RB25DE NEO into S30

[vosadrian]

Hi All,

We are doing an engine conversion on an S30 (260Z 2+2). We want to maintain the character of the car, but have a reliable engine, so we want to stick with an NA straight 6. Looking into this and it seems the RB25DE NEO engine is a nice NA straight 6 engine that would suit, but I have some questions:

* It seems these came in AWD and RWD with AWD being more readily available. It seems the AWD has some differences requiring oil pan modification and the oil pickup location is changed making it incompatible with RWD sumps. With an S30 this is further complicated as you need a rear sump oil pan to clear the cross member. So is there a way to get an AWD NEO into an S30 without too much effort, or is that too hard, and I should just limit myself to RWD engines.

* What cars came with the RWD NEO? Many NEOs seem to come with Auto. Are they AWD or RWD or both? I presume all Stageas are AWD. Are all Skylines RWD?

* Can all the usual RB manual transmission options bolt to any NEO engine block? Is the Auto block and AWD block compatible with any RB25 manual transmission?

* Has the NEO engine got any special engine management requirements that make it difficult to run with an aftermarket engine management computer? Is the NVCS system a simple on/off system?

We are considering later swapping out the block to RB30 for more capacity which I believe can be done with the NEO heads. I'm just wondering if we do that straight up to avoid the hassle with the AWD block differences. 

Thanks for any advice!

 

Edited January 20, 2022 by vosadrian

[Duncan]

AWD blocks have bolt holes for RWD sump, so that part is OK. I am not sure how the pickup should be dealt with, the pickup is further forward in AWD block to avoid the front driveshaft which passes through the sump. I guess "something" custom is required there. 

There are both AWD and RWD Neos in Skylines, Stageas, Laurels, all sorts of things. Either should work as the base for your conversion, noting you will need a RWD or custom sump if you buy a 4WD engine

Yes, auto and manual are the same block, the only difference is ring gear/torque converter vs flywheel and clutch and be aware the autos don't have a spigot bush (but you can insert on to the crank)

Engine management is simple, any decent RB ECUs will support it.

RB30 with a NEO head would save you 2 sets of changes (noting the Rb30 deck height can cause rework in exhaust, intake, coolant etc piping)

Also, be aware that the RB25DE/DET NEO heads are the best of the RB series heads and are often in demand for conversions. You may find it easier/cheaper to go with a non-NEO engine.

[vosadrian]

Thanks for the info!

For some reason in the places I am looking for RB25s, I am mostly seeing RB25DE NEO with Auto. A couple are unspecified. Are the RB25DE NEO Autos all RWD? On carsales when I look for an R34 with Auto, they are all RWD. I am wondering if it is safe to assume that a NEO auto has the RWD block and is therefore easier to source an oil pan for? There is an aftermarket oil pan available for the RB25 fitting to an S30, but it states it does not support NEO, and I assume it is because of this oil pickup location issue on the AWD variant of it. I presume an RWD NEO would be the same in the oil pan as older RB25/30 and should fit this oil pan.

That is a good point about the deck height changing the position of things. Will have to consider if we want to go that way. 

[Duncan]

I can't say for certain, but this was a common engine in AWD vs RWD and Auto vs Manual. It may simply be that most manuals were behind turbo engines.

I'm not aware of any reason a RWD sump would fit a non-NEO, but not fit a NEO, as I believe all the material differences are in the head and intake (again from memory, I think the rods may be rb26 in the NEO but that has nothing to do with the sump). It can't even be related to NVCS feed or return because that was on the non-NEO heads too. I'd ask the seller what the issue is.

A RWD oil pan bolts onto either RWD or AWD blocks no problem. From memory something is required with the pickup using an AWD block and RWD sump but from a quick search on here it may be as simple as modifying the standard sump baffles to suit. Again this issue was across non-NEO and NEO blocks and did not change AFAIK.

[vosadrian]

Thanks again!

I did some research on the AWD NEO oil pan. It seems in the AWD the front shafts go through the oil pickup location the RWD block uses. So the AWD block has a different pickup location in the casting. The mounting points for the RWD pickup are still there but it is not drilled into the oil pickup gallery... and apparently the casting does not have a gallery, so you can't just drill it. The AWD block does have the mounting bolt holes for the RWD sump, so it seems a common solution is either to cut/weld an AWD sump to remove the shaft holes, or to fit a RWD sump, but modifify the internal baffling for the moved pickup. Unfortunately neither are an option on an S30 since you need a "rear sump" oil pan to clear the cross member, so neither AWD or RWD  oil pan for a "front sump" pan will work. 

