Big rebuild Help needed

[ZILR-34]

Hi Guys

i have a R32 GTS-T RB20DET with 91,000 on the clock.

I’m in the middle of deicing to work the RB20 head or buy a RB25 head and work that with a RB30 bottom end. The RB20 is like brand new and it goes hard for the age of the car. I’m going to go all out on the engine I have a big budget,

Help me deiced which head to use, if I end up going with the RB25 ill be selling the RB20 complete with 91,000 on the clock

[proengines]

If you've got the budget to cover it, buy an RB26 head and ancillaries.

[pnblight]

by the time you do a build up like that you mos well have bought a good rb26dett ,seen complete motor,turbos and loom etc 96 vspec $6500 9100kms old how could you go wrong.

[RB26VL]

dont mess with anything on the rb20, sell it and get a 26 as others said and with 17psi, high flow turbos, 700cc inj, mine made 350rwhp only revvin to 7100rpm still pulling hard! thats 118mph and 12.0 at drags in a vl too (mph is low 11s)

i have had a rb30et engine and it is like a truck engine, slow, doesnt like to rev, and also had a rb25, which aint nuthin compared to the 26 so thats my 2c worth.

26 is like a reliable rotory i reckon, they just love to scream and rev

best engine by far (my opinion)

[Cubes]

Unless you were going to keep the RB26DETT relatively stock (.9bar of boost 240rwkw) I wouldn't bother with it as you are going to spend $$ on injectors/turbo and possibly cams anyway.

I would spend the money on a RB25DET with some nice internals & head work.

My thinking is for ~$6000 you can get a decent RB25DET built up that's head will flow more than the stock rb26dett head + it will be a fresh motor with a known zero thrash history.

All things being equal (turbo's etc) the RB26 has very very little over the rb25, cam specs is basically all it has. This can easily be fixed.

There is no point comparing a RB30ET to a RB30DET or RB25/26DET. They display completely different traits. The SOHC being a slow narrow rpm power band rev'r.

From a legal point of view I would go with the RB25DET.

If you want to build up a nice motor and don't want to shell out for a R33 RB25DET front cut I would look at the R32 RB25DE motor.

Rebuild the head with a mild port/polish & inlet/exhaust valve deshroud.

RB25DET 8.5:1 Forged pistons (9:1 if you are going to run bigger cams)

Shotpeened Rods or if you can spend the extra 1k over shotpeened rods on forged rods by all means do it.

Blueprint & Balance

There you will have a reliable 350rwkw stormer, if you have the forged rods say hello to 400+rwkw.

Honestly I think much over 300rwkw using an RB25 begins to lag a little too much for the street, this is where I would consider the bigger 3ltr.

The 3ltr apparently has issues with rods bending at around 550ft-lb. So if you balance out the torque x rpm using turbo sizing boost & rpm then you will have a motor that will hold together.

500ft-lb x 7000rpm / 5252 = 666hp on stock rods.

You need to keep tabs on the amount of torque and the motor will be fine.

In theory

The SOHC is good and proven but to get anywhere near the flow levels of the DOHC head it needs to run some seriously large cams that return bad drivability and fuel economy.

I've posted this previously but just to note it appears the R32 RB25DE head has the same sized valves as the RB26DETT head. Being 35mm on the inlet and 29.5mm on the exhaust.

The R33 RB25DET head appears to run 34.5mm on the inlet and 29mm on the exhaust.

I've done a few measurements lately and this appears true.

I would like to see more heads or hear from others that have access to heads to let me know if it isn't just a couple of freak heads I've measured.

BUT the R32 RB25DE ports are slightly smaller than the R33 RB25DET & RB26DETT heads. The RB25DET & Rb26DETT ports share the same design and size.

When you look at the valves of a RB20DET (30mm inlet & 27mm exhaust) they really do look like little baby toy valves next to the Rb25/26's.

There's an old saying - There's no replacement for displacement.

The RB30DET really needs cams to unleash its top end power as it essentially flowing the same amount of air at a much lower rpm over the rb25 & 26.

Obviously.

[ZILR-34]

yea that sounds about rite cubes" i will go with the RB25DET head and the RB30 Botton end so it will be a RB30DET.

ill be doin

Rebuild the head with a port/polish & inlet.

Forged pistons

Big high spec cams

Blueprint & Balance the RB30 block

HKS GT30/40 turbo or HKS T51 turbo

Motech M600 ecu.

Nismo 1000cc injetors

bosch high pressure fuel pump

how much will a new RB25DET head compelet cost?

[Roy]

If you are going for that sort of setup just go straight for the RB26 head. It has solid lifters meaning that you can run much higher lift cams. A wider range of cam specs are available, and you get a better inlet manifold arrangement then that used by the RB25 head.

Also if you want to run the T51, it has a v-ban exhaust manifold, again more readily available for the RB26 head.

[Cubes]

yes.. Do check out how much you can get a RB26DETT head for as they are much cheaper now than when I did my setup.

If you go for a greedy plenum or use the stock rb26dett inletmanifold/plenum you won't have to lower the engine ~13-15mm.