Which head to use on RB30DET?

[600hp]

Hi guys my mate just bought an R34 non turbo with the idea of putting a big combo into it and making big power.(up to 450wrkw).

I suggested useing the RB 30 bottom end and using the GTR head.he has heard of putting the neo head on!

as for turbo/s (he wants an external wastegate).I would use a set of 2835's as he wants to use the car for circut work as well.i would think that with the 3L and the work done to the engine it should come onto boost around 4500 i would think mayby sooner.

any ideas with turbo combos and engine set up would be great.

Cheers BEN

[25t_sedan]

Hi guys my mate just bought an R34 non turbo with the idea of putting a big combo into it and making big power.(up to 450wrkw).

I suggested useing the RB 30 bottom end and using the GTR head.he has heard of putting the neo head on!

as for turbo/s (he wants an external wastegate).I would use a set of 2835's as he wants to use the car for circut work as well.i would think that with the 3L and the work done to the engine it should come onto boost around 4500 i would think mayby sooner.

any ideas with turbo combos and engine set up would be great.

Cheers BEN

He's obviously not worried about $ so the GTR head would be the best way to go but there are some slight modifications that need to be done when mating the GTR head with the 3L block. If your going to go aftermarket turbos then why not just go for one large highmount one? Its much easier to set up and is probably cheaper too. But when looking for 450rwkws hes going to have to look into some body strengthening too as producing 450rwks and being able to use 450rwks is 2 completely different things especially in a RWD.

Just some things to think about sorry i couldnt help with the specific details you are after

[whistla]

Why not just go the single cam head?

No matching required

No fuss

One cam

Proven application

*shrugs*

[Cubes]

GTR Head.

[DoughBoy]

RB20 SOHC head, it's very very rare, so it must be good.

[600hp]

When i said 2835's i meant in hight mount configuration.

Also i spoke to CRD and they said that the torque you gain down low is not worth the revs you loose up top.

any coments.

[R33S2]

GTR head will flow much betterer than standard 3ltr

[R33S2]

An exworkmate of mine Nick built a 3ltr with 25 head it cost him 5000 with forged pistons blue balance to run on no2 in VN for burnout comp works well havent seen him since I left.

[Cubes]

When i said 2835's i meant in hight mount configuration.

Also i spoke to CRD and they said that the torque you gain down low is not worth the revs you loose up top.

any coments.

Its got everything to do with airflow. The extra torque at low rpms is nice.

That depends on where you plan the rev the rb25 or rb26.

An RB30 making power to 7500rpm may push say 52.8 lb/s of air.

To match that same 52.8 lb/s of air the 2.5ltr would have to rev to 8650rpm.

How many RB's do you see making their peak power at 8650rpm. Not many.

The higher you rev a motor the higher the power loss is through friction.

Obviously the lower reving motor is more efficient at making its power.

Besides the point, a set of cams to rev the 2.5ltr and make its peak airflow (power) figure at 8650rpm would have to be pretty wild and unstreetable.

[Cubes]

modr33s2,

5k is around the mark with a set of forgy's.

Thats not touching the head, no port work etc. Just bolting it on.

Its also obviously not including labour to drop the motor in.

[600hp]

Cheers fellas, i thinkthe idea of the 3L would be good as i don't see the engine reving much more than 8500rpm.

with the 2835's i think the car should have enough power for a good track car.

[Cubes]

Be sure to stiffen up the bottom end (crank girdle) if you are going to be reving the 3ltr to 8500rpm. Thats fairly insane RPM.

Not even the Gibson Motorsport GTR rev'd its RB26 that hard.

They found the rebuild frequency was very high over 7000-7500rpm.

You are probably better off running more boost and keeping the rpm lower.

If you run out of effiency running the higher boost step the turbo's up a size.

Depends how often you like the rebuild motors.

The Benifit of the 3ltr is for any given RPM its always going to be pushing more air. Take this in to consideration when selecting the turbine a/r.

With the right cams and turbo specs its always going to be making more power.

[race_snooze]

I have heard that the rb25 head is easier to fit on a rb30 bottom end than the rb26 head is due to the water jackets or something like that. My 2 cents

[600hp]

I don't know that much about about the 3L RB26 combo so if all i can rev it to is 7500 so be it.just run some more boost.

cheers

[Cubes]

600hp,

What were you planning on reving the rb25 or 26 to????

