RB25 (250) - Pictures & Spec....
Posted: Fri Jan 16, 2009 12:31 am
Here we go again!!!! 
This post won't be nearly as 'in depth' as the RB20 (200) post i made earlier, as the RB25 (250) is obviousley very similar in many ways, but with a few distinct differences that we can easily cover. If you wish to see a bit more detail about the RB kit in general, refer to the RB20 post first: http://scooterotica.org/forum/viewtopic.php?f=7&t=296
OK, so....the RB250 kit:
Here next to the RB20, both externally similar, using same size reeds, manifold and exhaust:
Inlet ports on both RB20 & RB25:
Rather interestingly, the entry to the transfers on the RB20 are practically the same size as the RB25....which means in percentage terms they are bigger than the RB25:
RB25:
RB20:
The transfers also seem to be meatier on the RB20:
RB25:
RB20:
So what about the inside, lets take a look at the port layout:
You can see that, like the RB20, we have a triple boost port again (3rd port being more of a transfer due to its angle of entry) but unlike the RB20 there is an exhaust port with two auxilaries. The main exhaust port is smaller than the RB20, but the auxillaries make up for that. Something to note is, that the RB20 is therefore easier to widen and work on, and the RB25 will require welding up first if you wish to re-work the exhaust port to any great extent.
The inlet, from this external shot, can be seen to be very similar to the RB20:
The internal shot below shows the boost port and transfers....note that although the boost port looks offset, it is actually inline in terms of the two main boosts seated between the transfers, and the 3rd port/transfer is the only 'offset' port.
Below is a shot of the boost port from the underside:
And a close up, you can see the angle of entry as the boosts face upwards, and the 3rd port is flatter, like the main transfers, you can also see the direction of the ports from the side:
The feeders that wrap round the studs, come through to the transfers......flow!
Last, but not least, we have the exhaust port with auxillary side ports:
A closer shot:
And from the outside, the bridged auxillaries can be seen joining the main port:
So that's your lot, not so much text here....because i dont want to just repeat whats already been said in the RB20 post. The port map below, will give you a rough idea of how the ports are measured out on the RB25, and at least one thing worth noting is that the port sizes an the RB25 are not proportionally bigger than the RB20. In my mind this will result in the RB20 being branded as more of a screamer, and the RB25 as more of a thumper....both performance based motors in their own right....and both tunable with slants bewteen touring and racing.....but as the inlet port and the transfers on the RB20 is almost physically identical to the RB25, this means as a proportion/percentage of the bore the RB20 comes in a more extreme state of tune as standard.......which is what i like.....and the exhaust port is easier to alter that the RB25 too. However, the RB has the wider exhaust by way of the auxillaries as standard.....and it's 40-60cc extra will give it some real umph!! Two cracking kits, both from the same range, both looking similar....but with subtle differences that will give each its own character.......and power delivery. In terms of progress, the RB range is undeniably a huge leap forward in tuning terms, and takes Lambretta's to yet another level............i just want to get one on the track now!
Take a peek at the port map, and see what you think:
RB20 map for comparison:
Note: The port maps are rough guides...not super-accurate, just for illustration purposes.
I hope you enjoyed that, and dont forget to draw reference from the RB20 post: http://scooterotica.org/forum/viewtopic.php?f=7&t=296
Cheers
Dan
This post won't be nearly as 'in depth' as the RB20 (200) post i made earlier, as the RB25 (250) is obviousley very similar in many ways, but with a few distinct differences that we can easily cover. If you wish to see a bit more detail about the RB kit in general, refer to the RB20 post first: http://scooterotica.org/forum/viewtopic.php?f=7&t=296
OK, so....the RB250 kit:
Here next to the RB20, both externally similar, using same size reeds, manifold and exhaust:
Inlet ports on both RB20 & RB25:
Rather interestingly, the entry to the transfers on the RB20 are practically the same size as the RB25....which means in percentage terms they are bigger than the RB25:
RB25:
RB20:
The transfers also seem to be meatier on the RB20:
RB25:
RB20:
So what about the inside, lets take a look at the port layout:
You can see that, like the RB20, we have a triple boost port again (3rd port being more of a transfer due to its angle of entry) but unlike the RB20 there is an exhaust port with two auxilaries. The main exhaust port is smaller than the RB20, but the auxillaries make up for that. Something to note is, that the RB20 is therefore easier to widen and work on, and the RB25 will require welding up first if you wish to re-work the exhaust port to any great extent.
The inlet, from this external shot, can be seen to be very similar to the RB20:
The internal shot below shows the boost port and transfers....note that although the boost port looks offset, it is actually inline in terms of the two main boosts seated between the transfers, and the 3rd port/transfer is the only 'offset' port.
Below is a shot of the boost port from the underside:
And a close up, you can see the angle of entry as the boosts face upwards, and the 3rd port is flatter, like the main transfers, you can also see the direction of the ports from the side:
The feeders that wrap round the studs, come through to the transfers......flow!
Last, but not least, we have the exhaust port with auxillary side ports:
A closer shot:
And from the outside, the bridged auxillaries can be seen joining the main port:
So that's your lot, not so much text here....because i dont want to just repeat whats already been said in the RB20 post. The port map below, will give you a rough idea of how the ports are measured out on the RB25, and at least one thing worth noting is that the port sizes an the RB25 are not proportionally bigger than the RB20. In my mind this will result in the RB20 being branded as more of a screamer, and the RB25 as more of a thumper....both performance based motors in their own right....and both tunable with slants bewteen touring and racing.....but as the inlet port and the transfers on the RB20 is almost physically identical to the RB25, this means as a proportion/percentage of the bore the RB20 comes in a more extreme state of tune as standard.......which is what i like.....and the exhaust port is easier to alter that the RB25 too. However, the RB has the wider exhaust by way of the auxillaries as standard.....and it's 40-60cc extra will give it some real umph!! Two cracking kits, both from the same range, both looking similar....but with subtle differences that will give each its own character.......and power delivery. In terms of progress, the RB range is undeniably a huge leap forward in tuning terms, and takes Lambretta's to yet another level............i just want to get one on the track now!
Take a peek at the port map, and see what you think:
RB20 map for comparison:
Note: The port maps are rough guides...not super-accurate, just for illustration purposes.
I hope you enjoyed that, and dont forget to draw reference from the RB20 post: http://scooterotica.org/forum/viewtopic.php?f=7&t=296
Cheers
Dan
