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Difference In Blocks

daisu

By daisu,
in Engines & Forced Induction

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daisu Mentor

daisu

Posted
Posted

People, I'm considering an engine buildup based upon a certain block with an 86mm bore.

As far as I know, the RB25 block is basically the same as the 26 block in terms of height and bore.

So my question is, are there other differences like oil galleries, water jackets etc

Also, interested to know if the RB25DE block was any different to the DET, as it could possibly be cheaper to purchase compared to a 25DET block/head.

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Cubes Grand Master

Cubes

Posted
Posted

The blocks are different due to the R33's VCT. Providing you use the RB25 from the R33 and not the RB25 from the R32. The R32 RB25DE does not have VCT.

Unsure if there's any differences with regards to piston oil squirters or crank/rod design.

daisu Mentor

daisu

Posted
  • Author
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The blocks are different due to the R33's VCT. Providing you use the RB25 from the R33 and not the RB25 from the R32. The R32 RB25DE does not have VCT.

Unsure if there's any differences with regards to piston oil squirters or crank/rod design.

I don't know because I haven't seen before, but I would have thought that the VCT differences would be in the head?

daisu Mentor

daisu

Posted
  • Author
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well vct has a third oil feed thru to the head from the block.. i think all the rb25s,26s and 30s all have the 86mm bore with different stroke lengths? also the 26 block is more rigid than the other blocks

what sort of car are you building up?

yeah the 30 block is something like 38mm taller, but besides that they all have the same bore. The 25 and 26 block have the same height.

Basically it's going to be pretty much an RB25DET. But I figure I might be able to save some money by starting from a cheaper R32 RB25DE.

Was the VCT available on the DE engines? Is it worth having if I'm going to use aftermarket cams?

jarrod83 Community Regular

jarrod83

Posted
Posted

im pretty sure that no rb25de's came with vct, im also pretty sure the more power you make the less useful the vct is, so with some descent cams it shouldnt make any difference its mainly for some extra down low response, of hand the only differences i can think of are the different compression ratios, a few weaker components in the head like the springs.. and quite possibly weaker pistons and rods etc.. have you maybe considered the rb25de head on a rb30e ? they are pretty cost effective and strong

daisu Mentor

daisu

Posted
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Yeah, still weighing up options. It's hard to know when to stop, spend money on RB20, or do RB25 conversion, or build RB30 with twin cam head, build a low stroke RB25 (ie the RB24). Too many decisions. A lot of research...

Either way, an RB30 build or the RB25 I'd be building with the R32 RB25DE head, due to cost and not having to mess with VCT.

So regarding this head I have some more questions...

From what I've read the valve springs aren't as strong as say a DET head, this will be a problem with high lift cams, high revs, and boost?

Would if be worth using parts from a DET head (valve springs, lifters etc) should I stick with hydraulic lifters or go solid?

There is a thread a few pages in about differences between the lifters in RB20DET and RB25DE head (both from R32).

Link here

Cubes Grand Master

Cubes

Posted
Posted
im pretty sure that no rb25de's came with vct, im also pretty sure the more power you make the less useful the vct is, so with some descent cams it shouldnt make any difference its mainly for some extra down low response, of hand the only differences i can think of are the different compression ratios, a few weaker components in the head like the springs.. and quite possibly weaker pistons and rods etc.. have you maybe considered the rb25de head on a rb30e ? they are pretty cost effective and strong

R33 RB25DE's definitely do.

VCT is good for mid 300rwkw at the wheels. Much more and you really need larger cams with big lift of which renders the VCT useless.

daisu Mentor

daisu

Posted
  • Author
Posted
R33 RB25DE's definitely do.

VCT is good for mid 300rwkw at the wheels. Much more and you really need larger cams with big lift of which renders the VCT useless.

So you're saying that standard cams with VCT is good for 300rwkw? I would've thought I'd need larger cams well before that power level.

R31Nismoid Grand Master

R31Nismoid

Posted
Posted
So you're saying that standard cams with VCT is good for 300rwkw? I would've thought I'd need larger cams well before that power level.

I was 270rwkw on pulp, stock head no problem in the world, did over 350rwkw with fuel

daisu Mentor

daisu

Posted
  • Author
Posted (edited)

Well I'll probably start with standard cams and then if I feel the need for more power later I'll upgrade.

So the DE springs, would they be fine for most setups, or should I get rid of them and use DET or aftermarket springs? What about the hydraulic lifters?

Edited by daisu
jarrod83 Community Regular

jarrod83

Posted
Posted

would depend on how much boost your planning on running, i know if you run to much boost they start to valve float, the de's are like 39Lbs and the dets are like 42(or 43?)Lbs, i can't remember the exact limits on boost for each of them im pretty sure its around the 20psi mark or just under.. hopefully someone else can add to this

what sort of power are you aiming for?

Cubes Grand Master

Cubes

Posted
Posted

I haven't heard of people having issues with the R33 NA springs but when it comes to the R32 Rb25De there's definitely issues.

The R32 Rb25DE's run the same springs as the rb20det. The spring in the rb20det controls a lighter smaller spring.

Another issue I believe causes problems with the R32 Rb25de's is the lifter design. The r32 rb25de lifter has holes to allow oil to enter where as the rb20det lifters are quite restrictive in allowing oil in to the lifter. Holes = increased pressure trying to pump the lifter up. All though not 100% im fairly certian this is the case.

The rb20det lifter runs the same as in the vg30det.

I would like to see the lifters in an r33 rb25det and rb25de.

They are easy to pull apart clean and inspect.

daisu Mentor

daisu

Posted
  • Author
Posted (edited)

I don't have a specific power goal at the moment, just trying to gain a bit more knowledge before I start working out what I can afford and what is worth doing.

After reading the RB30 conversion threads, it seems that you can get reasonable results with standard RB30E bottom end and standard RB25DE head, so the valve springs are probably fine for my needs.

If I do decide later that I need more power then I will probably pull the engine down and rebuild with stronger bottom end (aftermarket rods etc) and redo the valve train to handle higher boost.

I'm only about 15pages into the RB30 conversion thread (333pages)

*Edit* Just read cubes post above,

Still haven't decided whether I want the VCT or not, it would probably be smarter to use it since I probably won't be making enough power to render it useless. Still early stages, lots more research to do.

Edited by daisu
Cubes Grand Master

Cubes

Posted
Posted

When the rb30 thread was first born not a great deal was known so no doubt there will be a fair bit of incorrect or lack of knowledge.

I will have to get off my arse one day and update the rb30det guide with details on vct and 4wd. one day. :D

  • 6 months later...

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