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Old 08-29-2009, 10:02 AM   #1 (permalink)
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New 2 stroke design

I was sitting working on my Goped and I remembered turbo charging 2 strokes. And how it doesn't work because the both the intake and exhaust valves are open at the same time. (that and there isn't enough exhaust pressure IIRC) This is also the reason 2 strokes waste a lot of fuel through the exhaust port. So my question is, could you just re-engineer the two stroke with only and exhaust valve? Then you could have it close at the engine of the exhaust stroke and then have the supercharger push in air. I think it would have to be supercharged and have a heavier fly wheel, due to the nature of two strokes. I am having a hard time getting a grasp on what i'm trying to say, so if any of you could tell me if this is/isn't possible that would be great. Does doing this defeat the purpose of a two stroke?

This is sort of the same thing, but it does not require a supercharger.
Rotary exhaust valve for two-stroke engine - Patent 5267535


Last edited by MadisonMPG; 08-29-2009 at 10:08 AM..
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Old 08-29-2009, 10:31 AM   #2 (permalink)
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The engine you describe does exist. Large ship propulsion two strokes are build that way including the super charging. But they run only as far as I know 102 rpm. The most difficult part in a small engine application is the exhaust valve drive. It is running double speed compared with four stroke cycle (small valve lift and more valves could be the solution) and the valves have also more heat load.

http://people.bath.ac.uk/ccsshb/12cyl/

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Old 08-29-2009, 10:34 AM   #3 (permalink)
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A properly designed expansion chamber wil do a job similar to a supercharger.
It MUST be designed for the specific engine/rpm/curve you are looking for.
The way they work is harmonics. The pressure wave exiting the ex port draws some of the intake charge into the pipe. At the right time it is reflected back into the cylinder. As the intake ports have closed, the cyl is charged with a higher than atmospheric volume.
There are a few books out there on proper design of expansion chambers from the 70s and 80s.
After that time everyone went from single to multi stage units which are beyond anyone without a fluid engineering degree and cant be easily home rolled.
On a single stage the math is simple, and some basic welding will get it done in a weekend.
While youre at it have the cyl ported by a pro.
Uhhh,,, I guess I should add that this will result in more efficient use of fuel to stay on-board........
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Old 08-29-2009, 11:04 AM   #4 (permalink)
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My Goped is ported and i'm running a tuned pipe, I was just wondering if it would be possible. I see that it sort of is. Thanks guys.
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Old 08-29-2009, 04:49 PM   #5 (permalink)
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GM 2-stroke diesels are supercharged and have exhaust valves.
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Old 08-29-2009, 06:39 PM   #6 (permalink)
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Here's the future of 2 strokes.

Geneva Preview: Lotus to unveil Omnivore concept engine — Autoblog Green
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Old 08-29-2009, 07:45 PM   #7 (permalink)
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Quote:
Originally Posted by Frank Lee View Post
GM 2-stroke diesels are supercharged and have exhaust valves.
Son of a b****, if I was born 80 years earlier.
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Old 08-30-2009, 12:58 AM   #8 (permalink)
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You have probably rode in a GM bus which had one, they are virtually indistructible.
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Old 08-30-2009, 01:05 AM   #9 (permalink)
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I was always impressed with that design and have always wondered why it wasn't scaled down for cars and such?
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Old 08-30-2009, 01:39 AM   #10 (permalink)
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Quote:
Originally Posted by Frank Lee View Post
I was always impressed with that design and have always wondered why it wasn't scaled down for cars and such?
Duh... diesels are dirty, smelly, and don't pass emissions tests here in the states... don't forget that they're unreliable, also.

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