So on an S30 I needed another sump anyway. Typically when fitting an RB (RWD) to an S30, they either get a very rare sump from a rare Sxx model that had an early RB engine... or they get a Nissan Patrol RB oil pan which is rear sump, but it needs some modification to clear, but seems fairly minor.... or they get an aftermarket oil pan made for the purpose. But none of these options are available for the AWD block that I can see. So getting that working would be full custom oil pan which would be expensive and a one off. So I will do my best to get a RWD block. 

I am surpised that noce of the RB25DE NEOs I see for sale are listed as AWD or RWD... but many are listed as Auto. Hopefully the Auto means RWD... but I will have to get pics of the sump to see if they have driveshaft holes. 

[GTSBoy]

On 1/20/2022 at 1:17 PM, vosadrian said:

So getting that working would be full custom oil pan which would be expensive and a one off.

Yeah, worth it, if needed. Also not difficult. Just need a pan rail water/laser cut and then some fabrication.

On 1/20/2022 at 1:17 PM, vosadrian said:

So I will do my best to get a RWD block.

Sensible option anyway. Why make life harder than it needs to be?

On 1/20/2022 at 1:17 PM, vosadrian said:

I am surpised that noce of the RB25DE NEOs I see for sale are listed as AWD or RWD... but many are listed as Auto. Hopefully the Auto means RWD... but I will have to get pics of the sump to see if they have driveshaft holes.

I think there can't have been too many AWD NA Stageas around. The RB25DE is a toothless piece of shit (no offence to your chosen engine for your conversion) when in a heavy station wagon. You wouldn't want to add the burden of AWD transfer case and front diff etc. Therefore they are likely all from 2WD Stageas or NA Skylines.

[Duncan]

OK the Patrol sump is potentially available in Aus but I'm not sure where you are (no location on your profile), there were a reasonable number sold here.  I guess the rear sump still uses the regular RWD oil pickup point (obviously the Patrol is 4wd but it is likely the 4wd system is different to the other RB AWD systems), all of which sounds like the AWD block will make the pickup issue worse.

One other option to consider, it is straightforward to modify the RB oil pump to use an external oil pickup, which you could then plumb to wherever your sump is. I don't have pics hand but there is an external bung on the pump that you can tap a fitting into instead (and block off the internal pickup of course)

[Dose Pipe Sutututu]

ASR Sumps do a AWD -> RWD conversion to fit a few different cars to clear any steering racks, etc.

I once had an AWD RB25DET NEO in a R33 and ASR was able to supply a sump, pick up to suit the motor

 

I hope you port it, stick massive cams in it, and make it brap  

[vosadrian]

Thanks! I'll check out the ASR options. The website does not have much info on standard products, so will give them a call. Our plan at this stage is to stick a stock engine in and get it running, debug any issues and registered etc. Our eventual plan is to do some mods... and we don't want to solve all the problems again for a different sump arrangement... so if we go AWD setup and then change to an RB30 bottom end again, we have to do it again. So RWD is preference for compatability with any block we might change to.

The plan is definately to make it brap! Eventually we were wanting RB26 ITBs (with velocity stacks) and porting with cams and a bottom end for 8-9000RPM. It will still make a lot less power than a basic DET setup... but it should sound and feel old school cool like the 260Z should! There are some cool high revving NA RBs with ITBs running around that sound and look cool. The S30 is light so it should go OK even without a turbo. I also have a 500hp GC8 WRX I use for motorsports that does a high 10@125mph. This car is more about fun cruise/meets than taking it to the drags. 

[GTSBoy]

On 1/20/2022 at 2:08 PM, vosadrian said:

we were wanting RB26 ITBs

Waste you money not. There are better ways to get ITBs than to strap on 30 year old GTR taxed stuff.

On 1/20/2022 at 2:08 PM, vosadrian said:

a bottom end for 8-9000RPM

So....stock then?

But I urge 12:1 compression and E85, 300° cams and the best extractors money can buy (ie built, not bought, seeing as there probably isn't a decent off the shelf option anyway).

[Dose Pipe Sutututu]

Go even higher comp, throw in E85, why stop at 12? haha

VCT, big comp, big cams, big braps in a classic zed would make and grown man's balls tingle.

