help with rb25 head modification

[dnb]

hello all. i am building a 25/30vvt. itis a largish set upwith gt3540 forgies and scat rods. now i am looking to rev this thing to around 8500 at the track(strip) and i wish to build the head to suit these revs.i was originally looking seriously at tomei poncams as they seem a very good camshaft.

my question is are these the best cams for my application? should i look at the procams?also what springs should i use as i am a bit worried about the stock ones at high rpm.another thing, will the hydraulic lifters survive at these revs or should i go solids?

any help would be much appreciated guys

[Gilly]

I take it you mean RB30 with 25vvt head. If so and you realy want to rev it to 8500 then you will need heavier springs and some big cams. Ime not sure how long the standard lifters will last but tomei suggest that over 8.5mm lift should have solid conversion. tomei's procams have the higher profile cams,lifters and springs to convert to solid however the springs and lifters alone will be more than$1200 but then they also need longer valves to be fitted which would cost another $1000 plus fitting. another thing is the procams have a smaller base diameter so the head does not have to be machined for the higher lift. If you use GTR poncams then you will loose your vvt.

All this said it would be easier and cheaper to either buy a GTR head or keep your cams under 8.5mm lift, keep your hyd lifters and buy heavier springs.

You should be able to get 350+rwkw with no more than 7500rpm on a RB30DET.

[Cubes]

You will also need forged rods and an aftermarket crank cradle.

You will make 700hp with 7000rpm on board. No need to rev to 8500rpm..

Rev's are not everything.

350rwkw is done easily with an Rb30DET while still having good response.

Just make sure you get rods done.

To build an engine to handle 350rwkw expect to spend a smidge over $8000.

That includes rods, pistons, aftermarket cams, purchasing of the head, rebuilding the head and mild porting/polishing of the head.

Its not cheap, and thats getting the build done at a good price as well.

So.. Expect up to $10,000.

BUT.. If you still want to rev the nackers out of it I'm unsure how much an aftermarket crank cradle is worth.

[dnb]

thankyou for your imput. looks like i will just get the springs and run poncams

[Gilly]

Some other brands do make higher lift than Tomei for GTST Might be worth looking at.

[dnb]

such as?

[Trust33]

No matter what cam you go that is larger than the poncams the need for a stronger valve train will still be there.But the larger you do go the more compressed air you can pack into the cylender and he more you will be able to exhaust from the motor.

For the first time today i got down to reading the last 10 pages or so of the rb30/25 conversion conversation and i must say that it is an interesting read.And -joel- you have done a great job there .

What issues with alignment of the motor have you encounted.Eg..Mounting it back into the stock location.And was the stock tailshaft still able to be used?

I read that you said the sump just clears the sway bar.

[dnb]

dude did you mean to post this in the rb30 thread?

[Cubes]

I had the motor dropped by around 12mm.

It sits perfect.. Doesn't hit the bonnet with the stock plenum.

Its the stock plenum that causes the problem. With a GTR head or GTR style plenum you don't need to lower the engine.

Everything else can be used.. Its as simple as drop the engine slightly and everything will still bolt up fine.

The RB30 guide will have a big going over in a few weeks (after exams).

I've got lots of pics and if every one posts their findings it will help the guide out as the guide is really just what every one has posted and what i've came across during my rb30 install.

The conversion is definately worth it though.

Pop it in to any gear out of a corner and it just hauls the cars arse out of it.

Taking off in second gear is easier than taking off in first in a rb20t.

[Gilly]

such as?

HKS8.8.apexi 8.9

[Trust33]

dude did you mean to post this in the rb30 thread?

Why does it look like it should b there

[Trust33]

I had the motor dropped by around 12mm.  

 

It sits perfect.. Doesn't hit the bonnet with the stock plenum.

 

Its the stock plenum that causes the problem. With a GTR head or GTR style plenum you don't need to lower the engine.

 

Everything else can be used.. Its as simple as drop the engine slightly and everything will still bolt up fine.

 

The RB30 guide will have a big going over in a few weeks (after exams).

I've got lots of pics and if every one posts their findings it will help the guide out as the guide is really just what every one has posted and what i've came across during my rb30 install.

 

The conversion is definately worth it though.

 

Pop it in to any gear out of a corner and it just hauls the cars arse out of it.

 

Taking off in second gear is easier than taking off in first in a rb20t.

arr and thats where you ran into the tailshaft not getting an optimum enuff angle.Eg..uni's may be under some stress etc..

[dnb]

Why does it look like it should b there

yes it does

[Cubes]

arr and thats where you ran into the tailshaft not getting an optimum enuff angle.Eg..uni's may be under some stress etc..

It was a concern so I took measurements of the before and after. I worked out the angle. Its literally nothing. Believe it or not from factory they also have a slight angle. Its not 100% perfect.

I did space down the gearbox by around 5mm as did I also space down the center bearing by 5mm which brought it all inline.

Even without the spacing down you can't see an angle.

[Trust33]

It was a concern so I took measurements of the before and after. I worked out the angle. Its literally nothing. Believe it or not from factory they also have a slight angle. Its not 100% perfect.

 

I did space down the gearbox by around 5mm as did I also space down the center bearing by 5mm which brought it all inline.

 

Even without the spacing down you can't see an angle.

There is somthing in me that wants to go through with this conversion when my engine lets go.But then theres somthing saying that i should just leave it and go a forged rods and piston kit complete with gaskets and lighten and balance the stock crank with a ported and polished head and match ported manifolds etc....The engine will be strong enuff for a kick ass turbo to pump up to and over 300rwkw and an 11 second street car is a fast car indeed.

[KamikazeR33]

i have a tomei poncam 256 deg 9mm lift for nvcs and a hks 264 deg 9mm lift ex cam going into my 25/30 conversion

[Cubes]

I started off with an RB20DET.

The reason I went the 3ltr is I like displacement. Always have.

One day I'll have my V8 twin turbo.

If the RB25DET has enough torque down low to drive around and keep you happy with a turbo that starts pulling from ~4000rpm then by all means stick with the rb25. Less hassles and less problems when and if you get defected.

But.. Chances are.. One drive of an RB30DET and you will be wanting to build one.

I've owned a few cars all that have been modified by cams and fueling. Apart from the VL 3ltr NA.

In order.. How much torque off the line and how they drove.

1. RB30DET (is far the most torquey and responsive motor)

2. 250 Cross Flow in a TE Cortina that had a mild cam holley 4speed etc.

3. VS 5ltr 5speed exhaust, cam ecu. & VL NA 3ltr 5speed exhaust.

To be honest the VS and the NA 3ltr VL was very close on par with acceleration through first by simply popping out the clutch.

The 5ltr was a slug I thought.. Under 3500rpm there was stuff all.

Up until now the 250Xflow was the most fun to drive at traffic lights.

Now its the RB30DET.

My little old cortina used to go pretty damn hard.

It used to be quicker than the new EFI V8 VN's lol that were the shit around that time and also a mates 318 Valiant, 307 Broughm, 308 4 Door HQ 4speed, 13B NA Series 3 RX7.

It used to kick some mighty arse back in its day.

Then there was my mates mild TC 250 Pre Crossflow that had a 2v head, holley and cam. That thing used to pull away from mine easily.

The 2v head on the 250 was an awesome motor for its time.