Scooterotica

i once saw a mallossi barrel for an italjet dragster that a mate had opend the transfers, they were huge, he also seid it wouldnt run right and it was that unridable they couldnt run it up on the Dyno even, he then showed me one that Ryan Saxilby had done and the transfers were a lot smaller, that one was about 30 horse power and ran sweet as,,,, bigger isnt always better it seems,,

also i thought everyone knew its rough in and smove out ,,, well thats what i thought anyway

i wonder if its not so important to have hage transfers at the base, but a good flow through the transfers as the volume of fuel in the crankcase is compressed by the downward stroke of the piston, and pushed up the port

is the same amount of charge forced into the combustion chamber whether the transfers are tapered or not - as long as the transfer is smooth without resstrictions??????

wouldnt another port allowing more transfer area in the bore be better? but then again it needs to fire into the chamber and not down into the exhaust port........

OK, this seems to be the dullest game of forum post ping pong i've ever seen, so whilst you guys p155 up each others legs, i'll try to add something of my own to try and help other forum members get something out of it....no idea if it will be any less interesting but here goes:

As far as crankcase porting around the transfers goes, here's my take on the subject:

We have mixture in the crankcase that needs TRANSFERING into the cylinder, so we have a volume of gasses in there including everything below piston level at TDC, leading right back to the reeds/or inlet port. As the piston lowers PC starts to compress that cc of gasses into something we wish to squash into the cylinder area, right up until the transfers start to open, and then shoot that compressed gas through the transfer/boost ports into the cylinder (where secondary CR will squash it again before combustion). How the gasses get through that tract/process efficiently is another matter that i will come to next, but before i do, lets think about what just happened.....

A volume of gasses has been drawn into the crankcase, as the piston comes downwards from TDC it compresses a large volume of gasses into a slightly smaller volume of gas (PC) the exhaust port opens first to allow previously burnt gasses to be expelled and the timing between that and the transfer ports opening is called the blow-down timing. This timing needs to be sufficient to allow the pressure of the incoming transfer charge to be higher than the pressure in the cylinder, so the fresh gasses can TRANSFER effectively. So as the transfer windows open in the cylinder the gas will start to move from the transfers and enter the cylinder........now depending on lots of things, such as blow down timing, the draw of the pipe, primary compression, port time/areas angle of entry and so on, this will dictate how efficiently we transfer the gasses below the piston in the crankcase area up to the cylinder area above the piston for the next cycle of combustion.

Now we have the basics, how do we relate that to crankcase porting.....well we have a limited time/area in which to transfer the gasses from A to B and everything that goes on in that process has to match the rest of the engine cycle so that harmony is produced over the desired rev range. But in addition to that, we have to also think about the shortcomings of Lambretta design and how we integrate that into the process.

So think about the spigot/transfer window in the crankcase when piston is at TDC, it is open to its max, but even so its still not very large when compared to a modern tuned 125 that produces 33+ bhp....but even more so....when the piston lowers and the cylinder transfers first crack open to their 'most open area' at the upper end of the stroke, most spigots are covering the possible area of the window down in the crankcase, and furthermore....as the piston reaches BDC the piston skirt around the gudgeon pin almost completely closes that transfer window......thus limiting availability of gasses to be drawn up be the transfer cycle/pipe etc. So in this instance, benefit can be found by enlarging that area in the crankcase by enlarging the transfer ports in the casings/cylinder spigot/piston skirt/cylinder transfer windows.....thus maximizing the available route that the charge can take up to the cylinder. Whilst being careful not to over-enlarge the area, thus reducing velocity into the cylinder:- everything has an upper and lower level of benefit, one figure can be too high, whilst if you go too far in the other direction the figure will be too low......both will effect the results in a negative manner and reduce performance. But most importantly, these things have to been done in conjunction with the rest of the motor/components, in relation to your desired tune and rev range. So you might not need to enlarge crankcase transfers on one engine/carb/pipe/tune combination, yet you would on another....even maybe with identical cylinder kits.....DEPENDING ON WHAT PIPE/CARB/COMPONENETS/REV RANGE/BHP/TQ FIGURES YOU ARE WANTING TO ACHIEVE!

Consider also, the addition of a reed valve over the piston port version of this, you can add a third transfer port to the casings at the back for additional charge to be routed up into the cylinder, so not only then can you get more charge up into the cylinder and increase power that way, but also the additional port will create what is know as a 'schnurle loop' to help scavenge the cylinder/head gasses more efficiently. In its simplest terms, on a two port motor the transfer ports in the cylinder direct the gasses across the piston crown towards each other (mostly) where they collide and then get pushed up by the piston into the head for combustion. When a 3rd port is added at the back of the cylinder (known as a boost port) this third port is angled upwards at a steep angle compared to the main transfers and so it not only helps to transfer extra gasses from the crankcase into the cylinder for combustion, but it also helps to create a 'loop' of gasses in the cylinder by drawing the incoming charge upwards into the head to scavenge out burnt gasses, thus ensuring the next charge is as fresh as possible. This is why entry angles/areas/duration of transfer are so important. Then the pipe can also draw out burnt gasses, and some of the fresh charge will follow also, but as the return wave of the pipe comes from the tuned length/cone angle etc it will return that fresh charge into the exhaust port and stuff it back into the cylinder.....so a strong draw on the pipe is very good, if it is also returned well and stuffed back into the exhaust (inlet? ;o))) port as this will maximise charge in the cylinder over the rev range the pipe is designed to work at.

