R33 Rb30 Conversion

[The Ant]

The idea of the 3ltr is it spools a larger turbo quicker and makes more power 'under' the 300rwkw curve.

An rb20det can make 300rwkw but it will be as laggy as hell and have bugger all mid range.

The rods fit but the pistons will NOT unless you also run with the rb26dett crank.

The rb26 gains its additional 100cc by using a slightly longer stroke and pistons with a reduced pin height. Drop 'just' the rb26 rods and rb26 pistons in to an rb25det and the comp ratio will suck not to mention the piston sitting down the bore. So definitely not a wise move.

No the rb30 has a longer stroke and rod length. So no.

You can but the rb30/25 will ALWAYS make the power easier and be much more fuel effient and friendly to drive.

Start working the sohc head with big cams to get near the stock flow level of the rb25det and fuel economy/driveability suffers.

Thanks, now I'm getting to the nitty gritty of it. If I did go rb30 top and bottom, I'm looking at maybe porting the rb30 head (may include bigger valves) and regrinding the cam specifically the exhaust lobe to make it open longer and/or higher to help get rid of the exhaust to assist the turbo spool. Shouldn't this now be in par performance wise with fitting a rb25det vvt head? Yes?

I know If I did the same mods to the rb25 det head it would probably go a bit better than the rb30 head but it would also cost me the use of the head (which I may sell the rb25 motor) and supplying an extra cam which would be more expensive than modifying the rb30 head to the level I explained above.

How much maximum power can I expect with the rb30 head mod I plan above and how much could I expect if I went 30/25det with vvt keeping them both bottom ends standard crank fitted with forged H beam rods and forged pistons? How much difference are we talking about here? Is it marginal or is it like 40% or more in power difference between the 2?

Can I use my rb26 pistons in the rb30 bottom end with standard crank and if so what compression ration would I get with either rb30 head or rb25det head fitted?

.

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Edited May 11, 2008 by The Ant

[Dahtone Racing]

Straight fit or did you use some aftermarket/GTR items to fit?

straight fit

brand new nissan RB26 valve springs in R32 RB25 head

[dano4127]

super noob questions but to fit springs is it head off?

[GTRgeoff]

Not necessarily, you can use compressed air inside the cylinder to hold the valve up while you replace the springs, but I'm not sure who does it and drop one valve and it can be head off....

It would take a very specialised toll to compress the springs to remove the retainer collets.

[mr_rbman]

i fitted springs with my dad with the head on but if you have a choice definitely fit them with head off.

I used a tool like geoff has described, its a very fiddly job but only took about half a day!

[dano4127]

dammit sounds like too much paperwork how far do ya reckon the stock ones are gonna take me?

I was gonna DIY RB26 standard cams install, just dont think I could attack the springs too that would be a workshop job and $$$ I dont have at the moment

[Cubes]

If you pull the head off and have a workshop fit them definitely spend the extra and have a set of decent springs fitted.

Get the seat pressure up to 70lbs so you don't have to worry about float and a flat top end due to high boost and 7000rpm.

[Sydneykid]

Not necessarily, you can use compressed air inside the cylinder to hold the valve up while you replace the springs, but I'm not sure who does it and drop one valve and it can be head off....

It would take a very specialised toll to compress the springs to remove the retainer collets.

I have found that if I put that cylinder at TDC, the valve (exhaust or inlet) doesn't drop far enough so that you can't retrieve it. A bent screwdriver blade does an OK job of compressing standard valve springs. Especailly when they most commonly have only 40 lbs on the seat.

Cheers

Gary

[Adriano]

dammit sounds like too much paperwork how far do ya reckon the stock ones are gonna take me?

I was gonna DIY RB26 standard cams install, just dont think I could attack the springs too that would be a workshop job and $$$ I dont have at the moment

Hope you arent planning on fitting rb26 cams to a 25 head

[dano4127]

Hope you arent planning on fitting rb26 cams to a 25 head

Thats exactly what im doing...

[Adriano]

Solid lifter conversion?

[dano4127]

nup just slotting them in possibly with springs, why do you hope im not doing it?

Edited May 13, 2008 by dano4127

[Spoolup]

Because it isnt a successful transplant. RB26 cams are designed for solid lifters and RB25 heads have hydraulic lifters.

[dano4127]

Some explanation required............

RB25's have VVT and RB26's don't.

But RB20's don't have VVT, so you CAN use RB26 cams in an RB20.

Hope that clarifies:cheers:

I have an R32 RB25DE Head which is basically an RB20 hardware wise

Before we start, I need to clarify a couple of things. I have NEVER tried RB26 cams in an RB25. However I have used RB26 cams in 3 X RB20's. One was at high k's (170,000) and had slow to pump up hydraulic followers. This one definitely received R32GTR standard camshafts, they came out a of Production Race car engine and the camshafts had been scrutineered a few times and were definitely STANDARD. That engine had stronger than standard valve spring seat pressure. The RB26 cams that went into the other 2 X RB20's were not as certain to be STANDARD.

[Spoolup]

They definitly fit - but my old RB25 engine ran like a bag of s--t with them installed. I could not get it to perfrom well with them.

Try it and see how it goes - you may have better luck, especially if you play with the cam timing on the dyno. Theres not alot of gain to be made with them anyway.

Edited May 14, 2008 by Spoolup

[Adriano]

I tried it with an rb20. Basically anything with hydraulics wont work, unless you get the cams reground to suit the different ramp angles that hydraulics require. I think cubes found someone who does it cheap.

[Spoolup]

Tighe cams do it

[WHITER33GTS-T]

I fired up my 25/30 last night. Cant wait till its run in and tuned

[mr_rbman]

Tighe cams do it

this is who did mine!

My car went from 228 rwkw's - 254 rwkw's with absolutely no changes but the cams!

[dano4127]

Tighe cams do it

And he seems to have dissapeared! do you have his contact details?