Family engine parts interchange

[Turbine]

Hi guys,

what would you get if you could place an RB20 crankshaft into an RB30 block. Would they fit??

I know rod sizes will differ, that's not a problem just need to know if those cranks will go in the big block.

Turbine

[proengines]

It would physically fit, the main journals are the same size, the conrod journals on an RB20 are the same as a CA18 so you'd have to have rods and pistons made to suit the journal and the length. To do something cheaply, why not try an RB25 or 26 crank in the RB20, a set of RB26 rods and have some pistons made or modify some 4AG-ZE pistons? The RB20 head will bolt straight on and apparently they still rev really well. You would want some decent quality valves and springs and solid lifters if you were planning on 9000rpm though, I doubt the hydraulics would take it for too long or if the head would flow enough air with the std valves to make worthwhile power at those sort of revs. It also still looks like an RB20 so if it runs good times it will look pretty impressive.

[BHDave]

By putting the 20 crank in an rb30 wouldn't you just end up with near enough to a 2 litre engine anyway?

[TurboX]

By putting the 20 crank in an rb30 wouldn't you just end up with near enough to a 2 litre engine anyway?

That is sort of the idea - we want revs with less capacity.

Does anyone know of a definitive list of all interchanging components on RB's?

[Turbine]

By putting the 20 crank in an rb30 wouldn't you just end up with near enough to a 2 litre engine anyway?

This may be true, but it would have an advantage of having a longer conrod,short stroke and larger pistons compared to the standard RB20 setup.

Does this sound right??

Turbine

[Turbine]

It would physically fit, the main journals are the same size, the conrod journals on an RB20 are the same as a CA18 so you'd have to have rods and pistons made to suit the journal and the length. To do something cheaply, why not try an RB25 or 26 crank in the RB20, a set of RB26 rods and have some pistons made or modify some 4AG-ZE pistons? The RB20 head will bolt straight on and apparently they still rev really well. You would want some decent quality valves and springs and solid lifters if you were planning on 9000rpm though, I doubt the hydraulics would take it for too long or if the head would flow enough air with the std valves to make worthwhile power at those sort of revs. It also still looks like an RB20 so if it runs good times it will look pretty impressive.

Thanks for the respone pro engines. I'm glad that these cranks will fit the blocks.

I could just stick with our RB30DET, but I'm after the high RPM option, at least untill I get enough feedback that it's a silly option, too costly and stuf like this.

Turbine.

[Sydneykid]

Thanks for the respone pro engines. I'm glad that these cranks will fit the blocks.

I could just stick with our RB30DET, but I'm after the high RPM option, at least untill I get enough feedback that it's a silly option, too costly and stuf like this.

Turbine.

There seems to be a couple of threads on this subject. This is as good a place as any;

1. Why do you want a "high rpm option"?

2. Surely a "high power option" is better?

3. On a $per HP basis the RB30 is waaaaay cheaper than the RB20

4. Then there is the average power, which is what gives the time down the 1/4

5. Regardless of the engine involved, high rpm is expensive to build and expensive to maintain, buying a higher diff ratio is cheaper.

6. Buying off the shelf high rpm parts for an RB20 is even more expensive, if you can actually find any. You would have to get many things hand made, and that's going to be even more expensive.

7. BHP = torque (in ft lbs) X RPM / 5250

So 10% more torque at 10% lower rpm = same BHP

8. The reality is 10% more torque is 40+% cheaper to get than 10% more RPM

Sell off the RB20's and buy an RB30 bottom end and an RB25DE top end, spend the same amount of money and the car will be faster, easier to drive and more reliable.

PS; this is not knocking RB20's , great engines, but the economics say there are better alternatives for your purposes.

[Turbine]

Ok the high RPM option was to gain reasonable HP with the smaller capacity engine to run in a weight brake class of racing. Smaller capacity = less total weight to carry.

So after reading your reply Syndey Kid, the idea is slowly running away, but.

If we can get the RB20 crank in our RB30 block with our RB25de cylinder head, that would give us the low capacity with the ability to breath at high rpm!

From what I've read so far it seems as though this can be done with rod and piston mods.

If I run a higher diff ratio (numerically high that is), you need more RPM to get you MPH.

The only thing that is preventing me to go with it is cost. Those special cams are unbelievablly expensive, I can't believe people pay so much for them??

Just a side note: I hear of one particular engine runnig at 10,000rpm, I've even heard that some of these guys running RB30's in VL taxis running up to 13,000RPM so the engines must be cappable of doing it.

Turbine

[Sydneykid]

Ok the high RPM option was to gain reasonable HP with the smaller capacity engine to run in a weight brake class of racing. Smaller capacity = less total weight to carry.

So after reading your reply Syndey Kid, the idea is slowly running away, but.

If we can get the RB20 crank in our RB30 block with our RB25de cylinder head, that would give us the low capacity with the ability to breath at high rpm!

From what I've read so far it seems as though this can be done with rod and piston mods.  

If I run a higher diff ratio (numerically high that is), you need more RPM to get you MPH.

The only thing that is preventing me to go with it is cost. Those special cams are unbelievablly expensive, I can't believe people pay so much for them??

Just a side note: I hear of one particular engine runnig at 10,000rpm, I've even heard that some of these guys running RB30's in VL taxis running up to 13,000RPM so the engines must be cappable of doing it.

Turbine

13,000 rpm out of an RB30 :wassup: :wassup: :wassup: :wassup:

In whose dreams :bs!: :bs!: :bs!:

What is the capacity break you are aiming for?

