RB30E Head on R33 RB25DET Block

[teng]

Ok. As per topic. Hope this is the right place for this post and yes I have read the RB30 Twincam conversion PDF many times now.

I just want to make sure, if a R33 RB25DET head with VVT blocked off can fit onto a RB30 block, then the same can be done for the reverse. I just need to block off the VVT feed from the RB25DET block and everything will bolt on, fit and run perfectly? Right?

Reason for doing this is because my RB30 block is already worn out, needs to be re-bored and 86.5mm pistons installed etc. Pistons sets are not cheap. RB25DET blocks are plenty here and I was thinking why not use them. Our RB30's here are all carburetted hence I would like to keep that setup.

I'm just looking for opinions.

Thanks.

[Ben C34]

Sounds like it will work. Timing belt length will be a problem though, due to the lower deck height so will take some thinking,  but on the plus side there is already the idler that you can choose to use or not depending on belt availability

[KiwiRS4T]

RB30s commonly run to 300,000km - sure a set of rings and bearings won't keep you on the road?

[teng]

47 minutes ago, KiwiRS4T said:

RB30s commonly run to 300,000km - sure a set of rings and bearings won't keep you on the road?

 

Edited July 26, 2018 by teng

[teng]

I have already done two General overhauls, All the Gaskets plus seals, piston rings etc have all been changed. On the 2nd overhaul, the connecting rod bearings were damaged so we had to rebore the crankshaft and use 0.25mm bearings instead. Main bearings were changed as well. Our R31's odometer comes in miles so it has already travelled 238,332miles which is equivalent to 383,558km.

 

Edited July 26, 2018 by teng

[teng]

Ben C34. Seems so. Plus the compression is the same for both engines 9:0:1

 

[Rusty Nuts]

A R32 RB25 non vct bottom end would suit better as they have same port configuration and can use rb30 head gasket

[GTSBoy]

2 hours ago, teng said:

Ben C34. Seems so. Plus the compression is the same for both engines 9:0:1

 

The resulting compression ratio is NOT the same.  One has a 500cc per cylinder swept volume and the other has 416cc per cylinder swept volume.  Put the smaller cylinder's head on the large cylinder and the ratio will go up.  A lot.  Put the large cylinder's head onto the small cylinder and the ratio will go down.  A lot.

Edited July 26, 2018 by GTSBoy

[teng]

GTSBoy. That would mean I still need to get high comp pistons prolly around the 10:x:x mark?

[GTSBoy]

1 hour ago, teng said:

GTSBoy. That would mean I still need to get high comp pistons prolly around the 10:x:x mark?

Yes....but caution is advised.  RB30 is 2 valve engine, so the valve reliefs on high comp RB25 pistons might not be right for the larger RB30 valves.