The end of the Lambretta crank as we know it ???

[Avantone]

By the way, FALC does a €1600,00 crank for a Honda GP1, and guess what ........................... it's round!

Isn't that a four stroke?

Well if it is, it's got a very funny shaped exhaust

http://www.falcracing.it/catalogohonda.html

[drunkmunkey6969]

Maybe i'm mistaken then, i was thinking of something along these lines: http://www.motorcycledaily.com/18june01hondagp1.html

[J1MS]

I have to agree with an earlier post.... I did hear Mark Broadhurst on two occasions say that he had only put the crank on display to give the forums somthing to talk about, and actually mentioned one persons name...

How many people have actually worked out the Primary chamber volume on a Lambretta.. Not Many Im sure... Most wouldnt even know the differance in primary compression ratios when fitting a full circle crank (owing to the loss of free space taken up by the full circle crank webbs) versus a standard crank... So to a very few on here this topic is a serious debate, but to most others with a passing interest, its a bit of banter on the forum...

So can anyone post actual figures of primary compressions and or preferably Geometic figures, as actual figures depend on knowing when a port shuts and another opens, this will vary from engine to engine... Whereas reeds close when the pressures are equal, so this figure is not a consistant actual... as the ramming effect in the venturi will have an effect as will the inlet tract length, not forgetting the stiffness of the reeds... factor in the size of carb used, these all effect air speed... while the Primary chamber draws in the air/fuel mix, the inlet tract also has ramming effects which will vary the actual primary compression over the rev range.... I know a small amount of the theory, and have in the past bothered to work out my Geometric primary compression on a couple of engines... but now I just try and make mine High (Or higher than standard) Primary Compression, and keep the engine low reving whilst trying to keep as much torque low down as is possible without over tuning the engine, keeping port timing relatively low... Would any of the scooter racers like to divulge a little info here LPC or HPC whats yours..?? Preferably those riders finishing on the Podium...

[drunkmunkey6969]

Preferably those riders finishing on the Podium...

Out of 800 members, that'll be.....um.....just Tony?

But......as RinB previously calcd:

The amount of metal removed from your own race crank, was equal to approx 40cc, so based on PCR calc on a 198cc barrel 40cc would decrease pcr by about 0.07 not a lot really.

We need to really do some proper measurements of the reed induction volumes & use
the geo calc not the simple one. As the 2 give very much different results as to volumes.

Really need to find out this 1.2 being banterd is geo or simple PCR

Either way 40cc not a lot to PCR.

So thoughts on better balance, reduced vibration, and reduced rotating mass are of more interest when you isolate the crank alone, rather than its LPC benefits.......but when combined with bigger transfers, longer rods, different pistons and packer plates etc......it all adds up and becomes part of the equation. And as many quote, an engine is the total sum of its entire parts, and not just a crank or a cylinder in isolation..........every item needs to be considered in context to its other operating parts and their purpose in the equation.

[davidblythe]

You forgot Ralph

[drunkmunkey6969]

I know a small amount of the theory, and have in the past bothered to work out my Geometric primary compression on a couple of engines... :

What figures did you come up with?

[drunkmunkey6969]

You forgot Ralph

Yes, sorry....humble apologies Ralph!

And there actually one or two other VERY well known racers (old and new) that are members here, but not under thier actual names......but until they decide to enter the forum discusions of their own volition, i shall not draw them into the foray.

Now back on track! PC calc gents??

[J1MS]

1.2 seems low I worked mine out as 1.45 many many moons ago... this was the first engine I tried this on... But prehaps my calcs were a little off back then... It was on a 200 with a 107 rod running on a Yam piston with the barrel shortened 9mm, running a padded crank (Balsa wood and messy stuff) which would have increased the primary a little but not much....
Do you think I was that far out, I really hope not...

Forgot too mention no reed valve just a welded piston...

[drunkmunkey6969]

No, the 1.2 figure relates to a quote from C.E. in Scootering as the figure lots of MX machines are down to, where as he suggested that Lamb's were up to approx 1.7, which in his opinion was much to high.

He suggested that the original 1.7 PC figure was due to the fact that the scooters were originally manufactured with crappy box pipes that had no real pumping action, so that engine had to do all the pumping, and went on to say that with decent expansions that now work, the original PC figure of 1.7 may be too high for a Lambo.

I guess its all all about flow, speed, volumes.......and getting the balance correct for your needs.

[Avantone]

Wasn't the Scootering article written in the context of racing? and comparison with MX (High-revving competition machines with more than 4 gears)?

I think it's been established by the "internet massive" that you need an expansion chamber suited to LPC, but even then the pipe is only going to work within a narrow RPM, so how do you get the charge moving under 7000RPM?

In the context of a 4-speed box, it's probably a racing application only, and like I said earlier, are the crank webs the best place to take material from? ................... adjustable/dynamic crankcase volume anyone?.......................................