Author Topic: Inlet port KX250 78 and 79  (Read 4244 times)

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Offline oldyzman

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Inlet port KX250 78 and 79
« on: August 28, 2013, 09:31:33 pm »
The cylinder on my A4 has extra slotts on the inlet port which go downwards (sorry upwards) from the round port. I think this is off an A5 as i have another cylinder which has a more standard oval shaped inlet port. Did this extra port slotts make much difference and if so what? as its looking likely that i might put the basic cylinder back on.
« Last Edit: August 29, 2013, 05:58:26 pm by oldyzman »
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Offline Davey Crocket

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Re: Inlet port KX250 78 and 79
« Reply #1 on: August 28, 2013, 10:12:00 pm »
They are boost ports.......way better cylinder.....leave it on.
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Offline Lozza

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Re: Inlet port KX250 78 and 79
« Reply #2 on: August 28, 2013, 10:18:27 pm »
The cylinder on my A4 has extra slotts on the inlet port which go downwards from the round port. I think this is off an A5 as i have another cylinder which has a more standard oval shaped inlet port. Did this extra port slotts make much difference and if so what? as its looking likely that i might put the basic cylinder back on.

Is the cylinder a reed valve or piston port? Inlet ports have probably the least influence on engine performance. Best way to evaluate is a dyno or a track.
Jesus only loves two strokes

Offline Davey Crocket

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Re: Inlet port KX250 78 and 79
« Reply #3 on: August 28, 2013, 10:20:05 pm »
They are reed motors....A4 didn't have the boost ports, A5 did....A5 motor was way smoother to ride.
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Offline Lozza

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Re: Inlet port KX250 78 and 79
« Reply #4 on: August 29, 2013, 07:32:08 am »
Riding is a subjective test, "smoother" could be for a number of reasons
Jesus only loves two strokes

Offline rustedstud

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Re: Inlet port KX250 78 and 79
« Reply #5 on: August 29, 2013, 08:27:35 am »
If you "Google" "Boyesen boost ports" you will find out where these ports originated from.

Offline GMC

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Offline oldyzman

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Re: Inlet port KX250 78 and 79
« Reply #7 on: August 29, 2013, 06:51:50 pm »
Thanks for the information, very helpful
I now know that they are called boost ports and seemingly can smooth out power.
GMC: I went to the link and had a read, my head is spinning - but i will re visit
Cheers Brett
I have a soft spot japanese mxers with aluminium tanks. Two stroke classic Dirt Track...

Offline Lozza

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Re: Inlet port KX250 78 and 79
« Reply #8 on: August 30, 2013, 10:41:12 pm »
What your talking about is a 'Boyensen Tunnel' they are most certainly not 'boost' ports, they basicaly just add case volume. Poor old Enyvid never realised when the transfer is open the reed is shut so the only thing that can move is whatever residual intake charge is sitting near to the transfer.The bigger the tunnel the more it ruins the flow from the duct. Rotax took the idea to the enth degree on a 257 kart engine, makes less hp than the Aprilia 125(same engine with gearbox) but revs more. Also a fuel/air molecule takes roughly 20 cycles at 12,000 rpm to go through the engine, there is always more than 1 thing happening at a time in a two stroke, nothing happens in isolation.


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Offline oldyzman

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Re: Inlet port KX250 78 and 79
« Reply #9 on: August 30, 2013, 11:01:35 pm »
The best way i can describe what i am on about is when you look through the top of the cylinder at the inlet port it is an oval shape but it has 2 extensions going upwards it looks like a pair of cats ears, they do not tunnel to anywhere....
Brett 
I have a soft spot japanese mxers with aluminium tanks. Two stroke classic Dirt Track...

Offline Davey Crocket

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Re: Inlet port KX250 78 and 79
« Reply #10 on: August 30, 2013, 11:20:25 pm »
That's not what where talking about Lozza.
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