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N/a Rb30 W/ Rb26 Head?

Tonba

By Tonba,
in Engines & Forced Induction

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Tonba Rising Star

Tonba

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Posted

Hey all.

I own a '72 HQ holden one tonner. At the moment i am riding around with a 186ci straight six. Now, ive gone out to buy a 308ci V8, as any holden owner would, but i have a infinity with nissan 6's...I love them...

So what i am looking at doing is buying a cheap RB30 bottom end, buying a RB26 head with the 6 throttles, rigging up some trumpets, lumpy cams w/ adj cam gears, light weight and balanced crank, RB25de pistions and a haltek ECU...

Would it work? What would i need to make it work??

--Alex

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Eug Grand Master

Eug

Posted
Posted

would be cool.. but to get the full potential out of a hardcore NA engine, it just wouldnt be suitable for street.

the key to NA power is revs (or cubes) and since it'll only be a 3L, then you're stuck with revs...

the rb26 head alone will set you back close to 2g's. prepping the block another few grand. ecu, roughly 1g - give or take.

it would sound oh so sweet... and if you want to do it, then i say do it! bang for buck... i've looked into it, and i can think of alot more cheaper alternatives.

Tonba Rising Star

Tonba

Posted
  • Author
Posted
would be cool.. but to get the full potential out of a hardcore NA engine, it just wouldnt be suitable for street.

the key to NA power is revs (or cubes) and since it'll only be a 3L, then you're stuck with revs...

the rb26 head alone will set you back close to 2g's. prepping the block another few grand. ecu, roughly 1g - give or take.

it would sound oh so sweet... and if you want to do it, then i say do it! bang for buck... i've looked into it, and i can think of alot more cheaper alternatives.

Yeah...im very keen on it...$2k for the head you think?

unarmed_skyline Experienced

unarmed_skyline

Posted
Posted

its an easier conversion to use the non turbo rb25 head its ment to almost just bolt straight in, plus it would be way cheeper you can get full rb25de's for like 800, then get the individual throttle body system from an rb26 make a custom mounting plate for it and if you high flow the head a little in all complete build would turn out a little less for the rb25 and the power difference would be minimal with the high flowed head you might even be able topull more power than the 26 head

Eug Grand Master

Eug

Posted
Posted

the significant difference between an RB26 and RB25 head mainly lies in the valves and valve springs, nothing a few upgrades and a port and polish should be able to achieve. probably a few other things too.

the ITB from an RB26 alone is worth a few pennies, and a custom adapter plate can be fabricated from a CAD program. just trying to deal with the custom stuff on the cheap side will be the real mission. then you will have to adapt the throttle cables and deal with R&D into runner intake lengths etc etc etc.

very cool, but not without people who can help you out cheaply

Tonba Rising Star

Tonba

Posted
  • Author
Posted
the significant difference between an RB26 and RB25 head mainly lies in the valves and valve springs, nothing a few upgrades and a port and polish should be able to achieve. probably a few other things too.

the ITB from an RB26 alone is worth a few pennies, and a custom adapter plate can be fabricated from a CAD program. just trying to deal with the custom stuff on the cheap side will be the real mission. then you will have to adapt the throttle cables and deal with R&D into runner intake lengths etc etc etc.

very cool, but not without people who can help you out cheaply

I know people in the business...lol

so the RB25DE head should fit without much issues? do all the water/oil gallerys line up? With the RB25DE pistons in the RB30E block, i should get a little higher compression right?

--Alex

Cubes Grand Master

Cubes

Posted
Posted

The 26 heads have came down in price a hell of a lot.

I've seen complete rb26 heads with manifolds etc for as low as 1.2-1.5k.

So keep your eyes peeled.

I'd be inclined to speak to LukeVL (Tighe cams) and question regarding a regrind. BIG lift with a reasonable duration to prevent it being a peaky/lumpy/lack of down low bastard.

The jap cams tend to run quite a bit of duration and lack lift.

unarmed_skyline Experienced

unarmed_skyline

Posted
Posted

oil and water gallerys show line up pretty right if not perfect from reading around ive never done the conversion but thats what everyone says, although you will either have to blank out the vct, run an external oil line for it or buy an r32 br25de head which doesnt have vct, other than that its all sweet, and yes the rb25de pistons will give you the highest comp i think its around 10.5-11:1 ish a little lower for rb30 and then way to low like 7:1 for 25det pistons, with the rb26 head you will have to modify some parts of the head to get it to fit perfectly but as said earlier it is a better flowing head but you can make the 25 head flow just as well for not much outlay,

Rancher Community Regular

Rancher

Posted
Posted

Both of them line up perfectly, The only thing that needs to be changed on the 26 head, is the headstuds. The 26 ones are too long. A 26 head would be the better option in my opinion. about the same to flow and stuff on the 25 head would cover the cost of a 26 head.

As someone said before in this post, The 25 heads valve springs are soft and will valve float at higher RPM. I think Ive read before somewhere if your leaving it NA, leave the standard RB30 ones in there. better compression. Dont quote me. Read the RB30DET thread.

Cubes Grand Master

Cubes

Posted
Posted

The stock r32 n/a springs only have issues with over ~17psi boost. No boost and they are fine.

RB30 N/A pistons achieve an 8.2-8.3:1 comp ratio, so too low for N/A application.

Sort out the deck height and I believe rb25 pistons achieve 10-10.5:1 which is closer to what you want for N/A.

BADR33 Collaborator

BADR33

Posted
Posted

rb30 block, 25det head and 25de pistons = 10.43:1 compression.. well thats what the engine dude told me when he built mine.. you can get up to 12:1 if you deck the block .75mm to make up for the pistons sitting 1mm lower in the block then rb30e pistons.

all though i dont know aussie prices here is a gestimate from what iv seen on your forums.. i would go with the rb26 head if your going to go the full hog.. cus if you spend $800 on a head, $800 on ITB, $300 for an adaptor plate thats basicly the cost of a rb26 head and it wont flow quite as nice.

if i decide to build a new engine i will be going with a rb26 head just for the ease of everything.. although VVT is quite nice.

put a nice lightweight flywheel on there. a good clutch and youll have a very exciting car.. even with a stock weight fly its very revvy. ill try get some vids when i do the 1/8th mile drags in 2weeks.

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