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Discussion Starter #1
as per title..what is the realistic max power one can run on a unstroked rb26(say max 1mm oversize) in a way that it is fully usable on the road,enjoyable to drive and not too laggy??(basically not overkill and spoiling the whole experience)

Also what is the best turbo/turbos to use to achieve that power enjoyably on that bottom end?

Opinions and experiences please
 

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GT SS's or -9's i think they are. Nice round figure with a fair bit of poke and very very responsive. A set of Pon cams with a computer and the usual exhuast/fueling mods.
 

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Discussion Starter #3
yes they are nice but i am talking more like huge power..i already have -5s(600bhp) and im just looking at the future.Want to get the most drivable power i can get enjoyably without changing my .5mm oversize current bottom end.

Basically i want to know what is the max usuable power limit you can push an rb26 to before it becomes overkill.(too laggy and just undrivable)and the turbo/turbos to achieve it
 

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Surely a matter of taste to a degree????

Lot's of owners want power from idle and will bleat on about torque and lag, but then others like a big hit high up in the rev range and will therefore go with that little bit bigger turbo and wilder cams.

It's your car, what do you like???
 

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It depends on what you are looking for...
Different people have different tolerance for "boost threshold".
It depends alot on driving style.

Here is my current dyno plot: (still need a little tweak later)



The power look useable, but the kick seems to be a little hard.
This a RB26 with a 2mm overbore (stock stroke), running 256/9.0 cam (step1), and a Forced Performance 88HTA Turbo.

I don't know how it will drive on the street as I haven't driven it yet... I'll let you know in a few weeks time. :D
 

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what the best power for your engine driveability wise is i dont know but personally i wouldnt go single turbo as the car doesnt do much till on boost which is too late around town
 

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Discussion Starter #7
thanks for the replies..Nocturnal thats a pretty wild looking graph!

Ideally im looking for a usable 700 to 750 bhp without loosing much of the responce that i have with the -5s i have now.(say 500rpm, max 800rpm later on boost threshold)I know im going to have to uprate the fueling even more,might uprate the inlet manifold,and mayby some cnc head treatment and definately put in wilder cams but i dont want to touch the bottom end i have at the moment.

What turbo/turbos and A/R size would be best suited to what i want?
 

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you're up for a challenge my friend

the 2530s (-5) didnt gain their reputation accidentally. if there was something like you describe readily available, ppl would have that instead. the limiting factor is capacity. turbo design can only do that much.

i'd look into borgwarner's forced performance and maybe the new holset series from endless (the t-70). noctural's setup may have been perfect for you if the jump wasnt that steep. it may as well have been a glitch somewhere, since fp turbos usually retain "stock" turbo characteristics (stock meaning the turbo they're based on) but flow a lot more up top
 

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diminishing returns past 600bhp - the lag becomes a problem for street drivability. Past that mark, you've decided on a specialized machine.
 

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I think a Great setup is a GT4088R I run one one my race car and it does [email protected] wheels and is still really drivable, although I must admit that it is strapped to a 2.8 stroked motor. My Road car is also a 2.8 but I have replaced the twin 3037's with a single GT4094R so I can use my road car as a development platform for the time attack car.
 

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stroking makes a difference. RB30 makes a difference. For an unstroked motor, lag will always be a problem IF "street drivability" is a factor. The problem is that you simply cannot drive around in these 700-800bhp cars with the pedal to the floor - on the streets you'll see bursts here and there, but that's it.

I liked the idea of GT-RS on my unstroked motor, but have since come to my senses. -5s, pushed to the limit, change them every 20,000km. Set up properly -5s make good power at 1.9 bars boost.
 

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Discussion Starter #12
thats all well and good when you have the fuel kismet ! All i have here is 95 octane.My tuner stopped at 1.4kgs boost as any higher would be too risky with these turbos and our fuel.If i had the fuel i wouldnt think twice about running them at 1.7 + bar..

