Jump to content
SAU Community

Recommended Posts

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

  • Replies 55
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

Posted Images

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.

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

:rofl: 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 by salad
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.....

:no: 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... :wub:

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.

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

post-7066-1173242936.jpg

Rb 26 rod top rb20 rod bottom

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

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.

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 ?

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.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now



  • Similar Content

  • Latest Posts

    • just an update to this, poor man pays twice  Tried sanding down the pulleys but it didnt do the trick. Chucked another second hand alternator in the na car which I got for free off my mate and its fixed the squelling. Must have been unlucky with the bearings.    As for my turbo car, I managed to pick up a cwc rb alternator conversion bracket + LS alternator for 250 off marketplace, looked to be in really good nick. Installed it , started the car and its not charging the battery.... ( Im not good with auto elec stuff so im not sure if this was all I needed to do but I verified such by using a multimeter on the battery when the engine was running and I was only getting 12.2v )   I had to modify the earth strap for the new LS alternator , factory earth strap was a 10mm bolt which did not fit the bolt on the LS alternator which was double the size so I cut it off , went to repco bought some ring terminals that fit, crimped it onto the old earth strap and bolted it up to the alternator , started the car and same issue. Ran like shit and was reading 12.2 at the battery.  For a "plug and play" advertised kit thats not very plug and play but alas.  My question is , am I missing something ? Ive been reading that some people recommend upgrading the stock 80 amp alternator fuse to a 140 amp but I dont see how that would stop the alternator charging especially at idle not under load.  Regardless ive pulled it out and am going to get it bench tested by an auto elec tomorrow but it would be handy to know if ive missed something silly or have done something wrong.   
    • My wild guess is that you have popped off an intake pipe....check all of the hoses between the turbo and the throttle for splits or loose clamps.
    • Awesome, thanks for sharing!
    • To provide more specific help, more information is needed. What Android screen? What is its wiring diagram? Does the car's wiring have power at any required BAT and ACC wires, and is the loom's earth good?
    • So, now all you need to do is connect the 2 or 3x 12v feeds into the unit to permanent 12v, ACC 12V and IGN 12V that you can find in the spot behind the stereo, and the earth, and then it will switch on with the car.
×
×
  • Create New...