Project "I needed to clean the air filter so I blew the motor"

[motopunk]

my theory on how air will travel.    (look at arrows in middle section.. and imagine if there was a big hole cut in the piston... how that would starve the rear boost port (which is at the top of the middle section), and the floor ports...     making the air travel MUCH further than it has to to get to the comb chamber)

and my theory.. bring as much as possible flow to the engine for as much as possible performance, that is needed, but dont cut to much, to be safe that the cylinder dont crack up there... 

[Motorrad]

I guess my theory is... why would one add a piston port right in the middle of a Rear boost port...   causing the intake charge to go to the crank case, instead of a direct path to where it needs to go....

I hope people jump in on this discussion.    Im not a one man band here.

Don't know, but it dyno proved 3 hp to have it.  How does a posi track rear end work on a Plymouth, it just does );

I agree there is an improvement in running a window vs not.    But I think we can improve on the current design.    

to me , the current one is like slapping a U-turn in the transfer ports, making them go back to the crank case before they can then go to the comb chamber again.....   kinda bass  akwards

[sandblaster]

So any pics on what your thinking?

[Motorrad]

So any pics on what your thinking?

very crude ones... I cut the holes with a drill press and a dremel..        since we are just playing at this point.. didnt feel like tooling up the mill...

[Motorrad]

the windows seem to just Skirt (yes pun intended)  the re-inforcing ribs in the piston (wiseco)  will have to test the wosssener.    so that is a good thing..   that was one thing I was worried about.

[sandblaster]

Oh yeah!
I think your on to something...
Anybody with a Dyno? 

Love the cylinder clean up work 

[Motorrad]

this design could also let ya cut the bottom of the intake skirt  somthing like Yz250 skirts... for even more intake ............
(esentially a bottom window)

[sandblaster]

I just gave away my last used k5 piston 
I'll have to dig deep to see what I can find

[alward25]

I have 2 used k5 wiseco pistons

[cbrfrenzie]

the windows seem to just Skirt (yes pun intended)  the re-inforcing ribs in the piston (wiseco)  will have to test the wosssener.    so that is a good thing..   that was one thing I was worried about.

Good day folks.  I think you are on to something here Motorrad.  I too think that the large lower port starves the boost ports, as the boost port pressure differential is higher than the huge gaping hole in the middle of the skirt creating a short circuit.  By moving the piston port to the sides like that, the air will be diverted to the sides much better due to the pressure differential in the intake being moved outwards to the side triangle shaped ports, like you have cut.  I believe this will in turn direct much more air to the side boost ports while the piston is still covering the main intake port.

I have a dyno at my work that I have full access to, anytime I need / want.  I am already working on a test using two different window porting options to see what the relative results are.  Perhaps I can help you guys out with some distinct numbers on these mods and the result (torque curve is what we are really interested in here).  I will be plumbing in a couple pressure sensors so I can see the resulting waveforms with respect to the dyno run, to give me a closer idea of what the air is doing in there.  I will be logging exhaust pressure, intake pressure at 2 different points, EGT, RPM and torque.

[sandblaster]

Alward25, I'll check what I have and get back to you if I need one.

[Motorrad]

awesome CB..  glad Im not out in left field here....

     another thing I was thinking about.. on my triangle ports.     is make it so they DONT open (unshroud) till RIGHT after the transfer ports uncover.   in my mind, making the piston act more as a PLUNGER and getting more pressure and air moving through the transfers before it has a chance to suck through the windows  keeping the charge that is in the crank case from pushing back out of the window and ending up around the reeds, as the piston compresses the new charge,,  (gets the flow directoin moving in the right way first)

this will also make the boosters start sucking before the piston windows pull anything... once again. getting the flow moving in the right direction first...

thoughts?

[Motorrad]

you following all this USMC?    this is your motor after all...

[USMC 500]

you following all this USMC?    this is your motor after all...

I'm following as best I can.......I have to sit here and close my eyes to picture the flow characteristics that everyone is talking about but I'm good.......I'll ask if there are any gaps in my brain to fill.

I think sticking my piston might have initiated a new way of modding this piston and I am glad to have sacrificed my K5 engine "For Science"!!!

[Motorrad]

once again. this is all just REALLY REALLY ROUGHed out stuff.   dont judge radius's, exact shape, size etc    etc etc..

here is what I was thinking from the yz250 pistons.

this bottom cut CLOSES just as the transfers open......  which should keep it from starving the lower floor port and the boosters...


(last 2 pictures taken right as transfers open)