Jump to content
SAU Community

Recommended Posts

Has anyone here attempted to cyro treat a Rb block? I've seen a few build threads where guys suggest it, but never any results. 

MotiveDVD proved the Rb blocks are soft, cyro treating would help harden the blocks and make them less likely to crack between the bores. 

I've got my Rb25 series 2 block at the cyro treaters atm and will compare it when it gets back (hopefully this Friday)   

Rb25 series 2 block (untreated) : 238

 

Link to comment
https://www.sau.com.au/forums/topic/480204-cyro-treating-rb-block/
Share on other sites

Hardness != crack resistance.

It does correlate with wear resistance. Generally harder materials are less tough and more brittle. It's a cake and eat it too situation.

The reason RB blocks like to split is about how material is where, and the weak design features (where a little more bracing here and there would have made the block stiffer, even if they had cast it with cheese).

Is that 238 number a test of hardness ?

If so which one ? Is it Brinell, Rockwell, Knoop or Vickers ?

My understanding of Cryo treatments is that it is a stress reliving process - cooling the metal down to a very low temp and bringing up to a very high temp over a long period of time, usually around 48 hours.

I believe this realigns the dendritic crystalline structure of the metals for greater rigidity and thus greater strength. 

I think it is fair to say that cryo treatement is not about hardness. It is, at the minimum, about toughness, which is an engineering term.

I don't know if it is as useful on cast iron as it is on steels though. And there is much more anecdotal evidence that it toughens things like transmission input shafts and the like (ie, I cryo treated it and I haven't broken it yet) than there is really good materials lab measurements of what the mechanical improvements to parts actually are. It's getting better than it used to be, but I think it's still a little vague as to exactly what happens to the materials.

I know that RIPS has built a number of tough RB30s which rev to 10,000 and more and make 1000 Kw without blowing up with a number of measures including bracing and grout filling - but I don't know if RB25/26 blocks differ radically from RB30 blocks.  The ideal solution seems to be Bullet billet blocks but at $14.000 they are probably not for everyone!

RB30 blocks are weaker up the top because they are taller up there without any real additional bracing. The cylinder walls on RBs are not all that thick, the block deck is not all that thick. It's really just a fairly light casting in that area and its surprising that they do as well as they do. It's not surprising that they split when you push them too far.

RB26 blocks are broadly the same as 25 blocks in that area. Not as good as JZ blocks though.

24 minutes ago, Blakeo said:

Yes I'm using a hardness tester using the Leeb rebound hardness test.

But note what I've said above. It's a bit like measuring the colour change and trying to infer a strength change. Not necessarily related, not necessarily related with a positive or negative coefficient. Just not the right measure of the change that you're looking for.

Very interesting approach Cryo treatment of a block. I think every one will be interested to see the results - good on you for having a go. That said I'm really not sure how you can really measure / quantify the improvement. This is a pretty interesting read:

https://www.enginebuildermag.com/2017/03/big-chill-cryogenic-metal-treatment-benefits-may-not-visible-real/

One thing as previously mentioned is that the material definitely becomes more brittle. Another thing I picked up which I thought was interesting was the mention of completing any machining before the Cryo process, indicating a substantial increase in hardness. Whether this translates to a cast iron block not cracking as easily is yet to be seen I guess.

Got the block back from the cyro treaters today. I tested the block, using the same tool as before. It tested as 242. I don't believe this is a big enough increase for it to be due to the cyro treating, could be more due to different testing temperature differences or slight tool inaccuracy. 

Time for full build to begin now :) 

  • Like 1

When you originally tested the hardness, did you run multiple tests and take an average? Or did you test multiple areas of the block and take an average? 

What I'm wondering is, is the 242 within the range of your original hardness testing? 

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Similar Content

  • Latest Posts

    • I refreshed the OEM injectors with the kit and connected it up. It now ideals okay even with the IACV removed. Driving still has the same cutoff issue like the 550cc injectors so the issue is somewhere else. I bought FPG's Fuel Pump Hanger. I will be installing it next, but it is not as straightforward as I thought it was with my limited wiring knowledge and no instruction on the specific model I purchased (FPG-089). I also got the incorrect billet clamp as I could not find info on the OEM sizing.
    • Stop looking at the garage floor, and turn the radio up a bit louder if there's any strange noises...
    • No. Turbo shuffle and surge/flutter are not the same thing. Specifically, on a GTR, turbo shuffle has a definite meaning. On a GTR, the twin turbos are assumed to be the same thing and to operate the same way, exactly. In reality, they do not. Their exhaust sides are fed and exhaust a little differently, to each other. Their inlet sides are fed and exhausted a little differently, to each other. Consequently, when they are "working" they are often at slightly different points on the compressor map compared to each other. What this means, particularly when coming on boost, is that one of them will spool up and start producing extra flow compared to the other, which will put back pressure on that other compressor, which will push the operating point on that other compressor up (vertically). This will generally result in it bumping up against the surge line on the map, but even if it doesn't, it upsets the compressor and you get this surging shuffle back and forth between them That is "turbo shuffle" on a GTR. It is related to other flutter effects heard on other turbo systems, but it is a particular feature of the somewhat crappy outlet piping arrangement on RB26s. There are plenty of mods that have been attempted with varying levels of success. People have ground out and/or welded more material into the twin turbo pipe to try to prevent it. Extending the divider inside it works, removing material doesn't. There are aftermarket replacement twin turbo pipes available, and these exist pretty mush purely because of this shuffle problem.
    • You can temporarily* use lock collars to keep it in place until you can do the bushes, back the nuts off, slide them in, snug back up. *temporarily is often for ever
    • Thanks for the quick reply. To be clear, when you say turbo shuffle do you mean turbo flutter "stustustu" or referring to something else? I had thought they were the same thing. When I wrote the post my intention was to say it wasn't a flutter/compression surge sound. My understanding was that a flutter sound would be occurring when throttle is released, whereas I can keep the throttle in the same position for this noise
×
×
  • Create New...