Author Topic: Twostroke back pressure  (Read 4287 times)

Bob Purton

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Twostroke back pressure
« on: June 07, 2006, 09:36:39 AM »
Does anyone know about the importance of exhaust back pressure on a twostroke, the question arose when I came to the piont of selecting a silencer for the old INTER. originals are not available not even to copy. The space would accommodate a compact flatish square box and the vespa scooter boxes fit the bill, I have a choice of using one from a P200 or a 150, bearing in mind the inters ydral motor is 175cc In the words of Bruce Forsyth should I go higher or lower? What do you think? Would it make much differance?

marcus

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Re: Twostroke back pressure
« Reply #1 on: June 07, 2006, 10:01:45 PM »
Even when I had a Velorex I never really got to grips with two strokes and their odd ways, but I did learn that back pressure can make a huge difference to performance, and some people use pressure boxes as well as exhaust systems. It is always worth contacting bike shops, I think you live in Essex, not a million miles from Kickstart motorcycles in SE London, and they helped me several times. Good luck.
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Bob Purton

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Re: Twostroke back pressure
« Reply #2 on: June 07, 2006, 10:38:20 PM »
Thanks Marcus, I know what you mean, modern scooter exhausts they are incredibly complicated with several boxes, cones, bulges ect, obviously designed to squeeze every last drop of performance out of the machine.I on the other hand will be grateful if the Inter just goes! On my first inter I used a silencer from a mkC Bond minicar which was a straight through job with a bit of fibre glass wadding around the pipe, the car ran very well on it , I guess the pipe its self must create some back pressure, so maybe im worrying about nothing. I fitted the P200 silencer this afternoon and it runs fine with it, very quietly really, but of course I will not know about performance till its on the road and that wont be for some time. So far I have only fitted two non original parts to this car, the silencer and the other is a whacking great 6volt Optima battery mounted under the rear seat, originaly they had a small motorcycle type battery but such is the nature of the gyrostarter that if the engine doesnt start by the third try the battery is as flat as a pancake! I think this Optima would start a real aeroplane! That fancy dress car show you went to sounded a real hoot! Regards, Bob P.