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Rb20 To 2.2 Or 2.4 Ltr.

grippy

By grippy,
in Engines & Forced Induction

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grippy Collaborator

grippy

Posted
Posted

I am rebuilding my RB20 with forged internals and the block needs to be bored. I have a RB25 crank and I'm hoping I can bolt this into the RB20 re-bored block?

Does anyone have any experience with building this type of engine combinations that can shed some light on the possibility of this working well or not?

Do you know what size re-bore I will need from stock to fit oversized forged pistons? I know 20thou is available.

Any idea what size the engine will end up being? Are stock RB25 rods up to the job?

$$$ are very tight but I will spend on the essentials. Looking at making up to 300kw when done.

Any help appreciated.

Rgds,

Grippy.

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grippy Collaborator

grippy

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I already have a crank and when I buy rods I will get RB25 ones as I believe the big ends are bigger on RB25.

82mm CP's pistons will be close enough to 2.2 ltr. I have spare RB20 heads so I will run one of these. I think for the money I will get a good performance 2.2 that can run 250kw all day and be wound up every now and again without an issue.

The block is ready to go off for crack testing and machining. I'll advise how the progress goes.

Thanks for info.

grippy Collaborator

grippy

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I will persevere with the RB20DET head as I have 3 of them and one is already ported. I would love to have a great combination of 20-25-26 and 30 parts to throw at this engine but the budget says no!

I am still looking at the option of possibly running the 4A-GZE 82mm forged pistons to save some $$ but not sure if the big ends will fit the RB25DET crank?

This will become more clear as the build progresses. I will drop the RB25 crank in before it goes away and see if there is any clearance issues with the block or girdle.

Grippy..

jdmser Enthusiast

jdmser

Posted
Posted (edited)

I'm in the middle of a RB24 build. I've found the RB26 crank with RB26 Eagle rods clears the block and girdle. It doesn't have a lot of clearance but, if the clearance goes away your motors already trashed away so who cares. After talking to my builder he would have rather seen me just put the crank in and keep it closer to stock bore than bore it to get the extra displacement. We ended up filling the block up to the welsh plugs to help strengthen the cylinder walls.

Edited by jdmser
grippy Collaborator

grippy

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Good to hear I'm not completely alone here. Unfortunately for me I only have one block to work with and it has light scoring on the #3 cylinder wall so a rebore is a must. I might as well take it out to 82mm and have a go at a RB22.

I will get some more input before I get the block done as $$ will be coming in slowly for this one.

Will you be o-ringing your block also?

I have been jumping back and forth on this subject for a while now and I still cannot make a decision.

I think I will have the block o-ringed as I want to pump at least 25psi through the new engine, but I have heard mixed reports on whether it is a good idea or a bad idea??

Rgds,

Grippy

jdmser Enthusiast

jdmser

Posted
Posted

I'll be running a 2mm thick Cometic mls head gasket until I have the combustion chambers reshaped. So, I can't o-ring or it's not going to seal. My builder runs 30+ on his motor without o-rings on a mls gasket and has no problems. As for the piston I think the 4agze piston are 81 or 81.5. The more meat you can leave in the bore the better.

mattR32gtst Explorer

mattR32gtst

Posted
Posted (edited)

After Reading alot of posts on this iv decided to do the 2.2 conversion I'm going to source rb25 crank with conrods iv read about using the 4agze pistons, however I have someone who has some 4age pistons for sale are they the same in size and strength and up to the job for this conversion ??

Also what headgasket can be used as it needs to cater for new piston width ??

Edited by mattR32gtst
STATUS Grand Master

STATUS

Posted
Posted (edited)
After Reading alot of posts on this iv decided to do the 2.2 conversion I'm going to source rb25 crank with conrods iv read about using the 4agze pistons, however I have someone who has some 4age pistons for sale are they the same in size and strength and up to the job for this conversion ??

Also what headgasket can be used as it needs to cater for new piston width ??

the gze pistons are forged, the ge are not.

TBO a rb25 complete engine is have the price (we see them weekly for 750-1k as long engines no access or turbo), easily available and far more reliable than a 2.4.

Edited by URAS
mattR32gtst Explorer

mattR32gtst

Posted
Posted
Have you thought about using a R32 RB25de? works out a lot cheaper than trying to put a bigger crank in a RB20

Will this mate upto the standard rb20det box though and will it bolt to the standard rb20det head i only say this as i have the chance of getting a 25de for cheapness ???

grippy Collaborator

grippy

Posted
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I agree that the RB25DET is a cheaper option as a direct replacement. My issue is that I have a R32 GTSt, and I wish to keep the RB20 block due to the fact that I wish to use new forged pistons and rods and I wish to keep the car as close to factory spec as I can. I don't have a ready ported RB25 head as I do a RB20, I don't have a RB25 gearbox, I don't have side feed injectors or a power FC to run it.

I already have two RB25 cranks and once the cost of machining is out of the way I will only need to pay for gaskets rods and pistons.

If I spend this money on RB25 complete engine I will not end up with a bulletproof 2.2 ltr that can be easily eprom tuned. I will have a brand new engine instead of a ready thrashed one also.

If I could get a forged and tuned RB25 for the same price I would go for it. But ECU is still a big cost on top.

Problem is that I have spent so much already on the RB20 and I'm happy with the way it goes on the track as there is only ever one or two cars that can keep up, so I really have no need for the RB25.

I also have Tomei pon cams for the RB20 wich cannot be used in the RB25. If engine upgrade does happen it would most likely be a RB30/25 build anyway.

Any other opinions on O-ringing your block??

I'm leaning towards not having it done!!

Grippy.

nismoman Community Regular

nismoman

Posted
Posted

Don't bother o-ringing the block. The thicker head gasket will lower your compression enough to handle the extra boost. Providing block and head are decked nice and flat, should be no problems.

I like your plan with the rebuild of the RB20 out to RB22, because you're making the best out of the parts you have available. The larger tomei pon cams will certainly help with getting the head to flow more air as well allowing you to push past 250rwk's, question is will your turbo go that far? If not at least you'll get good response from the set up with the cams and larger capacity out to 2.2ltrs. Forged internals will give you reliable performance. Low down torque is what's lacking the RB20 so it sounds like you are doing the right things to rectifying this.

After the rebuild, you might even be able to beat a couple of pesky S13's out on the race track!

mattR32gtst Explorer

mattR32gtst

Posted
Posted

Any more news on this iv got another rb20det got the crankshaft and rods from an rb25det now need the pistons struggling though ??

What else will i need sorry to take over thread just need some help :(

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