Rb25 Bottom End With Rb 20 Head

[nIsMo86]

Hey,

I've been doing some searching on whether you can bolt up an rb20 head to an rb25 bottom end and havent found any topics on it.

My questions are:

* Does it bolt straight up?

* Is there any merit in doing this?

Any help would be appreciated.

Cheers.

[discopotato03]

I think the issue is that the water jackets don't line up between big and small bore RB engines ie RB20 is from memory 78mm bore and 25/26/30 85mm .

Even if you could the RB20 heads smaller valves and ports would be a backwards step .

A .

[nIsMo86]

Well its the rb20 head that i have. My 20 bottom end is gone and i was considering putting a 25 bottom end if they bolt up. And also if its not gonna lose power.

[MBS206]

You'll see a much better gain by bolting up the whole RB25.

What is said above is correct also, water galleries do not line up.

The RB20 head flows no where near as much as the RB25 head. So it would be a huge backward step to do to the RB25 bottom end.

Considering you can grab a cheap RB25DET and drop the whole thing in, and your old turbo setup etc will bolt to it (If you're using a stock turbo, use the RB25DET turbo!)

[[200]]

Nope

Fail

F

[nIsMo86]

Hmm i guess i'll stick with the rb20 and get a new bottom end.

Thanks for your help guys!

[MBS206]

Hmm i guess i'll stick with the rb20 and get a new bottom end.

Thanks for your help guys!

Dropping another RB20 in, VS picking up an RB25... Will be a bit more for the RB25, BUT you'll see MAJOR amounts more torque.

Much better engine all around.

[nIsMo86]

Dropping another RB20 in, VS picking up an RB25... Will be a bit more for the RB25, BUT you'll see MAJOR amounts more torque.

Much better engine all around.

Yeah i know but with the mods i have i'll need to get a new ecu, dial in the cams again, get it tuned etc. If i just put 20 back in i'll have awesome power as is. Had 267atw with current mods.