RB25DET vs RB30DET ?

[Steve]

THIS IS A COPY OF A THREAD I POSTED ON SDU FORUM, BUT I AM AFTER AS MUCH INFO/IDEAS AS POSSIBLE PLEASE - ALL POINTS OF VIEW VERY WELCOME!

Hi,

I am at a bit of a cross roads at the moment. I am about to start a major rebuild of an RB25 - to allow for 600bhp approximately.

What I was thinking is that to rebuild an RB25 would be a similar cost to rebuilding an RB30 and fitting an RB25DE head, with the added expense of a RB30 block and RB25DE head being more than amply offset by the sale of a compele RB25DET that could be sold on completion of the transplant.

Does anybody have any ideas on the practicality of this?

Are there any major hiccups likely to occur that I cant see?

Would it be practical?

Thanks for any opinions or advice - I want to make sure I have weighed up the pros and cons before proceeding, at the moment the only con I can see is having to change engine numbers on the rego?

Cheers

Steve

EDIT: I would like any thougts on whether a hks3037s 56t turbo would be ok for an rb30 as well (exhuast ar is 0.61!), or will this just be too small?

[darkhalf]

heres some links that may help. rb30 second hand blocks can come cheap

http://trinity.frontierisp.net.au/~rowan/twincam.htm

http://www.autospeed.com/A_0268/page1.html

http://www.autospeed.com/A_0012/page1.html?src=twr

[ParaDoxx]

Hey there,

Idd definatly go the 3l!!

and stick a gt35/40? on it!!!

1.01? hot side,

spot on for a big hp 3l!

THe only problems i have seen with the 2.5l revie head on the 3l block is the harmonics? you have to get everything blueprinted and balanced spoton!!

[meggala]

MY thoughts on this are know but i will go through them again.

how much power do you want how much do you want to spend.

to build an rb25/30 you are looking in the 10 k+ bracket I have heard even more. it looks cheap at the out set but I think there is more to it I could be wrong but every one I have spoken to all mention high costs.

why not put an rb26 in seriously 3-400 rwkw very doable the motor revs higher and is stronger or rb 25 with 26 internals.

I have heard that with stock roids the rb30 bottom end can only be reved to 7k may be a bit more the rb26 will go to 8500 easily.

with a 3037 I would stay with the rb25 you could make 280 -300 rwkw with that turbo and when the motors blows do a rebuild but if tuned right the motor should be ok . note the tuned right none of this she will be right mate and forget to get it dynoed.

also there are issues as to wheather you can put an rb30 in a later modl r33 cause the rb30's finished in theearly 90's didnt they I"m not sure on that one . also insurace with an engine swap is out of the question unless your prepared to get raped.

the list goes on. a a gt35/40 is the way to go as suggested.

have a good long hard think b4 commiting and dont talk to only one engine builder talkt o a few and make sure you get a written quote on letter head for the motor.

cheers

meggala

[Steve]

Thanks for all the replies. Some thought provoking stuff.

My main concern I suppose is that if I spend $7k+ on gettng a rebuilded engine, then all the other costs involved - I was budgeting 10k - it would be a similar cost to do a 3l engine and rb25de head - just added expense for initial cost of block and head. I could then sell an rb25det complete and come out a couple k in front? If anything at least I would have better bottom end and midrange, which also is a pretty good motivator - who like lag.

The insurance thing is definately worth investigating though - no point putting it together and not being able to get it on the road.

Thanks again for the replies, anyone got anything else to add?

Cheers

Steve

[turbomad]

I'm sure the RB30 block looks identical to the 25 so why tell the insurance company what's inside, there's a million 5.7l commodores insured as 5.0l's.

[Steve]

I think I agree there turbomad, also if I accidentally remove the rb30 block number and when I restamp it it reflects the original motor

Just wondering if they would check such things in event of a claim?

[HEL-RZA]

the insurence companies will definately check the chassie NO and the engine NO. but i dout they will pull the engine apart and check the displacement just to make sure its still 2.5L. so if the engine No matches with whats written on the policy and the head still says RB25 24 valve twincam then i dont think they would be any wiser......

[crooser]

i'm interested to hear more about the 30 bottom end

what would it roughly cost to build up an old rb30 bottom?

i mean to get it ready for the transplant

whats the most expensive bit.. the pistons?

what if you dont want massive hp?

Also i have heard this will raise the height of the engine...

anyone know by how much?

[meggala]

crooser if you go a stockish rb30 bottom end the cost wont be to high say a couple of grand with cast pistons. but someone might charge you a bit to bolt it to a 25 head . and you might consider a headf reco at the same time there for adding more cost'

at least you have the link to make it easier to tune

cheers

[teka]

You would get real nice linear (ish) torque curve out of the RB30 bottom, however it is just so easy to get 300kw at the treads with an RB26dett, and there relatively cheap, (under 10,000k)

[calvintys]

Sorry out of question..... Does anybody know how much it cost if i wana put RB26DET in my R34GTT. is so what orther costr involve if i wana get 280 -300 rwkw ... thanks

[Steve]

have seen shops advertise an rb25-rb26 upgrade for about 10k.

