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What Pistons For Rb30det W/ Rb25de Neo Head

Nigel.

By Nigel.,
in Engines & Forced Induction

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Nigel. Rookie

Nigel.

Posted
Posted

I'm in the process of building my RB30DET, but am unsure what pistons to use. I'm using an RB25DE Neo Head. Has any got any info on RB30E, RB30ET, RB25DET, RB25DE, RB26DETT pistons, specifically deck heights and dome / dish cc volumes.

The Neo head has a smaller combustion chamber volume, which with the standard RB30E pistons it'll give me 10.45:1 compression ratio.. well that's what i've worked out :banana:

I'd love to know from someone that's built an RB30DET with a Neo Head what pistons they used and what CR they have.

Thanks.

drgnball34 Rising Star

drgnball34

Posted
Posted

im doing the same thing but with a NEO RB25DET. I would assume the cc on a turbo/na head would measure the same? The work shop is using CP pistons designed for the rb25/30 33 head. I wonder how they are going to get the desired comp ratio, being that its a smaller cc? And can anyone confirm if the neo exhaust valves are larger then the rb26?

Nigel. Rookie

Nigel.

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I'm pretty sure the heads are the same bar the cams.

Pistons are what determines the compression ratio on the RB25's isn't it?

Yup, both RB25 neo heads cc around 50-51cc, both RB25 R33 Head are around 63cc.

The only difference in turbo and no turbo neo heads is the cams. Even the valve springs are the same (I thought they'd be different).

Good luck to me trying to find RB30ET pistons in NZ :glare:

Adriano Grand Master

Adriano

Posted
Posted
im doing the same thing but with a NEO RB25DET. I would assume the cc on a turbo/na head would measure the same? The work shop is using CP pistons designed for the rb25/30 33 head. I wonder how they are going to get the desired comp ratio, being that its a smaller cc? And can anyone confirm if the neo exhaust valves are larger then the rb26?

I would be asking the workshop what they plan to do about this, as it will end up with around 10.5:1 compression

drgnball34 Rising Star

drgnball34

Posted
Posted (edited)

the pistons have been delivered and sent off to enginering along with rods crank etc. I mentoined that the head had smaller cc but i am no mechanic and want to interfer with their jobs. But there are other ways to bring down the comp ratio? Eg: head gasket size and decking of head and block?

Also any particular reason why nissan designed the head to be smaller cc? disadvantages/advantages?

Edited by drgnball34
STATUS Grand Master

STATUS

Posted
Posted
the pistons have been delivered and sent off to enginering along with rods crank etc. I mentoined that the head had smaller cc but i am no mechanic and want to interfer with their jobs. But there are other ways to bring down the comp ratio? Eg: head gasket size and decking of head and block?

Also any particular reason why nissan designed the head to be smaller cc? disadvantages/advantages?

decking of head and block will increases comp ratio. Removing quench / squish areas in the head will decrease comp ratio (but has associated advantages and disavantages depending on application and in some instances induce knock at lower timing values than the higher comp high quench setup). see below pic of 26 head with quench area removed;

post-34927-1201529808_thumb.jpg

discopotato03 Grand Master

discopotato03

Posted
Posted

IMO if this workshop is worth their salt they will get a burette and cc the chambers first up . I think it would be highly irresponsible to build a customers engine with aftermarket pistons and not be certain what the static compression ratio was going to be .

Just for the record I'm sure many here would like to KNOW for certain if R33 and R34 chambers are same or different volume . It sounds like some are guessing without knowing for sure .

Cheers A .

Lil_Bobby_260 Mentor

Lil_Bobby_260

Posted
Posted

So if im running a Neo head (series two stageas run Neos) i should run the RB30ET pistons from ACL, but use say a 1.5mm head gasket to drop the compression?

I will be running a max of 15-17 PSI, through a largish turbo. Aiming for 350kw with supporting mods.

Adriano Grand Master

Adriano

Posted
Posted

I would do that with maybe a 1.2mm H/G, dont drop the comp much as youll mess with the piston/head clearnace. BUT you need to cc everything, dont go on what ive said, as rb30et pistons vary, and the head may have been decked(mine or yours) at some time which will effect the result.

Spoolup Mentor

Spoolup

Posted
Posted

I am using ACL RB30ET pistons - comp ratio is 8.5:1 with Std Nissan Headgasket.

I am about to build a new bottom end as I want more compression, so will be using Cp pistons.

CP make 2 pistons for the RB30/25/26 ( With R33 head ). So there 8.2:1 piston will come in very close to 9.0:1 with the NEO head - Ill cc everything to confirm but current calculations are around 9.0:1.

The Mafia Grand Master

The Mafia

Posted
Posted
I am using ACL RB30ET pistons - comp ratio is 8.5:1 with Std Nissan Headgasket.

I am about to build a new bottom end as I want more compression, so will be using Cp pistons.

Any reason why you want more compression?

Is the car a bit of a dog off boost even though its a 3l?

I want to built one, but I'm not sure what compression I would run.

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