Reflections in Blue the RB22 Rev 2 update

[red]

Might see you Saturday at Donny

[RinB]

Might see you Saturday at Donny

Yes m8 be good to put a face to a name.

[eibargum]

I read that your going to see about a low pc crank smiffy, i take it you mean low primery compression, if so what are the addvantages of low pc over high pc, most people i know are useing full circle cranks these days to help get the pc higher, in laymans terms please as i know F all about tuneing , regards.

[Knowledge]

There has been a general shf=ift in thinking about primary compression ratio (PCR).

Ther has been a long standing debate about high and low PCR. With high PCR, you should get a better transfer of fresh charge from below the piston to above the piston. The counter arguement was that any extra pressure below the piston slows the piston during decent (firing stroke) and consumes power.

A parallel issue has always been the knowledge that a good expansion chamber will draw fresh charge through the transfers regardless of the PCR. This only happens at certain engine speeds, but it was proved by creating an engine that was only required to run at one speed. It featured an expansion chamber designed to run at one speed, and no PCR. All the charging of the upper cylinder was attained by the pulses generated by expansion pipe.

This all came together when I read Scootering's interview with Charlie Edmonds. Charlie seemed (to me) to be the first person who have bothered to measure the PCR on a Lambretta. He had learnt that modern 2 stroke tuners were working with a PCR of about 1:1.2, where as a standard lambretta was already at 1:1.65. His arguement for lowering the standard PCR was also enhanced by the acknowledgement of the role of the expansion chamber in drawing fresh charge into the upper cylinder regardless of the PCR.

Now I doubt this was news to some reading this post, but it was the first time I'd seen figures put to the PCR, and the first time I'd seen someone relate this to the characteristics of the pipe.

This does need to be read with a degree of sanity. Afterall, building an engine for the track is very different to building one for the road. Charlie is building race engines that will spend much of their lives at near full throttle. That's not how you or I ride on the road . Charlie only has one set of traffic lights to deal with. Therefore, the alterations that you can make to low PCR cannot always be offset by the expansion chamber when you need a range of engine speeds.

Discuss.......

Martin

[RinB]

There has been a general shf=ift in thinking about primary compression ratio (PCR).

Ther has been a long standing debate about high and low PCR. With high PCR, you should get a better transfer of fresh charge from below the piston to above the piston. The counter arguement was that any extra pressure below the piston slows the piston during decent (firing stroke) and consumes power.

A parallel issue has always been the knowledge that a good expansion chamber will draw fresh charge through the transfers regardless of the PCR. This only happens at certain engine speeds, but it was proved by creating an engine that was only required to run at one speed. It featured an expansion chamber designed to run at one speed, and no PCR. All the charging of the upper cylinder was attained by the pulses generated by expansion pipe.

This all came together when I read Scootering's interview with Charlie Edmonds. Charlie seemed (to me) to be the first person who have bothered to measure the PCR on a Lambretta. He had learnt that modern 2 stroke tuners were working with a PCR of about 1:1.2, where as a standard lambretta was already at 1:1.65. His arguement for lowering the standard PCR was also enhanced by the acknowledgement of the role of the expansion chamber in drawing fresh charge into the upper cylinder regardless of the PCR.

Now I doubt this was news to some reading this post, but it was the first time I'd seen figures put to the PCR, and the first time I'd seen someone relate this to the characteristics of the pipe.

This does need to be read with a degree of sanity. Afterall, building an engine for the track is very different to building one for the road. Charlie is building race engines that will spend much of their lives at near full throttle. That's not how you or I ride on the road . Charlie only has one set of traffic lights to deal with. Therefore, the alterations that you can make to low PCR cannot always be offset by the expansion chamber when you need a range of engine speeds.

Discuss.......

Martin

NNNNNNNNNNNNNOOOOOOOOOOOOOOOOOOOO Not again Martin we've only just come back from rehab the last time we disussed this

But on serious note read here

http://scooterotica.org/forum/viewtopic ... ow+comp%2A

& Here

http://scooterotica.org/forum/viewtopic.php?f=7&t=40

Basically 2 good old Schools of thought some say
High let crank piston do work or
Low suck the bleeder out with Exhaust.

Who's right well may be the track scoots tells you this ?????

Smiffy

PS Martin nice write up

[eibargum]

Thanks for your time lads, interesting but confuseing, am i right in thinking that if you use a pipe built fot the kit your useing [ie franspeed] for a RB you should be ok useing a crank thats not full circle, but if you adapt a pipe to use on a RB you,d be better off useing a full circle crank, if thats the case ive done it the wrong way round , ive got a full cicle crank in my RB and i use the franspeed pipe, iam going to put my spare RB barral on are lass,s GP [she says she needs more speed ] which allready has indian webs in and i was going to adapt a pipe to fit, might invest in another franspeed for her for xmas , mind you, iam very happy with my RB as it is. regards and thanks again.

[RinB]

Just found this on Low comp

It all started here

http://www.phpbb88.com/scooterotica/vie ... ooterotica

Didnt it Sean

[RinB]

Thanks for your time lads, interesting but confuseing, am i right in thinking that if you use a pipe built fot the kit your useing [ie franspeed] for a RB you should be ok useing a crank thats not full circle, but if you adapt a pipe to use on a RB you,d be better off useing a full circle crank, if thats the case ive done it the wrong way round , ive got a full cicle crank in my RB and i use the franspeed pipe, iam going to put my spare RB barral on are lass,s GP [she says she needs more speed ] which allready has indian webs in and i was going to adapt a pipe to fit, might invest in another franspeed for her for xmas , mind you, iam very happy with my RB as it is. regards and thanks again.

Eibargum

I think you've got confused m8

If you have an RB with standard crank or full circle high comp, it will be ok with Franspeed

If you go low comp crank the Exhaust will prob need to be modify to suite.

Smiffy

[sean brady scooters]

its now quite generally accepted that HPC works better for std type silencers/mild pipes..........
where as the more racey/high performance pipes.....which suck harder......benefit from a lower primary comp.......
especially when working in balance with the correct inlet tract tuned length........

[drunkmunkey6969]

Just found this on Low comp

It all started here

http://www.phpbb88.com/scooterotica/vie ... ooterotica

Didnt it Sean

This other topic was my favourite though!! http://www.phpbb88.com/scooterotica/vie ... ooterotica