Is ~400whp realistic with this?

[BongRips]

So basically I can do my build and my engine will hold the 400whp but my tranny will blow shortly after correct? So could I do the build then run it with the rb20 tranny and diff until they go and replace them with gtr or aftermarket parts?

[Skym]

Engine should last longer at higher boost levels with lower compression.

There's 2x ways you can do it -

Lower compression and worse offboost performance, higher boost level (racecar)

or

Higher compression for better offboost performance, lower boost level (street use)

The higher compression, bad tune is why most RB25DET's fail (ringlands can't take the pressure and combine with engine knocking, ringlands fail and punches a big hole in side of piston). I was told RB20DET stock pistons have stronger ringlands, but haven't compared them to RB26, RB25 stock pistons to confirm.

The solution for RB25 is the lower compression RB26 bottomend (should have bought a RB26 that has front mount intake plenum, etc as stock equipment) with forged RB26 pistons.

Depends on the km gearbox has done, how it was serviced (used correct oil?), how it's driven (don't flat shift into 3rd gear) and do you lock drivetrain up with hand brake before launching to reduce drivetrain shock?, etc. Most RB20DET gearboxes are due for a refresh (new synchros, bearings, seals, reprofile worn teeth, etc). With a refresh they can take a little bit more hp and last a little while behind bigger capacity engines. Same with diffhead and can be reshimmed with thicker shims when you rebuild it.

But RB20DET gearbox, stock diffhead probably will eventually fail if using for dragracing with dragslicks, hard launches. With GTR gearbox you have the option of fitting stronger PPG internals and drivetrain is good for around 700hp+ with upgraded diffhead, etc.

On Group-A GTS-R in above link with 500hp or so RB20DET they used a custom bellhousing, Hollinger dog? gearbox. Some use a 350Z or 300ZX gearbox with custom adaptor plate for bellhousing behind a rwd RB26 or Nissan V8 that has alot of torque.

[BongRips]

That was extremely helpful, thanks a lot!!

[Skym]

Both headgasket thickness and forged pistons can lower compression. Some just upgrade pistons and use stock conrods with cheap rebuilds on RB26, RB20. Just have to keep revs lower for peak hp (around 6000rpm) to reduce the load on conrods and use boost level (bonus of having a turbocharged engine) to make up for the lack of revs.

Can aim for 380-400hp at engine and concentrate on getting hp to ground, making car lighter.

This is an example of what I mean -

http://forums.gtrcanada.com/media/35446-400hp-rb20det-powered-r32-gts-t-tsukuba.html

[jrhdohc]

that car is not 400hp. 280-290hp is more like it.
his rb20 is mostly stock. headgasket, cams, IC, OC, GTR injector, resistor pack, intake, exhaust, rb25 turbo, hks fcon-v pro.

the above upgrades are the best bang for the buck. anymore go rb25 swap.

[jrhdohc]

if you do build the RB20. look into RB26 crank & rods with custom pistons. gives 2.3-2.4 liter depending on pistons size.

[Skym]

His blog mentions around 1.2-1.5kg/cm2 (17.04psi-21.03psi) with stock RB25 turbo, so didn't think to question the hp output. Looking at that dynochart again, 314.4ps is at engine, but that can be done with around 1bar (14.5psi) or less, depending on how restricted engine is by exhaust, intercooler.

I know stock RB20 turbo can produce 268rwhp at 14.5psi (around 330hp at engine) on dyno when engine is derestricted with full exhaust from turbo, FMIC, etc (has been done with a few RB20DET's). But not a consistant 268rwhp. So I would think with stock RB25 turbo, it would be less than 14.5psi on that 314.4ps at engine dyno run.

To get an idea of what stock RB20DET pistons can handle on a dyno with a good tune (done with stock ECU), higher octane gas (E85?), this RB20DET would be a good example (500rwhp) -

http://www.nissansilvia.com/forums/index.php?showtopic=298289

But that engine has been rebuilt / refreshed.

Stock RB25DET engine with similar gas (E85) and Link ECU with map sensor, etc has produced around 400rwkw / 536rwhp.

[jrhdohc]

rb25 turbo higher than 1.25bar (~18psi) on rb20 and it basically blows hot air. usually it works out to 245-265whp @ 1.25bar on RB20.

also, I've normally seen 190-200whp @ 0.9bar (~13psi) stock RB20 w/ RB20 turbo. intake and full exhaust.

The point is not 20's piston strength. It's that you need a custom piston for use with RB26 crank and rods. 2.4 liter stroker! Change in compression height and larger bore = custom piston. used RB26 rods and crank are cheap. even a used RB26 oil pump if you know someone upgrading. just check all the clearances.

[MKIV]

Hmm...
My setup for this summer was a stock RB20. The internals were not touched.

- GTR Injectors
- RB25 R34 GTT Neo Turbo (Steel)
- 3.5" Turbo Back Exhaust
- HKS Intake
- AEM FIC ECU
- Greddy FMIC
- Walbro 255 Fp

265~whp @ 1-Bar
288~whp @ 18psi

Not to burst your dream but your goal really doesn't sound realistic...

Even with less than 300whp I had issues with the RB20 tranny.

The money you're going to spend to make a similar number as me could be used for a RB25 swap.

Cheers

[BongRips]

If I had to do the rb25 swap in the beginning of the summer I would still need everything I've already listed plus an extra 1600 for engine and tranny, 350 for a clutch, ??? for a custom driveshaft and ?!?!?!?!?!?!?!?!?!?!?!?!!?! for the install. I would still need the fuel pump, injectors, and all the supporting mods even with the engine swap as I got a uprated T3 turbo with a .63 A/R that's rated to 450hp with steel internals already installed. I won't have the money for the swap in the beginning of the spring so it will have to wait until **** starts failing. I know that the tranny will be the first thing to go and then engine should last past that, and once the tranny goes, I'll have the money for the whole swap. I just need to get my rb20 upgraded a bit and tuned. I sprung for the Haltech Platinum Pro ECU as there was a group buy of them for only $1600 and they can be used on any r32 or r33. I know my engine should be able to make the power no problem, and I know my tranny is gonna fail, but that's fine as it will be replaced when it does.

[MKIV]

No offense but if you "already" know, why ask so many questions?

If it's just for clarification then all the power to you.

Good luck.

[BongRips]

I am just looking for clariffication so I guess the right way to word that would be "from what I already know and understand..." As I'm making my speculations off of what I've already read posted in my threads and in others on this forum and others

[MKIV]

No worries, I'd do the same. Good luck to you and make sure you update the progress of the build

[cschepp]

I have an rb25 you would save money on buying all the parts to make the power with and everything will be transferrable from a 20. Let me know if your interested

[BongRips]

Uggh, I keep hearing different things on what's compatible, and what's not. I've heard many times that the plenums are different, truth? And I was gonna be able to grab the rb25 engine, tranny and turbo for 1600, so the price of the engine isn't the problem, its the actual labor for the swap and custom driveshaft fab and all those wonderful things. Once I get the car back there will be updates in my build thread with pics of everything that's been thrown on.