Not as straight forward as it may at first seem. you need new computer, afms, dump pipes, fuel pump - the list goes on.

If you just want the extra capacity you could just change the internals - put on an rb26 head and you have a similar package.

[B6Tmeteor]

Plus the oil sump modification...

I can't remember if it's this forum or the SDU forum, but there's a guy called Sydneykid, who from what i can gather works at or is associated with a performance shop that does RB30DET's. I think i read they have one in their shops race skyline. He might be someone to answer your questions...

Also Nizpro in melbourne have built an extreme RB30DET, with a 26 head i believe, there's details of it on Autospeed.com

[Sydneykid]

Hi Guys, there are a lot of pluses from doing a RB30DET and very few minuses. As Megalla said it all depends on what you want to do with the car and how much horsepower you want.

If you want 450 bhp then stick with the RB25. The standard internals will handle it and the cost basically doubles once you go over that bhp.

If you definitely want to go more than 450 bhp then the cost of an RB30DET is cheaper than the same horsepower RB25DET.

What?

It's pretty simple really, they both need rods, pistons, balancing, o'ringing, camshafts, porting etc. So no difference there. The cost of buying an RB30 bottom end, suitable for rebuilding, is less than what you can get for a good condition RB25 bottom end.

Someone mentioned revs, we don't like revving the RB31DET over 7,500 rpm, but the good thing is you don't have to. At 3.1 litres (all other things being equal) it will develop the same power at 25.4% lower RPM. ie; at the same horsepower, 7,500 rpm in a 3,103 cc engine is the same airflow as 9,400 rpm in a 2,476 cc engine.

Again all things being equal, an RB30 at 7,500 rpm is going to last a lot longer between rebuilds than a RB25 at 9,400 rpm. So it will be cheaper to maintain. Plus we can use the standard valve springs, collets, retainers, alternator, water pump, power steering pulleys etc at 7,500 rpm, but we can't at 9,400 rpm. There's a cost saving there as well.

I could delve into torque curves, piston speed, rod angles, valve acceleration etc, but the bottom line for us is that the RB30DET is a better solution for our purposes. It has better off boost performance, builds boost earlier, is ultimately capable of more horsepower, is more responsive to throttle inputs and costs less for 650 bhp than an RB25DET.

Hope that helps clarify.

[DESCR8]

SydneyKid:

What combo do you use to get 3.1 litres and would the standard rods if shotpened, side polished and cryogenically treated be good for around 600HP as long as the revs are kept under 7,500rpm. The crank will be nitrided and the bottom end balanced.

Also, would you recommend stud kit's ive been told the crank, head bolts and rods bolts are good from factory.

This engine is to use an RB26 head, forged pistions, N1 bearings, N1 oil and water pump and the head will be oringed and the block D-grooved it will be mainly for street use and i would like around 350-400kw at the wheels, through an auto

Thanks in advance for your input

[Sydneykid]

Hi GR8NES, my suggestions to your questions follow.....

**What combo do you use to get 3.1 litres

We use 88 mm JE Pistons, gives 3,103 cc's.

**would the standard rods if shotpened, side polished and cryogenically treated be good for around 600HP as long as the revs are kept under 7,500rpm

No, we use Carillo conrods

**Also, would you recommend stud kit's ive been told the crank, head bolts and rods bolts are good from factory.

I don't really understand this question, but we specify ARP rod bolts with the Carillo conrods and use ARP main bearing bolts and head bolts. You know to use the RB26 size head bolts, yes?

**This engine is to use an RB26 head, forged pistions, N1 bearings, N1 oil and water pump

Good move

**the head will be o'ringed and the block D-grooved

We O'ring the block, use standard headgaskets, never had a problem

400 rwkw = 600 bhp, should be achievable.

I did not see balancing on your list or porting the head or camshaft, and pulley upgrades. All essential, particularly balancing.

Hope that helps

[Steve]

Thanks everybody who has replied, has brought up some great ideas. I think things are in the favour of the 3l. The idea of having a motor built while the car is still on the road, then the bonus of being able to sell the old RB25, helps further tip the scales.

Just hope there isnt too many insurance and registration hassels.

Anybody done this with a streeter? Or know anybody who has done it?

Cheers

Steve

[slip]

3l. The idea of having a motor built while the car is still on the road, then the bonus of being able to sell the old RB25, helps further tip the scales.

Exactly, and when you go to sell the car, its got an RB30DET with big hp = good resale to the right buyer.

You know what to do

[Sydneykid]

Hi Steve, when you buy a new block from Nissan it comes without engine numbers on it. The idea is that you stamp the same numbers on the new block as were on the old/damaged block you are replacing.

If you want to build up the new engine while driving the old one around then you will need to buy another RB25DET to pinch the bits off (head, manifolds, sump etc) to put on top of the RB30 bottom end. So you should use the numbers off that RB25 on the new block.

Otherwise when you sell your RB25 the person who buys it will have rego problems because it will be the same numbers as your new block.

Hope that makes sense.