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Quick Question On Engine Internals

T-u-R-b-O

By T-u-R-b-O,
in Engines & Forced Induction

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T-u-R-b-O Collaborator

T-u-R-b-O

Posted
Posted

hi there!

just a quick question... i am about to purchase a set of wiseco pistons with 87mm bore on GTR rods removed from an RB26 block, and was wondering whether my RB25 block can take these parts?

and if so, how much HP/boost can I push due to the thinner cylinder walls? or wont this have any effect?

thanks guys,

Nico

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R31Nismoid Grand Master

R31Nismoid

Posted
Posted

Have you got your motor apart yet?

I personally wouldnt bore anymore than i needed too.

Like, if your motor is A-ok and you can get 86mm in there after machining etc, then thats what i would do.

But then there are some using 87mm without issues i *think*... someone will confirm as im sure there are a few :P

B0oStEr Mentor

B0oStEr

Posted
Posted
hi there!

just a quick question... i am about to purchase a set of wiseco pistons with 87mm bore on GTR rods removed from an RB26 block, and was wondering whether my RB25 block can take these parts?

and if so, how much HP/boost can I push due to the thinner cylinder walls? or wont this have any effect?

thanks guys,

Nico

It seems as though you are doing something similar to me.

I just bought the bits I need to build an rb25 with 87mm rb26 wiseco pistons stock rb26 rods and rb26 crank.

To use gtr rb26 pistons you have to use a gtr crank.

If you're using an rb25 crank then you can use the rb26 rods with rb25 pistons.

I was going to buy 2nd hand rb26 wisecos with rb26 rods but with new rings it would have cost nearly as much as new pistons.

I bought new wiseco pistons, cometic head gasket,acl race bearings and arp rodbolts/headstuds for a very good price

Boring 87mm shouldn't affect block strength too much and I'm not worried about leaving material for further rebuilds as 2nd hand rb25 blocks cost a lot less than forgies.

T-u-R-b-O Collaborator

T-u-R-b-O

Posted
  • Author
Posted

hmm...

this is bad news... i am about to buy RB26 rods with RB26 87mm Bore Wisecos on them...

so you are saying that they will not fit on my RB25 block?? what if i use a 1.6mm cometic HG?

is there actually any chance of these RB26 fitting onto my RB25 crank?

THanks!

Nico

SECURITY Grand Master

SECURITY

Posted
Posted

rb25 and rb26 rods are almost identical, except rb26 rods are beefier so using them with rb25 pistons is fine as long as you're using the rb25 crank. the rods arent the issue.

to use rb26 pistons in an rb25 block, you'll need an rb26 crank. no machining is required to do so, and ive seen some floating around for around the $150-200 mark.

the rb26 has a larger throw, which is the reason you've got the .1L extra in capacity. using the rb26 rods on an rb25 crank will give you really shit compression as the throw is smaller.

Sydneykid Grand Master

Sydneykid

Posted
Posted

RB26 and RB25 conrods are the same length

RB26 has 2 mm longer stroke than RB25

Hence an RB26 piston has the gudgeon pin 1 mm lower than an RB25 piston

So if you want to use RB26 pistons with an RB25 crank you need to machine 1 mm of the block to achieve the correct deck height,

Note that because of the smaller capacity of the RB25 (compared to the RB26) the compression ratio will be slightly lower than would be the case if you used those pistons in an RB26

None of which is a big deal

:D Cheers :D

T-u-R-b-O Collaborator

T-u-R-b-O

Posted
  • Author
Posted (edited)
RB26 and RB25 conrods are the same length

RB26 has 2 mm longer stroke than RB25

Hence an RB26 piston has the gudgeon pin 1 mm lower than an RB25 piston

So if you want to use RB26 pistons with an RB25 crank you need to machine 1 mm of the block to achieve the correct deck height,

Note that because of the smaller capacity of the RB25 (compared to the RB26) the compression ratio will be slightly lower than would be the case if you used those pistons in an RB26

None of which is a big deal

:D Cheers :O

aha ok...

so I can use 87mm Wisecos from RB26 and GTR Rods on my RB25 block with crank :(

dont you think that instead of having to machine 1mm of the block (see attached pict) away, it would be easier using a 1,6mm cometic head gasket? isnt that an alternative?

Thanks for helping guys :wave:

post-20771-1153127587.jpg

Edited by T-u-R-b-O
Craved Grand Master

Craved

Posted
Posted
aha ok...

so I can use 87mm Wisecos from RB26 and GTR Rods on my RB25 block with crank :(

dont you think that instead of having to machine 1mm of the block (see attached pict) away, it would be easier using a 1,6mm cometic head gasket? isnt that an alternative?

Thanks for helping guys :wave:

if im not mistaken 1.6mm is BIGGER than a std gasket thickness...

so using that instead of taking the 1mm of the block will make everything WORSE ..

your taking 1mm off the block to INCREASE the compression... adding a larger gasket REDUCES compression..

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