Rb20det And Rb25det

[Roy]

Intrestingly enough we measured those as well the engine machine shop came up with the deck heights being the same as I have an rb25 block as well he wanted to make sure but when I measured them here at home I came up with less than a mm differance though that was after machining had to run a bigger head gasket than I allowed for

So RB26 crank and rods with RB20 pistons will give a long stroke 78mm bore Rb20? I have a spare motor and want to play with building an engine. It may be funny to buy a unwanted R32 RB26 crank and some 2nd hand rods. Get some bearings and slap it all back together with a relieved block to clear the crank swing. Could be a budget banger...RB20 pistons seem pretty strong

[Cubes]

But if its making 300rwkws at 5,500rpm, when is it making 200rwkw. 4,000rpm? 3,000rpm?

Thats the problem. It leaves for a very narrow short peaky power band.

A gt35r for example.

They tend to make a shade over 200rwkw at 4000rpm and spool all in by ~3500rpm then fall over by 6000rpm.

The plenum really has made an unbelievable difference to the 'fun' factor of the car. As you know not being able to hold that gear out a bit longer isn't much fun when 'driving' the car.

[Cubes]

So RB26 crank and rods with RB20 pistons will give a long stroke 78mm bore Rb20? I have a spare motor and want to play with building an engine. It may be funny to buy a unwanted R32 RB26 crank and some 2nd hand rods. Get some bearings and slap it all back together with a relieved block to clear the crank swing. Could be a budget banger...RB20 pistons seem pretty strong

I'd have a guess that the rb20 piston runs a greater pin height to allow for the shorter stroke. (given the rods and deck height are identical in measurement between the rb25 and rb20)

So by simply dropping a longer stroke in to it will have the pistons poking out the top.

Legend.. 100% those rods haven't been mixed up? Sorry to question. lol

I may be wrong. :S

[simor32]

jeez u guys no ur stuff dnt ya

[Cubes]

I hope that avtar of yours isn't copyright Troy!! lol

[salad]

Nice one Cubes

And Roy, I realise that the RB20DET-R is the king of the RB20s, but still I dont like how Nissan gave the RB20s max power at pretty much the same RPM as the SR20.

Afterall, the SR20DET doesn't like to rev at all, and the RB20 loves it, but it doesn't seem to show when power is concerned.

Eh, it's just my thoughts, I like the RB20 and wish it was better...

Edited March 6, 2007 by salad

[Kozeyekan]

You want to know the strongest RB, well i say its the RB20. Hang with me for a second.

They only have 78mm bores so they have plenty of meat between the cylinders. So the block is very strong.

They also have a very short stroke meaning that for the same rpm they have lower piston speeds. The big end bearings are about the same for all RBs so you have a very similar surface area of bearing for lower loads meaning the bottom end wont be as stressed.

The smaller bore also means smaller and lighter pistons meaning that again the forces from rotational mass is reduced. The rods in the RB20 are very strong std. Throw in some aftermarket rods and it would be near impossible to damage them.

Now the problem with the RB20 is the same small bore means small combustion chamber which means smaller valves then the bigger RBs. But the difference may not be as much as ppl make out. Isolate one cylinder and look at the surface area of inlet and exhaust valve and compare it to the displacement of that cylinder. The ratio may not be as dramatic as ppl make out.

So you can only really go 1mm oversize in the valve department. And the other big problem is the small displacement Rb20 will have a hard time spooling up the turbo required to make 500hp. So the bigger RBs will make the power easier and sooner.

So whilst on paper the RB20 is probably not the motor to use for 500hp...it could very well be the strongest at 500hp.

But that doesnt really matter, because looking at it. 500hp is about 360kws. So in a GTSt thats about 310rwkws. An RB30 or RB26 would do that number in its sleep. Std RB30 bottom ends, and std RB26s will easily make that power with the right turbo.

But getting back to it, if you are building the strongest RB you can. Then i would say the strongest would be an Rb20 with RB26 crank. So the stroke and piston speeds would be no worse then an RB26. Only you would be running a smaller, lighter 80mm piston. The block would still have plenty of meat in it and handle huge cylinder pressures.

