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No worries at all Tangles, happy to try and help make the engine building journey smoother for you.

The standard RB25DET bottom end can certainly support over 300rwkw - I've witnessed a few that have managed this feat. However, in most of these case, if not all, they had reduced compression (via 1.6mm metal head gasket etc) to give a little bit of 'margin for error'.

Having said all that, the cylinder pressures and temperatures that come with a 300rwkw engine means the standard cast pistons will not tolerate even the slightest hint of detonation, detonation that can come from a host of variables - fuel quality, injector flow variations, cylinder temp variations and so on and so forth.

At the end of the day a poor tune can just as easily lead to detonation killing expensive forged pistons. But it's those minor variations, that can and do occur, that a decent forged piston may cope with long enough to allow the issue to be resolved without doing any serious damage, something that the standard piston ring-lands will not survive.

Rods, on the other hand, are more likely to fail due to rev's at the 300rwkw mark. Keep the rev's under 8000rpm (say about 7800rpm) and the standard rods will last for a reasonable length of time at 300rwkw. Mind you, give the price of a set of rods these days ($600-700 for Spool rods)...

I'd suggest a three possible approaches to the making the most of the head upgrades:

Basic) Drop compression a smidge - via a 1.6mm head gasket

Medium) Head gasket/o-ringing and forged pistons

Advanced) Do all of the above + rods and fasteners

  • 2 weeks later...

Cometic intake manifold gasket, intake collector gasket, exhaust gasket, and 1.2 x 87mm head gasket

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arp head stud kit, intake / exhaust valve seals, intake / exhaust valve seats, intake / exhaust valve guides, oil restrictor,

2x700cc sard external intake manifold setup

DSCF0137.jpg

clear cam timing cover, q45 throttle body & adapter kit

DSCF0136.jpg

256 poncams and 8.8mm hi lift springs

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DSCF0134.jpg

  • 2 months later...

Hi fella

whats going on with your car?

seems like a heap of money's been thrown at it for minimal results.

the crack in the head still seems fishy but i guess the machinist will allways blame a part that he didnt supply.

too late now but you could have purchased my forged long engine for $4500.

comparing our graphs is like chauk and cheese, there is certainy something holding your car back from making power,

wether its the turbo or something else im not sure but at 80kph i have 40kws more then you and then finish 120kws more up top,

so the high flow dosent look as responsive as it should be. not to forget that i have over 500nm of torque from 90 kph onwards.

same trans, and same dyno.

i was hoping for your sake that the work was gonna make a decent improvment but it hasnt turned out that way.

new turbo time me thinks.

yup, new turbo time me thinks too

had a 2hr 200km Hills run tonight, the package as a whole is insane and very very quick, but the turbo is mismatched to the engine/auto in top gear @ 3000rpm.

pushing the boost at .9bar but at that mark (.9bar, 3000rpm, 110kmph overdrive) its not quite right

in 3rd gear the cams are awesome, engine runs thru past 6000 rpm and its beautiful, quick but being held back

can feel it, Although, the car as a whole is very very nice to drive. feels mean

better turbo & cat will gain 40kw I reckon (got the fueling for it)

not disappointed at all, was hoping for around 220kw (does it fine with no cat, dynoed) but 206kw with the cat constricting the boost

so its thereabouts

come over catch up, yarn and go for a drive>?

cheers

Bw

madaz:

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very happy honestly, but yeah tonight showed the turbo is peaking at 220kw(no-cat vs 206with cat) frankly

alls good for a $600 turbo, 3yrs old now

need to meet you down at anzac raceway and give you a run in the wifes legnum.

back on topic, once you start making over 200 kws the amount of air that needs to flow thru your whole system is massive.

have you ever stood behind your car during a dyno run to see how much air comes out of your exhaust at full revs?

im sure my car gets pushed along from the thrust coming out of the exhaust.

point being that anything in your system that interfeers with this high flow rate is going to rob you of power.

last time i seen you you had a small muffler etc has this been addressed?

needs to be 3 inch from dump to rear tip.

you mentioned your intercooler was only small.

wonder if you can fit my ASE cooler in there? the 33 and stag front end would be fairly similar? maybe?

im stripping my 33 for parts so let me know if you want any bits.

highmount gt35?

Edited by dangerman4

very happy with the package

more in it with tuning and derestricing the exhaust

darren, 3" all way thru but the cat is robbing 18kw proven on dyno, justjap bellmouth to cat, 3" metalcat, cat back is 3" to gtr kakimoto 3"in/out straight thru muffler

Im thinking GT3071r-iw :(

and more tune time, but yes the current slide turbo is holding it back along with the exhaust restriction

But very happy with it as a whole, TW Engineering did the head work... and its now so easy to tell that the slide turbo is mismatched (too small; aka journal-gt2530) to this engine !

the engine is tops !!

let me know darren when your pulling stuff off, can come round have a chat etc. Just got no $$ for a while now, got to concentrate on the home loan finance seeing I havent been working for half a year now. knees, Disability Support Pension starts Feb. no income for 7months, filled in the pool, got a spa, head work plus parts, lol silly me :P

1

haha, pot stirrer!

I'll give you a run in my new twin turbo V8 (650Nm torque at 1600rpm) over 60 feet ;)

i will be keen sled, but i should mention i will be on my quad....

can that big fuel guzzling twin turb beat a 4 cyl?

you better have your front wheels in the air if you hope to keep up.

i certainly will have

Edited by dangerman4

hahahaha!!

saw a yellow 750cc 2000 gsxr for 7k the other day. :drools:

going to sell the Nubira '03 4cyl 5spd man. 2.0L, 24000kms, leather interior, blue sedan, 14" wheels, 4wdisc-brake etc

we'll eventually swap for a mazda tribute, I can fit in the back of those so it'd be great for the kids and missus. probably a 5k changeup

the Stag is a great package, went for a quickie again. TW Engineering + BoostWorx have done a top job. loving this head+cams greatness ;)

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