S2 Rb25det Head Porting Question

[WizardBlack]

Hello, I have my S2 RB25DET that I am tearing apart (after being imported) to bring everything up to new condition (or maybe a bit better ). During the disassembly of the head, I noticed bumps in the exhaust ports right at the flange surface that go into the runners 3/4" or so. They seem like they might merely be a reinforcement of the exhaust stud holes, but it seems a bit overkill for such large bumps. Is it possible to port these all the way out? Is there perhaps a coolant jacket waiting to pounce on me if I try to remove them?

TIA,

Mark

Edited November 21, 2009 by WizardBlack

[Cjmartz2k]

The only reason they are there is to match the hump that's in the exhaust manifold. Loose it. That's really the only major thing that needs done for a street port on an RB25/26 head other than polishing the bowls and matching up the intake ports.

[WizardBlack]

The only reason they are there is to match the hump that's in the exhaust manifold. Loose it. That's really the only major thing that needs done for a street port on an RB25/26 head other than polishing the bowls and matching up the intake ports.

Thank you for responding. I didn't even think of the factory exhaust manifold. Might I ask a few more questions?

In admiring the RB26 valvetrain, might you be able to install this into a 25 head?

Are the cam journal, height, etc. dimensions different?

How would the Tomei solid lifter setup in a 25 compare to a factory 26 valvetrain?

Does the Tomei lifter kit allow you to utilize 26 cams if you somehow deleted NVCS oil journals on the head?

The bottom line is I really want the solid lifter setup (like my previous engine; L28Et) of the 26; presuming that is most of the flow/rev difference between the Series 2 R33 RB25DET head and RB26DETT head.

[jarrod83]

Hey I have just pulled apart my car for a rb30 conversion and noticed the exhaust ports as well having the little bumps in the corners to direct the airflow for the standard manifold as well and decided to give the head a bit of a tidy up myself. I was wondering if anyone had any back to back results from a some minor port matching and polishing...I did do a search but only found a post where someone claimed that because of the restriction of the turbo being greater that it wouldn't make much of a difference

Wizard back can i ask what sort of mods you are doing? I think generally the stock 25 head is good for about 500rwhp standard with the appropriate turbo, if you are after considerably more its generally cheaper and easier to just buy a rb26 head, i dont think any of the rb26 parts from the head can be easily transferred to a rb25

Jarrod

[WizardBlack]

Hey I have just pulled apart my car for a rb30 conversion and noticed the exhaust ports as well having the little bumps in the corners to direct the airflow for the standard manifold as well and decided to give the head a bit of a tidy up myself. I was wondering if anyone had any back to back results from a some minor port matching and polishing...I did do a search but only found a post where someone claimed that because of the restriction of the turbo being greater that it wouldn't make much of a difference

Wizard back can i ask what sort of mods you are doing? I think generally the stock 25 head is good for about 500rwhp standard with the appropriate turbo, if you are after considerably more its generally cheaper and easier to just buy a rb26 head, i dont think any of the rb26 parts from the head can be easily transferred to a rb25

Jarrod

I am after as much as I can get; just like anyone else. :-) In all seriousness, I am just tearing the entire engine apart (after importing) to clean it all up and rebuild. My car was at 2500 pounds (with a full tank) before switching from an L28Et to the RB25DET, so I'd imagine 400 whp sounds good. At the moment, this is just the basic stuff to get it into the car. I don't plan on taking the head back off when I upgrade the turbo, etc., so I wanted to get it fixed up now. When I have all the supporting stuff done, I was considering swapping to an RB26DETT. Getting a 26 head by itself is not cheap in my neck of the woods, unless I can coax an SAU member to export to me. :-) I could always export some Summit stuff in return (since I am in the same state with them). :-)

I suspect no one has a back to back comparison since you usually do much more than just that for a dyno check.

Edited November 22, 2009 by WizardBlack

[Cjmartz2k]

Are you in Ohio? I'm from Cleveland! 26 head casting flows the same as a 25 BTW. Only advantage is solid lifters, different cams, and the intake. You can do all of those aftermarket style, but the solid lifters are vastly over rated for a street car with mild cams and a smallish turbo IMHO. So are the ITB's.