Lambretta Boost Port & Cylinder Scavenging

[drunkmunkey6969]

Good info there Darrell, would love to see the 3D image if you get time to finish it and post.

My Mrs thinks I'm some kind of weirdo as it happens.....I was sat in the living room one night cylinder in hand, spent a few hours trying to visualize various changes. It was clearly distracting her from watching Downton Abbey....lol, she took a pic of me and posted it in facebook.

Darrell you've seen a lot of GP what would you say is the most common angle used in boost ports that youve seen?

[drunkmunkey6969]

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

Yes, the way i 'visualize' it is that as the crown very first cracks open the boost, the angle of the piston crown + the angle of the boost will dictate flow, like a spray nozzle if you will. And the flow will fan out as it travels up the cylinder to the head and the piston continues to descend....opening the nozzle wider. But surely as the boost is only 45 degrees the and the head/bowl is offset to the rear of the cylinder, then the initial flow/spray will leave a dead spot above the boost?? And a steeper opening angle would direct the spray to that area? Do you disagree?

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

Am i wrong to say then, that when you cut 'Darrell Ports' into the casing, that you join them to the reed area via cylinder base?

The 'theory' for any change has to start somewhere. Usually it comes from working knowledge and an idea for development, before it can then be tested. We cannot hope to attain an accurate answer from just the theory, of course.....but starting with the best theory possble before cutting and testing is helpful. Thus, it seems plausable to specualte on what the best angle for the boost might be on a tuned lambretta cylinder.....45....or higher?

[Darrell Taylor]

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

Yes, the way i 'visualize' it is that as the crown very first cracks open the boost, the angle of the piston crown + the angle of the boost will dictate flow, like a spray nozzle if you will. And the flow will fan out as it travels up the cylinder to the head and the piston continues to descend....opening the nozzle wider. But surely as the boost is only 45 degrees the and the head/bowl is offset to the rear of the cylinder, then the initial flow/spray will leave a dead spot above the boost?? And a steeper opening angle would direct the spray to that area? Do you disagree?

i feel the boost flow will travel along the piston inlet face which has no angle so flow will fall halfway between that and the roof angle and as the piston is falling the angle returning nearer to the roof angle
secondary flow will push under and clear/force up boost flow further and cleanse the rear cylinder wall.
i think the examples of other cylinders may not be comparable ? case reed / entry ducts from case / dual walled ducts , are they same bore size too? as that will considerably change the variable landing point and what secondary transfer design is employed in conjunction with the boost port

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

Am i wrong to say then, that when you cut 'Darrell Ports' into the casing, that you join them to the reed area via cylinder base?

the ports i cut in the case arent any form of boyessen feed designed as a delivery method from reed to case
i simply did them as extended transfer ducts to ease/pass stored crankcase charge from the case area and between crank webs to the main transfers

The 'theory' for any change has to start somewhere. Usually it comes from working knowledge and an idea for development, before it can then be tested. We cannot hope to attain an accurate answer from just the theory, of course.....but starting with the best theory possble before cutting and testing is helpful. Thus, it seems plausable to specualte on what the best angle for the boost might be on a tuned lambretta cylinder.....45....or higher?

its the kind of question asked if you were designing a cylinder from scratch how would you design the boost...... which opens too many other variables
but on a ts1 ive left it as is ,not an area ive experimented with yet ,i have retuned many other ts1 cylinders with previously widened boost ports and had no better results than when i leave them standard