Rb25/30 How Long Will It Last?

[Tony1981]

Hey guys,

Was looking for some real first hand experience :-),

I am in the middle of putting together an RB30 N/A engine and R33 RB25 head, but was curious about how long this thing will last,

I have quite a few RB30 blocks lying about the place, but I also have a very decent complete RB30 engine, 155 across all cylinders, about 190,000km's on its clock and one complete RB25DE from an R33,

What I was thinking of doing is basically slapping on the RB25 head without touching the RB30 bottom end, I figure this should give me a reasonably boost friendly compression ratio of somewhere between 8.2 to 8.5:1 - looks like the head has been off at some point and replaced, so maybe someone decked the block, dont know,

I was going to run standard Nissan head gasket, standard nissan RB25 head studs,

From what I have gathered the only difference between the RB30E and RB30ET pistons is one is dished, but both are made out of the same stuff, so as long as I am not chasing big big HP, my stock RB30 N/A bottom end should hold together???

Just interested to find out if other people have gone down this route and had success, I remember speaking to the fellows at RIPS a few years back and they said they did something pretty similar, re-freshed the bottom end, used 2nd hand RB30 N/A pistons, slapped an RB25 head onto it, and put 600hp through the engine and 5yrs later it was still going strong,

[daisu]

I can't say specifically where I saw it, but I'm pretty sure it was in the 300 and something pages long thread (R33 RB30 conversions) where someone talked of installing an R32 RB25DE head onto an untouched RB30 bottom end.

From what I've read through this forum and others, the standard RB30 bottom end is quite reliable, providing it is in good condition. 155psi across all 6 cylinders sounds good to me, what are the factory specs for a standard RB30E?

Reliability is a bit of a fuzzy area due to the many variables that affect it, boost pressures, compressor efficiency, tuning etc.

If you do a bit more reading in the forum here you will find some first hand accounts of setups similar to this.

Personally, I have no previous experience, I'm only at the stage of collecting parts.

Do some more research and figure out what other people have done regarding factory bottom ends, and you will see what kind of power outputs they are achieving.

[Sydneykid]

Cost $1200 (RB30+RB25DE) to build 9 years ago, 80,000 k's and still going strong at 475 bhp (engine dyno). Simple rules, ZERO knock, maximum 1 bar of boost, no leaner than 11.5 A/F ratios when on boost, no more than 6,750 rpm, service it regularly and use good oil (Castrol Edge 10W60).

Cheers

Gary

[VB-]

what valve springs are you using just out of curiosity?

[CEF11E]

I have built the same thing.

I used a stock rb30e out of an R31 that was rebuilt 35000 k's ago.

I just cleaned it and the top of the pistons and replaced all the gaskets and bolted on an untouched rb25de vct head. its running on all stock internal parts and makes 270rwkw and 650nm of torque. and it runs like a factory engine and has no signs of stress at all.

It has been daily driven for nearly a year and has clocked up over 20,000 k's

[xsv_32]

Yeah im building a 30det for my skida but ive used a fully forged internal setup with race bearings and arp bolts. Been told that thirtys are great for reliable torque and power all day every day if you keep them looked after. Have fun with your build.

[Sydneykid]

what valve springs are you using just out of curiosity?

Standard RB26 valve springs shimmed up for seat pressure to suite the cams. Performance Springs for mild cams up to 264 degrees and 10 mm lift, then Jun valve springs for more aggressive cams.

Cheers

Gary

[Tony1981]

Thats for the stories guys, certainly put my mind at ease!!!

Have a few questions for you guys,

What is this engine like to live with everyday by just slapping the RB25DE head onto the RB30E engine?

Is it a pig off-boost?

Also, what turbo's are you guys running with the RB25 head slapped onto a stock RB30E N/A engine?

Guess this sorta relates to the "off-boost" question - but you use a stock RB25 turbo might come on boost at 2000rpm and "off-boost" wont really exist :-),

Just had a pretty ordinary experience in the past with slapping an EBAY T3/T4 turbo on the side of an RB30 n/a engine, did the right things, R32 GTR Injectors, re-chipped ECU, but the end result was just ordinary, doey as down low, didnt come on full-boost (14psi) until about 4200rpm, just want to avoid the same sorts of pitfalls - because they are expensive :-)!!!

[VB-]

your past experience is because of the turbo, a better turbo would spool much earlier and give better results.

[Tony1981]

Yeah I was thinking of using a stock R33 RB25 turbo or the turbo from the VG30DET, I wont be chasing big HP, more daily drive-ability!!!

