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headwork for RB25 (RB30 hybrid)

Bradyz

By Bradyz,
in Engines & Forced Induction

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Bradyz Rookie

Bradyz

Posted
Posted

Is it worth modifying the rb25de head or should I be looking for an rb26 one?

At present I'm looking at a port n polish, reground cams etc which will see a 15% flow increase. If i go the whole hog ( and almost double the cost) and get oversized valves etc it could be upto 35% increase, but is it worth spending that sort of cash on a RB25de head?

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https://www.sau.com.au/forums/topic/64638-headwork-for-rb25-rb30-hybrid/
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ace_nz Apprentice

ace_nz

Posted
Posted

you dont need to touch the buckets, to get back the lifter preload you loose buy reducing the base circle size on re-ground cams you need to increase the stem height of the valve, buy either welding the valve tip, using a lash cap, or if your doin a valve grind at the same time cut the seats deeper, wouldnt go deeper than about 20 thou. though

Bradyz Rookie

Bradyz

Posted
  • Author
Posted

Thanks for the input so far guys, just thought I should point out I wont be doing the work myself so talk about buckets etc goes over my head.

Haven't looked into cams to much, was gonna go with Tomie, but was told not to bother with Jap stuff as they can be made locally for a lot less.

More interested in wether or not to spend the cash on the rb25 head or start looking for a gtr one. Final target for car is 800hp.

Sydneykid Grand Master

Sydneykid

Posted
Posted
Thanks for the input so far guys, just thought I should point out I wont be doing the work myself so talk about buckets etc goes over my head.

Haven't looked into cams to much, was gonna go with Tomie, but was told not to bother with Jap stuff as they can be made locally for a lot less.

More interested in wether or not to spend the cash on the rb25 head or start looking for a gtr one. Final target for car is 800hp.

Go the RB26 top end, it WILL work out cheaper in the long run.:)

Bl4cK32 Grand Master

Bl4cK32

Posted
Posted

So what are the options for cams for the rb25de head?

Can u buy off the shelf items like 260 degree, 9.5mm lift cams for the head.....?

Or would you have to convert to solid lifters (how much for the kit?) and use cams designed for another head altogether.....?

non vvt of course in my case....

Cubes Grand Master

Cubes

Posted
Posted

It really depends on your final target.

My goal is ~300rwkw with 340-350rwkw for the odd run.

The RB25 head with a set of cams will do nicely.

At the time of purchase my Rb25 head was $750.

For the GTR head I was quoted over $2000, and thats if I could find one.

Now the GTR heads are cheaper and more common than they were 2-2.5years ago. :/

As I didn't buy the GTR head I was able to save that $1250 and put it towards getting the RB25 head rebuilt, ported/polished & inlet valves deshrouded.

I always knew I wasn't after huge cams as I want to keep respectable fuel economy. For myself the RB25 head suited my needs.

The RB26 head will make a little more mid range due to the use of higher lift cams.

I had to draw the line some where. :P

A GTR head not rebuild and stock with a set of aftermarket cams would have cost the same as my RB25 head rebuilt & worked slightly fitted with a set of aftermarket cams 260duration with say a 8.5mm lift.

I like things new, hence I wanted it rebuilt.

If I were to rebuild the GTR head and do a little bit of work to it sure it would flow slightly better than the rb25 head BUT it would have also cost me more.

Some thing a full time Uni student that works during the holidays doesn't really have much of when the build is already going to cost at least $12,000 in total.

DCIEVE, You sound like you are in another boat BUT remember one has to be realistic about their HP goals, 800hp is a LOT of hp and requires a LOT of money. ;)

You wouldn't want to be skimping on a set of what sounds like dodgy aussy reground cams for this build.

Sydneykid Grand Master

Sydneykid

Posted
Posted

Add it all up........

RB26 used "brand name" cams are much cheaper and easier to get than RB25 used cams

RB26 already has solid lifters

RB26 already has a good plenum and throttle bodies (Theo does 9's with them)

RB26 has better valves, standard

RB26 "brand name" exhaust manifolds are easier and cheaper to buy used

RB26 has 12 mm head bolts standard

RB26 doesn't have VVT, so no mucking around blocking it off or adding external feeds if you want it to work like an RB25

RB26 has superior water jacket around the exhaust ports, whic his important for high power applications

I could go on, but I think you get the drift......

If you add up the cost of the above, you will find even paying $2K more for an RB26 head is still cheaper. I bought a complete RB26 with a blown head gasket for $3K, sold the bottom end for $1500, sold the RB25 head for $600, sold the turbos for $400, used the std cams in an RB20 $300. So the RB26 head cost $200. It took me 3 months to find what I wanted so shop around, it's out there, have your money ready and move quickly the good ones go fast:cheers:

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