3ltr to 8500rpm is like reving the rb25 or 26 to 10,200rpm.

3ltr to 7500rpm = rb25 or 26 to 9000rpm.

Race_Snooze,

The RB26DETT head and R32 RB25DE N/A head are the easiest to fit.

The R32 RB25 head simply bolts up.

The RB26DETT head needs to have the block headbolt holes enlarged and retapped.

The R33 RB25 head needs to have the vct's oil galley in the head welded up, then an oil feed from the oil pressure sender to the vct supplied.

Bit of a pain in the arse but the slightly extra mid range is worth while if you are sticking with relatively stock cams (up to 260duration).

[nedb]

Edit: I guess thes got answered - How hard is to mate the GTR head to the RB30 block?

Also, what compression would you get with the RB26 head and RB30 block combo?

[Sydneykid]

Edit: I guess thes got answered -  

1. How hard is to mate the GTR head to the RB30 block?  

2. Also, what compression would you get with the RB26 head and RB30 block combo?

1. Easy, no mods required, other than drill and tap the block for the 12 mm RB26 head bolts, RB20/25/30 are 11 mm. We use 12.5 mm ARP head studs for their higher clamping pressure.

2. Depends on what pistons you use, what head gasket and how much you polish the combustion chambers. I have seen compression ratios from 7.5 to 1 to 13.5 to 1.

If he is REALLY going to use it for circuit work, then ~ 650 bhp would be my target. We have found it very difficult to get more than that to the ground in a 2wd application. And we have very sophisticated shock absorbers, adjustable anti roll, anti dive, anti squat, caster camber and toe and a larger selection of spring rates.

The main problem however, is response. Over 650 bhp even in a 3.1 litre, gets very difficult to tune for the rapid throttle response necessary for running decent and consistent lap times. Even at that power level, driving it fast requires considerable skill and experience.

[race_snooze]

600hp,

What were you planning on reving the rb25 or 26 to????

3ltr to 8500rpm is like reving the rb25 or 26 to 10,200rpm.

3ltr to 7500rpm = rb25 or 26 to 9000rpm.

 

Race_Snooze,

The RB26DETT head and R32 RB25DE N/A head are the easiest to fit.

The R32 RB25 head simply bolts up.

The RB26DETT head needs to have the block headbolt holes enlarged and retapped.

 

The R33 RB25 head needs to have the vct's oil galley in the head welded up, then an oil feed from the oil pressure sender to the vct supplied.

Bit of a pain in the arse but the slightly extra mid range is worth while if you are sticking with relatively stock cams (up to 260duration).

Cheers.

[nedb]

1. Easy, no mods required, other than drill and tap the block for the 12 mm RB26 head bolts, RB20/25/30 are 11 mm.  We use 12.5 mm ARP head studs for their higher clamping pressure.

2. Depends on what pistons you use, what head gasket and how much you polish the combustion chambers.  I have seen compression ratios from 7.5 to 1 to 13.5 to 1.

If he is REALLY going to use it for circuit work, then ~ 650 bhp would be my target.  We have found it very difficult to get more than that to the ground in a 2wd application.  And we have very sophisticated shock absorbers, adjustable anti roll, anti dive, anti squat, caster camber and toe and a larger selection of spring rates.  

The main problem however, is response.  Over 650 bhp even in a 3.1 litre, gets very difficult to tune for the rapid throttle response necessary for running decent and consistent lap times.  Even at that power level, driving it fast requires considerable skill and experience.

For a reliable street setup:

For the argument sake, if you could get a RB26 head at the same price as the R32 RB25de head which one would you use and why?

What compression ratio would you aim for and (if not stock) what pistons and head gasket would you use to achive that?

What would be a reasonable power target?

[Alf]

2. Depends on what pistons you use, what head gasket and how much you polish the combustion chambers.  I have seen compression ratios from 7.5 to 1 to 13.5 to 1.

If the bowls of the head are polished to a mirror finish, would this benefit a compression of approx 8.8:1?

The pistons are ARIAS rb30 forgies to suit the twin cam head (25 VVT). The pistons and valves have been ceramic coated.

The bowls in the head had some "pitting" around all of the inlet valve areas of the bowls, I assume this was from detonation (head came of a worn bottom end). These "pits" were smoothed out and polished to a mirror finish, the bowls are yet to be cc'd.

Doing this to the bowls would lower the comp slightly? (head gasket hasnt been chosen yet).