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Rb25Det Neo With Rb30 Block Build..need Info Please

Nuttyguy300
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Nuttyguy300 Explorer

Nuttyguy300

Posted
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Hi guys I'm new to this forum,

Ok iv purchased an rb30 block, it's been deck,honed, blue printed, balanced ,

New stock rb30 rods, race bearings, acl dura light pistons ra9301y 1.00 rib 0.025

Iv got a rb25det neo head that I plan on using for the build, I'm wondering what head gasket

I should use? Any info would be great please.

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GTSBoy
GTSBoy

Did you know that the Neo head has approx 10cc smaller combustion chambers than the normal RB25 head and that you must therefore use suitable pistons, not the same pistons that you would use for a nor

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GTSBoy Grand Master

GTSBoy

Posted
Posted

Did you know that the Neo head has approx 10cc smaller combustion chambers than the normal RB25 head and that you must therefore use suitable pistons, not the same pistons that you would use for a normal 25 head? If you don't, compression will be sky high.

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R32Abuser Mentor

R32Abuser

Posted
Posted

^^^ Exactly.

IIRC Neo heads have approximately 50-51cc chambers. R32/R33 RB25 and RB26 heads have 62-64cc chambers. This difference will shoot your static C.R. into the 10's if you dont get pistons suited to this head. That might be OK if your running E85 or race fuel, but definitely not on 98.

Read the RB30 thread and associated RB30 DOHC pdf. Its there for a reason.

It even states the brand of head gasket recommended for this build by many others on the forum. Im sure if you searched the R33 RB30 conversion thread, you might even get a part number.

R32Abuser Mentor

R32Abuser

Posted
Posted (edited)

Has anyone done the calcs to see what the static CR would be with a Neo head on a std RB30E or RB30ET short engine ?

I have wanted to, just haven't found the details regarding the OEM RB30 pistons. TBH I havent looked that hard as I already have a built RB30. But one day I wouldn't mind swapping the motor out to use the Neo head :yes:

From memory when I disassembled my RB30, the RB30 OEM pistons have a dome but to what extent (cc wise) I'm unsure.

Attached is my own calculator I used to work out my RB30's static C.R. Bare in mind, I used all metric units. So some converting may be required.

static compression ratio calculator.xls

If anyone can shed some light on the OEM RB30 piston specs, would be greatly appreciated.

Edited by R32Abuser
Nuttyguy300 Explorer

Nuttyguy300

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Ok but I've just read a tread where a guy is doing the same build. And has used the exact same pistons as me. The acl rb30et pistons with 1.1mm head gasket and it gave him a 8. Something compression ratio. I've seen 2 different forums where guys doing this build have used the same pistons that I am

wolverine Grand Master

wolverine

Posted
Posted (edited)

How can you expect an answer unless you give all the information including which pistons have been used and you have cc'ed the head?

Everyone will be guessing about your final comp ratio.

Just read the first post again (are the pistons you have listed 30ET pistons?)

Edited by wolverine
Nuttyguy300 Explorer

Nuttyguy300

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At the start of this post I put what my build was. Pistons etc. yes they are rb30et acl pistons . I haven't flow tested the head yet but guessing it will be around the same as every other factory rb25det neo head

urtwhistle Proficient

urtwhistle

Posted
Posted

Hey theres nothing wrong with using a neo head I know I have.

I used ACL 8.5:1 pistons on my 1st motor and Mahle 8.5:1's on my second. On the second I decked the head and also decked the block to a 0 deck height. standard nissan rb25 head gasket & I also run BP98 with no problems. I don't think you will have any problems unless your trying to put 65 psi of boost into it. but hey thats just my experience so far.

KiwiRS4T Grand Master

KiwiRS4T

Posted
Posted

I wish I had a Neo head. With stock pistons and the 33 head my compressions are 132psi (leak down test is fine) so I am guessing about 8:1 if I'm lucky. Only making 230-awkw at 15psi so soon to be retuned to 25 psi or as much as poss till it stops making more power (GT3540). I'm using a Tomei metal head gasket.

R32Abuser Mentor

R32Abuser

Posted
Posted

I wish I had a Neo head. With stock pistons and the 33 head my compressions are 132psi (leak down test is fine) so I am guessing about 8:1 if I'm lucky. Only making 230-awkw at 15psi so soon to be retuned to 25 psi or as much as poss till it stops making more power (GT3540). I'm using a Tomei metal head gasket.

Likewise.

Only thing I would change about my build.

discopotato03 Grand Master

discopotato03

Posted
Posted

In a perfect world a compact chamber with a flat or slightly dished piston giving the desired static CR and stopping approx 25 though short of the heads deck face works pretty well . IMO the dama is people using all kinds of weird and wonderful ways to get the CR they want ie thicker or thinner head gaskets . Few of these methods works best and ends up being a compromise . Making changes the worst possible ways can actually give you a low compression ratio engine thats not very detonation resistant .

I think if you could emulate a Neo engines pistons and static CR with a deeper dish or whatever you'd have a pretty good solution in a Neo RB30DET .

I would have thought by now plenty of people would have buretted std RB30E and ET pistos to get those volumes . Getting either engine to top dead center and placing a feeler gauge between the piston edge and a steel rule across the bore is not exactly rocket science .

I bet plenty an RB26 engine builder would have loved smaller chambers and flat or dished pistons .

A .

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