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Rb25 Stroked To 2.7 Or Rb25/30?...ideas And Recommendations?

henson

By henson,
in Engines & Forced Induction

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henson Collaborator

henson

Posted
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Hi ya'll..

I'm currently running a mere 260kw at the rears with a HKS GTRS turbo, hks 740 injectors, hks evc-s b/controller, hks SSQ bov, haltec ecu, split fires coils, hks dump pipe, front mount and a bunch of other associated junk on 19psi from my unopened rb 25.

Obviously im chasing my power (around 350 - 400kw), and wanna get more serious with this... i built mine to where it is now but i want solid power with reliability and strength while keeping the original engine.

So question is, Do i go a stroker kit bringing it out to 2.7 or rb25/30bottom end?

Anyone with some knowledge in this area or other options i could take would be much appreciated as this isn't going to be cheap and wanna go down the right path!

Cheers...

Daniel

TiTAN Grand Master

TiTAN

Posted
Posted

that entirely depends on how you plan to use the engine.

the 3L will have nice fat low down off boost power

if the 2.7 kit has full counter weighted crank its going to love to rev (not that a 3L wont rev) but you will then be held back by the RB25's hydraulic lifters

henson Collaborator

henson

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  • Author
Posted

i want a tough streeter that will be good for the track as well whilst being reliable..

i know its a lot of power to chase out of the 25...how do i get around the hydraulic lifter situation as i am leaning towards the stroker kit.?

TiTAN Grand Master

TiTAN

Posted
Posted

the hudraulic lifters are fine to around 8000rpm, if you wanted to push it harder than that you can (as above) Install a conversion kit to solid lifters or change to an RB26 or RB25NEO head as they have solid lifters from factory.

a GT35 will get your power goals on a 3L without having to rev it super hard, (expect real boost around 3500-4000, or for the 2.7 kit, 4000-4500) mine is making almost 400kw well before its 7500rpm rev limit.

R32Abuser Mentor

R32Abuser

Posted
Posted (edited)

that entirely depends on how you plan to use the engine.

the 3L will have nice fat low down off boost power

if the 2.7 kit has full counter weighted crank its going to love to rev (not that a 3L wont rev) but you will then be held back by the RB25's hydraulic lifters

Its horses for courses IMO

How is the car being driven? 100% street? Majority street (90% Street / 10% Track)? 100% track? All makes a difference when considering what avenue to go down...

For the street, IMO torque, throttle response, and low down power off boost are the most important things. 99% of the time will be spent at <5000RPM unless you wish to lose your license, bring the wrong attention to yourself or get defected. Hence, having a car which has plenty of punch off boost allows you to take of from the lights at quite a pace, without having to look like a hoon "stalling" the motor up to get it off the line quickly. In saying that, IMO the RB30DET conversion is the better option.

For the track; its a different ball game. All depends on what you're actually doing i.e. motorkhana, private track days etc. etc. If it were me, and I was doing motorkhana I'd still prefer the RB30 for the low down punch and other reasons stated earlier. If its for private track days the 2.7 kit might be a goer with regards to having a few extra rev's up your sleeve.

However, as TiTan stated, the hydraulic lifters in your RB25 head is what will let you down. I built my RB25/30 using an R32 RB25DE head and my only regret is that I didnt use an RB26 or RB25 NEO head to being with. No real downside except for legality (looks-wise) and wiring.

Edited by R32Abuser
Roy Grand Master

Roy

Posted
Posted

Nothing wrong with just buying the turbo you are after and running it on a well tuned RB25 on E85. If you grab something like a 3076 or T67 and throw E85 at it you will make 350rwkws safely and reliably. Sure a stroker will give you more bottom end, but meh... at what cost.

If you are doing track work there is thousands to be spent on radiator, oil cooler etc before you worry about a built motor. Also if you are going down the road of a built motor then you need to really look at oil pump, sump etc which in themselves instantly add 2.5-3k to the price of an engine build.

The secret to any RB that is going to see prolonged open throttle like you expect at the track is to go to a tuner with a proven track record with circuit cars.

