I need help making a decision. I'm coming up on 50k miles on my original motor, and I've had plans to do FI for a while. I absolutely will not boost the vq without internals. I know good tuning can do wonders, but I'm hard on my car.

Labor alone to rebuild the vq... resleeve, install pistons, rods, balance and blueprint, install a headgasket, install cams, valvesprings, retainers, fuel injectors, and the turbo kit... LABOR alone is 4000-ish, quoted from some top notch tuning shops.

That is without the parts, or twin turbo kit, which is 7k alone (APS, or PE, add 2k!).

That doesn't even bring up the issue of my tranny, which is a 5a/t. My goal is to put out 450rwhp reliably on 91 octane. I know a built vq with an aps kit can put out much more, but I'm really not looking to go that fast. I don't know how much power a 5 a/t can handle, but I'm not seeing 450-500whp as a happy amount for an automatic transmission.

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so the question is, should I just do an engine swap to an RB25DET? I believe I'd need, custom motor mounts, tranny mounts, driveshaft, and a way to make all the electronics work.

The RB25 is rare, but can be found for around 4K with tranny. It is essentially the same engine as the RB26 just without individual throttle bodies and a single turbo.

From my research, the stock head/turbo and only boltons and tuning can turn as much as 350whp, with 450whp possible with cams, new injectors, and tuning. 500-600whp doesn't seem to be a problem with the stock internals, and there are many turbo kits for the engine.

For the cost of pistons and a twin turbo kit for the VQ, I would have enough to purchase an RB25 in good condition, and have the head rebuilt, install cams, have a new headgasket installed, do a custom fmic and exhaust, and installed and tuned in the car.

 

The RB25 doesnt have as strong a bottom end as the RB26. Ive heard 550rwhp tops. If you choose this route, do it right and get an RB26 motor with an RB25 tranny. Ive also considered this route and it might actually end up being cheaper then a fully built VQ if the shop you deal with knows what they are doing. I dont think there is a kit for an RB swap in the 350 yet so keep in mind custom work is always more expensive. The main draw back is you will lose functionality with the lose of the stock ECU. No more ABS, power windows, etc.

 

Ignoring the loss of ABS, electric windows, airbags, TCS, VDC, EBD and all the custom work involved etc.

An RB26 internals could handle 550rwhp but theres no way a RB25's could. The RB25 is different to the RB26 in many ways. The RB26 is designed like a race engine with little compromises while the RB25 is designed like a street engine. So you'd still need to change the internals on the RB25 if you plan on going higher much higher than ~400rwhp, check the Australian skyline forums for examples. Which is about the same as a 350z except you dont have all the torque or drivability the 350z would have. The bottm end would be stock but you'd still have to change all the other parts. The turbo needed would have to be big, so boost wouldnt come on till around 4000rpm and it redlines at 7200rpm so your only on boost delivering all that power over ~3200rpm. Where a 350z is at full boost by 2000rpm till 6600rpm redline so its delivering its power over 4600rpm with a much broader power band because of the twins and its extra liter of displacement etc with potential for alot more with some new internals.

Rb26: Fully Counter-weighted Crank, High Volume Oil Pump, Stronger Forged Internals, High Volume Water Pump, Solid Lifter Cams, ITBs, high flow heads etc etc

Rb25: Forged Internals, Hydro Lifter Cams (low Rev Limit)