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Rb25det To Rb26dett Conversion

Tomei_Powered
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Tomei_Powered Rising Star

Tomei_Powered

Posted
Posted

Pratically im rebuilding my engine again due to my bearings that have given way.

My engine is a RB25DET and ive just purchased a RB26DETT engine intending to use its

block.

Should i go with the RB26DETT or stick to my RB25 cyl head?

Thing is, my head is prep with Tomei Cams, Valve Springs, Solid Lifter conversion, Adjust shims and

ive spent quite a sum on machining and time to get it running.

Ive a few questions below and would like some answers.

If i would use the RB25 cyl head, will it be a direct fit onto the RB26 block? Do i need to purchase a new cyl head gasket

to have it fit or just stick with the RB25?

What should i do with the VTC?

For the individual throttles, how do i make it fit into the RB25 cyl head?

OR

Should i just sell the damn RB25 cyl head and go with the RB26 and sort out all the fuss?

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https://www.sau.com.au/forums/topic/229677-rb25det-to-rb26dett-conversion/
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stricnynel0s Collaborator

stricnynel0s

Posted
Posted
Pratically im rebuilding my engine again due to my bearings that have given way.

My engine is a RB25DET and ive just purchased a RB26DETT engine intending to use its

block.

Should i go with the RB26DETT or stick to my RB25 cyl head?

Thing is, my head is prep with Tomei Cams, Valve Springs, Solid Lifter conversion, Adjust shims and

ive spent quite a sum on machining and time to get it running.

Ive a few questions below and would like some answers.

If i would use the RB25 cyl head, will it be a direct fit onto the RB26 block? Do i need to purchase a new cyl head gasket

to have it fit or just stick with the RB25?

What should i do with the VTC?

For the individual throttles, how do i make it fit into the RB25 cyl head?

OR

Should i just sell the damn RB25 cyl head and go with the RB26 and sort out all the fuss?

i own a rb25 and i soooo wish i just bought a rb26, it has better head, more choice of cams, slightly larger displacement, all a bunch of things i did that cost me more on my rb25 and came out to be more than a rb26

TiTAN Grand Master

TiTAN

Posted
Posted

There are other issues with putting the 25 head on the 26 block.

No oil feed for the VCT on the the block (external feed required + modification to the head)

The RB26 uses larger head studs than the 25 does (26 studs wont fit the 25 head without modification and 25 studs wont screw into the block)

Cut your losses sell the 25 head and use the 26 head on the 26 block or buy another 25 block if you really want to use the head that badly.

Tomei_Powered Rising Star

Tomei_Powered

Posted
  • Author
Posted

Ill stick with the 26 head.

I really love the 26 from day one. But, financially at that point i couldnt afford a GTR.

Titan,

I dont understand the term u said on the VCT. Could u elaborate to me in detail

I will be building this engine myself. Dont want to be mislead or screw the 26.

Thanks!

James_03 Mentor

James_03

Posted
Posted (edited)

yeah go with the 26 head, and sell the 25. What I would probably do is sell the 25 head and then invest the money into a rebuild on the 26 ie new stem seals, valve regrind, etc. Obviously if the head is recently rebuilt but you wouln't need to do this.

The 25 head on the 26 would involve modifying the head to use 26 head studs as already mentioned, and also running an external feed for the vvt, or you loose the vvt cam gear and also change cams. You mentioned you had tomei cams, are you still using the vvt cam gear then?

Also the shape of the water gallery on the 25 vvt head differs from the 26 block/head. It also needs slight modifying so that it has optimum flow. Then you need an adapter plate made up to use the 26 throttles which trust me, is a complete pain in the arse.

Edited by James_03
Tomei_Powered Rising Star

Tomei_Powered

Posted
  • Author
Posted

After a long consideration,

Im going with the 25 head and 26 bottom.

A lot of extensive modifications have to be done to keep the 25 head.

Its nothing much but just the time and effort spent on building the 25 head and the hectic measurements for the shims!

Its just not worth selling the 25 head.

Im planning to transfer all the 26 bottom parts to the 25 block.

Ive measured and i think it most probably fit without issues..

dano4127 Veteran

dano4127

Posted
Posted
After a long consideration,

Im going with the 25 head and 26 bottom.

A lot of extensive modifications have to be done to keep the 25 head.

Its nothing much but just the time and effort spent on building the 25 head and the hectic measurements for the shims!

Its just not worth selling the 25 head.

Im planning to transfer all the 26 bottom parts to the 25 block.

Ive measured and i think it most probably fit without issues..

What 26 parts you going to use? Pistons/Rods/Crank in the 25 Block?

  • 2 weeks later...
FineLine Grand Master

FineLine

Posted
Posted

I converted my 25 head to solid operation and blocked off the vct.Its no longer an issue. I have no desire to change to a 26 anything. once modified there is stuff all difference between the 2 engines so whats the point. In my 18 months of linership The weakness of both engines would appear to be A. the 26 is hell on spun bearings. B. the 25 has a propensity to shit pistons.

I'll take B. A set of forgy's and the issue is no more. The 26 however would appear to continue to have the bearing gremlin wether rebuilt or not. Both great engines. Use what you have.

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