RB25DET bottom end parts info needed please?

[Chris Wilson]

OK, I think I have decided to stay with an RB25 or RB26 block, with RB25 DET head, modded to take solid lifters and under bucket shims using the Tomei stuff.

I stripped my RB25DET engine today, expecting to find forged pistons and rods, which is how it was sold to me, but found stock Nissan cast pistons and stock Nissan rods... Oh well!

So I need pistons and rods, forged. Current head gasket is a 1.8mm Apexi multi layer steel one. When I rebuild though I want to keep stock squish, so want to run a stock thickness, or close to stock thickness head gasket, I believe a 1.1mm steel one is about the same as a stock composite gasket? So I need forged pistons in 87mm bore format, to give about 8 to 1 compression., witha 1.1 mm head gasket. What's available, preferably not something from the US, as they tend to be heavy out of too big a forging die. Do JUN sell a Cosworth made piston for the RB25 pin height, or should I do the below? It's all quite complicated!

Now I have another dilemma. I want to run a steel crank. Do I try and find an RB25DET steel crank (do they exist?) or do I just get an RB26 steel crank and run RB26 forged pistons? I would really like to keep it at the shorter RB26 stroke though.

So at the moment I need to balance the desire to stay slightly shorter stroke and 2.5 litre, or get the seemingly more common bits for an RB26 bottom end, and put an RB26 bottome end together, for which I am sure JUN do Cosworth pistons.

My final dilemma is the head. I definitely want to keep my Apexi RHX6 single turbo on its Apexi cast manifold with external wastegate. Am I right in thinking that precludes me using an RB26 head casting, as the exhaust port studs spacing are different to an RB25DET head casting? I don't want to get into adaptor plates, I'd rather stick with a modded RB25 head if the exhaust manifold fitment differs...

A lot of questions, sorry, but all help eagerly sought, with gratitude. Thanks.

[discopotato03]

Chris I think you'll find ALL RB crankshafts are forged steel .

I would always always go for the greater capacity .

I think the RB26 head offers lots of advantages over built up 25's and often much cheaper , better cams , spings , inlet system and the shim type buckets - all std .

HKS did make a cast split pulse T3 flanged exhaust manifold , with provision for an external waste gate , to suit the RB26 head . I understand they're not common but a few out there .

Cheers A .

[R31Nismoid]

Chris.

To help with procedings... what is your projected rwkw power goal from your car... and what you want/can live with in terms of lag and so forth.

As i have close too 300rwkw and i aint even touched the RB25 head yet. Mine is still stock as with many other peoples here. Some have just dont a set of CAMS and thats it.

cheers - ash

[Chris Wilson]

The engine made a genuine 500 BHP at the flywheel on UK pump fuel. That was with the Apexi RHX6 single turbo on a n Apexi cast manifold with external wastegate, and a pair of Apexi hydraulic cams marked LN1, whatever spec they may be. 1.8 mm head gasket, stock appearing bottom end. RX7 FD injectors (550 cc), big fuel pump, conservatively mapped Power FC, big AFM, stock throttle body and intake system, big bore exhaust.

Would like 600 BHP, car is track use only, circuit, not drag. I want to keep the same turbo and cast iron exhaust manifold, would like a forged bootom end, and convert to mechaincal cams. Can put up with quite a bit more lag than it currrently has, it makes peak torque at 4600 RPM. Thanks