rb26 head on rb25 block

I would say if u have the engine ur best bet would be to tidy it up and fit a sump and all ancillaries ect to make it work then sell it as you'd get alot then use the money to uprate a normal rb25 head.
But if u do want to use the head I think they need alot of work with the oil ways and water ways. If you check any rb30 threads u may get the info needed about the work needed.

 

hey i was running a rb26 bottom end with a rb25 head it gives you lower compression than standard which in turn makes it quite a strong and reliable combo hope this helps

 

The 26det head is alot better then a 25det head, better lifters etc.. put it on a rb30 block and your good to go. theres rb30 doc with pretty much anything your going to want to know about building one, google it you should find it

 

I didn't know u could do that might look at that through my rb25 block thanks

 

Why don't you just put the RB26 crank, rods and pistons into the RB25 block and land on the RB25 head.

Job done -

The RB26 head will bolt straight up, but you'll need to close off the front VVT oil feed. The RB26 head also has 12mm bolt holes and the RB25 uses 11mm.

 

done this already heres a pic and i sold the engine and it is now breathing in a nice r33

bolt holes need do be drilled deeper by 10mm and tapped out to 12mm
water jouranl near vvt hole needs opened up on one side and slightly welded on the other then machined flat ( obviously on the block side not the head )
use a 1'' long grub screw and tap the vvt hole using loctite round the grub for security

use an rb26 head gasket as a templete to open up the front water journal on the rb25 block

all in all its an easy job if u have the know how and a bit of savy with a welder ( cast rods only ) a dremel and a drill / tap

if u are seriously attempting it i myself have done it and to be honest is a lot easier than changing the bottom end over , my personal reason for doing it was that my rb25 bottom end was already forged so i wanted to keep the block


heres a pic before the welding but after the boring of the water hole compared against the original 25 gasket u will see they are different


and heres a pic after welding / grubbing etc with a cosworth 26 gasket ( they now match up after the work thats needed )

 

just to clarify the rb26 head is not a LOT better than a 25 head ? the ports etc are the same therefore they flow just about the same also , the only difference is a slightly higher tolerance to higher revs due to the solid lifters but if this is that much of a problem then fit the solid lifters and cams into the 25 head and have the head reshimed ,

the rb26 head is probably favoured more by its looks as it looks awesome and is the main reason for me changine it over plus i couldnt afford the rb25 greddy style plenum at the time , top feed injectors are also more favoured as they are easy to get hold of for a 26 bar the 25 have side feeds which are a lot harder to get hold of in higher cc ratings and often more expensive but cheap mazda rx7 secondry injectors are 800cc , they are side feed and they fit a 25 for the fraction of the cost of aftermarket side feeds

 

Hey buddy, for some reason the photos are not working, is there anyway of viewing them. I understand this post is very old now