So once the widths/areas of the crankase transfers have been enlarged and the the spigot/piston skirt matched, hopefully in relation to relative port timings, angle of entry, compression ratios, inlet tract lengths, carb sizes, pipe volume/lengths/cone angles, and all the other considerations of a variable flask and so on......you will have something of worth.

But of course in order to do all that, you would really need to know what you were doing, so until then, i'll just carve mahooosive holes in everything and run it up the dyno.......

jonny snatchsniffer wrote:i dont reckon that mahoosive transfers at the bottom of the barrel will make too much difference, say you had a ts1 barrel and dynod it as is and then made the barrel transfers as big as the barrel/cases will allow without weld you will gain very little if anything and the time doing so would be better spent on getting the exhaust port a good shape
does the angle of taper in the transfer duct have an optimum angle ? as if you speed the gasses to much or little will it effect how much charge goes where at a given rpm

Bigger crankcase transfers would certainly make a BIG difference, but in context to the rest of the tune and what you are trying to achieve. Its not something you would simply do on its own with no thought to the rest of the motor.

lifes a drag wrote:,,,, bigger isnt always better it seems,,

That at least is VERY true, ALL modifications have to be in context to the rest of the tune, there are optimum upper and lower figures for everything on the two stroke motor, and they can vary wildly depending on what sort of motor you are trying to produce and with what components. That's the mind bending thing about two strokes, there are so many variables and its very difficult to isolate one set rule that covers all applications. You may find that Italjet transfers are already huge by comparison to say Lambretta small block casings, so opening the Italjet ones up would actually conceivably make things worse.......so in that instance it might be a bad thing. But it might be the correct thing to do in other applications! ;o))

all i can say is no matter what you do to the case/cylinder ....if the pipe is s**t its a waste of time

Whats the exhaust duration eden?

drunkmunkey6969 wrote:

jonny snatchsniffer wrote:i dont reckon that mahoosive transfers at the bottom of the barrel will make too much difference, say you had a ts1 barrel and dynod it as is and then made the barrel transfers as big as the barrel/cases will allow without weld you will gain very little if anything and the time doing so would be better spent on getting the exhaust port a good shape
does the angle of taper in the transfer duct have an optimum angle ? as if you speed the gasses to much or little will it effect how much charge goes where at a given rpm

Bigger crankcase transfers would certainly make a BIG difference, but in context to the rest of the tune and what you are trying to achieve. Its not something you would simply do on its own with no thought to the rest of the motor.

im just talking about working with what you have, obviously if you started from scratch you wouldnt start with the wanky lammy transfers that are there, but thats what you have so have to optimise them,i wouldnt waste my time just doing the transfers either

drunkmunkey6969 wrote:

jonny snatchsniffer wrote:i dont reckon that mahoosive transfers at the bottom of the barrel will make too much difference, say you had a ts1 barrel and dynod it as is and then made the barrel transfers as big as the barrel/cases will allow without weld you will gain very little if anything and the time doing so would be better spent on getting the exhaust port a good shape
does the angle of taper in the transfer duct have an optimum angle ? as if you speed the gasses to much or little will it effect how much charge goes where at a given rpm

Bigger crankcase transfers would certainly make a BIG difference, but in context to the rest of the tune and what you are trying to achieve. Its not something you would simply do on its own with no thought to the rest of the motor.

thats a bold statement to make ,have you conducted a singular test to evaluate these results std transfers v enlarged transfers if not it would make for an interesting comparison

what i have done now is a 225 ts1 and a 242 ts1 with almost standard transfers225 and with huge welded transfers242 there graphs are on the forum both on same pipes/carbs/reeds/c.r/port specs except ex -3 degrees /rod length and the 225 showed higher peak but lower torque ,the torque was down due to engine size on those results id think smaller were better but is not conclusive

have you read my comment about transfer window size constantly changing
in my example a 20mm wide transfer at 1mm open is 20 sq mm the std duct entry is 600sqmm so the ducts entry is 30 times bigger !!
many modern race engines have larger transfer duct entrys but have you seen the ultimate 125 gp motors transfer ducts? approx 1 to 1 ratio


ive done it on a few development motors not lambretta (aprilia rs125/cobra 50 mx/derbi gpr50/minarelli am6/ktm50 and found the effort put in is not worth the results in fact the results were no different before and after so for these motors i dont bother no more
i once conducted a test on the derbi 50 of 7 different reed blocks and 5 different petals for the std reed block to find out that the standard reed block and standard reed petals gave the best results i can therefore say that on that engine spec the std reed and block provided best performance and money spent on any of the aftermarket reeds or blocks was money wasted,i passed this info to mb and you now have it in his latest reed valve conversion kits for the piston port lamby,i mention this as an example that through testing and evaluation a conclusion can be made.

drunkmunkey6969 wrote:

lifes a drag wrote:,,,, bigger isnt always better it seems,,

That at least is VERY true, ALL modifications have to be in context to the rest of the tune, there are optimum upper and lower figures for everything on the two stroke motor, and they can vary wildly depending on what sort of motor you are trying to produce and with what components. That's the mind bending thing about two strokes, there are so many variables and its very difficult to isolate one set rule that covers all applications. You may find that Italjet transfers are already huge by comparison to say Lambretta small block casings, so opening the Italjet ones up would actually conceivably make things worse.......so in that instance it might be a bad thing. But it might be the correct thing to do in other applications! ;o))

the italjet/gilera transfers on the large block piaggio motors are very narrow and are approx the same size as the port windows despite this at 172cc single ex port and 5 transfers and a low 176 degrees the kit has nothing better going for it than a ts1 ,with a good pipe make around 22-24bhp at 7500-8000 rpm on a 25mm carb