[bubba]

I have an RB25 turbo on my 25DE/30 (not a standard bottom end though). It makes 12psi by 2200rpm, 183rwkw @4600rpm but chokes the engine up at about 5800rpm so badly that by the time it gets to the 6800rpm limiter it's only making 67rwkw!

It is certainly a lot of fun to drive and there isn't really such a thing as off boost. I do have a real turbo that is going on soon which should be even more fun

[Guilt-Toy]

my stock 30 bottom end lasted 60,000km's (but was rebuilt with new rings and bearings) and i flogged the crap outta it. I pinged the shit outta it as well (learning how to tune and it lasted the time, the only thing that went wrong was it spun a bearing after using Nulon oil (never again)

Also most the rings were broken but it was still making some decent power. it was 265rwkw.. was in the car about 3 years (major blow by)

give it a go.. who cares if it blows up

[TiTAN]

If it blows up you just spend the the money you would have spent rebuilding it in the first place. If it doesn't thats a massive saving right there. Depends on how much power you want to make.

[Tony1981]

Its all in a 260z, so power actually is an issue - half shafts (good old UNIs) and stub axles (27 spline) are supposed to be quite the weak point and unless I cut out the original gearbox mounts all I can run is the skinny RB30E or RB20DET gearbox,

So realistically, unless I make some improvemets in the driveline I will be limited with what power levels I can chase - Think going for much more than 175-200rwkw would be pushing my little Datto to its limits!!!

Which I guess means I am in luck, that kinda power looks like its easily achievable with running 8-12psi, and well below 5500rpm - that should allow for the RB30/25 engine lasting forever!!!

"I have an RB25 turbo on my 25DE/30 (not a standard bottom end though). It makes 12psi by 2200rpm, 183rwkw @4600rpm but chokes the engine up at about 5800rpm so badly that by the time it gets to the 6800rpm limiter it's only making 67rwkw!"

I am probably safer with it spooling up a bit lazier than that, because quick snapping force is going to break things - just dont want it as lazy as it was before with the EBAY T3/T4 thing,

I wont be chasing big HP in this car, because even if I do fit an R230, get custom half-shafts with a set of 35 (maybe even 41) spline stub axles - how the f#ck will the car lay that kind of power :-)!!! Rwd with (if I am lucky) 235's on the rear, probably just sitting there spinning the rear wheels until the tyres burst :-)

[TiTAN]

Ask cubes what happened to his RB20 box. there is just too much torque from the 30 for the little 20 box to be reliable.

[bubba]

The power delivery of my motor is very linear because there is no lag so there's not really a quick snapping force (unless you dial in 4000rpm and drop the clutch.. then it's a quick snap into massive wheelspin.. hell even 2500rpm clutch drops result in massive wheelspin!).

To be honest mate, if you can't fit a 25 box in there I wouldn't be putting a 3L in.. those RB20 boxes really don't handle all the extra torque. Mine lasted less than 2 months of 3L goodness

Edited July 15, 2008 by bubba

[Adriano]

As bubba said, an rb30 may not really be fir you, however you could fit an xr6 style gt35/40, and leave the stock actuator on it, running 4-5psi should give you a nice flat torque curve, whilst still allowing for future drivetrain mods. PS there isnt too much work involved in fitting a complete skyline rear end, just need to be picky with your wheel offsets.

[Tony1981]

RB30ET is already in there :-) - making 173rwkw on 14psi, cant remember what torque figures I was making, certainly more than the old L26, but certainly less than what the RB30DET seems capable of - but your right, I have gone reasonably easy on the gearbox but starting to feel notchy and make noises!!!

You can fit the RB25DET gearbox just have to re-locate the mounts in the transmission tunnel, not a big issue, just a little fiddly really, actually not a problem in the 240z as the gearbox mounts arent in the transmission tunnel like they are in the 260z - half-shafts and stub axles are more of a concern, but your right Adriano start off with small boost and then when have built a more bullet proof rear end run more power through it,

"PS there isnt too much work involved in fitting a complete skyline rear end, just need to be picky with your wheel offsets."

Yes, there is unfortunately :-)

[bubba]

Oh if all you have to do is relocate gearbox mounts then that's no dramas, had to do that to fit the 25 box in my 32.. I thought you were talking like you had to chop rails n stuff!

[Cubes]

Mine has lasted 90,000km's so far. Expecting something to go bang.. I hope it hangs out until the 3.4ltr stroker kits from spoolup + gt40

Its ran on a diet of Motul 8100. The head is super clean as it has been off a few times troubleshooting valve spring issues and oiling issues.

The rb25det gearbox is not an issue in the R32. I used 6mm plate redrilled a couple of holes and its bolted up with the std x-member.

The rb30 making 270rwkw went through third gear a hell of a lot quicker than the rb30det with 200rwkw.