Rb20/30 Build

[DRIFTER]

doesn't need to rev, just want instant response. i'm looking foward to finding out how it goes, because it seems like a very rare conversion.

[Cubes]

If you have really thought about this conversion then you would not be here persisting.

The head has to be dissasembled, water galley weld and redrill, possibly machine the combustion chamber due to the 2ltrs smaller piston (78mm vs 85), crack test, machined flat, then you start to look at a head rebuild + maybe a little bit of port work. All of which is expensive to and and will see damn close to 2k.

You will break even if not be slightly infront dropping an rb25 head on it, you will have far better performance, spread of power and reliability.

Give the Rb25 head a freshen up and you will break even.

Edited November 5, 2005 by Cubes

[DRIFTER]

the head work won't cost me anything, but if anyone knows where i can get an r32 rb25de head cheap let me know.

[Cubes]

Consider:

RB30ET - 7.8:1 comp running 6-7psi on ULP 91 made 150fwkw.

RB20DET - 8.5:1 comp running 9psi on 100RON made 160fwkw.

That indicates the RB30 SOHC head flows marginally better than the rb20det twin cam head. The RB20det needs more boost, and higher octane fuel. I also believe the rb20det runs a bigger exhaust from factory.

Boost is the restriction placed upon airflow. i.e the head.

Ignore rpm as power is rpm * torque / 5252

Edited November 5, 2005 by Cubes

[DRIFTER]

there are lots of things that could explain those differences, you can't say that it is dirrectly related to head flow.

[R31Nismoid]

one that isn't just a theory but has some experience to back it up, has anyone actually done it and can tell me how it went?

Mate, sometimes theory is better than practice.

Im not stupid, not are a lot of others who have also posted in this thread (and past threads of this nature)

its very basic and easily attainable knowledge that swapping an RB30et head with an RB20DET head poses no performance gain in any stakes.

If you want to "drift" get a decent suspension setup and diff combo first

[R31Nismoid]

there are lots of things that could explain those differences, you can't say that it is dirrectly related to head flow.

if thats how you wanna be, go ahead.

Do your conversion and then after you have done it post up about how much better its supposed to be.

Dont forget your going to need more than your beliefs to counter common and logical sense

[sproosy]

Nismoid you have oficially pwned DRIFTER!

Im still saving my pennys for the RB25/30 conversion - it was all looking good until i forgot insurance was due!

[N I B]

Anyone looked at foolboost records and seen that the fastest RB30 VLs are still using the RB30ET head? I have seen some great stuff done lately with these heads so dont write them of as crap.

[Cubes]

Which is exactly my point.

If I were to choose between the RB20DET head on a 3ltr bottom end or the SOHC head on the 3ltr bottom end I would most definitely go the SOHC head, the money I save doing so I can spend on a mild cam for it.

[Trust33]

well someone tell the man he is crazy (ive done it and it seems he doesnt listen to me)

the RB20 head does not flow enough to cater for the RB30 bottom end.

If it did... eveyone would be using them as they are far cheaper than a 33 one (which has i think 30% more flow stock)

RB20/RB30 heads are almost the same in terms of flow.

Cheaper to drop an RB30ET in there than waste money, time and effort putting an RB20 head on it for absolutely no performance gain

<{POST_SNAPBACK}>

No shizz.It has allways been my knowledge,from here,that the rb20 head will outflow the stock item of a rb30 even if it has stage 1 cams.

[DRIFTER]

so do you guys agree on anything? apart from me being an idiot.

[Cubes]

lol...

[faster than you]

your all idiots, no offence, but the rb20 made more power on the same boost as the rb30 while being a litre smaller because of its more efficent head design and more flow. now if you increase the capacity of the rb20 it will create more exhaust pressure earlier and intern spool up the turbo earlier and make as much power (if not more) lower in the rev range, perfect for drifting. for outright power i would use the 26 head.

[Cubes]

lmao.

RB30ET 150fwkw on 91RON, No IC, 6-7psi + crap exhaust.

RB20DET 160fwkw on 100RON, IC, 9psi + an ok exhaust considering its stock.

How does that qualify the rb20det making power easier thanthe rb30et?

VL's make awesome power with very little mods.

