What exactly do i have here?

[ZzZleeper]

Well hello! New here and i do not own a Skyline. I have two Twin turbo Z32's. One of which is now receiving an RB25!

Alright, so i just purchased this RB25DET from a company called JDM Engine Pro out of California. Im just trying to gather a little more information on exactly what it is! On the ad, it says it was a "rare hybrid". It has an rb25 block, but rb20 trans, and ecu, and timing cover.

So once it arrived it came with a few other goodies i was happy to see!



So, i cant find a serial number or anything about this other than the "T" looks like the Turbonetics logo



Then i pulled the valve covers off and found out it has HKS RB20 cams?



And then i noticed it seemed to have top feed injectors aswell, maybe the gtr fuel rail? Im guessing these are Nismo 555cc injectors



I pulled the trans and saw it has an OS Giken clutch!



Then came the pan! From what i can see, it has Forged pistons (have no idea of the brand) the rods seem to be stock, but the crank has made me curious. I dont think ive ever seen Nissan stamp "JAPAN" on any of their cranks. correct me if im wrong!



Then this is how its going to sit! fits pretty well!

[/QUOTE]


So, my main questions are, could it possibly have RB20 heads, or just cams? does anyone have any idea of the brand of exhaust manifold? and what would you guess the power potential would you say this is capable of? Thanks again for the help in advance!

Heres a quick pic of my baby Z32

[BenOswald]

Holy crap you got lucky!

[ZzZleeper]

Lol, thats what i said! I bought it expecting to receive a stock rb25. I paid $2500usd for it shipped to my door haha. Taking it apart felt like Christmas morning

[Voodoo_ChildR32]

What exactly do i have here?

You might have gotten a built RB20 with an RB25 coil cover. That motor looks a lot like a 20 to me.
RB20 heads are not compatible with any other RB block.

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[ZzZleeper]

That is what is strange to me, The block is stamped RB25.

[Voodoo_ChildR32]

Weird, guess I'm wrong. Sweet find nonetheless, good luck with your build!

[Skym]

They removed the VVT from RB25DET engine. Then probably fitted RB20DET cams with adjustable camgears, RB20DET top cambelt cover. But RB25DET is better with VVT (more hp, torque).

RB20 heads are not compatible with any other RB block.

Tommy Kaira M30 (R31) has a modified RB20 head on RB30 bottomend. They welded onto RB20 head, ported head, etc to make it work. There was photo's of what they had done to RB20 head floating around the internet but can't find it again.

[Voodoo_ChildR32]

I always thought there was no way because the bore of a 20 is much different than any other RB block. It is a lot smaller.


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[ZzZleeper]

They removed the VVT from RB25DET engine. Then probably fitted RB20DET cams with adjustable camgears, RB20DET top cambelt cover. But RB25DET is better with VVT (more hp, torque).



Tommy Kaira M30 (R31) has a modified RB20 head on RB30 bottomend. They welded onto RB20 head, ported head, etc to make it work. There was photo's of what they had done to RB20 head floating around the internet but can't find it again.

Yeah, i figured someone bought the HKS cams and had them in his rb20, then did the rb25 swap and took the cams as well. But, it doesnt have adjustable cam gears, just cams which i also thought was kinda weird. I was told by someone on a Z32 forum that in order to fit that lift, i believe he said 264 or so? that the heads would need to be machined in order to fit them? But again, have no idea on the relevance of this. I Couldnt see the valves too much, they seemed clean, but didnt look to be machined.

[Dragon Humper]

Lift is the determining factor with cams, you can have a 280 cam with 9.0mm lift in an RB without issue. The cams, if they are ment for a 20, are a hydraulic grind (like the 25) as opposed to a solid grind ment for a 26. It's more of a base circle thing than ramp design, but the ramps are a little milder. There isn't a whole lot of selection in cams, especially on the intake side, for the 25 because of the VVT.

If I was shooting for max power on a 25 head, I would can the VVT too. It's not really necessary though as the VVT and the smallish intake cam that is avail. will be WAY better on a street car and still make 600hp if you bolt on the right turbo. I have read a few builds on the 25 where they used the VVT intake cam (a Tomei Pon 260 iirc) and a 270 10.1mm cam on the exhaust and the car was a torque monster and still made 500+HP at full scream.

If that trans really is a 20 trans, save yourself some grief and throw it in the lake. It will never last behind a 25 in a heavy car like a Fairlady. Get on the hunt for a 25 trans, they are almost as strong as the turbo Fairlady/GTR trans. You might get a season or two with the 20 trans with some Redline Heavy Shockproof in it but, its a ticking time bomb.




Jon.

[ZzZleeper]

Lift is the determining factor with cams, you can have a 280 cam with 9.0mm lift in an RB without issue. The cams, if they are ment for a 20, are a hydraulic grind (like the 25) as opposed to a solid grind ment for a 26. It's more of a base circle thing than ramp design, but the ramps are a little milder. There isn't a whole lot of selection in cams, especially on the intake side, for the 25 because of the VVT.

