Lambretta Boost Port & Cylinder Scavenging

[Rich_T]

You sound disappointed Chris, were you hoping for it to break out into a fisting fight?

[carlos fandango]

fisting fight?

[drunkmunkey6969]

Yes Adam, the gasses do of course diverge, and the combined angles/forces give the resulting loop and purge. And you are right, the boost port is not to be considered as a singular item, I'm merely highlighting that particular shortcoming. Another one of which in my opinion is the fact that it does, as you pointed out, open later/last......on my cylinders I change that so it opens first.

on the std ts1 the boost port is positioned/duration timed to open last but in its working enviroment will flow first as the primary and secondary are subjected to blowdown flow reversal.
at the time of transfer opening exhaust blow down is continuing and will back flow down the transfers especially more so on blowdown limited cylinder designs and port durations as are present in scooter cylinders this will drag the spent charge across the crown to the boost (now ex port as it will evacuate out of every hole it is offered)

I suppose one of the mistakes i've made is isolating a single area of the scavenging process to discuss, which makes the post appear as if altering the angle is something i would consider on its own.....which i would not. So....just to tease this post a step further Darrell......what would your (speculative and un-confirmed without testing) opinion be on altering the boost port angle along with some other modifications.

For speculations sake, lets make a theoretical example. Suppose we were fettling a TS1 cylinder and we wanted to increase ex blow down time/area to reduce trans blow back....so we raised the exhaust and widened it a tad (above trans opening). Maybe also we wanted to re-angle the boost port....but not raise it, so we back filled it with dev-con (or other technique) and ported to suit (say changing angle from 45 to 60) and fitted a centre plug head to better suit the new port angle. But then knowing we had reduced trans area slightly by changing boost angle......we brought some of this area back by increasing boost port width. Then also widened the aux trans and re-angled them slightly..........

So....in that theoretical example if you could have either version....would you say that the cylinder would work best with a standard 45 degree boost or a 60 degree boost? (of course this is theoretical, un-tested and speculative......but just for kicks)

[drunkmunkey6969]

I really do not think you are going to meaningfull scratch the surface of this topic with out some serious investment. If I were to consider how best to go about that it would certainly be a CFD programe (not cheap, but much cheaper than building and buying test equipment). In the end, it will all boil down to hypothosis and what people have done previously; which isn't a bad thing but don't expect a clear winner, if there were, there'd only be one two stroke tuning book.

i agree, only thing to do for those with time/money and facilitys to do so is start testing and see what results emerge,this represents a large investment in many ways which carrys well onto a later post

Ahhh.....time and money....i fall short on both counts. However as and when i get the opportunity, i do lik eto test stuff on my own bike, to try and increase my working knowledge, its about as much as i have the time/money to do.

[drunkmunkey6969]

Dan do you remember "Tom the tuner" who you met at Elvington.

He rubbishes the TS1 saying the boost port angle is wrong. He says that the Harry Barlow TS1 alike kit has the angle right and "works". He said this at Wicksteed last sunday whilst giving me one of his "lectures".

be interesting if you had continued questioning why the ts1 is wrong and why the new one is correct and if there was any test data to substantiate it
a lot of statements are merely speculation until tested,as well as my own i might add

If you know Tom, or ever meet him....feel free to have the conversation. Personally I'd rather stick pins in my eyes.

I'm not saying he hasn't got anything worth hearing.............its just the delivery that pains me.

[drunkmunkey6969]

For sure Ric. And thats what I said. This takes us back to the pipe design. Thats the only thing has changed that will affect really... So... someone says "thats all wrong" well... they maybe right... today.... but when it was designed, maybe not at all.

Its not a case of who is 'right' and who is 'wrong'.....cylinder port scavenging techniques can be a very subjective item, which is what makes conversations like this so interesting. And its certainly not a case of saying TS didn't know what he was doing, not at all.... despite possible difficult instruction from his employers, or what he did/didnt have to work with at the time. The aim of the thread is to analyse where we are at today, because as we select pipes, pistons, porting techniques and so on, we are only concerned with what is available today and the power we are creating today.....and hopefully debates like this will tease out more and more collaborative opinions in order to help us to continue to achieve those goals. That is my goal, as its always been with Scooterotica....to share information, to analyse and discuss. Hopefully then, we all benefit.