Using an RB20 block----

RB20 standard = 2 litres

RB20 with max (safe) bore = 2.3 litres

RB20 with max (safe) bore and RB26 crank = 2.4 litres

Using RB25 block---

RB25 = 2.5 litres

Using RB26 block---

RB26 = 2.6 litres

RB26 with max (safe) bore = 2.7 litres

Using RB30 block---

RB30 = 3.0 litres

RB30 with max (safe) bore = 3.1 litres

None of those options (2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 3.0, 3.1) require using an RB20 crank in an RB30 block, that makes no sense at all.

[Turbine]

13,000 rpm out of an RB30  :wassup:  :wassup:  :wassup:  :wassup:  

In whose dreams :bs!:  :bs!:  :bs!:

What is the capacity break you are aiming for?

Using an RB20 block----

RB20 standard = 2 litres

RB20 with max (safe) bore = 2.3 litres

RB20 with max (safe) bore and RB26 crank = 2.4 litres

Using RB25 block---

RB25 = 2.5 litres

Using RB26 block---

RB26 = 2.6 litres

RB26 with max (safe) bore = 2.7 litres

Using RB30 block---

RB30 = 3.0 litres

RB30 with max (safe) bore = 3.1 litres

None of those options (2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 3.0, 3.1)  require using an RB20 crank in an RB30 block, that makes no sense at all.

Whooo their sydney kid, it's just what these guys running 8's over the 1/4 tell me they are doing. Sounded a bit hard to believe, but I thought their may have been some truth in it :confused:

As for the weight brake. Smaller the engine smaller the weight. I think it's about 8kilo/cubic inch minimum, so 968 Kilo in total for the car, and driver.

Thats great that you did that capacity reference for me, but I don't see one their that says

RB30=3.0Litres

RB30 with max (safe) bore = 3.1 Litres

RB30 with max (safe) bore with RB20 crank = ___ Litres ??????

is that possible Sydney Kid?

[Sydneykid]

Whooo their sydney kid, it's just what these guys running 8's over the 1/4 tell me they are doing. Sounded a bit hard to believe, but I thought their may have been some truth in it :confused:  

As for the weight brake. Smaller the engine smaller the weight. I think it's about 8kilo/cubic inch minimum, so 968 Kilo in total for the car, and driver.

Thats great that you did that capacity reference for me, but I don't see one their that says  

RB30=3.0Litres

RB30 with max (safe) bore = 3.1 Litres

RB30 with max (safe) bore with RB20 crank = ___ Litres ??????

is that possible Sydney Kid?

= 2,516 cc's

Which is pretty much the same as an RB25, so there is no capacity break that isn't already covered.

I don't understand why the hell you would want to use an RB30 block. It's bore is the same (86mm) as RB25/26 but it is 38 mm taller, that is to accomodate the extra stoke and the longer conrods. You aren't going to use the extra stoke with an RB20 crank and none of the RB conrods would be long enough to bring the piston to the top of the block, or even close enough to mill the block. So you would have ot get special conrods made. You could build a 500 bhp RB30 for how much that would cost.

Simply put, the RB20 crank has the shortest stroke and the RB30 block is the tallest, they just don't go together.

[r33_racer]

What sydneykid has said makes perfect sense, its like your trying to put two negatives together...a short stroke crank and a long stroke block...last time i watched playschool the square didnt exactly fit the circle...but being a boilermaker i learned a hammer and oxy can change that! It would be interesting to see how that would work if you accomplish it Turbine. (no offence intended)

[Turbine]

What sydneykid has said makes perfect sense, its like your trying to put two negatives together...a short stroke crank and a long stroke block...last time i watched playschool the square didnt exactly fit the circle...but being a boilermaker i learned a hammer and oxy can change that!  It would be interesting to see how that would work if you accomplish it Turbine.  (no offence intended)

Thats fine guys, it's just my silly way of trying to learn about these group of nissan engines.

The real trick was to see if I could duplicate what the chevy V8 guys do with their odd size small blocks. Using a long conrod with the short stroke. It's like having a mechanical advantage, a second class lever if you like. I would also keep the piston at top and bottom dead centre longer.

Just one question for SydneyKid, what is the length of the longest RB engies conrod?

I'll work it out one way or another i suppose. Just got to keep digging

Cheers

[B0oStEr]

The rb30 rod would have to be the longest because of the 38mm taller deck.

If you want to build a cheap short stroke motor with more capacity why not use the rb25 block, pistons and head with the rb20 crank and rods?

[Sydneykid]

Thats fine guys, it's just my silly way of trying to learn about these group of nissan engines.  

The real trick was to see if I could duplicate what the chevy V8 guys do with their odd size small blocks. Using a long conrod with the short stroke. It's like having a mechanical advantage, a second class lever if you like. I would also keep the piston at top and bottom dead centre longer.

Just one question for SydneyKid, what is the length of the longest RB engies conrod?

I'll work it out one way or another i suppose. Just got to keep digging

Cheers

RB30 conrods are 6" centre to centre (152.5 mm)

Before you ask, RB26 conrods are 4.783" (121.5 mm)

That's where 31 mm of the extra 38 mm in the height of an RB30 block is used

The other 7mm is in the 11.3 mm of extra stroke and the 1.3mm balance is the piston deck height difference.

PS, when we are changing the rod stroke ratio of Chevy, we don't bother with a handfull of mm's, as you would get between RB20/25/26 cranks. It simply isn't worth the effort.