Scooterotica

Group 4 bottom end




Edit by drunkmunkey6969: After J posted pic above, Canbus posted this response, which i deleted by mistake whilst tidying up some threads:

CANbus wrote:Always admired people that can do this and make it look good, but what’s the objective, to make the transfer as big as possible, as smooth as possible, to match the transfers in the cyl block, do they have to be symmetrical Can they be oversized to the cyl block?

CANbus wrote:Always admired people that can do this and make it look good, but what’s the objective, to make the transfer as big as possible, as smooth as possible, to match the transfers in the cyl block, do they have to be symmetrical Can they be oversized to the cyl block?

this is not referring to jasons cases but case porting in general


this is a really good question Question everything!
its not until its broken down to the bare bones that useful answers come out so to add further

Q1 looking good is there a direct relationship between what looks good and what produces good performance ,do they look good because its what is expected
Q2 objectives of porting the crankcase,is it to sell a service,is it to provide a performance increase,is it because everyone else does it so it must be worthwhile scenario,or is it because someone has actually ported a crankcase with no other mods and measured an improvement in performance in a back to back performance test????
Q3 big transfers? why not make them smaller ? do we know that making transfers bigger is better or is it as per q2
Q4 smooth transfers is smooth/polished/textured/rough cast better or worse is it polished because others do or because its known 100% that a polished surface is better?
Q5 oversized to cylinder or undersize to cylinder

then what effect does the induction type on the chosen porting method have ,be it piston port/cylinder reed/or crankcase reed lambretta cylinders

also the exhaust system planned plays a very big role

OMG Darrell ,you must be related to Tony ...as he has the same way as you in answering questions
lots of questions back in a knowelegable sort of way but of no real help to us mortals lol

i intend to reply but i like to promote discussion first and create thought process from others then i might learn something too,my answers will only be my views so wont always be relevent to all engine types
i recently did the same exercise with eden planting seeds and asking batches of smaller questions and he came up with the same answer himself that i would have given him,because he thought it out im sure he will remember it forever and has a much greater understanding of the relationship between transfer duct and window now,or perhaps he may think my explanation was bull

yes yes whatever ,just cut the crap and just give us the low down then lol

the lowdown is that if a modification to the crankcase cannot be verified as providing a positive effect and is purely speculation then it should be left unmodified.
whats your thoughts ,2 way street and all

fair comment ,but then why do modern 2 strokes /crossers etc have such big /humongous ports ?

transfer ports would normally taper down the length of the tract so I would have thought to feed the transfers the cross sectional area of the feeds in the case should be slightly greater or at least equal to the combined initial cross section of the feeds; and I would think satin finish would be better than polished; if only to prevent pooling?

muppet,

cases are huge because the cylinders have huge transfer ducts/and the transfer ports in the bore are fully developed without restrictions imposed by stud locations, quite often designed for higher operating rpm than a typical lambretta and the very long stroke (current 250,s)create very deep ports as well as very wide ports
if you take a cast of the transfer duct there not as big as they first appear and the size is a neccessary requirement to achive the best duct shape

lol ,just look at any 125 cc motor ,...gagiva /apprilia etc ...they are twice the size of the biggest lamby ports