Lambretta GP 500
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sean brady scooters
- Dealer
- Posts: 2040
- Joined: Mon Jan 05, 2009 12:09 pm
- Location: Ripon, North Yorkshire
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further more............surely it is no coincidence that the use of boost bottles was dropped,as powervalve exhaust systems came in............?
Sean Brady Scooters - 01765 690 698
Thats what I was trying to find out Sean, as its sort of cylinder volume or slightly greater= the boost bottle volume... From what I have read.... but I wanted to know if it was at atmospheric pressure, or under velocity of the venturi pressure... I would have thought it would be under atmospheric, then expanding a little beyond this but only slightly... haven't got any to measure myself and saw this... Opportunity was too good to miss... and 500 cc should slightly iron out any little errors by a bigger margin... 
.. I like to understand how and why... I haven't given these Boost bottles much thought while running the TS, as they seem to be less affected than piston ported engines, and my only piston port engine runs a standard air box... but theres plenty of other factors in here, but just having a look at how and why as I didn't fully understand the theory, and still don't... 
.. I like to understand how and why... I haven't given these Boost bottles much thought while running the TS, as they seem to be less affected than piston ported engines, and my only piston port engine runs a standard air box... but theres plenty of other factors in here, but just having a look at how and why as I didn't fully understand the theory, and still don't... -
RinB
- Posts: 317
- Joined: Mon Jan 05, 2009 1:43 pm
- Main scooter: Reflections in Blue
- Location: Grimsby
- Contact:
Oh I love these kind of questions 
I can give you some insight into boost bottles
The main criteria for boost bottle design is that the bottle be at least as big as the displacement of the cylinder
Designed to work at a certain rev range.
The hose be at least as big as the throttle opening at the intended RPM.
As for pressure well you need to use the speed of sound at you elevation typically 340m/s as this alters the higher
you go.
As for the formula
It is a precise art
Oh as for keeping front end down put front mud guard upside down and pore melted lead into it
let it cool drill tap screws to keep in place
I can give you some insight into boost bottles
The main criteria for boost bottle design is that the bottle be at least as big as the displacement of the cylinder
Designed to work at a certain rev range.
The hose be at least as big as the throttle opening at the intended RPM.
As for pressure well you need to use the speed of sound at you elevation typically 340m/s as this alters the higher
you go.
As for the formula
It is a precise art
Oh as for keeping front end down put front mud guard upside down and pore melted lead into it
let it cool drill tap screws to keep in place
If its made of Metal Fettle it !!
I was going to use 1100 ft/sec as the inlet resonance, but you say its the speed of sound ..?? have got any literature to hand as I would have to google it to try and get a number... but would you know this figure so I can substitut it in as a Ft/sec ....Thanks.RinB wrote:Oh I love these kind of questions
I can give you some insight into boost bottles
The main criteria for boost bottle design is that the bottle be at least as big as the displacement of the cylinder
Designed to work at a certain rev range.
The hose be at least as big as the throttle opening at the intended RPM.
As for pressure well you need to use the speed of sound at you elevation typically 340m/s as this alters the higher
you go.
As for the formula
It is a precise art
Oh as for keeping front end down put front mud guard upside down and pore melted lead into it
let it cool drill tap screws to keep in place
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RinB
- Posts: 317
- Joined: Mon Jan 05, 2009 1:43 pm
- Main scooter: Reflections in Blue
- Location: Grimsby
- Contact:
Actural speed of sound
In dry air at 20 °C (68 °F), the speed of sound is 343 meters per second (1,125 ft/s)
PM email & ill send you a spreadsheet with some calcs on
In dry air at 20 °C (68 °F), the speed of sound is 343 meters per second (1,125 ft/s)
PM email & ill send you a spreadsheet with some calcs on
If its made of Metal Fettle it !!
