RB25DET mods and questions

Hello to everyone...im new here and have a couple of questions. I'm planning on getting an RB25DET motor for my 240sx project (i know not a skyline but atleast it'll be skyline powered!) and i was wondering about some performance mods. I know that the RB series engines are mostly interchangable and was wondering what parts. Also i was looking into get an N1 block (do they make a RB25 Block or only RB26 or are they the same block just diff cylinder size?) and have yet to be able to find one. where is a good source to go to get one. What is the best crank and cams to go with? (i would like a high rev high horsepower motor) Also i was told that the RB26DETT head will bolt onto the RB25 block is this true. Also in addition to my mods question...what is the best turbo upgrade,turbo timer, boost controller and BOV upgrade? (sorry if i am going over already gone over stuff, i.e N1 block)

Dont flame the Noob pleez! :eek7:

I was also wondering what problems the RB series motors have and how to fix them. I heard that the RB26DETT sometimes doesnt get enough oil flow to it and that a stronger pickup fixes this (true/not true) anything else would really help.

Hello to everyone...im new here and have a couple of questions. I'm planning on getting an RB25DET motor for my 240sx project (i know not a skyline but atleast it'll be skyline powered!) and i was wondering about some performance mods. I know that the RB series engines are mostly interchangable and was wondering what parts. Also i was looking into get an N1 block (do they make a RB25 Block or only RB26 or are they the same block just diff cylinder size?) and have yet to be able to find one. where is a good source to go to get one. What is the best crank and cams to go with? (i would like a high rev high horsepower motor) Also i was told that the RB26DETT head will bolt onto the RB25 block is this true. Also in addition to my mods question...what is the best turbo upgrade,turbo timer, boost controller and BOV upgrade? (sorry if i am going over already gone over stuff, i.e N1 block)

Dont flame the Noob pleez! :eek7:


The N1 block only comes in the RB26.

The bores are the same with the RB26 and RB25 but the RB26 is a much heavier block with a better support craddle which is very important with high hp. As far as the head bolting on I believe the RB26 head will bolt onto the RB25 block. Remember though the RB25 block is a higher compression block to start with.

The factory cranks are good for pretty decent hp. 650-750 on the RB25 and up to 850 on the RB26. I've seen those numbers on these engines though the longevity is not very good at those numbers. HKS, JUN, or equivelant cranks may be an option but they are very expensive.
Cams well there are a number to choose from depending on your needs and wants. You will need to do some research on that part. Same with the turbo(s).

driftking777 im not gonna flame you man, no worries :smile: I have researched the RB25DET swap into the 2470SX chassis extensively. The bores are the same, but the rb26 uses 12mm headbolts compared to the rb25 that uses 10mm. You would have to tap the block to get it bolt up. NOTE: This only works on early RB25 blocks, pre-VVTi (R34) as they have been found to have oil galley holes that arent found in the previous. If your vehicle is to be street driven I look for it to be highly unlikely for you to use the N1 block unless money is no object. They are endurance blocks so expect to pay some high prices for one. Joule Motorsports', http://www.joulemotorsports.com, shop car is a R32 GTR with loads of HKS goodies, 2.7 stroker kit using an N1 block. Ive seen the car and heard it myself (right down the street from me) its a beast and it puts down 850whp. So the N! is something i dont think you should consider.
Assuming you just go with a RB25DET and dont try to go with a RB26 head swap, you can make 600hp finely tuned on the stock bottom end. Cams are up to you. I'd suggest a conservative 246 intake, 264 exh with cam gears, 80mm downpipe, & 80mm exhaust. Just depends on what you are after. Do some research on the web about this swap. The RB25 is an involved swap with badass results. Ive driven a SR20 mildly modified s13 and a s14 modded rb25 in it. both haul ass. just you have to decide which is right for you.

Hello to everyone...im new here and have a couple of questions. I'm planning on getting an RB25DET motor for my 240sx project (i know not a skyline but atleast it'll be skyline powered!) and i was wondering about some performance mods. I know that the RB series engines are mostly interchangable and was wondering what parts. Also i was looking into get an N1 block (do they make a RB25 Block or only RB26 or are they the same block just diff cylinder size?) and have yet to be able to find one. where is a good source to go to get one. What is the best crank and cams to go with? (i would like a high rev high horsepower motor) Also i was told that the RB26DETT head will bolt onto the RB25 block is this true. Also in addition to my mods question...what is the best turbo upgrade,turbo timer, boost controller and BOV upgrade? (sorry if i am going over already gone over stuff, i.e N1 block)

Dont flame the Noob pleez! :eek7:

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I was also wondering what problems the RB series motors have and how to fix them. I heard that the RB26DETT sometimes doesnt get enough oil flow to it and that a stronger pickup fixes this (true/not true) anything else would really help.

as the RB26 crank will bolt right in but the journals have to be machines slightly. good luck and hope the info helps. drop me a line if you have questions. :iceslolan

Off subject a bit, what kind of turbo comes with the RB25DET, specific, if possible. And what type of flanges, thanks

how much psi does ur car boost

So, is it better to do an rb25 into a 240sx than an rb26? I saw a very well done rb25 swap earlier in the week but I didn't get a chance to ask the person why they didn't go for the rb26....Sorry if you already explained that earlier, if might have gone over my head a bit. "Tap the block to get it to bolt up?" Is this what I missed/didn't understand? Could you explain that for me a bit?

