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Rb27 Bottom End Build

32_Dave

By 32_Dave,
in Engines & Forced Induction

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32_Dave Mentor

32_Dave

Posted
Posted

Hey guys,

my 25's real sick atm and i wanna get my spare bottom end built up real quick as i want a spare or to replace the motor in September as I've got a big event later in the year. I've never gone down the track of rebuilding a bottom end, i usually just swap my head over to another bottom end, I just need to clarify what parts to use, i have done a search but there are still allot of things missing / i want to make sure i purchase the right stuff. The car currently is 360hp safe tuned on 14psi and is used for circuit / durfting. I want to make a strong / reliable bottom end to finish off the build. Don't want to chase huge HP either.

The plan is.

25 block

later model gtr crank with longer oil drive, 33GTR?

forged rod / piston package from USA (87mm) rods usually come with fasteners.

With the pistons is it worth changing the comp ratio or just leave it?

What crank girdle do i need, im guessing the rb25 one will work?

What bearings, i gather you use rb26 bearings, not understanding the tolerances necessary what sizing to i buy or do i get the machine shop to tell me what i require?

Headgasket, im gonna take a guess and say 1.2mm would be suffice, or is this another thing i have to get my machine shop to tell me what to get due to resurfacing? I also assume you get one with a 87mm bore.

Oil pump, just gonna use a N1

ARP fasteners top/bottom.

Another thing when it comes to oil control. Cars used for circuit and durfting. The head has non-VCT cams so should i block the VCT oil feed? And a 1mm restrictor in the rear feed according to sydkids topics, aswell as blocking the front feed. The front head oil drain back to the sump is that for VCT? And can i block it off as i have a rear external drain?

Is there any machining you would recommend?

Thanks !!!

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R31Nismoid Grand Master

R31Nismoid

Posted
Posted

Well for a start it wont be a RB27... With 26 pistons/rods you get somewhere around the 2665cc if memory serves correct.

By your post and comments it certainly sounds like you need to get a machine/assembly shop involved. Make sure you use solid ARP rod bolts as well.

Also what is the budget here?

32_Dave Mentor

32_Dave

Posted
  • Author
Posted

budget is around 2-3 for the bottom end, everything else i already have sorted out. i refuse to do a rb30. i just need more of a guideline to start with so i can order in some parts. don't want to miss my event.

Jaymie Rookie

Jaymie

Posted
Posted

You will need the matching girdle for the block you cant just use any old one as they are machined to size as a pair, as for bearings i would recommend ACL race series RB26 bearings, they come in two (2) sizes for standard journal size and that is 7M2428H & 7M2428HX, the HX's give you extra clearance than H's it all comes down to fitting them to your block and measuring the tunnel size then measure the crank and see what clearance you require.

Compression ratio between 8.5:1 to 9.0:1 will suffice.

As for camshafts if you want to run Non VCT then yes the VCT feed will need to be blocked off, to do so i normally tap the hole on the underside of the head and fit an A plug in it you also have to remove the brass segmented oil gallery plug at the front of the head and replace it with a normalplug like the rest of them and in the front intake cam journal the bigger hole also requires blocking. i would also leave the drain from the front exhaust side of the head to block in place as for restrictors you can fit some 1mm ones but if your retaining a hydraulic lifter setup i would not block one of them off as they require plenty of oil to keep them lifters filled up.

Also if not already done i would recommend drilling the 5 internal oil drains in the head and block to a bigger diameter.

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