Rb25 S2 And Rb25 Neo Block The Same Or Not?

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guys/girls,

can someone please comfirm weather the rb25 s2 and rb25 neo block is the same block or not?

Just got my mechanic to put in the rod and and CP piston 9.0:1CP in the r34 block and it is heating the head.

Thanks in advance.

[KiwiRS4T]

The block might be the same but the rods pistons and heads are definitely different. It has proved difficult for people to get the correct forged pistons for the neo - they are usually not available off the shelf and have to be made hence a long lead time.You may find that your cr is in excess of 10:1 and the shape of the piston crown is not suitable. Did you compare the pistons you put in with the ones you pulled out?

[lilcrash]

Did you buy neo pistons? From what I've seen while looking for pistons for my neo is the pistons are nowhere near the same shape to an rb25 non neo.

You can get cp neo pistons on eBay for $800ish delivered.

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it is for non neo, but my mechanic bought the r34 block which he believed it to be the same.

What i bought was for non neo cp pistion with 9.0:1CP and Manley Rod. the rod lenght of rb25 and 26 are the same? because on the box it says rb26.

[rondofj]

it is for non neo, but my mechanic bought the r34 block which he believed it to be the same.

What i bought was for non neo cp pistion with 9.0:1CP and Manley Rod. the rod lenght of rb25 and 26 are the same? because on the box it says rb26.

From what I read, NEOs run RB26 rods but not pistons.

[KiwiRS4T]

Yes Neos run the same rods as RB26. The critical difference is the heads. Do you have a neo head on your R34 block?

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OK, just to clear it, i've got r33 gtst, my rod (number 1 let go about 2 months ago and i have bought all the part for rebuild. My mechanic has r34 gtt block, i use his bottom block with my non neo head. I was told that the block is both the same. Is the crank for the neo and non neo (rb25det not neo) the same?

when putting one of the piston and rod in the top edge of the piston is about 1mm above the surface of the block (head gasket is not installed yet). is sthis normal? should the top edge of the piston sitting flush with the block surface?

[KiwiRS4T]

The Neo and RB26 have then same rods and a piston pin height of 30.3mm

The RB25 has a piston pin height of 31.3mm

[lilcrash]

As a guide my neo pistons in my neo block sat about 40thou under the deck height.

I think you need to go buy an r33 block.

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look like i will need to buy the r33 block. can anyone else comfirm?

thanks all

As a guide my neo pistons in my neo block sat about 40thou under the deck height.

I think you need to go buy an r33 block.

[KiwiRS4T]

look like i will need to buy the r33 block. can anyone else comfirm?

thanks all

I'm not too sure about that. Find an experienced RB engine builder and ask. You may be able to get away with thicker gaskets but find someone who has done it.

[KiwiRS4T]

double post

[Bronx]

The rb25 blocks should all be the same. The rb26 block was a bit higher from memory.

The main diff between the r33 and 34 engines is the head, pistons and rods.

Rods were same length all round from 26 to 25 but the pistons were totally different. The rb25 and 26 had same pistons with a taller deck while the rb25 neo had special valve cutouts and was shorter. If you used r33 pistons in a r34 the valves will hit the pistons.

[KiwiRS4T]

The rb25 blocks should all be the same. The rb26 block was a bit higher from memory.

The main diff between the r33 and 34 engines is the head, pistons and rods.

Rods were same length all round from 26 to 25 but the pistons were totally different. The rb25 and 26 had same pistons with a taller deck while the rb25 neo had special valve cutouts and was shorter. If you used r33 pistons in a r34 the valves will hit the pistons.

Yep but he's apparently using the R33 head.

[darrinspencer]

Yep but he's apparently using the R33 head.

Wrong pistons??

Measure pin heights etc and compare to catoglue data. ignore what the box says.

R33 and R34 blocks are the same height/stroke

Rods are the same length in R33 rb25 and R34 rb25 and rb26

The difference is the CC of the heads, R33 are about 62 and Neo is 51-52CC's

Hence the difference in piston crowns (and maybe pin height)

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without the head fitted the piston is sitting about 1mm above deck. If r34 block and crank are the same as r33 then the piston is wrong. But looking at the CP spec and having consult with CP people they confirm that they have the same compression height. this is what they said

"CP Pistons said that the valve reliefs are the same for both the 8.5:1CR and 9.0:1CR pistons. They say they design the pistons to accept high lift and +1.0mm oversized valves. Neo piston is different to non neo, the main different being compression height."

I have also post this in the Force Induction Performance section. seem like i still have no answer, I'm totally confused.

[KiwiRS4T]

Yeah but have you got the right pistons? As Darrin says never mind what it says on the box actually measure the distance from the pin to the crown (compression height) . Ask CP what it should be for the R33 piston and what it should be for the Neo piston and establish for sure that you have the right pistons.

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measured the piston and it is the same as the r33's. it is about 31.5mm compression height.