Not like the days of yester-year..... cloak and dagger tuning techniques, grinding details of jets....the 'dark art' of tuning and jetting.......b@11@x to that bullshit i say! Which other site photographed dozens of tuned cylinders and supplied port maps, port widths, dyno charts and jetting examples? Complimented with a variety of information (ever growing) to help improve things even further. Most tuners wont even let you see inside a cylinder they have ported.....we photograph them and publish them! lol And if you request it, when i dyno scoots, i include the final jetting spec on the graph!

dont think ive seen anywhere on here photo,s/port maps/widths/dyno charts/jetting specs for any tuned engines other than edens 240
Really? Look harder. lol

To be fair, i've hardly done any port maps or cylinder pics in the last year or two, and you've not been here that long. Im not even sure what eden has the forum 'auto prune' set to so not sure the posts would still be here if you did look for them. But there are still plenty of images, dyno graphs, jetting specs scatteretd accross the forum....maybe not just all in pne place together. We had a different version of this forum 2007-2009 and most stuff to do with port maps and photos were on there. We also started in 2007 with a static website.......when my tuning terminology was to raise a port in mm rather than degrees, or port/area........2007 was when i had no idea how much i didnt know about tuning, i now firmly know how little i know.....and enjoy the pursuit of knowledge all the more! In fact the more i realise the less i know, the happier i am

I think its a shame that most tuners who are actually good at what they do remain aloof and don't want to share. Its appears to be a terribly vain and self-serving way of trying to place themselves in some sort of higher-echelon (legends in their own minds) wanting to distance themselves from anyone who takes a practical interest in tuning as if they are beneath them. Happy to tell you what you DONT know, but not willing to discuss what they purport to know. But this backward view of not discussing anything publicly is usually more to do with fear of criticism......these people are often not willing to put their theory's up for debate, or share their working knowledge. Don't get me wrong, every year brings new development and new discoveries that keep the top people....at the top, and i'm certainly not suggestion anyone would discuss these finer details, not for one second. But there are generally speaking, very well known, understood and published tuning techniques....available to all and sundry in any tuning book, but most of the 'high end' tuners wont even chance a public discussion on these topics, or publish a picture of similar work they have done to explain the how/why.......shame really.

i agree Dan theres many who spend more time visiting sites placing adverts for there services and products but never contribute to discussions or share any info take a look down your members list click on some names and check there posts and it paints a picture of there intent ,im in the trade and often contribute but havent advertised my services
There are direct adverts and indirect adverts....you do not advertise directly. Your results are your adverts, its why you post the graphs, and i mean that is a positive way. Full respect to you for getting those results and being in that position.....

[drunkmunkey6969]

Wot benefit is gained by having the boost port open before or at the same time as the main and secondary transfer ports??

over the years many methods have been adopted,and during the honda rs125/250 years of production have moved above and below suggesting on them theres pro,s and cons to both but these cylinders have huge blow down area and long ex durations
all recent race cylinders run the boost low and is my preferred placement on a blow down limited cylinder too ,my thoughts are id rather back flow a little spent charge/ex gas into the nearest primary at the front cylinder wall and get it back out the ex port again without mixing it across the full length of bore contaminating fresh charge from all transfers whilst travelling across to blow down a high boost port

That is a good point, well illustrated Darrell. And makes complete sense ref the nearest primary rather than mixing across the full length of the bore. You have a great way of putting down on the keyboard a fantastic 3D visual of the cylinder.....not something i find easy to illustrate when typing.

[drunkmunkey6969]

Is that it!!!!!!!!! Lol

No....that is NEVER 'it'.

I find 2T tuning to have no....'it'......'it' just goes on, changes, evolves and hopefully improves

[Special X]

Dan . . . . . I would also rather have done some self harming than had the conversation with Tom, but I was helping out on Casa Corrados stall and had to be polite with customers (He does buy stuff from time to time)

I'll go on record as saying I'd rather him talk to you than me.

I'd love a chat with tuner Darrell though

[Darrell Taylor]

never met tom but i wont let previous statements cloud my opinion as its good to take people as you find them personally.

in reality the time and money testing comes without the spend as the years go by more and more tests are done and a good understanding of specific changes and there end results begin to form a working practice that you follow/work to and as a good friend said a tuner working without a dyno to measure results is like a builder without a tape measure,the exception being the drag strip which makes for probably the best dyno around

the boost port on a ts1 ive never tested or done changes to ,i leave them std or sometimes raise a little depending on stroke or cylinder position,but as i said previously which if you read again, is do take consideration of the pistons influence and the floor angle or curvature of the transfer duct as well as the direction of flow from the reed and loop scavenge feeds from the case,i dont cut a boost port in the case and cylinder base as a delivery method already exists from the reed and via piston windows in a loop thru method from crankcase to reed box to boost

i started drawing up a 3d visual on paint last night to put up but didnt get it finished

when spending 8 hours+ tuning a cylinder and just looking at it ,thinking about how it flows and its various processes/interactions is time that can be very useful ,just sitting down with a cylinder and more importantly a piston and sliding it to various positions talking yourself thru the various events and how they interact on each other will teach you more than any book does and allows you to get creative ,unfortunately the more you pick up every day and learn new things the more difficult it becomes and each time you go to cut a port your constantly weighing up pro,s vs cons of your actions