I disagree with just about everything that you said.
The GT30R is kinda small for a 25...
The 3076R is a perfect turbo for the RB25 if you want to drive it daily.
I have a friend here who's running a T-04R on his & even with that big of a turbo, he's in the boost VERY VERY quickly.
Boost might come on hard, but if it is a TO4R, it will not start to make good boost till after 3500. That is pretty laggy compared to some smaller GT turbos.
The biggest problems with the 25 is people don't tune them right & without proper air/fuel under boost,
This is the biggest problem for all turbo engines being built.
it's fragile pistons can't take the beating, due to it's relatively high compression.
The pistons are plenty strong. They just do not like to be detonated. Too many people are trying to run mega-high boost on questionable tunes, and not knowing if they have enough fuel supply. If you treat the engine nicely, it will make incredible #s stock. 570rwhp is the highest that I have seen thus far on a stock engine. There are probably higher #s by now though.
Other problems are the head's design (swapping a 26 head & putting real pistons in there would address the biggest problems)
The head design, port wise, is almost identical. The RB25 and RB26 heads have been flowed stock, and they are nearly identical on flow. The RB26 comes with a larger intake vavle than the RB25. That along with the bigger cams is "one" of the reasons the RB26 makes more power.
as well as the restrictive intake runner design...one cylinder is always starved more for air than all the others (I can't remember if it's #6 or...).
The stock intake is restrictive becuase of the small throttle body, and the long intake runners. The flow is actually pretty even from cylinder to cylinder on the stock RB20 and RB25 intakes. The RB26 intake manifold has a problem with the #6 port running too lean, due to the extra air flow.
Using an aftermarket intake will help, but the real answer once again is i the tuning.
Aftermarket manifolds will increase power, but are not necessary.
If you're going to use stock pistons, use a MINIMUM of a 1.5mm headgasket (Tomei or Apexi are preferred). Whatever you decide, good luck!
This is an old myth. There are plenty of 400+rwhp RB25s on the street with stock pistons, stock head gasket and stock cams. The stock head gasket is strong enough. You also do not need to lower the compression. 9:1 sounds like a lot, but if you can tune the car to run with absolutely no knock, then you will be able to make a lot of power on the RB25 with stock parts. I am running 19 psig boost and 20 degrees of timing on my stock pistons. No knock!
