13
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Quote:
Originally Posted by Scoobie Steve View Post
Its not hard to believe NA heads flowing well. It is hard to believe they flow better then Spec C. I am not questioning the fact that DOHC 2.5 head are very similar to early JDM heads. They are not like Ver 6 RA heads or Spec C heads.


What we need are flow numbers from a NA DOHC head (which i have never seen) and flow numbers of a Spec C head on the same bench pulling the same Inches of water. You can not compare 25" and 28", there is a formula to convert them but i dont know how.
Hey Steve, it seems like you know a fare share about the differences in all these heads. Are the ver6 sti RA/R & RA/R WRC heads different from the reg Ver6 STi heads?
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Old 01-09-2006, 11:21 AM   #14
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The NA 2.5L heads don't flow better than the Spec C, but very well for what it is. With some porting it can flow as much as Spec C's or comparable with other ported heads as well with some porting work.

Supposely we have 2 different port designs.
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Old 01-10-2006, 07:30 AM   #15
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nice thread. any way to tell what heads they are from the ports? any distinguishing factors?
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Old 01-10-2006, 11:47 AM   #16
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Quote:
Originally Posted by Scoobie Steve
Its not hard to believe NA heads flowing well. It is hard to believe they flow better then Spec C. I am not questioning the fact that DOHC 2.5 head are very similar to early JDM heads. They are not like Ver 6 RA heads or Spec C heads.


What we need are flow numbers from a NA DOHC head (which i have never seen) and flow numbers of a Spec C head on the same bench pulling the same Inches of water. You can not compare 25" and 28", there is a formula to convert them but i dont know how.
Steve,
Ask and you shall recieve. All four USDM heads (EJ205, Ej25 SOHC, EJ25 DOHC, and Ej22t) along with Cobb ported Ej25 SOHC heads thrown in to boot. Intake and exhaust, and thanks to Wedge for hosting...



And for reference, my SOHC Ej25 heads after porting were 267cfm intake and 216cfm exhaust.

Lastly, everything I have been able to turn up suggests that the '98-99 EJ25 DOHC heads are no different than Ej20K standard WRX heads. Yes, the HKS cams drop right in. Xephyr ran them for about a week. He didn't like them. He picked up about 20whp over the stock NA cams, but it was just too peaky. He lost a lot down low and went back to the NA cams. Those HKS cams are now used in an NA Ej25. In that configuration they are a lot of fun. Power comes on around 4200 rpm like the thing has got V-tec, and shoots all the way to the 7000rpm shift...
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Old 01-10-2006, 03:48 PM   #17
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Thanks Matt, do you know the test pressure that was used for these? 28"?
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Old 06-25-2006, 11:22 AM   #18
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here now the testing on the flow benches......the Spec C head was tested on 28" of water.......Cobb tested on 25" of water.......now that's 3" of difference, meaning that...with more water, it will have to push more water through the ports....

BUT I tell you what though, last night I got a local member to bring out his JDM STi Version 7 heads and WRX head (same or similar casting as the USDM STi heads; Liberty heads) for comparision. We look everything over. The intake ports ARE the same from the 2.5 DOHC NA heads and the JDM STi Ver 7, pressure sure the exhaust wouldn't be any different. The valve size are the SAME in intake AND exhaust; just that the Ver 7 are sodium filled. The splitters & valve guide all looked IDENTICAL. That cleared up A LOT of questions. We're planning on CC'ing the ports to see how much difference in port volume. But so far from what we can tell....it's just the same size, only slighty different where the injector boss is. So believe what you want to believe, we bought looked over everything.

And how are the Spec C heads different from STi heads?
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Old 06-25-2006, 12:52 PM   #19
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There are 2 different Ver 7 heads. Large port and small port "JDM and import". The Import heads are junk and cant be compared to a JDM head. I would be interested in port CC numbers but you need to find a real Ver 7 JDM head.
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Old 11-08-2006, 09:04 PM   #20
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Quote:
Originally Posted by Scoobie Steve View Post
There are 2 different Ver 7 heads. Large port and small port "JDM and import". The Import heads are junk and cant be compared to a JDM head. I would be interested in port CC numbers but you need to find a real Ver 7 JDM head.
yes, the STi head and then the STi spec C head...I would be very interested in the seeing a cc comparison of pretty much all the heads (minus the ej18 and ej22 sohc).
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Old 06-25-2006, 04:30 PM   #21
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well....."bikerboy" says it is a JDM Ver 7 head...so...ya, he knows his stuff.
But ya, we're going to CC the ports to see where it is. We'll probably do a ported WRX head, stock WRX head, DOHC 2.5L NA (dunno what to call 'em), and the JDM Ver 7s.
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Old 06-25-2006, 10:12 PM   #22
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WRX or liberty heads are not even close to a JDM Ver 7 head. Post some pics of this "JDM" head and I will tell you if it really is JDM.
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Old 06-25-2006, 10:22 PM   #23
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Becuase everyone knows Scoobie Steve is the authority when it comes to JDM heads
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Old 06-26-2006, 01:15 AM   #24
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What we were just looking at are the INTAKE PORTS. And I can tell you that his Ver7 heads and the 2.5L NA head ports are very identical. We even compared valve size. We even talked about the camshaft where it was seated differently, and how the combustion chamber was milled differently.

I know the WRX heads or Liberty heads don't come close, I've seen the intake ports myself. When he brought that Ver7 head I looked at the intake ports, I was like gah damn it looks just like mine. He can come in here and give you word....since it IS really hard to believe everything on the internet anyways....

Last edited by FuJi K; 06-26-2006 at 01:21 AM.
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Old 06-26-2006, 10:59 AM   #25
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And I am telling you that a JDM ver 7 head and 2.5 NA head intake ports are not even close to being identical.

You can compare the picture of my Ver 6 heads in this thread to the pics of the 2.5l NA head and see the HUGE difference.

Maybe the Import Ver 7 head has ports like the 2.5 NA head.
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