[vosadrian]

@GTSBoy, School me on the ITB options!! We are not committed to the RB26 option.

For us it is all about the sound and feel of the car. Big power figures are not required. Any RB25 NA engine is going to be a big power increase on what an L series NA can do. It has to run well on 98 fuel. I run my WRX on E85, and I like it on a big boost turbo, but it can be a hassle to get at times. The S30 has to be able to go on a cruise and get fuel in little town 2 hours from a major city. So that will probably set the comp. Then we will get the heads done and some not too wild cams. I think revving for max power around 8k (limit to 8500?) as it will cost lots to get a bottom end to stay together much higher.  That should set the cams. We want to run the NCVS which is one of the reasons I wanted the NEO head. Some nice headers with the ITB should do OK for power and sound great.  Light flywheel so it is snappy free revving. 

We just have to find the right engine to start with first!

[GTSBoy]

There are literally dozens of aftermarket throttlebodies in DCOE carby format. The RB26 ITBs are so very very close to the DCOE bolt pattern that it is difficult to believe that Nissan came that close and didn't actually just use the DCOE pattern.

Then, you can look at just about any EFI motorbike from Suzuki, Yamaha, Honda, etc that used single throttles, in whatever size floats your boat. 45mm? 48mm? Larger? They're all out there. Just build manifold and plenum and linkages to suit.

As for compression and cams - the larger the cam duration, the more compression you can run. Just sayin'.

And as for cost for bottom end.....8500 rpm is well within the limits of the stock bottom end. Especially NA. It won't cost much to make it good for >9000. Just need some light pistons and some moderately strong rods and bolts.

On the subject of VCT.....all RB25s have it (except for the very first ones in the R32). The vanilla 25s in the R33 era cars were all VCT. There's almost no difference in the VCT between vanilla and Neo engines. The difference between Neos and vanilla 25s is that the Neos have solid lifters, a different included angle in the valves with a shallow combustion chamber. And in the NAs.....not particularly good flowing ports.

I would not write off the power potential of an L series vs an RB25DE though, neo or not. 2.8L & 3L (and larger) L series builds, even running Mikunis, have made really large power. There is nothing wrong with the single cam engines. The twin cams are not inherently a massive leap in power potential.

[vosadrian]

WIth the RB26 ITBs, you get the linkages and everything sorted. There seems to be full RB26 setups around for $5-700. Can I do it any cheaper with DCOE? 

I thought I read somewhere that the early VCT on RB25 heads was prone to failure if run with aggressive cams/springs and that the NEO was better? Any truth to that? Also if doing port work, does it make any difference whether you start with NA or turbo heads? I would have thought the NA engine would be more sensitive to ports than a turbo so I am surprised they have worse flowing ports. Turbos normally get over poor flowing heads with boost.... they typically flow less volume but at higher air density.

I know a good L series can make good power... but a good L series is close to a mild RB25DE. A good RB25 should excel, and should be easier adaptable to EFI etc. I don't want carbys. And I think with aggressive cams and VCT, the potential for a nicer running wider power bands is better on an RB engine. 

[Dose Pipe Sutututu]

On 21/01/2022 at 3:13 PM, vosadrian said:

I thought I read somewhere that the early VCT on RB25 heads was prone to failure if run with aggressive cams/springs and that the NEO was better?

Non-NEO RB25DET with VCT utilise hydraulic lifters, they're actually pretty good however don't like the tits revved of them as the hydraulic lifters can't keep up.

To some extent, they're better as there are no shims to spit out and require pretty much no maintenance. In stock format, big cams and stock valve springs they are aids. Valve lift galore, with decent springs, cams they're a pretty good head.

NEO RB25DET, although in theory "It's a RB26 head with VCT" in practice is a touch different as it's shim over bucket, not bucker over shim. Problem with this, is that if your clearances are shit, you'll shit out shims when you rev the tits out of it or bang the limiter more than Stacey's mum.

[GTSBoy]

On 1/21/2022 at 12:13 PM, vosadrian said:

WIth the RB26 ITBs, you get the linkages and everything sorted. There seems to be full RB26 setups around for $5-700. Can I do it any cheaper with DCOE?

Cost is not the point. 30 yr old worn out linkages and butterflies that don't seal..... vs brand new something else. I know what I would be doing. If there wasn't already an ITB setup available for a similar engine, you wouldn't even be considering using 30 yr old worn out shit. You'd be looking at other options straight up. My brother-in-law built up a set of ITBs for a n NA 7M from scratch (from bike TBs), because that was the only option. He then did the same for a 2JZ.