IF the engine fails then it will likely just spin a bearing which leaves you with a perfectly usable head and block etc to use for the stroker or RB25/30 build. But I suspect that once you have the std RB25 humming along at that power you wont be worried about building a stroker engine to make 30-60rwkws more at 4,000rpm which is a power band you never really se when you are up it and having a go.

75coupe Grand Master

75coupe

Posted
Posted

I would of thought the cost of stroker compared to 30 bottom end would be the deciding factor, unless you really want to be able to stand up and say 'Ive done something different for similar results'

Roy Grand Master

Roy

Posted
Posted

Yeh, RB30 crank/block, forged rods and pistons, Tomei/Nitto oil pump, aftermarket sump all for less money then even the cheapest RB28 stroker kit is hard to go past. OR you can just be a cheap skate and use an RB26 bottom end for the extra few ccs.

If money isnt an option then may as well go an RB32...

henson Collaborator

henson

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appreciating the feed back guys!

but yeah at the moment its a daily, with the odd monthly track day (nothing to serious) and Mt Nebo/Mt glorious runs..

in saying that, after finding out which avenue to take, and as stated in above comments, it wont be a daily after build.. i will address all the cooling and associated running gear above on beyond its requirments to cope with demand.

I have a budget of 35g to spend. so slapping on a big turbo and winding the boost up to get numbers isnt on the cards, i wanna do things right the first time..

so over all, will rb25/30 be the more likely cheaper but just as reliable and effective option?

allowing me to budget for other gear..

@TiTAN: roughly how much did your build cost as it seems you have the set-up im after? and have you ran into any occuring problems since?

TiTAN Grand Master

TiTAN

Posted
Posted

@TiTAN: roughly how much did your build cost as it seems you have the set-up im after? and have you ran into any occuring problems since?

you can buy my whole car and have 15g left over or spend the whole 35g and then some as an idea of cost if you arent doing most of the labour on it.

no real issues with it other than the normal excessive oil in the head at track days issues, but since adding a possible fix for that i havent tried it out again.

there is a big difference in cost between a reliable 300kw setup and a reliable 400kw setup.

JonnoHR31 Grand Master

JonnoHR31

Posted
Posted

+1 for 25/30, depending how much you can do yourself you can have a solid, reliable 30 bottom end for under 5k, which leaves plenty leftover to do a bit of headwork and then the other crap (turbo, oil cooler etc etc).

Bsa Mentor

Bsa

Posted
Posted

For that money I would be selling the 25 and building a 26/30 heads can be bought for a decent price that also gives you some extra coin to spend on other bits. By the time the 25 head is converted might aswell buy a 26 head. That also sets up a better platform to build off

henson Collaborator

henson

Posted
  • Author
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yeah all good points.. i had this idea (probably not a good one haha) but i dont wanna buy an already built car as i wanna do it myself and i also wanted to keep the original motor and see what i could do with it... but from what everyone is saying on here, that doesnt seem like a very smart idea for the money. haha

at this stage, most likely going to go with rb25 head with conversion kit to solid lifters with rb30 bottom end for streetability and low down torque.

still a bit of head scratching ahead of me i think!..

R32Abuser Mentor

R32Abuser

Posted
Posted (edited)

Yup...all of these things about the 26 head were an afterthought for me. You can run bigger cams with less issues with a 26 head and overall the head has more potential to make big power.

The extra deck height of a 30 makes it a pain to fit a 25/30 under the bonnet of a 32 GTST without modding the engine mounts because of the intake. Whereas using the 26 intake and ITB, life would have been so much easier :yucky:

As its been stated, chances are the 30DET will cost less to build than the 2.7 kit.

IMO, I dont see the reason (except legality!!!) to build tough 25/26 bottom ends when it costs just as much to build a tough 30 bottom end. You get more "area under the power curve" via an RB30DET which translates generally to a faster car overall.

Edited by R32Abuser
BMYHOE Proficient

BMYHOE

Posted
Posted

im getting my Rb25 head converted to solids.. the full kit fitted ready to go will cost you around $3000..

im sick of the ticking noise that came and went... if i didnt already have manidolfds/ECU etc i would have a rb26 head on this one..

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