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Rb25Det Neo With Rb30 Block Build..need Info Please

Nuttyguy300
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R32Abuser Mentor

R32Abuser

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Posted (edited)

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.

I've looked (for the past 10 minutes lol) for the pistons you state above. I cannot find them.

http://www.acl.com.a...80?OpenDocument

Apparently, duralite are only for 202 motors. Sure you dont mean another style of piston from ACL?

The only information (cc details etc.) I can find on ACL pistons is their Race series available in 2 styles for the RB30ET:

One with a 4.5cc dish (http://www.aclperfor...rgedPistons.htm)

and the other with a 10cc dish (http://www.aclperfor...orgedPiston.htm)

Key this into my static comp spread sheet above and you get:

4.5cc dish pistons with a Neo head = 9.06 static CR

10cc dish pistons with a Neo head = 8.42 static CR

Of course, this is ASSUMING you have a ZERO DECK HEIGHT on your block and the head is standard item and has a 51cc combustion chamber.

Edited by R32Abuser
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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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R32Abuser Mentor

R32Abuser

Posted
Posted

Also I have found some conflicting details regarding piston compression heights for some RB30 pistons. Obviously this will affect how the piston sits in the bore and therefore the static CR. So depending on these values the above static CR estimates may or may not be accurate.

This drives home the point to measure everything up before/during the build.

Nuttyguy300 Explorer

Nuttyguy300

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Thanks for that r32 abuser, Them numbers are what's on top of the piston, i typed that number in google and it came up with some one quoting these pistons as acl duralight, I do know that they are acl pistons tho, And that they Are for a rb30et , ok so the head is standard, will just be taking it to head works to get it checked and stuff like that befor I put it on,

And by zero deck hight do you mean the piston being

Flush with the top of the block, ? Because yep that's all been done, and I'm thinking my piston is the 4.5cc dish, now for what head gasket to be used? I'm looking at a steel head gasket but not sure of what thickness

R32Abuser Mentor

R32Abuser

Posted
Posted (edited)

Ok so your deck height is the distance between the top of the piston at TDC and the top of the cylinder as per "deck clearance" below:

squishband.jpg

Obviously if the piston sits above the cylinder, this will increase the static CR (all things being equal). Similarly, if the piston sits below the cylinder, this will decrease the static CR.

I used a cometic 1.28mm head gasket as recommended in the RB30 DOHC guide. You can also use a standard RBXX head gasket IIRC. Once again, the thickness of your head gasket is going to influence your final static CR so first measure up what your motor has been built to and try a few different thickness head gaskets in a static compression ratio calculator. See what value you get and go from there.

Edited by R32Abuser
R32Abuser Mentor

R32Abuser

Posted
Posted

Why don't you get your head prepped and cc'ed and double check the deck height and piston dish and tell us what compression ratio you want.

Hopefully can get an answer that won't be a guess.

Agreed.

wolverine Grand Master

wolverine

Posted
Posted

Ultimately I reckon a stock head gasket will be fine but it is such a pain in the arse if you have assumed incorrectly.

I have a neo head sitting in the garage and I was considering getting a basic RIPS bottom end sent over (which will probably be very similar to your setup) which would comp up nicely with a neo head but I will still double check everything before closing it up.

R32Abuser Mentor

R32Abuser

Posted
Posted

Bare in mind, 0.020" (aka 20 thousandth of an inch) is only 0.5mm. If those pistons are sitting 20 thou below deck height its enough to shift the static CR quite a bit. In my build its enough to shift the static CR from 9:1 down to 8.64:1.

Food for thought.

urtwhistle Proficient

urtwhistle

Posted
Posted

This is what I used on my first Rb30 6MKRY9608 http://www.aclperformance.com.au/NissanRB30ETForgedPistons.htm

and these on the 2nd build. that and there like $800.00 from the US or like 1200 if you buy them in Aus. NIS264405i05 http://www.us.mahle.com/C1256F7900537A47/vwContentByKey/W26HSFB8505STULEN/$FILE/2010%20AP%20complete.pdf

Nuttyguy300 Explorer

Nuttyguy300

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I email acl and they for all the info I need in this piston

Bowl volume 12.0cc

 

Comp Ht 31.10mm

 

Clearance & Position .025mm At 45.3mm from bottom of skirt

 

So now saying that my head has about 51cc chambers and block deck hight being 0.5mm what size head gasket will I need to get my compression good

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