If I was shooting for max power on a 25 head, I would can the VVT too. It's not really necessary though as the VVT and the smallish intake cam that is avail. will be WAY better on a street car and still make 600hp if you bolt on the right turbo. I have read a few builds on the 25 where they used the VVT intake cam (a Tomei Pon 260 iirc) and a 270 10.1mm cam on the exhaust and the car was a torque monster and still made 500+HP at full scream.

If that trans really is a 20 trans, save yourself some grief and throw it in the lake. It will never last behind a 25 in a heavy car like a Fairlady. Get on the hunt for a 25 trans, they are almost as strong as the turbo Fairlady/GTR trans. You might get a season or two with the 20 trans with some Redline Heavy Shockproof in it but, its a ticking time bomb.






Jon.

yeah, ive heard it was a fail point and cant really handle much more than 350-400whp. But for right now, im going to use it just to get it all up and running. Luckly Z32 trans are dime a dozen over here. So i'll probably end up going with the Z32/RB25 hybrid trans in the long run. I just need to track down the 25 bell housing!
Thanks for the info on the cams, that makes a little more sense. I had a feeling the heads were not machined. Im really only looking to have reliable 450-550whp. Anything you guys see as a weak point to achieve that with this one besides the trans?
Ive been told by a few that they believe the weakest point would be the stock rods. But they are forged for the factory? Z32TT rods are good for 600, and the wristpins are the weak point in it. I thought that might be the case with these as well!

Thanks for all the info guys, this is extremely helpful!

[Skym]

It's not the hp, it's the torque. Gearboxes are rated in amount of torque they can handle (design limit).

The RB20DET gearbox runs same internals as the S13 gearbox (from memory the same part number, which is FS5W71C). The gearbox internals are rated to 294NM (design limit). Stock RB20DET engine is around 264NM from memory, so not much more than factory. Above 294NM the lifespan of 3rd gear is reduced and will fail alot earlier if thrash car. It's due to size of the blades on the gears which are really thin compared to aftemarket gears that are bigger, thicker.

Stock conrods are forged I beam conrods. Weakest point is the conrod bolts when exceding 550hp at engine (ARP conrod bolts fix this problem) and should be good for around 700hp (on dyno they are). Also you crack test test them to check for flaws and shot penn them if ok.

Z32 trans just needs the custom adaptor plate inbetween bellhousing, engine. They use a similar adaptor plate when running a Z32 trans behind a Nissan V8. Search the internet, as there should be an adaptor plate for RB engine into 300ZX.

[ZzZleeper]

It's not the hp, it's the torque. Gearboxes are rated in amount of torque they can handle (design limit).

The RB20DET gearbox runs same internals as the S13 gearbox (from memory the same part number, which is FS5W71C). The gearbox internals are rated to 294NM (design limit). Stock RB20DET engine is around 264NM from memory, so not much more than factory. Above 294NM the lifespan of 3rd gear is reduced and will fail alot earlier if thrash car. It's due to size of the blades on the gears which are really thin compared to aftemarket gears that are bigger, thicker.

Stock conrods are forged I beam conrods. Weakest point is the conrod bolts when exceding 550hp at engine (ARP conrod bolts fix this problem) and should be good for around 700hp (on dyno they are). Also you crack test test them to check for flaws and shot penn them if ok.

Z32 trans just needs the custom adaptor plate inbetween bellhousing, engine. They use a similar adaptor plate when running a Z32 trans behind a Nissan V8. Search the internet, as there should be an adaptor plate for RB engine into 300ZX.

Good to know about the rb20 trans. I will probably end up scrapping it now, as i will be using 3rd pretty heavily lol. I havent been able to find a trans adapter plate for the rb. Not sure if one is in production. As you all may know, the Z32 and RB25 trans have the exact same internals. The only difference is actually the bell housing. You can unbolt the bell housing from the rb and the z32 and bolt the Rb bell housing right to the Z32 trans, Verrry simple to do. Ive had some buddies say they've picked up just the bell housing for under $100 bucks! I just cant seem to have any luck finding one lol.

[gtrjon]

You keep saying heads. It's an inline 6 so only one head not like other cluttered 6 cylinder engines! Just kidding. Welcome to the boards looks like a solid starting point for a great project

[Skym]

Good to know about the rb20 trans. I will probably end up scrapping it now, as i will be using 3rd pretty heavily lol. I havent been able to find a trans adapter plate for the rb. Not sure if one is in production. As you all may know, the Z32 and RB25 trans have the exact same internals. The only difference is actually the bell housing. You can unbolt the bell housing from the rb and the z32 and bolt the Rb bell housing right to the Z32 trans, Verrry simple to do. Ive had some buddies say they've picked up just the bell housing for under $100 bucks! I just cant seem to have any luck finding one lol.

About the bellhousing swap over, that's interesting, thank you for sharing that information.

The 300ZX rebuild kit should work on R32GTR, R33GTR, RB25DET, 300ZX gearboxes (same gearbox internals).

Even upgraded internals are the same -

http://www.ppgearbox.com.au/page.asp?categoryid=12

I see that it's more about keeping cost's low (budget).

If cost wasn't a barrier, probably fit a upgraded T56 gearbox (rated higher with torque), custom CNC bellhousing -

http://www.rsgear.com/products/transmissions/tremec-t56.aspx