Rb20det And Rb25det

[Halo a]

Good luck Roy

[Cubes]

LOL...i know a guy with several Gibson RB20s, and they didnt limit them to 7,000rpm at Bathurst

Anyway, we will soon know how long a std RB20 can make 450hp for

Maybe having a lesser load hanging off the end of the rod and slower piston speed allows for more reliable high rpm.

[Roy]

Whats the Honda S2000 bottom end like, bore/stroke etc. Its a std road car that pulls 9,000rpm reliably.

[Halo a]

In my country (Malaysia) they use 4AG or 4 AGE piston in RB20. is that a good idea ?

[Simon-S14]

4AG and 4 AGE are the same thing.. and no they dont use them they use 4AGZE pistons which are factory ceramic pistons.

Works well but theres a lot of mods needed to make them fit.

[Simon-S14]

4AG and 4 AGE are the same thing.. and no they dont use them they use 4AGZE pistons which are factory ceramic pistons.

Works well but theres a lot of mods needed to make them fit.

[Big Rizza]

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.

Not sure that I agree 100%. I've always been of the school of thought that more displacement = more reliability for a given power output.

With lighter cylinders and more meat on the engine block, perhaps the smaller engine would be the strongest for a given rpm and boost (assuming all else equal between the engines). But since power is all about airflow, the smaller capacity require either a) more boost or b) more revs match the power of the larger engine, which might negate any increases in inherent strength over the larger engine...

Or conversely, the larger engine could match the power of the smaller engine with less boost and fewer revs, improving reliability enough to match (or better) the smaller engine...

Overall, I'd say the reliability would be much more dependent on the strength of the materials, the quality of the manufacturing and the skill of the tuning. And of course the mechanical sympathy of the driver.

[Cubes]

Whats the Honda S2000 bottom end like, bore/stroke etc. Its a std road car that pulls 9,000rpm reliably.

Good point.. A quick google revealed rb30 like specs.

87mm bore x 84mm stroke

Its rod length is 153mm which gives us a rod to stroke ratio of 1.82.

RB30 is 86mm bore x 85mm stroke. In my case 87mm bore.

The RB30 also runs what is considered a near perfect rod to stroke ratio of 1.77 (152.5mm / 85mm)

The apparent perfect rod/stroke ratio is 1.75.

It will be good to see how R33Racers? holds up as thats flicked to 8500rpm around the track.

http://victorylibrary.com/mopar/rod-tech-c.htm

Sums up rod to stroke ratio's fairly well.

So with a good cradle it might be possible to build a super reliable 9000rpm rb30 monster.

[salad]

Getting a bit off topic now, but thought this might interest a few people

http://hondaswap.com/members-lounge/engine...n-speeds-72614/

B18C5 is actually 81x87, oversquare engine, and redline at 8400

M3 is 87x91 with 8000 redline

Sorta makes you wonder why Nissan didn't make the RB20 have max power and redline a lot higher and use shorter gears...

[Cubes]

87mm B18C5 stroke. It runs a 1.58 stroke ratio.

So similiar to the one of the rb25/26/20 RB's. I forget which one.

http://www.superhonda.com/forum/showthread.php?t=125367

[legend01]

Just going of those figgers you've got there I could be wrong but rb20 rod is 121.5mm/69.7mm gives us a rod stroke ratio of 1.74.Is that right ?

[Roy]

Because they had the R31 GTS-R which got the better exhaust manifold. Better turbo, bigger intercooler. Different cams. They rev their little heart out, and in Grp A trim whilst not as powerful as the Sierras had far superior driveability.

And agree with Rizza regarding bigger displacement not needing so much rpm. I hear you but tell me when a 300rwkw RB30 makes 200rwkws?

[Rolls]

Yeah the 25det turbo would have been much better suited to the rb20, I guess fat midrange is more appealing to the mass market though.

[Cubes]

The RB26 and 25 rod is 121.5mm according to Wiseco's catalogue.

Are you sure the rb20 rod is 121.5mm?

[legend01]

yep just measured an rb26 rod and an rb20 rod with the digital verniers to get those figgers.Also when doing the rebuild on my rb20 we measured all three rods and all came up 121.5 although I put the rb25 crank in but that makes mine 1.69mm

[Cubes]

And agree with Rizza regarding bigger displacement not needing so much rpm. I hear you but tell me when a 300rwkw RB30 makes 200rwkws?

RB30's make 300rwkw's at 5500rpm if the inlet isn't changed. I'm still sticking by the inlet altering the rpm power band. I've seen it with my own eyes from 180rwkw right up to 270rwkw+ so its difficult for some one to say its the exhaust side and say its not designed for 250rwkw+ when I've seen completely different.

[Cubes]

yep just measured an rb26 rod and an rb20 rod with the digital verniers to get those figgers

Interesting.. So the rb26/25's and 20's run exactly the same rod.

So why do people bother with rb25/26 rods when doing their rb22/23/24 conversions? Why not just use the crank?

The Rb20 rods are quite meaty looking things.

If so.. The RB20 has a better rod/stroke ratio than the rb25 and 26.

1.64 for the RB26 and 1.69 for the RB25.

That being said whats the deck height of the rb20? The same as the 25/26?

If so it must run a highish pin height.

A good little diagram to help those who don't know what the rod/stroke ratio means.

http://article1.rboosted.com/rb20_stroker.html

[legend01]

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

[Roy]

RB30's make 300rwkw's at 5500rpm if the inlet isn't changed. I'm still sticking by the inlet altering the rpm power band. I've seen it with my own eyes from 180rwkw right up to 270rwkw+ so its difficult for some one to say its the exhaust side and say its not designed for 250rwkw+ when I've seen completely different.

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

[Cubes]

Its interesting to note the 1jz uses the same rod length as the 2jz.

2JZ

Rod - 141.98mm

Stroke - 86mm

1.68 R/S

1JZ

Rod - 141.98

Stroke - 71.5mm

1.98 R/S

My conclusion.. Who frekin knows. Manufactures don't appear to stick by any solid rule of thumb.