Crankshafts Rb25 V Rb26

[Dale FZ1]

Here's a question for any experienced RB engine builders:

Apart from the slight difference in stroke, is there any difference in weight, balance/size of throws, or construction between the cranks in RB25 and RB26?

There are various people who've fitted 26-spec rods into their 25-spec engines, but no indicator as to whether they required any work to the crank to deal with the heavier (by around 50 grams each) GTR conrods.

Are there any/many experiences in this area please?

[The Mafia]

Just from what I know, I'm sure the difference between RB26 and RB25 pistons is the gudgeon pin position (to make up for the stroke difference)

But you have an excellent question Dale - looking forward to the answer.

[Dale FZ1]

Searching the forum before posting this question, I found posts from several of the more respected SAU members

http://www.skylinesaustralia.com/forums/Rb...rods+in+rb25%2A

http://www.skylinesaustralia.com/forums/Rb...rods+in+rb25%2A

So I know the issue of higher reciprocating mass has been (sort of) discussed. One thing that wasn't resolved was how to counter it. ie. did Nissan do anything about it with the basic engineering of the RB26 crank? and do I do anything about it while preparing to put 26 rods in bed with a 25 crank? It's one thing ending up with stronger internals, but if the engine doesn't rev as quick or sweetly then I wonder about the value of the upgrade.

This really does need comment from people who've had their hands in the bowels of a few RB engines, so I'm calling for a response from GTRgeoff, Duncan and Sydneykid please. Also Security, who has more recently stuck GTR rods into his 25.

thanks in advance

EDIT: the same principles should apply for people doing mods including forged pistons and rods, due to the changes in reciprocating mass, so I don't see the question as relating solely to the cheap upgrade I want to do.

Edited January 31, 2008 by Dale FZ1

[SECURITY]

i havent noticed a difference in how my car runs. im going to be turning my rev limit up to around 7500 and ill report back if anything pops.

it picks up speed the same as always and ive been using my launch control alot, and apparently its not too good on the rods and its held up fine for around 1.5yrs.

i dont have any more info on the whole mechanics/engineering part of it because i pretty much just got them cheap and threw them in when i had the chance, i didnt really look at anything else.

[GTRgeoff]

Apart from the slight difference in stroke, is there any difference in weight, balance/size of throws, or construction between the cranks in RB25 and RB26?

While I haven't bothered with the detail of the 26 crank, the throw is longer to achieve the increased swept capacity. Remember they are lower comp than RB25 so the pin to deck height is a fair bit lower in the pistons. From brief inspection the cranks are a very similar style between all RBs and all are nitrided.

There are various people who've fitted 26-spec rods into their 25-spec engines, but no indicator as to whether they required any work to the crank to deal with the heavier (by around 50 grams each) GTR conrods.

I did no extra work when I fitted 26 rods in the 25, just lightened the flywheel, radiused the bearing journals, chamfered the oil holes and had the oil plugs pulled and tapped, then flushed and used grub screws with loctite. It helps to get the rods x-rayed to ensure they will do the job if second hand and you MUST at least replace the bolts with stock or better.

In the 26/30 I'll be going further since I went forged Spool rods and CP pistons and using a decent harmonic balancer.

[GeeTR]

Shame more ppl haven't coughed up any good info, as I've often wondered this.

Hell, im not even sure how one would increase the cranks counter weight to accommodate the heavier rods (all things being equal)

All I can think of, is threading the holes that are drilled into the counters (to adjust weight) and screwing in some mass, steel, depleted uranium etc

[Benji]

is it all worth it in the end?

and is there much gain in it??

[Spoolup]

The RB26 is a beefier stroner constructed crank to the rb25, as are the rods.

There are no mods required to the rb25 crank to run rb26 rods - and there is no noticable differnce in response when using the OEM 26 rods with a RB25 crank.

Edited November 23, 2008 by Spoolup

[SECURITY]

yeah, its just about building a stronger motor.

guys running nitrous on stock motors dont like to activate it before 3500-4000rpm as the rods wont take it, with beefier rods you will be able to cope with more torque at lower rpms, other than that you wont really get a performance gain.

[RNS-11Z]

beefier how? stronger how?

[skymugs]

i have wondered about doin this work to my rb25.. i was reading through this hpi magazine and it says a guy called PAUL CORNES president of sauwa has done it and says

" theres plenty of conjecture out there as to whether, the '25 block needs to be machined before it will accept the '26 crank, but paul assures us that it is a direct drop-in affair"

i think that would b the guy to ask

[Marco-R34GTT]

Yeah Paul is a good bloke, you'll find him in the WA section, I'm sure he'd answer any queries without any hassle what-so-ever.. Which is handy cause I too am looking at throwing an RB26 crank-rods into my RB25 NEO.. In that case, does having the RB26 crank and rods adjust the stroke at all??

[skymugs]

well im guessing it would have to... so u would either have to change ya rods or pistons.. pistons i think because the gudgen pin is in a diff location