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Rb25Det Neo Head On A Rb30

r33skylinegts

By r33skylinegts,
in Engines & Forced Induction

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r33skylinegts Contributor

r33skylinegts

Posted
Posted

hi.all the posts and info i've read usually on say how to fit the r33 rb25de/det and rb26 heads on the rb30 but whats involved fitting the rb25de/det heads.do all oil and water lines line up.i've read the neo heads ccs' are smaller then the r33 rb25 heads.what comp ratio will it give with the stock rb30 pistons.if it bolts straight up as the rb25 with the the vct and front water gallery mods can i use the stock rb30 pistons.sorry for all the questions

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https://www.sau.com.au/forums/topic/383259-rb25det-neo-head-on-a-rb30/
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Gerg_R31 Mentor

Gerg_R31

Posted
Posted

They have 10-12cc smaller chamber, it is pretty much the same as putting a vct head on, make sure you get the right pistons to suit or your comp will be too high for turbo

only oil line that doesn't line up is the vct feed, have it welded as grub screwing it will leak

urtwhistle Proficient

urtwhistle

Posted
Posted

I personally used Mahle 8.5:1 Rb30 pistons from the US. shaved the block 20thou to get a 0 deck height. The head was skimmed to make sure it was flat and using a standard nissan head gasket and to my knowledge I don't have any issues with excess comp and pulls like a freight train in it's midrange (I haven't given it a good hiding since it's only street tuned to about 5krpm)

R34GTFOUR Mentor

R34GTFOUR

Posted
Posted

Theres are a few differences, with the head chamber being smaller as mentioned above..

I have my head neo cc'd and each chamber came in at 53ccs, so if you used the "normal" pistons in a rb25/30 then the comp ratio would go through the roof.

I've purchased ACL RB30ET pistons with the -4.5cc dish in the piston which is just an off the shelf item. Based on my calc, with a bore of 86.5mm, 1.1m headgasket, 0 deck height (i.e. shave to block by 20thou) you get a comp ratio of 8.8:1 - which is pretty spot on in my books.

Also the VCT feed is definitely different and you have to use the drill/tap method for the oil feed at the front of the head for it to work again. Just make sure you have it grub screwed/welded to block it off as mentioned above.

Other than those two, everthing else should bolt straight up as a normal rb25 head:)

r33skylinegts Contributor

r33skylinegts

Posted
  • Author
Posted

thanks for the replies guys.im busy gathering as much info as possible.starting my rb25/30 build in the new year.so if you use the stock rb30 pistons would the comp be good for a n/a motor then.one more question.can sr20 and/or vg30dett rod bolts be used as an upgrade for standard rb30 rod bolts.

Gerg_R31 Mentor

Gerg_R31

Posted
Posted

If this is a budget build then i recommend to do a bit more research and save a bit more coin to do the job properly the first time, with using all the right parts

Links below, 1 is a tutorial i wrote up to give the basic understanding of engine internals

2nd is a link to the tutorial section, there is alot of useful information there other members have written up

3rd is the members project threads, look what others have done and see what ideas you can use or adapt things they've done for your intentions

http://www.skylinesaustralia.com/forums/topic/378823-engine-internals-comp-ratios-general-info/page__pid__6104330#entry6104330

http://www.skylinesaustralia.com/forums/forum/57-tutorials-diy-faq/

http://www.skylinesaustralia.com/forums/forum/190-projects-overhauls-and-build-ups/

  • 5 months later...

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