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Rb26 Internals In R32 Rb25de

B0oStEr

By B0oStEr,
in Engines & Forced Induction

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B0oStEr Mentor

B0oStEr

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Posted

I was going to replace my rb20det with an rb30/25det but now I'm considering using an rb26 crank, rods and pistons in the rb25de motor that I bought for the head.

My reasons for this are that I like a motor that will still rev and my hks gt2530 and the std diff ratio should still be suitable and it will still look stock under the bonnet.

I've got all the bits from my rb20 buildup

2530 turbo, 3" turbo back with split dump and metal cat, fmic, sf coils, ap eng. pfc, z32 afm, gtr injectors, 040 fuel pump

I know this turbo is limited to about 220rwkw or so but it should make this with less boost than the rb20

I expect this motor would make full boost 800-1000rpm before the rb20 although I expect boost will start to taper off earlier by a similar amount.

Just a few Qs

What compression ratio would this combo give?

Of the stock cams are the rb20det cams the best or should I use the rb25de inlet cam with an adjustable gear?

If I use an r32 rb26 crank will the rb20det oil pump be suitable?

If I use an r33 rb26 crank what oil pump would be best to use?

Should I fit the piston oil squirters?

Any comments on this combo welcome.

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Warpspeed Experienced

Warpspeed

Posted
Posted
I was going to replace my rb20det with an rb30/25det but now I'm considering using an rb26 crank, rods and pistons in the rb25de motor that I bought for the head.

My reasons for this are that I like a motor that will still rev and my hks gt2530 and the std diff ratio should still be suitable and it will still look stock under the bonnet.

I've got all the bits from my rb20 buildup

2530 turbo, 3" turbo back with split dump and metal cat, fmic, sf coils, ap eng. pfc, z32 afm, gtr injectors, 040 fuel pump

I know this turbo is limited to about 220rwkw or so but it should make this with less boost than the rb20

I expect this motor would make full boost 800-1000rpm before the rb20 although I expect boost will start to taper off earlier by a similar amount.

Just a few Qs

What compression ratio would this combo give?

Of the stock cams are the rb20det cams the best or should I use the rb25de inlet cam with an adjustable gear?

If I use an r32 rb26 crank will the rb20det oil pump be suitable?

If I use an r33 rb26 crank what oil pump would be best to use?

Should I fit the piston oil squirters?

Any comments on this combo welcome.

RB26 crank rods and pistons will drop straight into an RB25 block. Compression ratio will be 8.5:1, same as it would be in a GTR. The combustion chamber volumes are the same.

All the factory RB emissions cams have very similar timing (between 240 and 248 duration) with almost zero valve overlap. There is no real point messing around swapping factory cams around. Either leave the cams stock RB25DE, or get some proper aftermarket cams.

The HKS2530 will give a very strong mid range and be very responsive, especially with the diff you have, but the turbo is a bit small for flat out power. It will be very responsive and torquey driving around the suburbs, I think you will be quite pleased with the result.

Oil pumps vary in volume only because of the extra oil volume required for the turbos at idle. Even an RB25DE pump would work fine in a GTR at normal operating Rpm. But if the idle speed was set very low, the oil light may probably come on. At perhaps 2,000 Rpm or above ANY oil pump is going to give full rated pressure.

The RB25DE pump will probably work fine with one ball bearing turbo, but idle pressure may be very slightly less than it would be with an RB25DET pump, or an RB26DETT pump. The ball bearing turbos require less oil flow than the older sleeve bearing turbos. Try it with the original pump, or get an RB25DET pump, anything else is overkill.

Oil squirters are good, but fitting them to a block that did not already have them is going to be a very expensive bit of machining work. I would either try to find an RB25DET block or a GTR block that already has them fitted, it would probably be a lot cheaper. Or I would not bother with the oil squirters.

B0oStEr Mentor

B0oStEr

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My question about oil pumps was mainly to determine what pumps fit the r33gtr crank as they have a different drive collar for the pump gear.

Do I need an r33gtr oil pump or will an r33 rb25det one fit?

I intend to close off one of the oilfeeds to the head and open out the oil return galleries as suggested by SK and others but I need to find out more details about this mod.

It should lessen demand on the oil supply so pump volume is probably less of an issue.

With regards to the cams, being an r32 rb25 head the rb20det cams will fit but I read the rb25de inlet cam has longer duration but less lift (I think)

I think because they were designed for a turbo application the rb20det cams would be the safest bet but I'm wondering if the extra inlet duration could be beneficial if dialled in correctly.

Warpspeed Experienced

Warpspeed

Posted
Posted

Here is a list of all the various Nissan factory cams. The differences are only slight between all of them, they all have to pass strict emissions, hence there is not a lot that can be done by the factory.

http://www.tomei-p.co.jp/_2003web-catalogu...haft-specs.html

Replacing a cam with another that has only five degrees more duration and maybe an extra millimeter of lift will hardly make any noticeable difference.

Going from 240 to 262 degrees is the sort of worthwhile improvement you need.

Cannot answer for sure about the oil pump drive, but I believe after R32, the later ones are now all the same.

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