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Rb30 Bottom End With Neo Rb25de Head

25GTV

By 25GTV,
in Engines & Forced Induction

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gabzr34 Enthusiast

gabzr34

Posted
Posted

I am pretty sure nothing needs to be changed, you may need lower mounts as the rb30 bottom i think is 38mm bigger. I am also sure rb25 pistons will fit but may not be the best option you should go with, forged pistons will definently be the best option.

Aftermarket ECU is a must have and with a dyno tune you should be set mate.

R34GTFOUR Mentor

R34GTFOUR

Posted
Posted

this is exactly what im going to be doing, but i will be smacking GT35R on the side of mine :(

The neo head has slightly smaller combustion chambers than the normal rb25/26 head, its somewhere around the 60cc per pot compared to 64ish cc in the normal head. This makes quite a bit of difference to the CR.

With the na rb30 pistons, a deck block, thin hg and the neo head, that would have to net around the 10:1 if not higher. I think the na rb25 pistons might be a tad too much but just grab one of the online CR calculators and start plugging in numbers and you'll see what you'll need. I havent really looked that much into the na side of things since will be going the turbo route, but with mine acl rb30et pistons, neo head, decked block and a 1mm hg will get around the 8.5-9.0 CR mark. Obviously with the na route you would want much more than that

R34GTFOUR Mentor

R34GTFOUR

Posted
Posted

if you are using the neo head and want a high compression turbo motor (RB30DET), grab the flat top CP pistons that spool sell in his kit for the normal rb25/30. Depending how you set up the motor, you'll get anywhere from 9.0 to 10:1 CR, i doubt you'll want more than that

I want mine around the 8.8 mark, still responsive but will still like some boost :)

25GTV Experienced

25GTV

Posted
  • Author
Posted

Im aiming to run everything as standard just with the 30 bottom end and 25 pistons switched. Then a safc will prob do for the extra fuel. Wat machining is required? and do i need a better oil pump than the vL one?

R34GTFOUR Mentor

R34GTFOUR

Posted
Posted (edited)
You will need water pump collar and to relocate a pulley.

Google "RB30DET" and .pdf. there is an awsome file out there.

i'm going to take a stab in the dark and assume you meant oil pump collar instead, but thats only if he uses a widenose gtr pump :D

Edited by R34GTFOUR
R34GTFOUR Mentor

R34GTFOUR

Posted
Posted

if its going to be a daily the rb25 pump will do the trick, you wont need the crank collar sine the rb25 runs a narrow nose crank like the rb30

If you are going to spend abit of $$ on the conversion and track it abit, an upgraded oil pump is good insurance

  • 3 years later...
Gerg_R31 Mentor

Gerg_R31

Posted
Posted

before this goes any further, and before a motor blows up

a neo head has a smaller chamber, ive measured them between 52 & 55ccs

in the tech section there is a simple maths formular i wrote up to work out your actual compression ratio, guessing = problem waiting to happen

flat tops with neo head estimated around 9:1 static

  • 2 weeks later...
  • 1 month later...
docaam Rookie

docaam

Posted
Posted

before this goes any further, and before a motor blows up

a neo head has a smaller chamber, ive measured them between 52 & 55ccs

in the tech section there is a simple maths formular i wrote up to work out your actual compression ratio, guessing = problem waiting to happen

flat tops with neo head estimated around 9:1 static

So as OP posted what kind of compression it will reach Neo head and 30 block, couldn't find the answer and really bad in calculating compression I am looking around 11 for my NA setup

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