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Rb30/25 Conversion Questions!

N0Vus

By N0Vus,
in Engines & Forced Induction

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R32Abuser Mentor

R32Abuser

Posted
Posted (edited)

Here in NZ, Rb30's are very hard to come by so its not as easy as $150 worth of parts, when you'd be lucky to pay less then $300 for a bare block :/

I was planning on building it to around 350-400kw, for use on the road and to try get on the track as much as I can. Hoping it will be something I don't have to worry about to much in the longer(ish) run.

And I dont have the standard pistons, only the rods.

So you are pretty much saying if im only after 350kw, stick with std bottom end and put my money into the Neo head?

On the other side of things, by the looks of things the only way im getting a RB25DET Neo head is by buying a complete motor.

Thanks for all the feed back everyone, helps alot.

***EDIT

Ok, so Im thinking I will leave the pistons for now and see if I can get a hold of a 25DET Neo head. As R32Abuser said, the higher compression is better for off boost, which I understand. So my next step is, since I dont have stock pistons I will probably get some forged ones to achieve static 9:1CR and I suppose a bit of piece of mind to know I have a good set.

So should I run with stock rods or get forged rods? As I said im after 350-400kw, but will be good to have something capable of handling more as I dont see my self getting rid of this motor once built and would like the option of going further as years come by.

Well that changes things a tad...

A stock bottom end @350RWKW in a streeter would be fine IMO provided the tune is in check (SAFE!!!). That said, you would be needing to run something in the order of a GT3582 on 98RON to get there which generally would mean high mount. Something which doesn't exactly scream OEM...

400RWKW would be pushing the envelope a bit. Given the "rarity" that I'd imagine RB30's are over there, yes, you would be better off going forged pistons at the least to save you the hassle of sourcing another bottom end. But, like I said above, all it takes is a bad tune, a bad batch of fuel (or both!) and you can kiss either bottom end goodbye...

The Neo head has solid lifters, VCT (over the R32 RB25), more efficient chamber profile (LEV) and a larger range of injectors to chose from. For me, if going through the hassle again, I would take the Neo everytime. But your certainly pay more for them!

Edited by R32Abuser
N0Vus Contributor

N0Vus

Posted
  • Author
Posted

In the way of tuning, I have access to a tuner, who has lived and breathed link all his life and also owns his own dyno etc.

So I feel I can get a decent tune for sure!

Ok so my plan now is, source a RB25DET Neo Head.
Once ive got the head then I can proceed to get the pistons.
And carry on as I was :)

Im not to concerned if it will take me longer to build using the Neo head, but Im young and can wait haha

iruvyouskyrine Grand Master

iruvyouskyrine

Posted
Posted

Stock rods are fine for his target.

However, by the time you price them up to go with aftermarket pistons they end up costing almost as much as a forged 4340 set from SPOOL or similar...Or at least they did when I went down this path!

http://www.spoolimports.com/spool-conrods/nissan/rb30-conrods/nissan-rb30-conrods

I believe KiwiRS4T meant he should get ARP or similar rod bolts not conrods...

iruvyouskyrine Grand Master

iruvyouskyrine

Posted
Posted

Stock rods are fine for his target.

However, by the time you price them up to go with aftermarket pistons they end up costing almost as much as a forged 4340 set from SPOOL or similar...Or at least they did when I went down this path!

http://www.spoolimports.com/spool-conrods/nissan/rb30-conrods/nissan-rb30-conrods

I believe KiwiRS4T meant he should get ARP or similar rod bolts not conrods...

KiwiRS4T Grand Master

KiwiRS4T

Posted
Posted

Did you use 2x ARP SR20 rod bolts (which are apparently exactly the same size as RB30)? Had a quick google before and it seems ARP don't sell RB30 rod bolts

Sorry didn't source them myself. I guess whatever fits would be fine.

R32Abuser Mentor

R32Abuser

Posted
Posted

Did you use 2x ARP SR20 rod bolts (which are apparently exactly the same size as RB30)? Had a quick google before and it seems ARP don't sell RB30 rod bolts

If memory serves, I believe this is the case. But you'd have to confirm as its been too long!

R32Abuser Mentor

R32Abuser

Posted
Posted

I believe KiwiRS4T meant he should get ARP or similar rod bolts not conrods...

For some reason when I was pricing everything up, to use the CP pistons I had with the stock rods, I thought the pin size (or another dimension) was different.

Hence, when I priced them up (and a close mate also told me) it ended up costing like $4-600. As per my link above, a set of forged rods cost a touch more. Made my choice easy.

However, it seems I may have been misinformed!

R32Abuser Mentor

R32Abuser

Posted
Posted (edited)

In the way of tuning, I have access to a tuner, who has lived and breathed link all his life and also owns his own dyno etc.

So I feel I can get a decent tune for sure!

Ok so my plan now is, source a RB25DET Neo Head.

Once ive got the head then I can proceed to get the pistons.

And carry on as I was :)

Im not to concerned if it will take me longer to build using the Neo head, but Im young and can wait haha

Probably stating the obvious, but the pistons to suit the NEO head will be different (dome or dish) to the pistons suitable for a R32/R33 RB25 head.

So make sure you get the right items! If you dont, your static CR will be off the chart!

This is due to the combustion chamber differences (i.e. size).

Edited by R32Abuser
N0Vus Contributor

N0Vus

Posted
  • Author
Posted (edited)

Probably stating the obvious, but the pistons to suit the NEO head will be different (dome or dish) to the pistons suitable for a R32/R33 RB25 head.

So make sure you get the right items! If you dont, your static CR will be off the chart!

This is due to the combustion chamber differences (i.e. size).

Yeah I understand that, I will make sure I talk to the supplier and ask for what ones they offer for the 25 neo, for 9:1CP, and double check it here and with a couple of other places to make sure, I could probably ring RIPs.

Another question I have, Will a R33 head bolt onto a R34 Neo Block? Since the Neos are hard to find as just I head im tempted to Buy a complete package, raid what I need and put a R33 head on? And sell off, Would this work? And Does anyone have a clue on what the compression would end up being from this?

Cheers, Liam

***EDIT

Answered my own questions, but have come back with another, what is the compressed thickness of a RB25 headgasket?

CP Calcuator says 8.18:1CP, if the head does fit. I did have to fill the field "Compressed Head gasket thickness" with the size of a head gasket regularly available, now is the advertised thickness the compressed size? Or uncompressed? Just so I can have that information avalible

Edited by N0Vus
R32Abuser Mentor

R32Abuser

Posted
Posted

Without doing the calcs, that number seems about right. The 33 head has a larger cobustion chamber (more cc's), hence the static CR would be bumped down a bit when used with a neo bottom end.

I believe its compressed thickness but I am not 100% sure. Someone to confirm?

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