Scooterotica

the best engine ive ridden was a gt186 or maybe a 206,

either way my thoughts were that it was THE ultimate lambretta engine.....but too small

so after playing with ts1s mugellos iron barrels, i have to ask why isnt there a gt240 big block and whats the nearest thing to it in ali?

excuse me Nicky, wasn't there a big Gran Turismo? Didn't he do one for testing or sell to dealers only tipe of stuff?

Firstly, thankyou, always nice to hear.

Two problems in producing a big block GT kit.
1. 350LC pistons only go up to 66.5mm bore and a totally new piston is hellish expensive
2. Designing the barrel around a slightly modified TS250er piston or similar needs longer con rods (110mm) all adds cost to builds and reduces the flexibility of the kit.
3. There would be no clearence between the open petals and the piston in it's current configuration
4. L/H manifolds would require an aysemmetric tooling design which is twice the cost

The main problem is petal and frame clearence...oh and about 20 grand sterling.

...also, you got a problem with small blocks?

Excuse me Rich, I haven't had the pleasure of testing your kit, althou, as Cezeta said, I've just heard wonders of it.

1st. Is it true that there was a big capacity and a small capacity?
2nd Are you still selling some stock of the small capacity?

Best,

Jaime

230 ? - How about a lined Rapido barrel (not really confident of the original liner) with reed valve grafted on, 60mm crank, 115mm rod with Jap (or MB) pistons starting at say 70mm rather than 71, giving you plenty of oversizes and years n years of life outta the set-up.
Tricky n expensive but plenty of torque if tuned right with decent pipe say Taffy?

Hi,

The 206 GT kits all went on small block casings. There were no big block castings designed or made. I made some rough estimations on clearences based on what I knew from the small blocks and took a view that it would be very close to call.

Essentially, the outside pattern of a big block barrel would be the same as the small block but the internal bore larger. This means less space for the reed petals. As anyone who has looked inside the GT206 kits will tell you there were pretty F***ing tight on space at 66mm bore let alone running a 70mm piston.

Creating the extra space for a 70mm piston would involve tricks like angleing the reed valve over more (which isn't good). It all gets to be a bit too much of a compromise. Maybe I have a go at it on CAD and see what it looks like, if it worked I could rapid prototype one to see how it goes.

There are still GT186 kits left (about 30 ish) but that is it. Spares are readily available and if ever I got to the stage where I couldn't supply I'd post up details of where all the bits can be sourced.

If you went the Rapido route you could use one of the LTH reed manifolds but I don't think you'd see a performance advantage, only fuel economy. If you tried to graft on a GT type reed block onto a Rapido you'd end up either fowling the frame (unless you used a 30mm R/H manifold) or fowling the piston with the petals (as I mentioned earlier) and I think there would be all sorts or problems with the liner distorting when you cut one side of it away.

maybe the MB RT kit is your answer Nick but it doesn't have the reed valve - which Rich rightly points out brings its own issues. Is it the touring torquey nature of the GT kit that prompted the question?

soullad wrote:maybe the MB RT kit is your answer Nick but it doesn't have the reed valve - which Rich rightly points out brings its own issues. Is it the touring torquey nature of the GT kit that prompted the question?

yes the touring ability. tbh very few race their scooters and having had a road race tune i wonder why tuners let them onto the streets as they are just inpractical and a chore to ride.

the gt kit i first rode shocked me at how grunty it was, i pulled away on cobbles and had the thing in a sideways wheel spin with none of the screaming and revving you would have expected. it only ran a clubman.

im never impressed with power bands and the scooter i rode did not have one but had continuous power from tick over to about 7k. that's 7 k od useable power rather than power coming in at 6k and ending at 8k. just 2k of power.

what i dont know is what it was with the gt kit that gave this power, conservative port timings and smallish inlet and carb?

and so is something like the monza a big brother to the gt?