Think im going to have to go with one big single next, especially if i want to run big boost safely..which one is the question !have heard and read alot of good reports about the 4088s..im half thinkn mayby a T04z also with 1.00 a/r..could always rise my compression ratio to counteract against lag
 

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thats all well and good when you have the fuel kismet ! All i have here is 95 octane.My tuner stopped at 1.4kgs boost as any higher would be too risky with these turbos and our fuel.If i had the fuel i wouldnt think twice about running them at 1.7 + bar..
Run water injection. You'll be able to use the 95 octane with more boost.
 

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Hunt down the threads on my former missile. RB26N1 with half-mil overbore, GT-SS and V-Cam... plus a couple of other bits. 520 horse and 500 ft/lb or around there ATF.

Superb set up.
 

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but i already have 485ft lbs and 600bhp + atf..and im getting used to it..i want alot more,just planning ahead !
If you are making 600bhp at the fly at only 1.4 bar, that tells me you are running quite a large turbo already.

In short, you are at the acceptable range of boost threshold for a road car, anything more and you will be looking at giving up response for power.

There is no 2 way about this, you win some, you loose some.
If you want power, you are going to have to deal with the higher boost threshold.

If you want more power without having a higher boost threshold, then you stroke it... RB30.
But then you get less rev... there is never a win/win mod when it comes to tuning.
 

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considering your power at 1.4bar on the best fuel you can get;

i would say, get the best stroker kit you an get and the best head-work,

if you dont mind rev to 9000rpm a bigger turbos not really a problem, as you would use it in the lower gears for a short time, try the CROWER stroker with todays exchange rate, or if you got the cash go for the OSG 3.1L


then the head, use +1mm oversize valves, the lowest duration cams above 264 that have big [11+] lift, say e.g 272 cams with 11,35mm lift[ if you dont mind 9k rpm short bursts like gear 1st-3rd go for 280/272 11.35)

with a 3.1L OSG or 2.9 CROWER the car will drive quick enough around town, just like an N/A 2.7L Inline 6 motor with the differing compression ratio, which to me is fast enough for 30-40mph.

you need a bigger turbo if your at your max boost to flow more air, a better head cam/valve etc [maybe CNC from the states]to make your volumetric efficiency better for more bhp, and best of all more engine capacity cc.

big turbos aren't 'laggy' if you dont mind changing gear a few more times than say nismo n1's, on a 2.7L a hks T51r KAI with drop in step1 cams and cam pully's [important for aiming for earliest boost] then you wont drop out of powerband on a r32/33 gtr gearbox with the standard rpm limit.

Based on Nocturnals advice, id go for the CROWER 2.9L [2.85L with 87mm piston] for 9k rpm range compared to the OSG 3.1, not only for cosr, but also the extra 8-9000rpm range is going to make more power, and powerband than the OSG.....i would think.....

I'd go for a t51 kai / smallest garrett gt42 on the hks 2.8/ crower 2.9 with mid-duration/high lift cams, it will be swift enough around town, and when you want more power drop a gear or 2....:thumbsup:
 

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one more way is using a nitrous oxide n2o window switch, you can spool 1-2000rpm faster [depending on the bhp shot, 50,75,100,etc] using not much of the gas at one time making the bottle last and so it a 'relatively' cheap upgrade.
 

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Discussion Starter #19
Thanks for the advice.i have twin 2860-5s at the moment .wont get much more than 650 out of these no matter what bottom end i have.I dont want to touch the bottom end i have at the moment to be honest.Its a good bottom end...freshly built .5mm oversize,tomei pistons,rods,new stock crank,trust oil pump,acl bearings,trust sump, ati damper etc..I want to get the most power(usable) i can without touching it.It would be a shame to take it apart again this soon after the build.Then in the future i can go stroker or rb30 when its time for another rebuild..

I am thinkn of changing the diff ratios to gts-4 items if/when i do go single..will help with staying on the power band along with rising the engines compression ratio

Anybody else out there running a usable 700+bhp on a unstroked/30 rb??Whats it like?
 
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