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

[tony]

Really!! So why will this type of crank provide more power at high rpm then? Less mass? I think some people have strange ideas on primary compression. In fact as Adam said above no one had even thought about it until that article. Now we are seeing cranks like this appearing because the tuners out there think that this is what is best to try to achieve this desired low primary. Can someone explain low primary compression theory because up till recently everyone was padding cranks!

[drunkmunkey6969]

Can someone explain low primary compression theory because up till recently everyone was padding cranks!

Tut tut Tony...are you leading people along there?

You of all people (with your conections) understand HPL and LPC pros and cons better than most dont you?

[156 D]

......i am no tuning expert, but the "old school" way in the `60`s was higher primary compression as the design of exhaust pipe did not do much from the reverse exhaust wave point of view in packing some unburnt gases back in the combustion chamber and charging it to a higher degree......now they do the opposite, have a well designed exhaust to do half the work and reduce the primary charge and so the secondary compression is in theory lower........but then comes along turbo charging and the whole thing has to go back to "old school" as the modern scavenging exhaust pipe can`t do the job it was designed to do as the turbo won`t let it........imo the "old school" way is better as the higher primary you can get away with will allow the higher secondary compression and together with tapered transfer ports and a re-designed exhaust pipe will give just as much power more cheaply , unleaded doesn`t come into it,.........as in the article Sean found the lower torque or pulling power of the engine with the higher primary and the full web crank will give you extra revs because of the extra BHP ........racing is not only 500 extra revs at the top end.....but extra grunt out of corners than the other bikes ...will place you better for the next corner.....+ they have to get by you........


Quote:
"In a nutshell there's only two ways to make horsepower, by increasing torque or increasing RPM. Our low displacement Honda motors can make a relatively large amount of horsepower with a low torque output because of our ability to maintain that torque output at higher RPM levels."

[drunkmunkey6969]

The crank in the post is made by the same crank manufacturer as MB's full circle cranks, they are both computer aided balanced to suit Lambretta pistons, so Im told! The pictured crank took 10 tons to assemble both side, runs with no run out, and would fit it to any race engine without a doubt....maybe even a group 4!

There are various ways to increase crankcase compression, a new crank is just one way, balance is a factor also worth looking at. A smooth engine, should give better power and lower vibrations, perhaps this is more of a consideration than compression?

Whilst Charlie is probably (so im told) bordering on genius, and was certainly the first person to talk about LPC in a magazine.....i dont think its fair to say that nobody ever thought about it before? Cranks like this are not new in Lambrettas.......MB did a crank like this in 1990 in a LC Lambretta, its still running today! As for Low or high compression, everyone harps on about cranks and compression........but no one mentions the fact that various combinations of Lambretta pistons with different comp heights, con-rod lengths and packers alter comp ratios......then everyone opens up transfers, welds them, makes big ear transfers and that all lowers compression too!

But saying that, some tuners have are getting good power from UN welded TS1 engines, rather than totally over the top welded engines, proving high comp still works! It's all to do with how you get your power, how you want it delivered, and in what context the LPC/HPC is working with other componenets......but its not new.

So, as we mentioned in the previous raging debate on this very matter, when we featured our version of a similar style crank: http://scooterotica.org/forum/viewtopic ... +new+crank I guess that MB are seeking the same thing we are........

1) A decrease in rotating mass.......ever seen BHP increase when a lightened flywheel is fitted? Same principle.
2) Increased crankcase volume to lower primary compresion (to work with other componenets for an appropriate tune)
3) A better balanced crank with reduced vibration

Since we opened the dyno i have been rushed off my feet, and so havent had time to complete the engine that i fitted our crank to.....plus i dont really have a proper purpose for the engine, other than building it for my own amusement and testing etc, so its gone on the back-burner for now.

Plus....even if i had completed the engine, and it had put out great HP....no one would have been satisfied until i stripped it and fitted a standard crank to give a back-to-back comparison, so it seemed like a thankless task (not to mention costly). So i resided to do this instead...at the end of the race season, i will dyno the TS1 and i would be stripping that for a new piston and service anyway.....but i'll rebuild it with the cut-race crank of ours (see other post) and then i can dyno and give you the info you all want to know....back to back BHP figures.

Im not trying to convince anyone that this is the right way to go, and Charlies article in scootering didnt prompt Sean to do our version....he's been fitting them to Vespas for years, we just wanted to try it in a Lambo, and let you know what we were doing. So its OK if you think its all tosh....we're not doing it for you.

But, as to why MB are doing it, and what test results and info they have from these cranks.....well, only they can tell you that....but Mark doesnt produce random bits on a whim, he puts out good stuff (and lots of it) so if this is an option he wants to pursue, you can bet there's a good reason for it. Im sure his HPC cranks are the right crank for one type of engine, and his LPC cranks are right for another....but if you're going to better the best...who better to do it?

Its just nice to see that Sean and i arent on our own with the crank thing.

[sean brady scooters]

actually ,we have known for quite a while........that we were not on our own with this........................
quite a few other clever folk have had similar cranks for lambos done by me with excellant results.............

[J1MS]

Even on a near standard TS1 a small differance can be felt in response (I think) as my own Rally going TS now has a full circle crank fitted, its been in for a little over 1000 miles now "But vibration is alot worse" below 4000 rpm on the full circle crank...
It picks up a little quicker than it did with the old standard type crank (which was a Taffspeed 110mm Yam Rod Indian Crank Webbs), pulling a little stronger from lower down the rev range... I thought my low reving setup of my near standard TS would suit a Higher Primary Compression... Even had the crank checked twice, its trued up well enough, just must be a little out of ballance, which isnt good cus as mentioned in a previous post out of balance cranks cost power that should be propelling the scooter forward instead it causes vibration which is absorbed by the scooter... the old crank will go back in with some old school Balsa wood and araldite... Old sKool rocks...

But there are good arguments for and against HPC & LPC...

[sean brady scooters]

come on folks...............open your mind............
vespa cranks( rotary valve) are inherantly by design lpc..............
and when cut back to tune are even more so...............
and when further modified to accomodate reed valve induction are yet even more so..........................
and combined with crankcase mods on inlet ports.........even again more so...............
but some how..........do they not only manage to run at all ...............yet run really/really well............producing lots of power and torque...............
and in all cases very smoothly.................

[Diablo]

For me the Vespa is a bad example to use in the case for LPC because I think the gains come from getting the gas past the crank and not being obstructed by it rather than lowering primary compresion or rotating mass.
I do agree about vibration though Sean as Harry does ones for me very similar to yours and they are very smooth.
The trouble here is that direct comparisons are going to be difficult because I suspect that for either HPC or LPC to work at its best it needs to be mated to and expansion.
Broady doesn't do things for nothing though so I for one have an open mind. Not forking out for one to find out for myself though

[J1MS]

The theories for primary compressions to work well, altered when reedvalves were fitted.... But Old sKool tuning has been passed down "its done that way cus it works" is what you are told or read in published articles... But over time theorys alter and oppinions change and new formulas are applied to old technology and old theorys are applied to new technology... This is what pushes the limits forward....

[ralph95]

Really!! So why will this type of crank provide more power at high rpm then? Less mass? I think some people have strange ideas on primary compression. In fact as Adam said above no one had even thought about it until that article. Now we are seeing cranks like this appearing because the tuners out there think that this is what is best to try to achieve this desired low primary. Can someone explain low primary compression theory because up till recently everyone was padding cranks!

not everybody tony red herrings spring to mind