Rb25De Rebuild

[RedDrifter]

Basically I am in the process of pulling down an R32 GTS25 RB25DE and getting it ready for a fairly basic rebuild to replace my RB20DET engine.

I will be bolting on my HKS GT-RS turbo thats on the rb20 at present and Really will only be chasing the max 450 odd Hp that the turbo can produce.

Basically I am new to engine rebuilds and I have be wanting to do a build up for years and to do most of it myself.

The final build will be as follows.

Head

Basic clean and prepped for the following.

Cams - Tomei 256's or 260's 8.5 mm lift Lash Type (Undecided yet)

New Performance Valve springs

Valves - standard size.

Head gasket - GT-R (standard thickness)

Head studs - ARP

New set of Hydrolic liftors from states (Maybe depends if old ones clean up ok)

Engine

RB25DET forged Pistons 8.5:1 CR (CP Pistons ??)

Rods stock ones (These are GT-R rods in this engine)

Crank Stock RB25

Bearings will be all ACL - RB25 Rods and RB25 Crank

Tomei Oil restrict orifices

N1 Oil Pump

N1 Water Pump

Crank Collar

ARP Rod Bolds

ARP Main studs

Timing Belt - Nismo or Tomei

Sump to be modified to Have trap doors etc.

Gaskets - Genuine except head gasket.

Hoses - All silicon where possible and genuine otherwise.

I have a few q's to ask.

The block does not have oil squirter's so do I need to get the pistons ceramic coated or will it be fine because of them being forged?

Should I use a Normal water pump as the N1's are known to cavetate a bit at idle causing over heating?

What other things do I need to know about ?

What basic things need to be done to the block and head for Preparation?

Which cams do people thinkI use 256's or 260's?

What other things have I missed I need to know about?

Thanks Guys

[Dose Pipe Sutututu]

Do you already have the RB25DE? If not I would suggest getting a low comp/raped RB25DET motor and building it up, the upside of the RB25DET is mainly the VCT which is god sent considering you're going to head for high duration cams, this would shift your power band up and you'll lose some of the bottom end, which isn't fun for a road car.

Road car, OEM water pump, that's my opinion, it's not going to be a track broad minded person so no point of a N1 pump which flows less at lower RPM

[R31Nismoid]

IMO that build is rather expensive for what a GT-RS is capable off.

Lot of money for now much gain overall realistically. The GT-RS will only net around 250-260rwkw which is what a stock RB25DET will do day in, day out.

Agree with starting off with a VCT head. Best way to do it if you really do want to.

[GTScotT]

In my eyes you are heading down the wrong path. A built motor is all well and good but VERY costly and should only be done on a needs basis.

The first thing to note is you have the right motor for an easy install into your car. You will not need to change your harness or ECU/injectors and you will be able to simply remap the RB20 ecu to suit. Injectors are cheaper and you wont need to worry about a VCT capable ecu. Cheap and cost effective.

I also believe the DE's higher compression will not only match the benefit of VCT but it will make for a better feeling motor all round. I also think it will easily handle the GTRS scope for power. Another member here has 280rwkw out of his unopened DE as im sure many others have also met and exceeded. I do not see the DET is OVERLY more capable.

The next thing I have to say is you have the right motor for a cheap and easy RB30 swap.

So my advice to you is: slap it all together and get it tuned on the factory built bottom end. When you have had enough of what youve got, build an RB30 bottom end instead of a pissy 25 and mod your R32 Rb25 head to that block. Sell your used GTRS for more than the cost of a 35R and have an ANIMAL. Still utilising your remapped ECU.

Do it. Do it now.

[bubba]

The head on the engine you have is the PERFECT plug and play head for putting an RB25/30 in an R32 GTSt... they are getting as rare as hens teeth to find!

If I was you, I would be freshening up a RB30E bottom end, dropping the 25DE head on and bolting all the RB20 ancillaries to it.

[GTScotT]

The head on the engine you have is the PERFECT plug and play head for putting an RB25/30 in an R32 GTSt... they are getting as rare as hens teeth to find!

If I was you, I would be freshening up a RB30E bottom end, dropping the 25DE head on and bolting all the RB20 ancillaries to it.

Thats two of us recommending this now!

[bubba]

Thats two of us recommending this now!

You know what they say about great minds..

[Dale FZ1]

In my eyes you are heading down the wrong path. The first thing to note is you have the right motor for an easy install into your car. You will not need to change your harness or ECU/injectors and you will be able to simply remap the RB20 ecu to suit. Injectors are cheaper and you wont need to worry about a VCT capable ecu. Cheap and cost effective.

you have the right motor for a cheap and easy RB30 swap.

build an RB30 bottom end instead of a pissy 25 and mod your R32 Rb25 head to that block. Sell your used GTRS for more than the cost of a 35R and have an ANIMAL. Still utilising your remapped ECU.

The cost of parts/machining will be no different between a 25 and a 30. Massive difference in torque delivery. Stick with a GT3037, more than adequate for the job. Question marks over clutch and gearbox are the only issues I would have.

