OzVMX Forum

Clubroom => Tech Talk => Topic started by: oldyzman on August 28, 2013, 09:31:33 pm

Title: Inlet port KX250 78 and 79
Post by: oldyzman 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.

Title: Re: Inlet port KX250 78 and 79
Post by: Davey Crocket on August 28, 2013, 10:12:00 pm

They are boost ports.......way better cylinder.....leave it on.

Title: Re: Inlet port KX250 78 and 79
Post by: Lozza on August 28, 2013, 10:18:27 pm

Quote from: oldyzman on August 28, 2013, 09:31:33 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.

Title: Re: Inlet port KX250 78 and 79
Post by: Davey Crocket 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.

Title: Re: Inlet port KX250 78 and 79
Post by: Lozza on August 29, 2013, 07:32:08 am

Riding is a subjective test, "smoother" could be for a number of reasons

Title: Re: Inlet port KX250 78 and 79
Post by: rustedstud on August 29, 2013, 08:27:35 am

If you "Google" "Boyesen boost ports" you will find out where these ports originated from.

Title: Re: Inlet port KX250 78 and 79
Post by: GMC on August 29, 2013, 10:29:23 am

Smoother is better is it not?

Check out the induction specs...

(http://i15.photobucket.com/albums/a393/gmcloa/Misc%202/KX-250-420specs_zps84bd0f46.jpg) (http://s15.photobucket.com/user/gmcloa/media/Misc%202/KX-250-420specs_zps84bd0f46.jpg.html)

https://www.google.com/patents?id=SpssAAAAEBAJ&pg=PA2&dq=boyesen+patent+number+3905341&source=gbs_selected_pages&cad=2#v=onepage&q=boyesen%20patent%20number%203905341&f=false

Title: Re: Inlet port KX250 78 and 79
Post by: oldyzman 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

Title: Re: Inlet port KX250 78 and 79
Post by: Lozza 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.

(https://eikoms.com/ROTAX/RMCRegulation/Cylinder_571.jpg)

Title: Re: Inlet port KX250 78 and 79
Post by: oldyzman 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 

Title: Re: Inlet port KX250 78 and 79
Post by: Davey Crocket on August 30, 2013, 11:20:25 pm

That's not what where talking about Lozza.