There was already an omission on my behalf as I hadn't thought of temperature as part of the equationRinB wrote:Actural speed of sound
In dry air at 20 °C (68 °F), the speed of sound is 343 meters per second (1,125 ft/s)
PM email & ill send you a spreadsheet with some calcs on
Hi all, just measured the volume of the boost bottle and it is 300ml. The bottle itself is a very ridged abs plastic. I also shone a maglite with a fiber optic tip in to it. It is completely empty ie no bladder etc.
Seems it dosnt have to expand at all it just has to be big enough to absorbe some of the pressure resulting from the port closure. Which it does by taking a little of the charge from the inlet tract. To feed back on the next negative pulse from the crank case as the piston opens. Most of the theory (few formulas are coming to light) seems to ignore the exhaust and porting arangement as it's not a factor once a given engine at a given rpm, as only the reonance in the inlet and it's contributors seem to be in the basic equation.
Not saying it couldn't be altered by changing other factors it would obviously but when this is done the resonance in the inlet is sill mainly governed from the piston backwards to the bell mouth. But I am going to have another look at the spread sheet I was given and a couple of other small bits of info that I have looked up. But the main principle of the boost bottle seems to be a pressure bleed but so as not to loose the charge by say just fitting a one way bleed.. Instead it reverses to be drawn back in to the Inlet..
the size & length of the feed tube to the boost bottle is critical, also it seems the size of the bottle has to be big enough to accept one cylinders worth of charge to prevent the bottle pressure exceeding the slide apatures resistance otherwise the boost bottle could pressurise the system before the piston opens the port further adding to the problem of the charge returning. Once air speed increases the charge is pushed into the port by the ramming effects of the venturi and the charg dosnt reverse far enough to be a problemand once the ports resistance is overcome the boost bottle has a lesser effect as the charge dosnt enter omming back from the piston but is comming from the open end of the carb. This is a little of the principle of the boost bottle... Or what I am being led to believe from the little I have read. Not had the chance to work out any formula and it's not been easy finding any.
Not saying it couldn't be altered by changing other factors it would obviously but when this is done the resonance in the inlet is sill mainly governed from the piston backwards to the bell mouth. But I am going to have another look at the spread sheet I was given and a couple of other small bits of info that I have looked up. But the main principle of the boost bottle seems to be a pressure bleed but so as not to loose the charge by say just fitting a one way bleed.. Instead it reverses to be drawn back in to the Inlet..
the size & length of the feed tube to the boost bottle is critical, also it seems the size of the bottle has to be big enough to accept one cylinders worth of charge to prevent the bottle pressure exceeding the slide apatures resistance otherwise the boost bottle could pressurise the system before the piston opens the port further adding to the problem of the charge returning. Once air speed increases the charge is pushed into the port by the ramming effects of the venturi and the charg dosnt reverse far enough to be a problemand once the ports resistance is overcome the boost bottle has a lesser effect as the charge dosnt enter omming back from the piston but is comming from the open end of the carb. This is a little of the principle of the boost bottle... Or what I am being led to believe from the little I have read. Not had the chance to work out any formula and it's not been easy finding any.
Hi all, I will also measure the volume of the conecting hose aswell. It is a large hose with a large bore. I will do this tomorrow some time.
Hi all, just a quick update: I had a few pictures from our Frank. One of my big stumbling blocks was trying to find a new after market exhaust. Because the bike was more than 5 mins old it is had to get parts for. I had to get an exhaust made for it in the end. Pro-pipe in the states made one for me in the end. £189 including p+p. So I shipped that off to Frank for him to fit. Not an easy job he says. The panel work has been ordered and should be here with in 2 weeks. I got an order from Scootrs £400 worth. All good quality it would seem, the drops are really good, the rim fits really well. I had all the graphic done at Scooter Graphics, cheep as, as well. I should get the scoot back from Frank before Xmas I hope, in a rolling chassis, forks fitted with double anti dive discs. Then starts the long slow re-build, paint , powder coat etc.