Apparently the Left Hand Drive 240sx has clearance issues between the steering and the twin turbo set up on the RB26. You also have to source a seperate gearbox from an RB25.

The RB25 is cheaper, and generaly comes with the gear box.

Thank you---I do remember now that I was aware of the steering column issue...
If the RB25 is a twin turbo, do you not have the same TT/steering column issue, or are they placed differently on the 25?

The RB25DET uses a T3 exhaust flange.

If your vehicle is to be street driven I look for it to be highly unlikely for you to use the N1 block unless money is no object. They are endurance blocks so expect to pay some high prices for one. So the N! is something i dont think you should consider.

I've heard people refer to the N1 blocks in many different ways but this one is the first. A quick note though. The N1 was developed as a racing block using better materials and slightly thicker casting. It was designed and built to amalgimate so it could be used in the JGTC in the R32 GTR. Considering what the price difference is between the Gen III alloy LT1 V8 and an older cast iron block is the difference in price between an N1 RB26 block and a standard block is minimal at best. They can be purchased in Japan for a difference in price of only $600 USD. Now as far as outright strength, there is really little in it. There are so many myths about this I've lost track of them all already. Both the N1 and standard blocks don't last long when pushed beyond 900hp. Their life spans shrink dramaticlly. Both crack between the #3 and #4 cylinders and is obviously a design flaw. There is maybe at best 150-250 hp overall difference in the two as far as what hp they can actually take before shitting themselves. The difference in price doesn't justify it at all the more you look into it. For a car that is to be used as a street car there is nothing wrong with the standard RB26 block. If you have the funds to build an engine that can support or make over 700hp plus add the supporting gear to sustain it, then the differences in price don't matter.


Assuming you just go with a RB25DET and dont try to go with a RB26 head swap, you can make 600hp finely tuned on the stock bottom end. Cams are up to you. I'd suggest a conservative 246 intake, 264 exh with cam gears, 80mm downpipe, & 80mm exhaust. Just depends on what you are after. Do some research on the web about this swap. The RB25 is an involved swap with badass results. Ive driven a SR20 mildly modified s13 and a s14 modded rb25 in it. both haul ass. just you have to decide which is right for you.

Ok for those that know how to make big horsepower out of an engine all know it isn't the block that makes it, it is the head. Simply put the factory ports in the RB25 head will not support nor will they flow 600hp, even with bigger cams. You can only push so much volumne of air through and opening. 600hp out of stock bottom end on an RB25. Not impossible but not too bright either. Lets pick apart this one a bit more and I'm going to be pretty precise.

#1. Lets start with the very soft and weak cast pistons. I've seen now no less than 7 RB25 motors with the top ring land crushed due to cylinder pressures. The only way to make hp is increase the cylinder pressures either with boost or volumne of air/fuel. A wet Nitros system does the same thing as boost but with volumne as a good example.
#2. Conrods. For those that have never seen them they are very small. not only in overall dimensions but materal wall thickness. This was done, and this is a personal obvservation, to keep costs down in manufacture. How weak are they? A member of a club or should I say former member had his RB25 built from the ground up. I managed to get hold of a factory conrod. The motor in the original form was making an honest 425hp. The main journal end of the conrod was egged shapped by at least .007 of an inch. That is a shit load the world of clearances. This particular engine never saw rev's past the factory rev cut but just some bolt on bits and nothing outragous either. I put the conrod in a vise and was able to bend it quite easily with on my hands and a decent size screw driver! Not a pry bar but cheap and I mean cheap screw driver that had an apporx 150mm or 6" shank on it. When I say bend it I distored it sideways by a very large amount in being just over 26 degs of bend. This was by holding the conrod by the crank journal end not the wrist (gudgen) pin end.
Lets talk about the conrod bolts, the factory ones. The materials are not even of a decent tinsle strength. As a good measurement of strenght lets take a grade 6 bolt. I'm using this for our Amercian mates who would have a better understanding, not that I'm trying to insult anyone. A standard Grade 6 bolt which can be purchased at Farm and Fleet, Taylor, Napa etc is pretty strong. The Nissan factory conrod bolt wouldn't even make a Grade 4 . I am dead serious. It is nothing more than a standard strength, and standard material bolt. This means when pushed with some bigger hp than factory they have a very nasty tendancy to stretch. Factor in a constantly seeing 7,500+ rpms and you have a beautiful recipiet for disaster, as in a handgranading the motor.

Now I'm not picking on you Nurv even though it may look like it. We all want to learn and know as much as possible. I'm still learning all the time. I happen to have at my disposal quite a bit of reference including that of no less than 4 tuners builders, and 3 top racing teams. I quite enjoy picking their brains and they happily endulge me. Therefore I pass that knowledge onto you guys/girls. Sharing viable information only makes our little community stronger which is what it is and should be all about.

Sorry for all the editing but AF was giving me the middle finger on posting today.