Rb30 Bottom End With Neo Rb25de Head

[25GTV]

As topic suggests also can i use my 25 pistons for increased compression...

Just need some info cheers guys

[gabzr34]

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]

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

[dori34]

^ R34GTFOUR, im thinking of doing the exact same thing. i want to build a high compression turbo motor but if i cant get forged high compression rb25de pistons, im going to be doing 25/30 conversion instead.

[R34GTFOUR]

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]

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?

[GTS4WD]

You will need water pump collar and to relocate a pulley.

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

[R34GTFOUR]

  GTS4WD said:

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

Edited January 22, 2009 by R34GTFOUR

[GTS4WD]

Lol.. thats the one..

I cam back after work drinks yestureday and I just begin to type..

[25GTV]

wat if i just use the rb25 one?

[R34GTFOUR]

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

[25GTV]

In terms of keeping the vvt wat must be done?

[GTS4WD]

You will have to tap in to the oil galley and run an oil feed to it. The most common used feed is T’ing into the oil pressure sender feed.

[25GTV]

Oh ok so its that simple. I thought i needed to have oil passages welded up in the head... Will the head bolt on with welding mods if i decide to ditch the vvt?

[A31Shon]

iv got a neo 25de head and im building a 30det and just woundering if i should use the neo 25det oil pump instead of the standard one? or if a 25det non neo oil pump would be fine?

[Gerg_R31]

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

[luke gtr]

now youve all read that, blow up some motors and film results.

[docaam]

  On 22/01/2013 at 11:54 AM, Gerg_R31 said:

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