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rb26det vs rb26det

Guest skwertle

By Guest skwertle,
in Engines & Forced Induction

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Warpspeed Experienced

Warpspeed

Posted
Posted

Well thats not quite true. If you take just the short block, and replace the crank, rods, and pistons, you would still need to fit the GTR oil pump and water pump which are both different to the RB25 parts.

Up top, although the combustion chambers, ports, and valve sizes are the same, and the GTR head has no power advantage. But everything is totally different except maybe the cam drive sprocket on the exhaust cam, and the timing belt and idlers.

The RB26 has heavy duty parts throughout, and although a lot of things look the same, and fit, they are actually quite different.

RIPS Contributor

RIPS

Posted
Posted

DJ-L3ThAL, I don't quite know what your getting at??? (according to my thread name)???????

There is almost NOTHING even close to being the same between a R33 RB25det engine and a R32/33 RB26dett.

The blocks are different, The oil pumps are different, the heads are totally different, different port shape, different bolt pattern for inlet and exhaust manifolds, one has VCT the other does not, so I can't see why, being "my thread name" I should lie to skwertle and tell him there's NO difference????????

If he's talking about just a short block then he's going to need to get a block from a 4wd stagia, oil pump from a RB26dett etc etc.

Then, I think the head bolts are a different size so the block would still be different....Rob

Warpspeed Experienced

Warpspeed

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I think the point here is that the two engines ARE totally different, but all the differences have to do with long term durability under extreme operating (endurance racing) conditions rather than actual power potential.

Yes the blocks are different. The difference is the GTR block has different oil pan rails for the 4WD sump, and an additional oil drain hole for the second turbo. There is no reason why an RB25 block would not be just as good, unless you wanted to run 4WD, then you might have a bit of a problem. All the moving parts interchange perfectly, and there is no strength difference.

The oil pump has a slightly larger displacement and runs dual springs in the pressure relief valve on the GTR. The only advantage of the larger pump is at idle, when you have a second turbo. A GTR road car may spend a considerable time idling, and the lower oil pressure might cause the oil light to come on if a smaller pump was fitted. At anything above idle, the relief valve will be open, and there will be full oil pressure. I am not sure why the GTR has dual springs in the pressure relief valve, but the only reason I can think of is reliability. The cost of the extra spring is SFA, so if there was a technical reason why it was better, all Skyline engines would probably have dual concentric springs fitted.

For flat out racing, a smaller displacement oil pump would work fine. It is only the road cars that really need the big pump !

The GTR water pump has a different impeller, but is otherwise identical. This is to allow higher sustained engine speeds without cavitating the pump. For anything but sustained racing conditions the RB25 pump will work fine, including drag racing. But if you are planning to hold full throttle for over a minute at 9,000RPM plus, the GTR pump is definitely the one to have.

I could go on about larger head bolts (10mm/12mm), sodium cooled exhaust valves, and solid tappet camshafts, but you get the general idea.

The manifold bolt patterns are very slightly different, but only so you can get a spanner onto the nuts with the two different manifold shapes. The port shapes sizes and locations are identical.

The power potential of the RB25 with identical external bolt ons (manifolds + turbos) would be the same. But for long distance endurance racing the RB26 would be going long after the RB25 died.

There is no doubt that he RB26 is a far better engine, but if you actually need all that stuff to drive around at less than 100Kmh is doubtful.

RIPS Contributor

RIPS

Posted
Posted

Have a look at the RB26dett head on the left and then have a look at the RB25det head on the right, DON'T LOOK THE SAME TO ME????????? Ports are totally different, manifold bolt pattern is totally different etc etc. But maybe I'm wrong I've only got about 20 heads here to compare IN THE FLESH, Check your heads and take a Photo and let me have a look.......Rob

RIPS Contributor

RIPS

Posted
Posted

SUMO look at the first post mate, 2.6 is the capacity of the engine, and I think he was refering to making a RB25det into a 2.6 liter by using a RB26 crank pistons and rods and he wanted to know if there was any other differences, and there sure are!!

You could make a RB26det with a RB25det block with RB26 crank,rods and pistons and use a RB25det top end and it would be a RB26. Just not a real RB26dett.............Thats what he was getting at.

Warpspeed Experienced

Warpspeed

Posted
Posted

Those ports look the same to me, allowing for the fact that the GTR head has had the valves removed which effects the lighting conditions.

Also the viewing angle is different. There is a difference around where the injector sprays, but the actual port and valve sizes are identical.

Its an interesting picture to be sure. I have an RB25 head and an RB26 inlet manifold here, and when I find time, intend to make up an adapter plate. Some of the studs line up, and so do the ports, but an adapter plate is still quite a bit of work. This has been done many times before by others and is well worth the trouble.

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