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Discussion Starter #1
I know is place is not a for sale tread but I think the GT-R owner should know this before I post this ad somewhere else.

I got a set of new JE pistons custom cut pistons for RB26DETT.
Spec:
Bore 86.5mm (0.5mm over)
Pin height 30mm
Weight 373g
Dome .140" = 3.5mm dome
chrome pins I think

I got a set of Sealed Power Premium rings, wrist pins, and true arc locks to go with the pistons. Retail @ $850. I'm willing get rid of them alot cheaper. make me an offer.
 

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what are the rest of the specs on the pistons?

Ring widths, ring grove spacing, pin diameter, pin height etc.
 
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Discussion Starter #3
Ring widths are 1,5mm on top and 2nd and 3mm oil rings. it's same as SR20DET. Ring lands are alot and even between top and second but I've not measure them yet so can't tell you the measurement. I wrote the pin height already 30mm. Let me now if what to know something else
 
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Discussion Starter #4
will they fit an rb25det??? are they overboard at all or factory
 
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I think the RB25 can be bore up to 86.5mm as long as you have enought metal on the block. But I can't be sure.
 
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what is the stock bore on that block? and why not an 89mm bore over?
 

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stock bore is 86 mm.

I would not want to go over 86.5 mm and compromise cylinder wall thickness. My next motor is at 86.5 mm with N1 pistons.
 
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hmmm thats odd, the VG30DETT can be bored to 89 over and have no problems. What is the biggest bore you can modify on the RB26? The reason I ask is because the motor is a 2.6L and I don't see why you can't bore more than a 86mm like you stated. That doesn't make much sense to me. What is the stock compression on the motor and also, why wouldn't someone be able to bore it out to a 3.0L if the block was treated and sleeved correctly?
 

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I for one would not want to bore a VG to 89 mm. There is just not enough cylinder wall left. If you have .180" of wall thickness and now you .040" out with your over bore, you have no margin for error with any detonation, instant cracked cylinder. I am not saying it won't work, cause it's been done. I am just saying I would not due it as the displacement increase isn't worth the cylinder wall thickness in my opinion.

Now on my Z31 I used a VG33 block and overbored it by 1mm to 92.5mm, AFTER I sonic checked the block to make sure I still had enough thickness left and there was no core shift. It made 577 to the wheels and 598 ftlbs at 27 psi.

YMMV

OS giken makes a 3.0 kit in japan. It costs 13k. It's a crank, rods, pistons, sleeves and a deck plate. Not many people use it. Most of the big tuners use a 2.7 stroker crank and only over bore .5 mm. They still split cylinders with just this small an over bore. They like to run LOTS of boost and lots of revs. Like 2.4 bar boost and 10k rpm.

Stock compression is 8.5:1
 
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