I mean, shit, it's not even as if the RB26 setup is bolt on. You have to do so much f**king around to put them on that it is simply not worth the pain unless you like the pain.

On 1/21/2022 at 12:13 PM, vosadrian said:

I thought I read somewhere that the early VCT on RB25 heads was prone to failure if run with aggressive cams/springs and that the NEO was better? Any truth to that?

Not in any meaningful way. The age difference probably explained all those failures.

On 1/21/2022 at 12:13 PM, vosadrian said:

Also if doing port work, does it make any difference whether you start with NA or turbo heads?

RB25DE made no power from factory, so had no need to have good flowing ports. The Neo 25DEs in particular, used the concept of keeping the ports small to keep the velocity high to maximise in-cylinder mixing. Remember that the whole point of the Neo was to meet the ELV emissions requirements that the vanilla RBs had no hope of achieving.

On 1/21/2022 at 12:13 PM, vosadrian said:

Turbos normally get over poor flowing heads with boost.... they typically flow less volume but at higher air density.

Not really. It's just that you can overcome poor head flow with more boost. That's not a clever way to do things, because inefficiency is still inefficiency. So OEM engineers tend not to do it that way!

On 1/21/2022 at 12:13 PM, vosadrian said:

A good RB25 should excel, and should be easier adaptable to EFI etc. I don't want carbys. And I think with aggressive cams and VCT, the potential for a nicer running wider power bands is better on an RB engine. 

Meh - they're just not that exciting. Have a google around for how much power people are actually making out of worked NA RBs. They're OK, but they hardly set the world on fire. You'd probably make a lot more power with any of the more modern 2.4-2.5L 4 cylinders, as pedestrian and horrible as they are.

As an example - my NA 2JZ example from above. ITBs, good extractors, cams, 20% capacity advantage over an RB25, and certainly no worse engine design (actually a substantially better engine than the RB)..... made about 140rwkW. Was nice to drive, but certainly wasn't fast. Even if you can turn it to 9.5k rpm and maintain torque production up at those revs (ie, lots of cam!) then you still only make maybe 20 kW more.

I'm not trying to dissuade you from anything. Just pointing out that the NA RBs are not some super engine. They don't hold a magical key to massive power (TM) just because they are newer and twin cam. The RB bottom end is actually not that far removed from the L series bottom end on which it was based. The basic engine architecture goes back to the Mercedes in-line 4s and 6s of the 1960s that Nissan copied to come up with the L series.

http://build-threads.com/admin/z31-300zx-project-z432/

[GTSBoy]

Same car, I think they mention the power output in it, but I'm on a metered connection, so am not going to sit through any more of Jackie Chan's mindless f**king dribble.

 

[GTSBoy]

Doesn't rev to 12k , by the way. Typical American cock throttling.

[vosadrian]

I get that the RBs in NA form are not the best engines around. I'm not looking for the highest power NA engine around. We are really doing NA for sound and feel and we want to keep to the Nissan/Datsun family and we want to keep it straight 6. Obviously we could stick an E46 M3 engine in or something and that is a good NA straight 6. But we want to keep it in the family. Does that then leave just L series and RB series engines? Another point, is we want it EFI (I have worked a lot in aftermarket EFI and I enjoy working with it and tuning etc.). My take is that by the time you adapted an L series to EFI and modified it for good power, you would be down more $$ than doing the same with RB series. Have I got this wrong?

And we don't need huge power.... but we do want to optimise what we have. But not to 110%. I'm all for finding some easy extra revs with an oil pump upgrade and some decent cams and valve train... but I don't need fully lightened balanced for 12k RPM at very expensive $$. As I said, it is more about the sound and feel. But if we can spend a few $k on getting the bottom end to rev reliably and the top end to flow to good revs, we would go that far. Is RB the right choice for this? Is there another option I have missed?

[Diomedes]

 I mean, I'm no expert, but you kind of don't have a choice if you want to keep it in the nissan datsun family, straight 6, and EFI? It has to be some sort of RB? Or the only other option I can think of is the TB series? Like the TB42/5E or TB48DE? Could slot one of these badboys onto it https://rossperformanceparts.com/product/nissan-tb48-billet-dry-sump/ 😅

 

If it's about sound and feel, and not about the numbers you are going to see on a dyno sheet, then the RB25 seems like a decent option?