The head on the engine you have is the PERFECT plug and play head for putting an RB25/30 in an R32 GTSt... they are getting as rare as hens teeth to find!

If I was you, I would be freshening up a RB30E bottom end, dropping the 25DE head on and bolting all the RB20 ancillaries to it.

Keeping it simple gets it on the road sooner, I like the idea.

considering you're going to head for high duration cams ... you'll lose some of the bottom end, which isn't fun for a road car.

Road car, OEM water pump ... no point of a N1 pump which flows less at lower RPM

He'd get away with using stock 25DE cams, stock oil pump and water pump. Big cost savings there alone and making it worth a second look. Cost out the head studs vs brand new genuine head bolts, and depending on if he's prepared to restrain rev limits and tune sensibly then stock 30 rods, rod bolts, and replacement spec cast 30E pistons would seal the deal and release funds to put in a DET spec gearbox and a clutch (depending on if there is already an upgraded unit installed) that can handle the torque.

Massively different driving experience without overspecifying components or spending blowouts.

[bubba]

Stock 25DE cams are more than adequate, we managed to push 365rwkw through a standard RB20 throttlebody, plenum and R32 25DE cams.

[RedDrifter]

Do you already have the RB25DE? If not I would suggest getting a low comp/raped RB25DET motor and building it up, the upside of the RB25DET is mainly the VCT which is god sent considering you're going to head for high duration cams, this would shift your power band up and you'll lose some of the bottom end, which isn't fun for a road car.

Road car, OEM water pump, that's my opinion, it's not going to be a track broad minded person so no point of a N1 pump which flows less at lower RPM

I already have the RB25DE motor (picked it up for a song and the bloke threw in an engine stand as well) and its almost stripped (well Bottom End is anyway) .

I'll have the crank out tonight and remove the oil and water pump etc.

I'll organize it to be prepped sometime this week/next week, time permitting at work of course.

I'm not chasing RB30 mountain moving Torque but rather I'm trying a balanced setup.

The Rb20 with the GT-RS in my r32 already has the GT-R Injectors and a returned ecu, all supporting mods for max output from the turbo. The idea was for me to have a motor a little bigger and to look identical to the RB20.

I love the sleeper appeal.

I am hoping for a more balance setup with a a better bottom end and a better midrange with out to much top end reduction.

The RB30DET wasn't what I was after a little its a little too torquey. I think the Rb25DE+T will be a great setup if I do it right.

[Dale FZ1]

Yes a 25 would be good, but the John Holmes factor is too big to ignore.

It won't be less of a balanced package just because it has more torque. By using the R32 spec head you still end up with an easy build, sleeper appearance only the top of the engine is ~30mm taller than a short-stroke stocker. This is nothing really new, was done by Cubes a few years back to great effect.

I think the posts have only been intended to open up your perspective to a different approach. It's never good to find yourself spending twice, but it's always great to see people having a go at their own build. At this stage you've got the most options available before committing.

Good luck and keep us posted on your progress.

Edited June 7, 2011 by Dale FZ1

[bubba]

LOL *too* torquey?!

Whatever floats your boat mate but a fresh stock RB30 bottom end under your RB25DE head, with all your RB20 stuff bolted on (ecu, coilpacks, injectors, turbo etc etc) and that GT-RS turbo would be quite a formidable street car.

[discopotato03]

I thought the VVT RB25 heads had larger inlet ports and inlet manifold runners than the R32 era RB25DE ones .

I'm not certain but I think the R34GTt inlet manifolds take later injector styles which get gets around the expensive side feeds though I think the S15 ones would cope .

The DET short would have got you oil squirters and 9:1 CR pistons .

I have not heard of RB25s splitting oil pumps so not sure if the collar is necessary .

I can understand you wanting your engine to look like an RB20 but the number won't so if it has to change why not go for everything Nissan had to offer ?

Anyway I'd drill and tap the block for the piston oil squirters and use the R33 turbo oil pump and the std water pump , Imo water pumps are about the engines speed range more than anything .

Its really a case of recreating what Nissan did when they turbocharged the RB25 , sadly the updates may cost more than the difference in price of NA vs turbo bottom end .

Because RB25DE heads are sought after for easy RB30 conversions you could always sell it or the motor complete and just buy a used but not beyond help RB25DET without turbo . It may cost a little more initially but if most of it is reused then you can come out ahead in the long run .

People invariably find out in the end that factory engineering is the cheapest option if id does what you want .

Your call , cheers A .

[GTScotT]

Again, I am going to recommend you simply whack that motor in and get going with it. Especially considering you have your heart set a 2.5L... And a 25 with GTRS, I wouldnt blame you.

I see a number of recommendations to go to the DET, but I still feel its a step backwards. The reasons why are, OP is unable to retain his existing injection setup and it is a lower comp motor. Yes the plus side is VCT.. But he already has an adequate setup management wise. A tunable ecu, GTR injectors, bolt on manifolds..

OP, in your 'op' you wanted to use 8.5 CR pistons. I recommend again that you simply put the thing back together and strap it into the car. Its factory make up is more than adequate for your GTRS plan and a simple refresh now will see it last the duration of its remaining life (with the said GTRS).