So you would end up with a 2.3L motor with a longer stroke then an RB25 helping torque, which the boost in displacement would be helping two fold. The engine would rev easier and harder then any other RB. With a bit of attention to the head it will flow enough to spin a HKS 3037, or Trust T67 required to make 310-320rwkws. And the thing would do it all day every day and be very strong.

But again, a std bottom end RB30 would easily do the same job at lower rpm. Even though i dont think that ultimately the engine would be stronger...at that power you mechanically wont be stressing either motor.

The RB20/26 sounds pretty good, or at least an improvement on the std RB20. I hadn´t considered that upgrade to the R32, most people seem to transplant an RB25 in.

Would the 20/26 be legal? Would it be higher maintence than a straight swap for an RB25?

I guess it´d also depend on the skills of the engineer and mechanics, but just wanted some general ´feel´for the thing.....

[Roy]

I hope that avtar of yours isn't copyright Troy!! lol

Why you cheeky!

No fair, everyone is much better looking then me

[Big Rizza]

Nice one Cubes

And Roy, I realise that the RB20DET-R is the king of the RB20s, but still I dont like how Nissan gave the RB20s max power at pretty much the same RPM as the SR20.

Afterall, the SR20DET doesn't like to rev at all, and the RB20 loves it, but it doesn't seem to show when power is concerned.

Eh, it's just my thoughts, I like the RB20 and wish it was better...

I haven't really gotten into modifying the RB20, but I think the RB20 peak power rpm is more to do with the relatively small turbo running out of puff at high rpm, and possibly camshaft profile, rather than the inherent characteristics of the engine from the bore/stroke ratio. My almost stock RB20 (pod + catback) made peak power at only 6100rpm on the dyno. I'd suggest a high flow turbo and upgraded cams would see peak power RPM skyrocket, but I'd also suggest that Nissan steered away from this approach to minimise the gaping chasm that is the RB20 low rpm torque hole.

[legend01]

Hi cubes

No ya cant mix them up the big end on a rb20 rod is smaller

little end big end rod from end to end centre

rb20det 10.5 mm 24mm 87 mm = 121.5mm

rb26dett 10.5 mm 25.5mm 85.5mm =121.5mm

now I dont have the little end bearings pressed out so these measurements were taken with little ends in but no big ends

Rb 26 rod top rb20 rod bottom

[legend01]

Roy rb26 do run a different pin height to allow for the longer stroke but the rb20 and 25 do have the same pin height so you could probably run rb20 pistons and rb25 crank no worries but with a thicker head gasket by about 40thou going from memory

cheers Peter

[Cubes]

Good stuff Peter.

[Halo a]

hey Cubes, which cylinder head is better RB25 or RB26 ? Why most people use rb25 head rather than rb26 it is because of expensive or other reason ?

Thanks

[Cubes]

26 head is obviously better and from a $$ to performance view it works out cheaper in the long run. Especially for an rb30det when they really do require a decent inlet.

Most people use the RB25 because its what they start off with. OR because its just a touch cheaper initially.

If I were to do the rb30det again today with todays rb26 head prices I wouldn't think twice about the rb25 head.

[Halo a]

26 head is obviously better and from a $$ to performance view it works out cheaper in the long run. Especially for an rb30det when they really do require a decent inlet.

Most people use the RB25 because its what they start off with. OR because its just a touch cheaper initially.

If I were to do the rb30det again today with todays rb26 head prices I wouldn't think twice about the rb25 head.

why u wont use rb25 head ? wat is the basic to build a rb30det or rb30dett ?

[Cubes]

Because for myself I have an R32 so I have to go out and buy either an rb25 or rb26 head.

The added cost of a plenum on the rb25 head pushes its total cost up to and possibly slightly over the cost of a 26head with its inlet manifold/plenum.

So costs are evened out.. BUT the rb26 head flows better due to higher lift more agressive ramped solid cams, better port angles, slightly larger valves etc.

So unless you own an R33 the rb26head is a financially better option.