Cubes, cubes, I want more cubes!!!

[RManson]

I would take a long, hard look at the current aftermarket case offerings and figure out which one can accommodate a 300cc+ cylinder setup. I would keep the stroke around 64mm unless the case is designed for larger. That would limit you to a bore under 80mm unless you want to upset the typical dimension formula (bore V stroke). A long rod would be nice as well.

Look at what Rich Taylor at Gran Turismo is doing with his new case and the Rotax cylinder similar to what I used (76x64 w/ 125mm rod). It's water cooled but it gives you an idea as to what's possible.

I can only speak to my experience with the setup (not sure he's got his up and running) but it pulls 3rd gear through the Malibu canyons of Los Angeles all day long. I was very surprised and in fact thought I was in 3rd gear when in 4th and 2nd when in 3rd a number of times when it came to climbing hills, etc. Gearing is 15x46 with a Jet200 gear box, so nothing exotic. Pulls 70mph+ on the highway at 3/4 throttle at 4,500rpm. Runs 165F degrees all day long.

Of course, this is a liquid cooled solution, but a real world answer to consider. With all the new cases and cranks available, I would think an RB250 on steroids would be a very real possibility that could present similar results.

Good luck!

-Ryan

[GeorgeS]

Is there an estimate of when to convert from air to LC on a lambretta engine based on cc? I mean, when is air cooling no longer sufficient on larger engines?

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[Adam_Winstone]

Ryan,

Thanks for your feedback. I've already exchanged a number of emails with Richard and do like what he is doing but I'd like to stick with air cooled to suit my own likes.

Yes, the current casings do interest me for the very reason that I've experienced issues with warping when heavily welding original casings for long stroke machining. As it stands 64 stroke is already doable so I'd ideally want an increase on this. Bore and barrel to suit is a current head scratcher and constraint for me and stud repositioning is something that needs doing... again taking me back to the small block to big block development that Innocenti undertook.

My current 72 x 65 runs a 125mm rod and configures well.


GeorgeS,

Not sure but Ron Moss's increase of barrel and head fin cooling area is something that might be employed to advantage.


Cheers for now.

Adam

[holty]

there is no replacement for displacement, i have gone down this route myself, firstly with my yamaha hybrid, 374cc lc twin, 55bhp as docile as can be at low revs, will even pull 30mph in 6th gear, but get it in the powerband and its dangerous, i get the best of both worlds. my quest is much like yours adam and i have gone down a similar route to ryan with my rotax engine, 64 stroke 76mm piston, its nearly ready to start up, i would go down the gt case if i were to build another, i am pretty sure they have a lot of meat around the area next to the mag flange so you could make a massive crank to fit in there, martin at chiselspeed built mine from scratch so im pretty sure he could scale it up for a longer stroke, or make use of one from a donor engine, as for barrel you could have a look at large capacity trials bikes, you might find something that can be used although realy large air cooled barrels seem to have massive fins, also inlet position can be a no go, but case induction is always an option as you have already done, the idea is good, getting all the parts that you need to make it all work can be a pain, but i hope you have a go at it, and do a build thread so we can see how you work it all out, good luck in your search for more displacement,
holty

[johnny650]

I'd say it could be useful to approach this from the opposite direction and consider gearing first if low rpm cruising touring speed is what you're after.
Have you considered a 5x speed box ?

Might be worth looking at a gear chart and working out an ideal gearbox to suit your requirements then look at what sort of engine you need to achieve the performance you need at the any given rpm /speed

https://www.google.co.uk/url?sa=t&rct=j ... XQBsZ9z6C-

[Adam_Winstone]

^... I like the way you're thinking as my current 260 runs a Cyclone for that very reason.

[johnny650]

more cubes ...? stick a Evo400 in there and hang on
33bhp 100mph

[Darrell Taylor]

what would you like it to do the most of in order of preferance as the final design can be focussed on that as your no1 requirenent and the other elements will be as they will be as a result . ps the top speed quoted will dictate the hp requirement , i feel 80-85 is ideal maximum on the 4 speed without spoiling the lower gears that you spend a greater % of riding using
1 more point about rpm ,,, an engine that peaks at 6k sounds like its being tortured at 7k if the power nosedives after peak yet a pipe that peaks at 9k can feel / sound sweet as at 7k

[Darrell Taylor]

also big pistons and weights vibrate a lot more so without a specific balanced crank will suffer the bigger/heavier the piston is , motorcycle engines have countered this for years with balance shafts even when appropriate crank and piston design has been applied it still hasnt succeeded without a balance shaft.
i have some parts on the shelf for a new build that uses a very long rod yet light and a very very light 72 mm piston that i hope to drop back onto as an experimental engine some time ,but wont be soon.

[RManson]

Is there an estimate of when to convert from air to LC on a lambretta engine based on cc? I mean, when is air cooling no longer sufficient on larger engines?

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There sure are a lot of 1600+cc air cooled Volkswagens on the road, so I'm not sure there is a limit as to when it's necessary to go liquid cooled, but I would imagine space and air flow are a big factor. There are also a lot of big displacement Harley-Davidsons out there that rely on air cooling as well. Apples and oranges in a way, but my point illustrates that you can build big engines and keep them cool without going to a liquid cooled scenario.

I think there will be a point in an air cooled Lambretta setup where the cylinder/head/shrouding fouls the frame and becomes a problem, preventing proper cooling once the bore gets too big. Unless the case is machined with an angle to point the top end toward the ground slightly in order to clear the frame tube, that is.

But, you're still robbing power by using a fan to drive air over the top end and at some point, that fan will probably need to be increased in size or the blades redesigned similar to what a turbo/centrifugal supercharger uses. Which is a whole 'nother conversation.

Look at most modern cars, as they use an electric fan to draw air through the radiator as opposed to the old method of a mechanical fan attached to the engine, which robbed power. An electric cooling fan on a air-cooled Lambretta could be a neat idea and allow a light flywheel to be used. Of course you'd need a decent charging system that could provide the needed power, of which there are already a few on the market. Couple the fan with a thermoswitch and it could shut itself on/off as needed, saving power and wear and tear on the stator, win/win in that regards.

The other item that no one has mentioned yet and one that I've encountered is the fact that a larger bore cylinder, in general, will require a larger pipe, at least in the belly section. For example, on my Rotax setup, the math calls for a belly that is larger than the current pipe, which already drags when ridden with any kind of aggression. So, there's a limitation there as well. That is, unless you want to redirect the pipe so that the belly isn't under the runners, which at that point, why bother with aesthetics at all?!

Anyhow, food for thought and an interesting topic for sure.

-Ryan