Up to 4c now, I'll stop flogging the dead horse.

OH and I still +1 to get an RB30E bottom end, refresh it AS IS and bolt all your crap to that. God it will cost you a case at most and everything else remains the same as I have already recommended.. Just HEAPS more torque.

GL

[Dobz]

+1 for rb30 block.

If you're going to spend that sort of money on the bottom end you may as well make it worth while and do an rb30. It's better bang for buck and the extra torque makes it a lot more bearable to drive off boost rather than having to kick it in the guts to get it moving.

To answer one of your questions the non oil squirter blocks like yours and the rb30 do have a rudimentary style squirter that squirts out of a little hole on the side of the con rod when the crank oil feed hole lines up with it.

[RedDrifter]

So basically not many of my q's were answered but rather I get the whole anything other than RB30 bottom end is wrong.

Let me explain my self better here.

I wish to go down the Rb25 path NOT the RB30 path.

So if anyone else wishes to tell me to go down the RB30 path please keep you comment to your selves.

I Just was after advise on what I am doing with the RB25DE build.

Edited June 8, 2011 by RedDrifter

[Dale FZ1]

I get the whole anything other than RB30 bottom end is wrong.

I Just was after advise on what I am doing with the RB25DE build.

There is nothing inherently wrong with your plans/approach. A 30DET is just an alternative approach. Nothing more to say on that.

Many of the same things that apply to building a 30 will apply for your 25.

Head: have a competent cylinder head specialist check the casting for integrity/straightness. Just making sure it hasn't got hot at any point. The R32 spec head does have smaller inlet ports, no big issue with your goals. Not worth playing heavily with port work, but if you have the head disassembled and available funds then port matching both sides is worth it, and smooth/reduce the size of those lumps in the exhaust port outlets where the studs screw in. Keep it simple, no radical/expensive/time consuming work required but you have the opportunity.

If you want cams, the smaller spec will be more than enough improvement. Ultimately the smallish GT-RS turbine will restrict the engine's capacity to keep making torque at higher rpm. Makes the larger cams pointless. New/uprated valve springs would be a good idea, Performance do a good product. Hydraulic lifters are simple but time consuming to disassemble and clean, but once done they become perfectly serviceable again. And if you need to replace one or two then it's much cheaper.

Stock 25DE spec water pump, inspect/clean and reuse OEM oil pump with 1mm shim under the relief spring.

Crank: inspect the drive collar already fitted to see if there is full engagement on the OEM pump. If so, it's just a clean and install.

Pistons/rods: Good approach. Some advocate 9:1 or higher, up to you. If you have the time and gear available, weigh them individually and look to get the least variance in assembled/installed reciprocating bits. If you choose to install new rod bolts then it can become questionable whether to use OEM gear or just go to a set of brand new forged rods for nearly the same cost. Coatings - see comment about block. Not sure about durability of ceramic coatings on piston crowns.

Fasteners: head studs overkill, contain costs just use new bolts straight from Nissan. Install new exhaust manifold studs throughout.

Gaskets: a full rebuild gasket kit will include a head gasket, suggest a steel head gasket would be worth using.

Belts: Bosch or Gates will do something suitable for cam drive. Don't forget your idler/tensioner. Competent bearing supply company can supply eg CBC.

Block: overall reliability will be improved if you use a DET spec block with the oil squirters. Highly recommended but not essential. Drill out the oil returns (don't forget to do those in the head), and oil feed restricters are good. Brand name? Have your machinist check/install suitably sized MIG wire tips. Much cheaper, and works the same.

Sump: the stock 25 sump has all the goodies it needs.

Other: you need an oil cooler of some description.

Your checklist is pretty comprehensive and generally shows there has been some thought about componentry. The performance objectives don't seem sky-high so the above is intended to spark some thought about gearing the purchases to match the output/performance level. Costs can run away.

Make sure you have a competent machinist (much emphasis here), and pay a LOT of attention to clearances and cleanliness on assembly.

Edited June 9, 2011 by Dale FZ1

[bubba]

On the topic of restrictors, I got some 1/4" x 1/4" grub screws and some mig tips and ended up going with the grub screws. Went to see my mate with a drill press and 4 drill bits later I had two 1.5mm restrictors (running front feed at 1.5mm and rear feed blocked).

Tapping them in to the block means that I can easily remove them in the future if I need to change restrictor size.

But yeah, everything Dale said is spot on. I would still go with a 30 though but I'm slightly biased seeing as that I have a 30 in my 32gtst

[GTScotT]

Is there a need in an expensive build for a GTRS RB25? 250rwkw?

I highly doubt forged pistons will do anything for the longevity of the motor at that power..

Again, keep it simple.. Save your cash, enjoy what you have.

From memory I was quoted $500 to drop off and pick up my long motor to a builder. That encompassed a tear down, clear up and refresh of a working (not damaged) motor. Included was rebalancing the crank and fitting a crank collar I supplied.

This is exactly what I'd do in your case, then get a factory gasket and hose kit for it and put it in the car.

[bubba]

Forged pistons aren't really power dependant, they just allow more tolerance for detonation.