A friend of mine has one that was purchased completely stock bar a 2.5" exhaust.

He fitted up an AVO fmic and dialed in 14psi, by peak power it made 187rwkw and boost had tailed off to 11psi. So thats 187rwkw using 11psi.. Pretty damn good.

R33 RB25DET's running 11psi, pfc, exhaust, and fmic's were making slightly more power being ~190rwkw.

Check out the SAU dyno day thread.

So you 'drifters' never see rev's past 5000rpm???

Thats what it will be like with an rb20det head, hell with the rb25 head it appears unles syou start doing some serious mods your not going to see peak power made and held decently after 5800rpm.

Edited November 7, 2005 by Cubes

[DRIFTER]

the latest hpi magazine has an rb24 on the dyno and it makes the same power as the standard motor only 800rpm earlier, with less boost and didn't sign off any earlier. food for thought.

[R31Nismoid]

im chuckling too... *turns it off*

your all idiots, no offence, but the rb20 made more power on the same boost as the rb30 while being a litre smaller because of its more efficent head design and more flow. now if you increase the capacity of the rb20 it will create more exhaust pressure earlier and intern spool up the turbo earlier and make as much power (if not more) lower in the rev range, perfect for drifting.

I'll treat this as a serious post... for the time being.

Ok. its been put out many times RB30et/RB20 heads flow around the same.

Dont forget that you are dealing with 2 motors 1000cc in capacity (give or take) from each other.

You will rev the RB30 less (as it just wont rev like a 20) and it will be flowing the same amount.

EG. In the below example im using random numbers just to explain, could be more or less, but it wont matter

Say RB30 will flow "X" @ 5500rpm

The RB20 will also flow "X", but @ 7500rpm

Tell me how putting a 20 head on a 30 block is then going to give an advantage when they are almost identical in flow

Remember his initial point... it was for more response. You wont see that for the cost.

If he was trying to make more power that way, you wont see that either for the cost.

If you want response, raise compression a little bit, or use a smaller turbo.

the latest hpi magazine has an rb24 on the dyno and it makes the same power as the standard motor only 800rpm earlier, with less boost and didn't sign off any earlier. food for thought.

... were they absolutely no other mods to the car? Thats not surprising though with a increase like that. Anyway....

You cant compare. Its not the same.

If (hypothetically) made your RB30... and RB34, you've get the exact same thing now havent you <_<

[DRIFTER]

so if you increase your capacity a little bit you get more response and power, but if you increase it anymore you loose power. please explain?

[Cubes]

Increasing engine size doesn't make more power, UNLESS the old motor was a little tired. Increasing engine size under the same head will simply scrunch up the power band (make it shorter) and shift it to a lower rpm.

The only time it will make more power is if you help it breath easier.

A good example of this is my rb20 -> rb30 experience.

The stock turbo on my RB20DET made 164rwkw with 12:1 afr's and 15psi.

The stock turbo on my RB30DET with the better flowing rb25 head made 176rwkw with 12:1 afr's and 9psi.

The RB20DET got up and started pulling hard at ~3500rpm all the way to 7000rpm, I would slightly over rev it to around 7200rpm as it felt and timed quicker doing so.

The RB30DET with the same turbo got up and went hard from idle but was wanting you to change gears as 4000rpm approached, reving it to 5000rpm made it feel as if you were screaming it.

The bulk of the torque was up to around 3500rpm, after that you could really feel it fade off.

At the moment it is very badly suited to drift, the power band is too short and it won't hold a slide over reving, power drops off to quickly causing wheel spin to simply fade off. There's no throttle control holding the car sideways as the road speed too high for the gearing that requires you to select the next gear.

Hope that makes sense... Its very much like driving a turbo diesel. Turbo diesels are not good for drifting.

Edited November 7, 2005 by Cubes

[natho]

im pretty sure you wont get an rb20 head on an rb30 block without welding all the water/oil gallerys up and drilling new ones, so unless you're really keen scrap that idea and get a rb25 head!!

yes my vl rb30et made 187rwkw with very little mods, it is a relatively healthy motor though (considering its never been rebuilt).

cubes i believe the factory power figure was on 95RON? however i do know a friend managed 140rwkw from an auto VLT on 91ron before it pinged!