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R33 Rb30 Conversion

JNR24

By JNR24,
in Engines & Forced Induction

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The Ant Contributor

The Ant

Posted
Posted (edited)
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 by The Ant
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Duncan
Duncan

Just thought I would bump this 20 year old thread because the Skid Factory have just posted up a video summarising a lot of the content, format might be more familiar for newer members

JNR24
JNR24

fyi guys, Well yesturday i picked up a RB30 for my conversion into my R33. I will be using my RB25DET head on the RB30 block. So i started stripping the motor down, pulled the crank, pistons, girdle

Cubes
Cubes

Here is all I have at the moment: http://www.geocities.com/r32_jjc/ Unless you are on broad band make sure you right click then save as. The file is around 120kb. If there is anything I have got w

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GTRgeoff Grand Master

GTRgeoff

Posted
Posted

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.

dano4127 Veteran

dano4127

Posted
Posted

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 Grand Master

Cubes

Posted
Posted

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 Grand Master

Sydneykid

Posted
Posted
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 Grand Master

Adriano

Posted
Posted
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 :P

dano4127 Veteran

dano4127

Posted
Posted
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 Mentor

Spoolup

Posted
Posted (edited)

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 by Spoolup

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