Rb25 Head Rebuild

[Husky33]

Hey guys,

Building an rb25(well collecting parts at the moment anyway as Im overseas for a little while) and need some input from people in the know.

Ok, so at the moment this is street registered but it will most likely become unrego'd at the years end and will be used solely

for super sprints and club events.

I'll give an insight into the car atm as it may help

So far engine wise I have:

full 3inch into 3.5 inch exhaust(no cat)

nismo fmic

walbro intank

hks oil cooler

jjr coilpacks

garret 3076 .63

hks manifold

tial 44mm wastegate

greddy inlet plenum with q45 throttle body

tomei 740cc injectors

sard fpr

bosch 044 external

z32 afm

power fc

Not installed, sitting at home

hks 256in 265ex cams with hks adjustable ex cam wheel

cp pistons 86.5mm

spool rods

arp head and main studs

n1 water pump

ross balancer

Haven't bought an oil pump yet still unsure whether to go N1 or the more expensive and obviously better tomei/nitto.

Which brings me to the head, and what to do with it.

Now, with the above turbo and ancilleries, coupled with E85, I'm hoping to make a responsive 300-320rwk. As it will be mainly used as a track car,

it's going to spend a fair bit of it's time in the upper rev range, so I really want to make the engine reliable. I'd like to rev it to 7500 or even 8000, but i'd be happy with 7500rpm, because if the turbo comes on pretty early, it still gives me a fair bit of rpm to play with, without the wear and tear value of high revs.

Sooo, as you can see I don't want a head that can rev to 10,000rpm. I just want a good, reliable head that will support the flow of the turbo and be able to be in the 7500 rev range day in day out. When the engine is out, I want to build it properly, and I don't want to go pulling it out again for a few years.

I've been looking at the supertech and ferrea kits, and for the price(which is bloody good), I could put new valves, springs, retainers, seats and valve guides in.

I don't think with my goals there is any point going solid head, am I wrong???

Also would going oversize valves add enough benefit to out way the costs of prepping the head for them?

I don't mind spending money, but ONLY if it is a worthwhile benefit to the overall result.

I know you can build a motor a thousand different ways, but for my goals, what do you think??

Cheers in advance

Simon

[Dobz]

Solid lifters are a good idea if you're wanting to hover around the 7500-8000rpm mark.

[GTSBoy]

How long is your piece of string? Actual usage will determine what you need in terms of revs (ie overall gearing versus the tracks you will run on). So, you may have a choice between spending X amount of money on making it able to rev to 8k all day, or you might be able to spend about the same amount of money on making it flow enough to make the same power but at approx 7k. Note, I have no idea whether the $$ spent on a light and stiff or solid valve train would be approx the same as the porting work needed to bump up the flow in the top half of the rev range, I'm just picking a rough example. And besides, even if it was ~$1k for one option and ~$2k for the other, that's still about the same sort of $$ considering what it costs to build the whole engine anyway.

Anyway, money spent on a good port job will give you more flow everywhere and more power everywhere - money spent on making it rev another 500rpm only gains you that small increase at the top. I think I know which way I'd prefer to go.

[magic1]

I don't think anyone on here knows how to do a solid lifter conversion on a rb25. When you find out let me know. when I find out I will do the same.

[Gerg_R31]

Ive done a few solid litter conversions at my machine shop tweak it can supply the tomeii solid softer kit, they will come with the valve to cam clearances.

Since your chasing a rev range buy all parts that will work in that rev range, most the time departs manufactures will state the products rev range.

pretty much every stainless steel valve ive seen for the rb motors have a + 1mm head

make sure you get valve springs to suit the cam, supertech and ferrera are the only parts id recommend

flow bench porting 4-5 angle intake seats and radius exhaust with 1mm 45° seat

[R31Nismoid]

What people have issue with tends to be using 10-15yr old heads, lots of KM's on them, and they then of course are going to have issues.

I had my RB25 head rebuilt with just stock stuff back when i had my RB25. Stock cams, values etc and it was between 270rwkw and 370rwkw depending on the fuel i had in @ the time.

With a forged bottom end and a GT3040 it was spun to 8000rpm without an issue. I think it was upto 140 dyno runs

I also did around 60-70 drag passes as well (some with 370rwkw/24psi) and it was spun to 8200rpm on those runs. So not quite extended RPM @ circuit, but it also saw 8000rpm on the street fairly often over 10,000kms.

Guilt-Toy was also running a GT35 and 350-370rwkw for aaaages on a stock head and spinning to 7500rpm

I think oversized values for your goal is a bit of an expensive trip for not much gain as at the end of the day the .63 housing is going to be the restriction in your setup, and your power goals aren't that high.

Also you'll probably find due to the housing, that you simply don't need to rev past 7500rpm as power will have well and truly falled over anyway

That said the comp ratio would be a good thing to pay attention too though and hasnt yet been mentioned.

If you are only going to be running E85 you could bump it up a bit more than normal PULP builds, this seems to be what a fair few guys are now doing with great results.

[kitto]

A stock head will flow more than enough for your power goals.

If you really wanna throw some money at it, just simply clean up the ports a little, match the inlet manifold a bit better to the head. If you want to do valves, its probably only necessary if you really want to; to put in iconel exhaust valves. Factory exhaust valves in RB's have a tendency to burn out. More common in RB26's though. Bronze guides are another popular thing, highly recommended when fitting stainless/iconel valves.

Some heavy duty springs, a set of cams if you wish and be done with it. Just have someone who knows RB's rebuild it.

A very good mate of mine made 347kW @ the rear hubs on 19 PSI on BP98 with a completely internally stock RB25.

It has;

Supporting fuel system

GT3076R .82, externally gated

Camtech 264/264 9.00mm lift cams

Garage 7 steam pipe manifold

Forward facing plenum - which actually almost wiped his whole mid range torque curve. Not worth it for the slight increase in power and slightly better response.

Thats all it had, no head work, just a really good tune. Unfortunately it recently threw a rod out of the block. Rod bolt failed, its now getting a forged bottom end. But hes not doing any headwork, just a rebuild.

[Husky33]

awesome reply's thanks

So in reference to Ash's post about the head being quite old, which it is, when the bottom end is getting done I may as well clean up the head.

With the price of the supertech/ferrea being so cheap, I may as well replace the valves with stock size ones, springs and put some bronze valve guides in there and just tidy up the ports a little.

I already have some hks 256/264 cams which will enable me to keep the vct, and also a greddy inlet manifold but that is moreso for the piping being in the way of the turbo.

Yeah, I realise the .63 is going to be a restriction before the head will, but I may change it to a larger housing or a different turbo later on, although the power levels aren't going to be rediculous, 300rwk is already plenty enough for a rwd track car

[GTScotT]

The main issue with RB25 heads are the valve springs, make sure you upgrade those and a quick tidy up on the head will be all it needs to that much power and more.

Im fairly sure most of the 400kw people just do tidy ups on their heads, removing dags and the knobs in the exhaust ports. Port and polishing would cost thousands, but its proven a stock RB25 can make 300kw. The fact your bottom end is built means yours will do it reliably, just work on the basics for a keen result