Rb25/30 Or Full Rb25?

[Jonahs33Liner]

Hi guys, im new to the site and know theres a heap of info on this but i cant decide which is the best choice for the set up ive been running

I have a 33gtst with a complete rb25det series 1 5spd manual, a few weeks ago i was giving it all its got down the motorway and all of a sudden heard a bang from the engine, lost all compression an had no response until it came to a stop, had a look and found a hole in left hand side of my block, its abit bigger than the size of a 52mm tacho face. It had a fully forged bottom, heaps of head work, bigger cams, injectors greddy plenum, nearly everything was replaced with aftermarket gear, 4inch exhaust, t04z ran 25psi low boost and 42 high making 690rwhp, using a custom made switch wired to the microtech handcontroller to change my settings. It was only on low boost when the engine failed. The guy i bought it off and that built it has sadly passed away and he was the only one that knew the car top to bottom and who i spoke to if i ever needed anything. Ive pulled it apart and the only thing wrong with the head is one of the valve heads has snapped right at the start of the stem. Conrod 2 & 3 have big chunks out of the left hand side where im guessing it hit the block. I was considering building an rb30 block, fixing the broken valve and fitting the 25 head back on top because of the lag i used to get, the only thing stopping me is ive been so curious as to why that wasnt done before, maybe the 25 bottom was more suitable for its setup? Any advice would be muchly appreciated as i want to get the rebuild started asap cheers

Will post pics of the hole in block, head and bottom end internals in the next day or 2.

[XKLABA]

go the 30 fully fordged with that head, fixed of course, more torque, more power and better response, it's win win win really.

[Jonahs33Liner]

after reading alot about the conversion and the high numbers its pushing out that is what im most keen on putting in it, just wanted to find out if there was a certain reason why it wasnt done before when they built the rb25 bottom end and pushed out just under 700hp, with all the parts i already have i should only need the fully forged 30 block and extra pin drilled in for the tensioner to complete the rebuild if ive read the topics correctly? If theres anything else im missing or should do before assembling please advise me

[XKLABA]

could be as simple as he already had the 25 and didn't want to change engine number, if you have to start from scratch with a new block then a well built, well balanced fordged 30 is going to give better results then a 25 anyday of the week, same technology more capacity.

you can run the standed idler and tensioner wheel locations with a 150 tooth belt ( but they get close ) or a 152 tooth belt and move the tensioner or idler wheel,

other wise just read as much info as you can, everything you need to know is here somewhere, reseach as much as you can and devise how you want to go about building one, I will say pay alot of attention to oil control and crank case venting as these done wrong can kill a RB quick

[N1GTR]

One thread is enough, the one in FI can stay open