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Old 09-20-2006, 07:48 PM   #45
FuJi K
Scooby Guru
Member#: 3687
Join Date: Jan 2001
Chapter/Region: MWSOC
Location: St. Paul, MN
MY99 GF4 JDM 6spd
NF Performance


Originally Posted by Hurley 2.5 WRS View Post
even the V7 smalls are big, there are ones that are even larger, ie: large ports, either way you go, itll be ok, youre just starting fires cause you think things and youre not necessarily correct.

the small port head is gunna be better for response and lower end, due to higher port velocities. theres pros and cons to each head, but your argument of EJ25D heads are EXACTLY the same is just stupid, almost childish. stop

and the K "era" heads had the triangle quench, which didnt quench well with that era turbo piston design
The STi Ver7 head is stamped with RHT20. This stamp is also found on the STi Ver8 Spec C. Comparison pic of a LHS20V head stacked on top the "SMALL PORT" RHT20. I cut away a few spots so you can SEE.

What I'm saying is same are the D-style port castings (you can't seem to catch that). All the big port heads seem to have this style, which is why I was thinking that it may be one of the first of the BIG PORT heads. The STi 7 heads that I compared mine to are slightly bigger, like 1-1.5mm in width from the splitter to the side wall of the port. My port entry however is wider but shorter from injector boss to the top.

How's your IMPORT small ports look like? Are the port runner castings the same like the USDM WRX/STi? You can't just say they're small. I just

want to know what to look for. What distinguishing factors?
CC'ing the ports would be the only way to tell if the ports are larger.

NOW....from further researching, the USDM DOHC 2.5L NA heads are based on the EJ20R head found on the JDM Legacy GTB. The other side of the port across the injector boss is filled in to increase velocity, thus showing some of the head when the gasket is fitted over. PORT this area and you'll have a NICE LARGE port like the EJ20G below.

Originally Posted by Matt Monson View Post
Fuji K,
I suggest you stop arguing with Steve as he is right. Last year about this ime a bunch of us measured head ports on various heads. I measured DOHC Ej25 heads at 54mm x 38mm and Steve measured his v6 ports at 57mm x 48mm. I am going to go with his gutt instinct on this and suggest you are dealing with small port v7 heads, and your friend, expert or not, doesn't know what he actually has there...
MY PORTs measure (do the calculation: 2 5/16" x 1 3/4")
58.7375mm across
44.45mm from injector boss to the top
NOTE: this is just the port entry. Where mine has the carbon buildup, that's where the STi Version 3/4 big ports are. That's where I'm short

the 4mm. It will even be as big as the STi Version 6 RA if this filled in spot is ported.

Where did your DOHC come from? Unless my head was from the '98 and yours from a '96? I'm trying to do a comparison and you guys arn't really helping. You guys aren't pointing out details at all. All you're saying is this is big port, this is small port. Where are the details we should be looking at? Splitter style, port runner style, splitter position,etc... BUT I'll just compare them so the rest of the BOARD can see

what's what.

Yes, my '98 2.5L NA DOHC heads are a stab smaller than the "BIG PORT" heads. They are based from the EJ20R engine with is found on the Legacy
GTB with the TT turbo setup. Combustion chambers are of the clover style. Valve sizes on my NA head appears to be same as with the RHT20 STi version 7 head. BOTH my NA head and the BIG PORT heads share the D-style port casting. The NEW heads seem to all have the larger injector boss
and sloped port to it. This USDM 2.5L DOHC NA head can be greatly improved on to flow LOTS of air. Only drawback is the intake manifold bolt pattern. You either find one that is the same or go custom and do whatever you want. I the only one who was actually comparing? ...such help, huh...whatever..
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