RB25 Head work.

[Chaos the Xile]

Ok after doing some dyno work on the S1 RB25, I want to upgrade the cams to Tomei Poncams 256 Degree, 8.50 Lift + Tomei Adj. Camgears and Belt. Now I want to change out the stock valve springs, but I'm a little curious about weither the RB25 NEO springs would provide any more stability over the stock springs. It was either going to be NEO Springs or Tomei Valve Springs. Just wanted input on this.

Also does JUN or Tomei make any aftermarket valve stems and retainers for the RB25? Or are the spring & valve sizes on the RB26 and RB25 the same, therefore interchangable?

[klh6686]

I'm 90% sure that NEO valve springs won't work because on a neo the valve is longer since the solid lifter is designed differently. I believe that case it the same on rb26's, due to the solid lifter as well. If you're baller, you can get gtr valves, valve seats, valve guides, springs, retainers, lifters and cams and swap all of it into the head and effectively have a gtr head. However, I don't know many people w/ that kind of a budget. Stick w/ springs made for the ECR33 rb25 and they will suit you fine.

EDIT: I decided to go grab some images to concrete what I was saying to prevent the jackass that's going to come on here saying that 'his boy' swapped gtr valve springs w/ no problem, etc etc.

Keep in mind the cam location will be the same

GTR and NEO valve and lifter looks like this: Notice the valve is only a few mm from the top of the lifter

RB25 (and vg30) look like this stock:

RB25 (and vg30) solid looks like this:

You can see the difference in height between the gtr lifter and the rb25 lifter. That difference is also a difference in the valve which causes a difference in valve spring.
Modified by klh6686 at 5:16 AM 12/3/2006

[ISUJinX]

Is that image showing two different cams? One small base circle and the other standard? When did the change come from hydraulic to solid lifters?

From what it looks like in the pictures, they changed the lock height on the valve, which would change the installed height of the spring (or greater seat pressure if you forced them in and reduced your spring clearance -bad idea-)

However, switching to solid lifters from hydraulic will reduce the effective duration of the cam because it wont have the same "stall" time at peak duration. The main advantage of hydraulic lifters is they open sooner and close later than solid lifters because of the internal spring. Also easier on valvetrain, but you can run higher spring pressures with solid lifters if the rest of the head is built to handle it.

To answer the question, I'd stick with the proper springs for your head, because changing them wont give any increased stability/durability over a good aftermarket spring. As far as IF the GTR stuff will swap over, somebody try it out and let us know :-p

(I kinda rambled a bit... so not all of it is pertinent to your question)

[Chaos the Xile]

ok so i guess it ECR33, Tomei cams, Gears, Belt and Springs. But what about retainers and valves themself?

[StricNyne]

i am curius about this as well, i got tons of rb26 info but none on rb25

[Chaos the Xile]

Yeah, true the RB26 is where I started then worked backward, but now that I have a RB25 powered car its like catch up... haha, The heads on the RB's are what really confuse me...