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My Neo Rb25-s14 Silvia Install


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Ive asked plenty of various questions on this forum in regards to issues ive had with this project and everyone has been of great help. So I thought id give a little back and hopefully entertain you guys with some pics of my project and a small run-down of the engine drop in.

First off, this is a pic of the virgin S14 Qs (Non turbo-SR20DE) as i saw it on the auction sheet in Japan. I could see in the pic that it had a front lip, skirts and some 17s. I got a nice surprice when the car arrived though, it was equipped with a set of Tein Type Ha coilover suspension and 5Zigen full 2 1/2inch exhaust.


I bought this when I was 18, it was fun at the time but the eventual need for more power led to an RB20DET re-power. I sourced a good deal on an RB20DET motor and gearbox package. But as luck would have it, the gearbox turned out to be in need of a rebuild. It was drivable, but 2nd gear was hard to engage. The clutch also blew after the first 3rd gear burnout. It was replaced with an Exedy 5puk. The string of bad luck eventuated to a run big end bearing on the engine. Here are some pics of the RB20DET and some other external modifactions that i did-





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The string of bad luck with the old motor led me to start looking for a much newer driveline. In the meantime, i started buying parts for the new engine. I already had a front mount intercooler, Walbro fuel pump, exhaust, HKS filter etc fitted on the car from the RB20 setup. I added to this a Masterpower T3/T4 (500hp spec), 38mm WG and SSQL Blow Off valve-


After alot of searching, i found an R34 RB25DET motor which was very reasonably priced. I went to pick up the motor and found that the seller also had an R33 RB25DET gearbox. So I made a deal on the lot and took my new babies home :) .


I 'dummy fitted' the turbo on the stock manifold but found two problems. 1. The compresser housing was not clearing the manifold. 2. It was obviously going to be difficult to mount the Wastegate on the stick manifold. So I scratched the idea and decided to get a custom top-mount manifold fabricated to suit my setup.


With the water lines blocked and oil feed and return lines for the new turbo sorted, a proceeded to get the new motor dropped into the Silvia. I used the same 5puk Exedy clutch I used for the RB20 (it was only one month old).

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We decided to drop the motor and gearbox in together. This wasnt the easiest of jobs for two people. The RB25 gear is very large and not usually at home in a Silvia. So it took a few tries and re-adjustments of the chain on the engine hoist to get the right angle. I had to stand on the gearbox in order to have it low enough to slide under the firewall and into the GB tunnel :cheers:







This is when we had to stop, as an engine mount problem that i never thought was an issue stopped us from going any further. The NEO engine mounts will not bolt into the S14. We had to call it a day with the motor just sitting in the car and the gearbox lying on the floor under the car :) .

I sourced some RB20 engine mounts and they were replaced. The motor bolted in perfectly. However, the gearbox crossmember does not bolt up like the RB20 box does. The RB25 box is longer, so only 2 bolts line up. We bolted up the two, ans I will have to sort this issue out later.


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Didnt really think i needed them because the RB20 was a perfect fit. Il stick to this at this stage and modify the gearbox crossmember. And yeah, im thinking of painting the rocker covers. Im also getting the plenum modified into a front facing plenum. Havent seen any NEO engines with this done to them so il update this with pics once everything is bolted up.

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yeah the rb20 fits fine using the skyline xmember however the rb25 doesnt......

most ppl here stateside use a mount kit for a decent fit, as the skyline xmember just causes too many problems when boltin in a rb25.

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from what i remeber they are a bit much...... check out the website for exact prices.

also since the s chassis/rb swap is quite popular here stateside check out www.racebread.com or www.nicoclub.com or www.240sxforums.com for info on cramming a rb into a s chassis.

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  • 1 month later...

Time for an update. Progress is a little slow but definately being made. I just came back from my mechanic's house where I took a few pics. We decided to relocate the throttle body to the front of the plenum and in the process totally ditched the traction control. The FPR had to be relocated but the throttle cable was a perfect leangth so no mods were needed in that respect. Im pretty happy with the plenum, it looks exactly like a 6cyl version of the SR20DET plenum IMO. Yes there are open questions in regards to air flow etc, but this will suit me fine as far as my budget is concerned. The manifold is pretty close to being tuned leangth (give or take an inch). Hopefully this setup will produce the results. My ultimate aim is 280rwkw. The turbo might not flow that and neither will the injectors, I have however spoken to many RB25 owners who have netted 250rwkw+ on the standard injectors so il be happy with 250rwkw.






I know the engine is filthy but im going to give it a good tidy up and paint the rocker covers once everything else is sorted. :P

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mmm im really against that sort of plenum modification. plenum design is very important for flow and even more important for cylinder to cylinder distribution. by changing the point of entry i would imagine all the design work that went into the plenum is out the window.

another thing is, i was told the rb25 plenums have runner dividers between them in the plenum, this would further restrict flow with a side entry, where they were purposeful for distribution between cylinders in its stock entry point.

the biggest problem with uneven distribution is when it comes to tuning. the tuner will only see the net average a/f ratio of all 6 cylinders, whereas some cylinders may be running lean and some running rich, and bang you blow an engine because you think a/f's are ok but there way off.

also, just days ago i was at a workshop and saw a 200sx with an rb25 as well, same plenum mod had been done with theres as well. rb25 with a gt30 turbo and only managed a measly 245rwkw ! the turbo is capable of 300rwkw, that was at 18psi though but its still off the mark by quite a bit

other then that, nice work !

Edited by mokompri
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Looking at the plenum with the top half off, its pretty apparent that cyl 3 and 4 will get most of the airflow in the stock plenum design. So I really dont think relocating the exit point will cause as much chaos as you say. But hey, im not an engineer and im only going by assumptions. This thread goes into the subject in detail for anyone thats interested-


And cheers caminperth. Wiring wont be an issue as such, sorting out the vvti with the LinkPlus is a different matter though. Ive had suggestions ranging from switching it right off to getting a Vtech controller. Il look into that side of things when I get the car wired up, right now i just want to get thing started :)

Edited by DRFT 14
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Don't just not use it. The difference in the midrange is staggering. Before I wired it up it felt very flat until about 5,500rpm. After I wired it up the midrange was much much better and alot more linear.

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Thats a little more reassuring. At least 60% of the RB powered drift cars here in NZ run this plenum mod and they all make 250+rwkw so it seems to be a safe option. I will post my experience with it once my car is wired and tuned.

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That conversion looks kind of strangely familiar :D

Have you or your mechanic run into any major problems?

Have you retained your air conditioning and stuff like that?

I'll be very interested to see the power results, might give be an idea of where to go next.....

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I havnt retained the air con. I didnt bother with it with the RB20 or the RB25. The only real problems ive had was the gearbox crossmember not bolting up using all 4 bolts because it sits further back. My mechanic/fabricater is working on this at the moment. Second, as ive mentioned before is the whole vvt issue. Apart from that, its pretty much just as easy as the RB20 conversion. I cant wait to get this running. Should be a far cry from the old RB20-IC, exhaust job.

More Pics-



Edited by DRFT 14
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