Blown Rb26.. Options?

[Erelyes]

Hey all.

I'm after a few answers regarding my upcoming RB26 build in my 32R. Ran a bigend bearing. Haven't pulled it apart to measure everything yet, but have heard my crank may be stuffed. Anyways...

What I want : safe squish (factory/40thou/whatever), reasonable compression (between factory 8.5 and 9, or maybe even up around 9.2-9.3), and around 300rwkw.

Factory motor made 250rwkw on lowmount mild turbos and a rich as hell tune @ 14psi. So know 300rwkw is easily doable. Will probably bore over and drop in forgies. Stock rods, cleaned up. Nothing fancy. Probably stick with around 1 bar boost, 8k rpm. Crank collar etc etc.

1) I know 26 pistons/crank and 25 pistons/crank must match. I have a good 25 sitting in the garage. If the 26 cranks f*ed, can I run the 25 crank with forged 25 pistons? Or even random ones for RB30 applications? What would this do for CR?

2) If my 26 cranks OK- I notice most aftermarket RB26 pistons are between 8-8.5CR. Thinner headgasket's not really an option (removes squish) to get the desired .2 extra CR. What can I do? Custom pistons out of budget.

Any advice much appreciated. Engine builders with a clean reputation are hard to find at the moment, it seems. And would prefer to tackle the job myself.

Edited October 24, 2007 by Erelyes

[13thracer]

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Edited October 24, 2007 by 13thracer

[13thracer]

If you use the 26 crank you will need to use 26 pistons.

If you use the 25 crank you must use the 25 pistons.

Rods are the same length 25 to 26 the 26 ones are just stronger so use them regardless unless there stuffed of coarse.

the 26 pistons are off the top of my head 2mm smaller in height to offset the extra stroke that the 26 crank has. So if you used 25 pistons on a 26 crank you will end up having the pistons poke out the deck and will try and punch the head off the block with every srtoke so dont do it. and vise versa 25 crank with 26 pistions = around 7:1 i think either way really low.

Answer to your questions

1... You could use the 25 gear but it would really suck have shitty 25 gear inside a 26, your going to have to rebuild it either way and forgies are a good option. 25 crank and forgies i assume would give you factory rb25 compression 9:1 but dont go defacing you gtr buy putting 25 stuff in it, if the crank is stuffed sell the 25 gear you have, and go buy another 26 crank.

2... Th only way to get more comprssion is to use custom pistons, deck the block, skim/shave the head or use a thinner gasket so if you wont do any of them so you can keep you squish you have to leave it factoryish 8.5:1.

[Erelyes]

Answer to your questions

1... You could use the 25 gear but it would really suck have shitty 25 gear inside a 26, your going to have to rebuild it either way and forgies are a good option. 25 crank and forgies i assume would give you factory rb25 compression 9:1 but dont go defacing you gtr buy putting 25 stuff in it, if the crank is stuffed sell the 25 gear you have, and go buy another 26 crank.

2... Th only way to get more comprssion is to use custom pistons, deck the block, skim/shave the head or use a thinner gasket so if you wont do any of them so you can keep you squish you have to leave it factoryish 8.5:1.

I know 25/25 or 26/26 pistons/crank must match. Said so in my post.

"shitty" RB25 gear. RB25/26 cranks are basically same except for stroke. And maybe bearing width. Will use 26 rods as I said. And forged pistons anyway. So whats the 'shitty' rb25 gear remaining? 300rwkw is a walk in the park for 25/26 cranks alike anyway.

26 cranks are pretty thin on the ground these days. Whereas 25 bottom ends are getting cheaper cause people keep using the heads for RB30s hybrids.

[13thracer]

yeah the 25 stuff will do it but not as well as the 26, and at the end of the day do you want a 25 in your GTR. finding 26 cranks is allittle hard but not impossible i know of two for sale at the moment. Im not nissan and dont know what they did in the factory back in the day but i say there would be a hole lot more preperation going into the 26 crank than the 25 one but thats just my theory.

some options...

1. 25 crank,26 rods, and 25 forgies. 9:1 but less capacity

2. 26 crank rods and forgies 8.5:1 but 2.6 capacity so makes up alittle for the less compression bore it 40thou and get to 2.7 if your keen.

best option would be to pull the engine apart and see what stuffed and go from there

Edited October 24, 2007 by 13thracer

[R31Nismoid]

I know 25/25 or 26/26 pistons/crank must match. Said so in my post.

"shitty" RB25 gear. RB25/26 cranks are basically same except for stroke. And maybe bearing width. Will use 26 rods as I said. And forged pistons anyway. So whats the 'shitty' rb25 gear remaining? 300rwkw is a walk in the park for 25/26 cranks alike anyway.

26 cranks are pretty thin on the ground these days. Whereas 25 bottom ends are getting cheaper cause people keep using the heads for RB30s hybrids.

26 cranks from what i've seen are just a 'little' better than RB25 ones. Although having said that 300rwkw shouldnt as much of a problem.

Then you've still got to get a crank collar (you'd be mad not to do so), and then machined up, tested and so on and so forth.

I'd wait and see if your crank is stuffed first, and if it is, just get a R33 crank new. Less hassle, no farting around.

Ye it costs a bit over the collar/machining etc. But least you know it'll be right the first time without spending $$$ only to find out you RB25/26 one might not be upto scratch and you've blown inspection costs.

13th - the capacity difference is literally f**k all. The RB26 isnt a 'true' 2600cc motor anyhow, its less.

So if your using slightly over-sized pistons its just a number that IMO really wont affect performance noticeably at all.

[Erelyes]

Spose that's a good idea. I was gonna whip the crank out and take it to a reconditioners to check it for bends, resize journals if necessary, so on and so forth. But have heard from one source that every gtr he's seen with a knocking bearing has resulted with a stuffed crank.

R33 cranks, new, are around 2k new from what I hear, here in NZ. Doesn't seem worth it to me when I have an RB25DE i got for $500 bucks, with a free car. And can use the head/pistons in an RB30 NA conversion for my drifter. So the crank is fair game - and if it's in OK nick, why not use it in the GTR? It's only 60cc different and if I had .5 or 1mm over forged pistons and GTR rods anyways it'd be pretty much the same capacity as a factory RB26. With slightly better revs and slightly less torque.

The main advantage of the GTR is the rods, block, and head. All of which people retain for their 450kw setups. And of course all the fancy stuff attached like hex throttles / twin turbs and a fancy 4wd system...

I was just wondering if RB25 pistons/crank would result in the same compression in a 26 block as they would in a 25 block. Cause if they can and there's aftermarket RB25 forgies that give 9:1, it'd be a good option...

[R31Nismoid]

2k over there?

They are like $1100 here, shipping surely isnt more than a $100?

[Adriano]

Curious to know what your thoughs on reducing the squish results in, i was under the impression the smaller the squish the better the swirl and reduced likelyhood of detonation, i would run 25 thou squish with second hand or new r33 rb26 crank(they are on here fairly often for $1000 new), use frogies then run a thinner h/g or deck the block/head to increase your comp to 8.8-9:1

[TriniGT]

Done some researching, I am in the same predicament, I have a stuffed RB26 and have a working RB25DET Neo. I want the RB26 head and want to know if I can use the RB25 crank in the RB26 block. Or maybe even easier maybe I can use the RB25 bottom end with the RB26DETT head. But will I have to do to have this working, I know it is a drop in but I hear that the headstuds are different. Getting someone competent ove rhere is a problem to machine the headstud holes and retap, some have said to use RB25DE headstuds to clamp the RB26DETT head to an RB25DET bottom end. Can anyone confirm, need to make up my mind urgently.