Reed Valves

[Moisstink]

While in comparison a hole would be easier, but what is fifteen minutes with a dremel? You want maximum port timing with reed valves, or so I have read because I am not an expert what-so-ever. A rectangle would optimize your port timing so you can get the maximum amount of fuel and air mix in there. Something like this

I have read through this a couple times and sorry if I am not understanding correctly but I want to dremel a rectangle basically 5/8" x 1" that is 1/4" from the bottom of the piston centered on the intake.

Nothing needs to be exact on this and doing this mod will not negatively affect the running of the engine? I did want to do the simple cleaning out of the flash around the ports so this can be done then as well.

After I am done with that I should do the spark plug test for correct jetting of the carb? Thanks for all the good info I am just hesitant on doing too much on internal mods without understanding the full spectrum of what I am doing.

 

[Theon]

The idea is that the intake port remains open, I would drop the piston to BDC and mark the piston at the floor of the inlet port.
This will be the top of your piston window hole/s.
The bottom of your window needs to be close enough to the bottom edge of your piston skirt that the skirt will not restrict to much flow, but without making it weak. I like two holes, as opposed to one larger rectangle, as I feel it weakens the piston less.
It also opens/closes the inlet a little more gradually, which may aid atomization.
Hope this helps explain.

 

[frank66]

try lowering the intake inlet a 1/4 inch. thus lowering the piston window away from the crown 1/4". this is most ideal.

 

[frank66]

sorry i have been doing work on my piaggio lately and im a little rusty.

i was lowering inlet 1/4" and maximum 1" wide
raise exhaust an 1/8" and maximum 0.9" wide

 

[frank66]

if you take the window only half way - the transfers will still be closed. thus it is not different from a piston port motor but it will have more time to breath but not be pipey or powerful.
real power is found by having the [inlet and transfers and outlet] open at the same time. this being very pipey traditional reed motor. on a china girl this means bringing the window very far up the skirt. so the transfer is open with the inlet/window at bdc.


hope this helps

 

[frank66]

another way to explain it is your trying to achieve 100% carb airflow at bdc. without ruining the piston.

this cannot be done directly. i have a cylinder and piston in front of me now.

 

[frank66]

when i marker in the inlet shape at bdc i see that the useable window space is very short indeed.

after a 1/4" is removed from bottom inlet. the numbers are much better. see below

 

[frank66]

so now after lowering the inlet 1/4" the useable window is much larger/ atleast twice as large as stock.

i see now on mine that piston window full open is great now.

~ my engine will be different so doing this yourself is the best way to nail it~

 

[Theon]

I wish every one used Metric,
No offence to any of you, But these days, with everything coming from China and all.
Good to see you back Frank!

 

[Theon]

Boost ports are the go, if your going to run a decent pipe.
As this helps increase inlet duration without having to use such a big window.
Also allowing Window to be higher giving better cooling to wrist pin.
My Latest piston has two holes at only 5mm under ring groove, 10mm Dia.
This is for my Case induced motor, so is only feeding the boost ports.
On a piston port conversion, I would however lower the holes as in my first example, and lift the skirt a little, the piston in the above link to my Dual suspension Roo, Has been well tested, duplicated and both motors HAUL ASS!

 

[frank66]

I wish every one used Metric,
No offence to any of you, But these days, with everything coming from China and all.
Good to see you back Frank!

thanks again theon

top of cylinder to inlet floor is X
stroke is S
top edge of piston to botom of piston window is W

X-S=W

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if the piston sits o.7mm low from the deck then subtract it from X first.
conersion is 25.400mm = 1 inch lol
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just find the measurement for X and S and your ready to begin.

 

[Theon]

I don't mind 1/4" (6mm), 5/16"(8mm), 3/8"(10mm),7/16"(11mm)1/2"(13mm),9/16"(14mm), 5/8"(16mm),11/16"(17mm),3/4" (19mm),ect.
But .7", I have to get my calculator out for that one, lol.

 

[Theon]

Here's what's inside my Dual Suspension Roo.
With the boost ports opening a fraction before the transfers, which I believe can help pressurize the crankcase, giving a boost to the main transfers?

 

[frank66]

yea like that. but use the formula or a magic marker. if the carb only flows 60 percent with the piston window the rpm/tune will suffer in several places. i would shoot for all or nothing. its the in between that is incorrect i believe now. it explains my results to a T.