back to the o-tuning stuff.
I've been reading lots of threads about LPC vs HPC and I must confess that on my previous works on vespa ( T5 especialy) using a flowed and tapered crank with a bolt on MRP R-block, large crankcase transfers, 6 mm packer made performances very high... I guess PC was quite lowered down and a bigger volume was avalable for fresh gaz at each circle, literaly sucked by a well designed pipe.
Just a few pics "in progress" to refresh (my) memory:
This o-tuning project is far from our T5 racer but some ideas could survive. As it's been told: 200 engines were originaly designed from 125/150 case/barrel and PC increased to a dangerous limit as cubic capacity raised too. At low revs part of the fresh gas is just thrown in the exhaust by this too high PC. Just a waste.... Reducing PC will allows gaz to scavange burnt gaz as they should do and stay in the cylinder till exhaust port shuts whatever the counter pulse given by the exhaust. Exhaust tuning will occurs later in a much usefull way...
Bigger transfers, empty space given by the LTH bolt-on reed block and a simple "non full circle" meceur crank will help reducing a bit PC and give a better torque spread all over the rev range. The 2 boost ports will also help sucking this load of gaz compressed between reeds and piston skirt. Less primary compression is more fresh gaz to be pumped by the pipe.... A good way to raise your power output on a modest 2 port iron barrel
